RC India

Just enough basics, which will improve our Knowledge on Air's Interaction with the RC aircraft.

Aim:-
1. to Design foamies better with this knowledge
2. To fly better
3.To make modifications in your aeroplane/heli.
4. on the lighter side, to tell family, we are doing something worthwhile

PLEASE do not cut copy, even if you do value add  ;D.

Learn through generating discussion, like Anwar Bhai says, it is always better. ;D

pulled out from my other post. Pruned it a little. To make understanding of RC flying clear.

firstly in level flight weight= lift =CL ½ σ V² S. CL is coefficient of lift, which depends on your wing angle of attack (position of the nose in level flight) shape, camber etc, ½ σ V² is called the dynamic pressure, simply put, number of air molecules for a given time, ALSO CALLED THE INDICATED AIRSPEED, 'S' is your wing area.

Now, aeroplane has lift and weight acting as one couple (noseup or down will in RC language, will depend on the cg, because weight acts along it, and position of wings because centre of pressure through which the lift acts).

It also has thrust and drag couple acting on it. nose up or down will depend on position of your engine and wings, which if you are not designing, is pretty much taken care of,

Couple of Forces. For aeroplane to fly in level unaccelerated flight all these couple have to balance so that the residual is zero. If the aeroplane is say designed to get airborne at 30 kmph, it will get airborne at 30 kmph, if the wind that is blowing is 30 kmph, the ground speed at which will get airborne will be zero. But remember the thrust drag couple will have to be zero, which means, you have to open power normally as you do in nil wind condition. If the winds are 40 kmph the aeroplane after getting airborne into wind will travel rearward at 10 kmph. With respect to ground, however with respect to air it is still travelling at 30 kmph. Bottom line CL and S being same it is the ½ σ V² (the number of air molecules for a given time above and below the wings) which matter.

"Coanda Effect", Tendency of the fluid in motion to get attracted to the nearby surface, AN 72, C-17 Globemaster, are some of the aeroplanes successfully uses this effect (Blowing of engine air to increase lift and reduce forward speed).

Coanda effect... I was watching this interesting thread : http://diydrones.com/profiles/blogs/coanda-effect-saucer-ces-uav

There is a cool build document too : http://ardupilotdev.googlecode.com/files/How_to_build_a_Coanda_Effect_Saucer.pdf

Since I have the ArduIMU v2, might try this some day !

I didn't see this post, see my reply in your other post (Link below).

also read

http://www.rcindia.org/rc-general-topics/aerodynamics-is-this-possible/new/#new

Anwar Bhai, I need to get intro to ArduImu, Help. your info link in this thread will help this thread

VGs (Vortex Generators) used on wing root which makes root stall before tip, so that the aeroplane does not wing drop during stall. (Example:- Jet Provost) They are also used spanwise at about 20% chord, this makes the flow go turbulent and a turbulent air flow sticks to the wing more than a laminar (Non turbulent) flow. SO ? so the aeroplane stalls at lower speed and higher nose up, does aerobatics well. PRICE TO PAY? more Drag and fuel consumption. (Example:- B Ae Hawk). VGs on the root of the Pitot Tube energizes Fin and this keeps the aeroplane 'directionally Locked In' and does not roll left and right at low speed (Like what the RC Extra 300L does at low speed). Example MiG 29.

This can be tried on a C/Foamie to have a clean stall characteristics

I am planning to build a plane with 75 inch span, root chord 16 inch, tip chord 1 inch (elliptical wing). Now the problem is stabilizer dimensions. i want the horizontal and vertical stabs to be as small as possible. This will be a slow flier/glider with a polyhedral wing an no ailerons. how much horizontal and vertical stab do you think i can get away with?

It is just a sensor board with an arduino and 3axis gyros, accelerometers and option to add a magnetometer.  Basically, it has everything you need to get sensor information for full stabilization and enough processing power to run a control system using these sensors.

PM me more details, basically, if you want to knock off fin elevator weight, give it more moment arm, (Restricted by weight increment due fuselage length) if it is going to be on a stick you can knock off a lot.

If you sweep back slightly a polyhedral wont require fin, two small winglet will give you directional stabilty and reduce Lift dependent drag as well. Elliptical wont work with polyhedral and winglet. with a 15 deg sweep winglet. believe me you can knock off fin.

if you are interested, this is the data. if you plot, you will come across the C of P should be able to determine moment arm from there, problem is i have assumed symmetrical wing, introduce camber , the stall model and the C of P will change.

this sounds good, the fuse is just a CF tube. sweeping the wing wont be possible. The wing is going to be slightly cambered one with, max height of the caber only 1.5 inch.
And thanks for posting the data, but unfortunately i am mathematically challenged person :(
is there a formula which gives stab surface area w.r.t to arm length and wing dimension?

Ok

Let me give you a practical solution. Theorically, if the point at which wing lift is said to act is on the CG, you wont require any tail down force. Thats not practical, So Have flexibity of shifting the entire wing forward and aft, now you are restricted by the amount of elevator force you want for any manoeuvrings you envisage the model will do. That's it you are sorted.

In a Nutshell. Keep your elevator restricted to the force you envisage you require for the manoeuvrings limits. Keep the point where you think the wing is lifting the ac (Determined by trial and error) very very slightly behind CG. if you can keep a all moving tail plane (Instead of elevator) which will reduce the size and weight of it.if you can have a small ventral fin as well. this will reduce the size of the dorsal  fin as well.

Any more query, feel free to PM

got it! thanks a lot augustinev!
There is one more question that is bothering me from some time. Check out the attached image. Notice the sharp angle on the upper surface. How will this airfoil perform w.rt. gliding performance? Which one will you recommend between this triangular airfoil and a flat plate for better glide ratio.

Interesting!!,

I guess it is easy to make that's why you chose this, if you are using coro, join at the ends and put a vertical piece at about 20 % chord, you will get a decent bi-convex. This wing is a single wedge design. I have flown a double wedge, great supersonic performance, poor low speed stall and subsonic performance. Your single wedge, At about 7 deg α this wing will stall. section CL will be at about 0.15-0.17 at 4 α.

The point of max thickness is good, before that point the air would have gone turbulent and will stick on until 7-10 α. Stall however will be abrupt. Glide ratio will not be too great to talk home about. landing will be at slightly high speed but will be good, rest assured on that.

Like us even air likes curves. keep it curvaceous for the air. These are just opinions based on scanty info you provided. Try it, if the results are contrary, give me a holler

Ah!! one other thing, FLAT plate Aerodynamics.

Is is an interesting, huge, ever debated, still enigmatic topic. Suffice to say, Advantages of Flat plate wings are at high RN, that's why you see them on missiles. low speed performance is poor, there is always a leading edge stall / bubble. BUT but, there is virtually no movement of C of P in the working ranges of α (angle of attack).

PS
Your single wedge, ?  if you invert it and give it a little reflex camber on the trailing edge, it looks more like Kline Fogleman's aerofoil. A sensational one during mid-late seventies.

you must be thinking why doesn't this guy just curve it a little. Thats why i am going to start my build and put it on a thread; that will clear the mist.
BTW i asked the airfoil question because of KF airfoil only. I thought it would behave just like KFm2.

yeah, we (My friend and I) tried some Spads with KFm2 and m3. flew well. it had a round LE (Coro Bends).

Waiting to see your model. All the best.

This is what I have experienced

Flat/pointed edged airfoils have higher stall speed and its unpredictable. So, you need to have enough airspeed to have control of the flying surface. If you need more adrenaline pumping flying then pointed flat air foil should give you that. Flying on prop is another story.

Rounded edges are always better as it gives predictable stall speed. More graceful and less nerve-wracking to fly.

Another thing, you would not see much difference with a triagular section airfoil and a smooth curved airfoil of similar dimension. All these airfoil doesn't matter much in RC flying as their effects are too small to notice. Either you need to have a proper wind tunnel with appropriate instruments to measure the parameters from your model or you need to have a larger aircraft to study the effects of airfoil shapes.

thanks for the tips Izmile.
this is good news for me, lets see how it turns out.

izmile
True to the bone. We do a lot of prop controlled flying for complex AD to matter.

For control forces and servo needed read my post

http://www.rcindia.org/beginners-zone/how-to-calculate-the-type-of-servo-needed/new/#new

Vortex Generators's on a RC plane, see this

as per them (http://www.precisionaerobatics.com/product_details.php?pid=648) it gives additional valuable extras which are used to enhance even further the low speed 3D capabilities of the plane and Knife Edge type maneuvers.

PS
Thanks Praveen and Santhosh for the correction

read 'Rep 34' of this post for Reynolds number and it importance on wing design (scratch build)

http://www.rcindia.org/self-designed-diy-and-college-projects/build-log-back-packable-2-meter-glider/new/#new

Dutch and Spiral Instability. This has been overcome in all modern aircraft with the introduction of Autopilot and Auto Stabilisers, however this problem is very live in RC flying, One of my colleague crashed his scratch built High winger, i suspect it was due to Dutch Roll. therefore this information.

Spiral Instability. Highly Directionally Stable aircraft (Large Fin, Long Fuse with medium Fin) suffers from this, this is not as dangerous condition as a Dutch Roll, provided you have enough rudder area and rudder throw to pick up a spiraling aircraft. when a yawing moment commences, and if the lateral stability is low, and yaw damping is small, the directional stability keeps turning the aircraft with bank angle increasing continuously, it gets steeper and tighter, ROD increases and the RC aircraft crash is spectacular. on the lighter side people blame it on 2.4 Ghz lock out, etc. Don't confuse spiral dive to a spin, because in spin the aircraft is in the stalled condition of flight and the speed is at or near stall speed, in spiral dive it is fast and the speed continues to increase.

Dutch Roll.   The second one is an oscillatory motion, normally not in sync with each other is a roll and yaw combo motion called Dutch roll, named by Dutch skaters. High wing, Large Dihedral, sweep back etc increases lateral stability and if directional stability is not as high, then you have created a recipe for a Dutch Roll. High lateral stability with vicious bank reversal can lead you to Dutch Roll and with control inputs out of phase, development to crash can be in seconds. You will wondering who switched to your frequency, and or how batt quit or was it sudden wind. not knowing it was Damn Dutch. (See the image in terms of roll and direction of yaw , carefully)

is it making sense ? ???

so many people saw and no comments/queries at all. ???

lot's of information from your posts,but it's not  digesting for a person like me,that's why i am keeping quiet

These are applicable only in deadstick situations, or when you are really really close to the ground, right ? And that too on planes without ailerons ?  Otherwise aileron (or even enough rudder) corrections should take care of it ? :headscratch:

thumb rule.
1. too much of fin...directional instability
2. too much of Dihedral/sweepback...Dutch roll

Aileron no aileron, rudder no rudder..

of course controls make you recover from the situation. ;D

Santhosh.
Plan a visit

Propellors
 
Thrust is the force that move the aircraft through the air.Thrust is generated by the propeller of the aircraft through application of Newton's Third Law.  The propeller consist of two or more blades connected together by a hub. The hub serves to attach the blades to the engine shaft. .

The blades are made in the shape of an airfoil like wing of an aircraft. When the engine rotates the propeller blades, the blades produce lift. This lift is called thrust and moves the aircraft forward. most aircraft have propellers that pull the aircraft through the air. These are called tractor propellers. Some aircraft have propellers that push the aircraft. These are called pusher propellers.

Leading Edge of the airfoil is the cutting edge that slices into the air. As the leading edge cuts the air, air flows over the blade face like it does on any wing.
Blade Face is the lower surface of an airfoil (Over a period people think it is that side that you see when you face the aircraft, it is not).
Blade Back or the Thrust Face is the curved surface of the airfoil.
Blade Shank is the Root section of the blade (nearest to the hub).
Blade Tip is the outer end of the blade farthest from the hub.
Plane of Rotation is an imaginary plane perpendicular to the shaft in which the blades rotate.
Blade Angle is formed between the face of an element and the plane of rotation. The blade angle throughout the length of the blade is not the same. The reason for placing the blade element sections at different angles is because the various sections of the blade travel at different speed, because of their distance from the hub, that is why the twist in the blade. Each element must be designed as part of the blade to operate at its own best angle of attack to create thrust when revolving at its best design speed
Blade Element is the airfoil sections joined side by side to form the blade airfoil. These elements are placed at different angles in rotation of the plane of rotation. (Something like a slice of a cake at any point on the prop, you cut and look at it side ways (See image)

Why Twist, say again! ??? The blade has a small twist (due to different angle in each section) in it for a very important reason. When the propeller is spinning round, each section of the blade travel at different speed, The twist in the propeller blade means that each section advance forward at the same rate so stopping the propeller from bending.

Thrust is produced by the propeller attached to the engine driveshaft. While the propeller is rotating in flight, each section of the blade has a motion that combines the forward motion of the aircraft with circular movement of the propeller. (see image), so if your model is going to travel at lesser speed the second number of your prop should be small, if it is going to screech through the second number should be more.(Not a rule though)

Pitch is the distance a spiral threaded object moves forward in one revolution. As a wood screw moves forward when turned in wood, same with the propeller move forward when turn in the air. More on Pitch later
  

hi,

this is fantastic information for the modellers who design and build models. infact i have problems with my model which will spiral down and crash. hopefully with this information i should be able to rectify my problem.

thanks for the info.

regds

So if I have a 10x6 prop and I am cutting it down to 7 inch, will I get a 7x6 prop or not ???

augustinev you are a saviour, now i know my scratch built suffers from spiral instability, it banks to one side and spirals before crashing just a few seconds into the flight, please please tell me how do i overcome this. Help appreciated

husein, sandeep, what i follow for my scratch build i can tell you, (i) i keep more than half my fin as the rudder, remember, in pattern flying we rarely use rudder, however it is a gr8 tool for  (a) picking up a dropped wing by inducing something called 'Yaw induced Roll' especially when the aircraft is at low speeds (b) rudder is the easiest way to get out of a spiral.
As i settle down in the model, I reduce the throw of the rudder. i keep it a high winger, di/polyhedral or sweepback a little. thats about it , you are sorted.

'Scratch built' as a rule should not have a flap, it is the cause for most failures, you may want to introduce it later.

Lot of tools are available before sitting down to cut the foam, coro or balsa, run the math. a lot of issues will get sorted on the drawing board believe me, i have heard people say 'iam a hands on old fashion builder, i care a damn about math and drawing' ain't true, in todays age you have gr8 sims available to run and fly your model virtually before you cut it.

also read

#15 and # 17 of
http://www.rcindia.org/beginners-zone/airfoil-for-trainer/new/#new

For Aerofoils

Phrozen Crew member!  :bow: not exactly, the tip section of the aerofoil needs to reduce in camber and chord so as to reduce its optimum angle of attack to very less value ??? (See blade twist image, above), you will ask why ? complicated question, more complicated answer is, 1. to reduce 'Tip Spillage' 2. to avoid 'Blade Interference' 3. to improve 'Blade Harmonics', in a nutshell yes it will become a 7x6 prop but since not designed to be one,  will not perform like one. :banghead:

PS
Did fiddle around with Softice for a while, till all AV hell broke loose and categorized it a dangerous HI virus  ;D ;D

tnx augustine, sure in may

Hi Amit,
After almost more than a year into this racket few people have have been able to give me answers to my queries... ;D... I am still going through the trial and error method :banghead:....I am sure nobody wants to be buried by rocket science :banghead:...But sure Anwar Bhai has been a great help...but of late he also seems to be hard pressed for time :o...IMHO simple answers to queries will help all fellow aeromodellers ??? I rest my case :salute:...
Regards,
Mohan

mohan, with you 100%, keeping it CCC (Clear , Concise, Crisp ) and short is not simple, atleast for me, i spend quite a bit of time to simplify and put it in a manner so that it is not intimidating (Unlike other RC forums, which is , like you said, full of rocket science). Have I been able to succeed ???, you all should tell me, i am sure some thumb rules will help. problem with the thumb rule is if you forget the rule, it is over, and it doesn't explain the logic to a action, in RC flying and in aviation, it is so very important. Will give an honest try to simplify further so that you don't  :banghead:

Thanks, but those days are gone. Opensource is the new revolution :thumbsup:

Thats what I do and I'm getting good results. Slow and steady..   :)

I tried this a few days ago and slow speed performance was awesome, maybe because a cut down 10x6 to a 7x6 has much wider blades than a regular 7x6. But open up the throttle and that thing was noisy as hell and not much thrust gain above half throttle.

On ram temperature rise rep #2 of

http://www.rcindia.org/chatter-zone/experimental-flight-at-mach-6/msg47947/#new

From what I understand, augustinev you are an aerospace guy, if yes can you please help with two projects I am currently working on, one is Design of a Ramjet and other one Environmentally responsible aviation, a competition at NASA, please PM me. Thanks

Firstly, Sorry Husein, i saw this now. PM me anytime

Secondly a lot of people are getting confused with these Basics, i guess they know the concept but are caught in semantics. Some of them are defined rather inaccurately on the internet and in other RC forums, so here we are, in the series of more accurate concepts.

Total Reaction (TR).  The resultant of all the aerodynamic forces acting on the wing or aerofoil section. Imagine this to the direction your hand gets pushed when you put it  flat like a aerofoil (I guess every child does it  ???) out of the window in a train or a vehicle

Lift.  That component of the TR which is perpendicular to the flight path or Relative Air Flow.

Chord Line.  A straight line joining the centres of curvature (It is not the centre, it is the centre of curvature ;D) of the leading and trailing edges of an aerofoil. (See Aerofoil Funda Image).

Chord (c).  The distance between the leading and trailing edge measured along the chord line.  The mean chord is often used as a datum linear dimension in the same way that the wing area (S) is used as a datum area.

Wing Area (S).  Area of the wing projected on a plane perpendicular to the normal axis.

Mean line or Camber Line.  A line joining the leading and trailing edges of an aerofoil equidistant from the upper and lower surfaces.  Maximum camber is usually expressed as a ratio of the maximum distance between the camber line and the chord line to chord length.  Where the camber line lies above the chord line, the aerofoil is said to have positive camber.

Angle of Attack (α).  The angle between the chord line and the flight path or RAF.  In many textbooks this is referred to as Incidence.

(Rigger’s) Angle of Incidence.  The angle at which an aerofoil is attached to the fuselage.  The angle between the mean chord line and the longitudinal fuselage datum.  The term is often used erroneously instead of Angle of Attack.

Thickness/Chord Ratio (t/c).  The maximum thickness or depth of an aerofoil section expressed as a percentage of chord length.

Centre of Pressure (CP).  The point, usually on the chord line, through which the Total Reaction may be considered to act.

Streamline.  The path traced by a particle in a steady fluid flow.

Aspect Ratio = span/chord or span2/wingarea.

Wing Loading.  The weight per unit area of the wing = weight/wingarea

More to Follow ??? ???

Why does a plane going vertical at full throttle stalls after reaching a particular altitude  :headscratch: Shouldn't it keep climbing at speed approximately equal to pitch speed of the prop :banghead:

Some part of the power system must be overstressed and giving up, otherwise you can get unlimited verticals (at least until they are get too small to control visually). 

We have some foamies and helis that can keep going up as long as I want, the same can be done on glow planes if you put the right power system.

Hey If I am not wrong you mean to say that it should reach moon till you keep full throttle and straight towards sky  :giggle:..... well they will stall after a certain height as gravity is pulling them desperately. TO breach it you need a booster rocket with huge amount of propellant and need a launching station (like sriharikota in india  :giggle:) then your rocket will not stall( if everything goes right ..) and may reach moon..... {:)}.... ( anyways we are trying hard to reach there through Chandrayana.....)  :)

Common man, you know what i mean. Just want to reach a little higher to get to the sweet thermals :)

@anwar: I never had any of my planes give unlimited vertical, may be I've never had enough power. I've got a habit of under powering my planes and under propping my motors.

 :giggle: :giggle:

Anwar Bhai,

It is a gr8 question. Answer is in two fold, they are :-

Reduction in Thrust due reduction in mass flow across the Propeller

Though this is not very accurate, for simplicity reasons I have chosen to show the thrust produced by a propeller using Newton’s laws of motion which give: (See Image)

Force=Mass x Acceleration
Thrust = Mass flow rate of air through Propeller × Increase in velocity of the air
=M x (Vj x Va)
Where M=Mass flow rate of the air
Vj =Velocity of slipstream
Va =Velocity of the aircraft(TAS) (What is TAS ? See below)

In the case of the propeller as compared to jet engine, the air mass flow will be large, and the increase in velocity given to the air will be fairly small.

So as the altitude increases the density reduces and the TAS increase, this makes the Mass Flow Reduce because the difference in the velocity in front of the prop and on the rear of the prop reduces (If at that altitude if you happen to stand behind the prop you will feel less of air as compared to when you launched it at the field)

True Air Speed (TAS)(V). The TAS is obtained by dividing the total Dynamic Pressure (The number of air molecules in motion hitting the prop face for a given time) divided by the square root of the air density.

I have kept this part simple, if you read it couple of times you will get it.

Reduction in Density also reduces engine thrust because of reduction in MAP (Manifold Air Pressure) inside the engine, this further complicates matters. Therefore reduction of Prop aircraft thrust as compared to a jet aircraft is near exponential. that is why you see not may I/C engine prop aircraft flying very high

So you are saying this is all because of reducing air density as the altitude increases. Does air density really varies this much in the 500~600 meter altitude range?

at 600 mtrs it is 8.3%, (see image). It is not the altitude, it is the thrust drop that counts, since the model weight is so low that any reduction affects the climb performance drastically.

Got it :salute:
One more question on this ;D Considering the motor can handle both, which prop should i use to get more altitude, a 9x6 or a 11x4 ?

Wow.. I didn't consider flying your RC plane for deliveries to the ISS :giggle: 

It was only around the 400m to 600m heights, that I am able to take my aircrafts vertically to ! (depending on the size of the plane, and I am guessing the heights!).   

11x4 would generate more thrust than a 9x6. Larger dia props generate more thrust as they are simply large... and the peripheral velocity of the blade tips are high.

Thanks Izmile, i was thinking more pitch speed will take me higher but now i understand its the thrust that matters in this case.

Think of pitch as gears in a vehicle. Fine pitch equates to lower gear and vice versa. So fine pitch will give you better acceleration but less speed, and so on.

makes sense, awesome analogy  {:)}

Flat Plate Aerodynamics

1. this is in co-relation to Rep#2 of this thread,
A few things i want to flag off, as regards Flat plate foamies, This does not include Kline Fogleman (Kfm) Aerofoils

(a) Any aerofoil at +ve angle to the forward movement of the aeroplane will produce an upward force and a rearward force (Exactly like the way the hand moving back when you put it out of a running bus or a train in an aerofoil shape) This upward force is called the Total Reaction, This total reaction can be resolved into two components one upward which is called the Lift and One rearward which is called Drag

(b) in climb the lift is less than weight ???, in true vertical climb and vertical dive lift =0, ???, Don't believe me ? see image

(c) In a flat plate upto the point of stall there is no movement of C of P, which means in the working ranges of angle of attack , its behavior is quite predictable.

(d) last but not the least, a flat plate has something called a leading edge separation , a small bubble of air, at and near stall this bubble continues to increase and at stall the bubble bursts and the stall is spectacular because there is a sudden loss of lift.

Also Flat plate has the least Supersonic drag, the reason why it is the choice of section in missiles and high speed aerospace applications.

Rep 35 for 1 'G' stall
http://www.rcindia.org/gas-glow-nitro-planes/my-first-plane-with-sunboard-sheet/msg48491/#msg48491

I saw a thread reg kFm buts its a year old so posting it here

I want to construct a kFm3 airfoil of wingspan 48" & 7" chord length using coro.
It is said that kFm3 has (9% to 12% thickness) step at 50% and 75% chord

what needs to be the thickness of the wing at 50% and at 75 %

Is it 12% of chord length(for me its 0.84") at 50% chord(3.5")?
then what is the thickness at 75%
Is the thickness from 50% to 75% of the chord is constant?

A pic with the dimensions marked would be very helpful(7" chord, 48" wingspan).

T/C (Thickness to chord ratio) decides a lot of things including stall alpha, t/c and MAC to has a lot of effect, actually they are decided by your flight performance requirements, short chord also is preferred for ease of carriage,

I want the wing to be used in a pusher model using coro(2mm)
If the wing is 48" long wing having 7" as chord length
what needs to be the values of X, Y , Z & P in the pic attached.
Also does the second step needs elevation(I am sure if Z > P then the second step needs elevation, but just for clarification)

Well, pardon my lack of knowledge, but is there a difference between symmetrical aerofoil and flat plate? If the aerofoil is uniform on both the upper and lower surface, the air pressure will be the same and hence no difference to cause the lift - right?

Flat Plate will have a bubble on the leading edge that makes flat plate behave in an unpredictable snappy manner, at high alpha the bubble elongates , does not elongate equally on both wings, this further addes to the woes, during stall the bubble bursts and stall is jerky, airflow transition from laminar to turbulent takes place not on the wing (at slightly high alpha) but on the bubble, this makes the air flow separate there, sometimes, all in all for low speed applications flat plate isn't good, if you are planning a foamie, Kline Fogleman is better :thumbsup:

As you said earlier, the air bubble effect on the flat plate is at the stall speed. but above that? What I meant to clarify was that most of the 3D planes ARF/RTF seem to have a symmetrical wing. So if this is not producing lift, then does it matter for the model to have such a well crafted shape and not just a flat plate with LE and TE shaped properly?

See theoretically, a flat plate without any LE radius will be in a stalled condition of flight at any positive angle of attack, however practically, Wind tunnel Experiments have shown the LE bubble in Flat Plate forms at 2-3 deg angel of attack and it continues to grow, and at stall it engulfs entire wing and bursts. Flat plate is suited for supersonic configurations because after the transonic regime the wave drag of a flat plate is the least, for aeromodelling this info is of no use (Unless you want to do supersonic FPV Flight)

As far as foamies are concerned, it flies because of the Thrust wt ratio being high, when TWR is high it pushes even the stalled airflow over the wing and generates enough lift to keep it aloft, another thing about stall is with the increase in angle of attack when there is no more increase in lift, then we call it stalled condition, however the wing will produce lift well after the stall state (See image ) I hope i have answered the question

I have been doing foamie scratch builds for some time. The best results for a slow flyer / trainers seems to be a UC aerofoil without ailerons, seems to work better that curved upper and flat bottom foil. Any reason for this or just a coincidence ? Does having an aileron have any effect on the lift as far as the model plane goes ( not talking about the actual ones)

What is the advantage of having stabilator instead of elevator and a horizontal stabilizer, in a glider ???

SLS

That is a very big question. i will restrict my answer to gliders alone. Apart from controlling the aircraft in pitch what is the purpose of a tailplane? ans. it is to balance the aircraft pitching moments caused by lift-weight and thrust-drag couple (Read in conjunction with earlier posts). A tailplane and Stab arrangement is because a stabilizer when deflected, in subsonic speeds, will modify airflow ahead of it and give you more than what you bargained out of the stabilizer. a stabilator or a a all flying tail as it is called moves as one piece and gives desired effect in less of deflection. advantage is less deflection disadvantages are plenty (a) to move a all flying tail is not easy in terms of mechanism involved (b) bigger servo will be required (d) hinge point will be the wing therefore hinge point got to be strong and lubricated as well


Why is it used i a glider
(a) you are supposed to glide a glider not maneuver too much, therefore you reach a trim point and thereafter the movement of the tailplane is negligible, does not affect the glide and the tailplane contributed lift characteristics greatly (tailplane lift and Trim Drag is a great contributor to glide distance)

Why is it there in a jet ?
some other time

PS
There is a lot to think about, think and ask me questions, open to answer all of them , no question is a stupid question remember that

Why in a pusher, If the motor is placed above the wing the motor is angled upwards (looking from back). It will be causing a down thrust  ??? which inturn pushes the plane down  :headscratch:.

For a Conventional Aircraft thrust drag couple is nose up and Lift Weight Couple is Nose Down (See Image)

However for aircraft like easy star or axn floater (Like a sea plane) the thrust drag couple and lift weight both are nose down couple , (Because the thrust line goes above the drag line) that is why thrust line is inclined, inspite of this you will see the trim point of the tail plane is for nose up (tail down).

With reference to 70

there is also split tail, works like a conventional stabilizer at subsonic speeds and the locks to become a all flying tail at transonic and supersonic speeds,

In some aircraft like the Kiran HJT16 and Jet Provost the stabilizer is connected to the pilots joystick and the tailplane to the trimmer, so when you trim the stabilator moves and when during piloting the stabilizer moves , neat yeah !!! can you figure out why shouldn't it be used in RC plane (If it is not already being used)

(In my scratch build I installed the motor alone without the control surfaces cutted out, for testing. the plane is not gliding well as it did without the motor)

So the motor is angled a little up so that the thrust is also angled little down so that the thrust drag couple doesn't push the plane complete down. but the thrust is also pulling the plane down right  ???. So normally without elevator trim the plane will be going down where other planes will remain in the same level  ???.

this diagram is wrong , lift always is behind the weight , lift ahead of the weight is a unstable config and can only be controlled using fly by wire ,

oops that was a mistake since we were concentrating on the thrust drag couple I just drew it there. So normally without elevator trim the pushers will be going down where other planes will remain in the same level?

Bingo, that's why easy star is meant for easy flying.

How does one determine the drag line? In a conventional tractor, it is shown as being directly opposite to the thrust line, so how is it different in a pusher?

thumb rule (1) for a low-winger, between the wing line and the fuselage reference line (See image) (2) for a mid-winger through the aircraft (3) for a high winger , between the fuselage and the wing line. if there is a fixed undercarriage, then it shifts marginally towards the undercarriage

The nose down couple for a Low winger seems to be very similar to the pusher(if the motor is not tilted) ?. Only difference is the starting point of the thrust line. but that causes adverse effect of the plane to be pulled down?

That is why thrust line is so very important. it is just a thumb rule 2 deg down and to the right, actually with controls neutral fly your foamie and small size aircraft vertically while holding the spine as you slowly release the pressure see to which side is it falling adjust motor mount to the opposite side. for big aircraft run in from right to left or left to right, right in front of you pull up and with power on see which side she is falling  opposite side is where your thrust line correction should be. for a low winger thrust drag couple is more nose up than high winger, high winger it is almost negligible.

some people like me are very very finicky of the thrust line, some trim it off or correct it while flying

This maybe a stupid question to ask...but havent tried it ..hence asking

In a brushless setup, is the thrust generated by prop the same in either direction of rotation of motor?

I use GWS props and in tractor setup the markings (eg GWS 11x4.7) are facing you, i.e away from motor (looking from the front side). In other words the convex side of the prop is in the direction of the flight.

Will the thrust generated be same, no matter which direction the motor rotate?

Sorry if its a silly question :)

 No it wont be the same, think of the blades as wings moving through air.
Also read post #31 on page 2 (http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg47707/#msg47707) of this thread.

where is the drag line for the following
1) AXN Floater type pusher which has motor above and behind the wing
2) Pusher jet which has the motor almost level with the wing

slightly below the wing line stubbier the fuselage lower the line

Dear Mr Augustinev,

I am in process of making a flying wing

Here is the plan..

http://www.rcgroups.com/forums/showthread.php?t=497083

I wanted to know, what care should i take to reduce the speed at which tip stall occurs.

I would like it to glide nicely and land at a slower speed without stalling.

Bakya

This wont tip stall, basically because there is a tip fence, this will glide extremely well, at very low speed this will do something called a Falling Leaf as the name suggests will fall like a leaf. this design is proven design . Flying Wings, B1B to name a few.

One thing though only this wing can do and that is inverted spin at very high rate of roll. after you fly it and gained confidence do the following :-

gain height , cut throttle and very low speed push right rudder and move Right stick diagonally to the right and forward(Mode II) now watch the fun,  she will spin like a top. for recovery simply open full power.

PS
my batix is coming real slow, but steady

Thank you sir  :salute:

I was doing some glide tests with it without installing the tip fence (by that you mean the stabilizers at the tips right?). I had a attached weight at the nose such that the CG was at the position as given in that thread. I held it above my head and let the glide with a little force. It would travel a little distance very nicely and then the nose would go up and it would fall down. Was this tip stall? If i do the same with the little stabilizers at the wing tips, would it glide better? or was my CG off ?

at stall she should go nose down that is conventional stall, however a delta or a swept back wing wont stall classically , if she was gliding well then CG is not the issue, wing fence also gives it directional stability therefore a must, all the best

BASIC PROPELLER PRINCIPLES - TORQUE REACTION

Newton's Third Law says for every action, there is an equal and opposite reaction. As applied to the airplane, propeller revolving in one direction, an equal force is trying to rotate the airplane in the opposite direction. this reactionary force acting along the longitudinal axis is responsible for torque rolling the aeroplane.  There are many compensating methods for a fixed wing aeroplane, they are :-

(a) Compensation by Rigging This method entails one wing producing more lift than the other , however this method had a drawback, compensation worked only for a particular speed, outside this rigged speed the aircraft flew cross controls.

(b) engine offset method This is more popular method and is used in RC Aircraft too (2 deg right and down)

(c) Compensation by cantering the fin This method is more popular in a transport aeroplane, the prop-wash is a rotating mass of air, by sufficiently cantering the rudder and or the fin provides adequate compensation. (see Image)

Let us discuss an example here All this is clearly visible in a Hover , you can see (http://www.rcindia.org/rc-maneuvers-and-skills/aerofly-pro-delux-sim-videos-enjoy-!!!/), to hold a hover you still need to hold opposite aileron, otherwise she will torque roll. Even this roll is controlled by adequately removing the Aileron Roll offset, some times in some aeroplane you run out of aileron and she no matter how-much ever aileron you hold, still torque rolls, to recover from the situation you open power to get some prop wash onto the aileron (More on 3D Aerobatics later)

The magnitude of this moment is dependent on many variables. Some of these variables are: (1) size and horsepower of engine, (2) size of propeller and the rpm, (3) size of the airplane

Torque Reaction in Heli [/u] However in a heli this torque reaction needs to be controlled by a (a) tailrotor (b) contra rotating blades or by using (c) two separate rotors like in chinook. The reason is pretty simple (See para above) it is to do with the Size RPM of the engine and Size and RPM of the Prop (In this case the Rotor Blade), The MAGNITUDE of the torque force is so high that an aerodynamic surface is not adequate to control this is also contributed by low forward speed at which a Heli is desgined to fly(In Jet engine sometimes you do reach such a situation at very low speeds) That's why when you loose tail rotor you loose control of a heli

Hot and High What is it ?

Aircraft including RC performance is affected by Density Altitude. What is Density Altitude

Density altitude is the altitude in the International Standard Atmosphere (A Standardized Atmospheric tables issued by ICAO) at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground. "Density Altitude" is the pressure altitude adjusted for non-standard temperature. (See image where the indicated altitude of the aeroplane is 5000 feet however due to temperature see how its true altitude varies)

Put in a layman terms: - Pressure altitude represents a physical distance above sea level as determined by the weight of the atmosphere, density altitude represents the number of air molecules in a given volume of space.  That space may be the area of air beneath the wings, the volume within the engine cylinders or the area of air surrounding a spinning propeller

Both an increase in temperature and, to a much lesser degree, humidity will cause an increase in density altitude. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude. if the place itself is at high altitude it makes matters worse. That is Hot and High for you (Explanation in Wikipedia sucks)

There are only Four types of altitude you need to know and they are :-

True Altitude  Actual height in feet above mean sea level.

Absolute Altitude  Actual height above the ground.

Pressure Altitude Weight of the atmosphere measured in inches of mercury, millibars, or hectopascals.

Density Altitude  Equals pressure altitude corrected for non-standard temperature.  

what effect does it have on the Aircraft

Fixed Wing
1. Take Distance is more
2. Take off speed is more
3. Braking Distance in case of reject take off is more
4. Take off angle is shallow

Helis
1. IGE Hover power is more
2. OGE to IGE hover transition is difficult
3. AUW for hover landing is less (If it was already overloaded for the said density altitude it wont hover at all, it will sit down like a lump of ...you know what)
4. Hover takeoff collective is more, hover take off load carrying capacity is less

Basically hot and high affects Heli more than Aeroplane and tests pilots skills a lot, including RC heli

Worth a watch  :thumbsup:

http://www.youtube.com/watch?v=S3MMHb0I268

Simplicity , thy name Bruce

Torque reaction...
Well my scratch built pusher tends to turn right on its own. I have to apply sizable rudder trim to keep it straight. Could this be due to prop/torque reaction?

On a pusher i am assuming you have a small prop, in that case its most probably the thrust angle :-\

well!! I got a 9 inch prop on with a low Kv motor. The motor is mounted straight in the sense the thrust angle is not visible.

9 inch is a big prop, if it turns only when you throttle up then the turning tendency is due to torque reaction which you'll have to correct by giving some correcting thrust angle.

is it happening on ground?

Nope. This was first noticed during maiden flight when I was trying to hand launch. When I threw the model straight into the wind, it travelled (maybe due to the force of the throw) in a straight line, but then very quickly kept turning right.
So it was solved by putting about 5+ degree left rudder as this is a 3 channel setup. since then it has been flying OK, but even then has a tendency to turn quickly to right but remains sluggish while turning left

too much of down and right thrust, adjust the mount, best is the hover test, inside house hover it ever so lightly holding the aircraft on its spine and see which side it is falling,adjust it to the opposite side. little bit of variation with varying power will be there, this is because of the corkscrewing air's interaction with the fin.

I thought it was right thrust, but then the motor is in line with the horz stabilizer and the nose. At least the right/down thrust is not visible.

There are 2 things [1] Torque reaction [2] interaction of corkscrewing air with the fin

[2] will depend on the pitch of the prop, RPM and distance from prop to fin

I think i have made my self clear.

now you need to counteract this, not my adjusting Rudder trim, but by adjusting thrust line

For post # 100 - Have you checked, the fin, tailplane and wing alignment individually and in relation to each other? Then is your fuse itself straight? All these will have direct contribution on your described characterstics.

For post# 102 - To centre the engine/motor after right thrust has been built it is common practice to offset the engine mount to the left (looking from tail).

Unless your motor/engine is rotating in a clockwise manner if the model turns right, it can only mean two things, either your thrust line is way off to right or the airframe is crooked. Start looking at thrust line (as adviced by Gusty) and then go on to other probable causes

could this also be if one wing is producing more lift than the other? being a scratch build I don't think I will be able to make exact aerofoils

The image in post #1 of this thread is the plane photo

http://www.rcindia.org/beginners-zone/i-finally-got-to-build-and-fly-a-pusher-trainer/msg42632/#msg42632

Pankaj
check your fuse, is it in the centre,? i have my doubts, used gimp to measure doesn't look like may be it is very slightly out

For Control Force , Power and What Servo to use read this thread

http://www.rcindia.org/beginners-zone/how-to-calculate-the-type-of-servo-needed/msg42979/#msg42979

Sir
My scratch built blue baby is doing exactly what you explained in dutch roll.
It oscillates the same way. If i do just the glide test (without power and without giving any control), it glides very nicely, very stable but as soon as the throttle is increased, it oscillates the way you explained and crashes.

How do i make it stable?

You can see the picture of the blubaby here:

http://www.rcindia.org/electric-planes/blu-baby-33-inch-using-monobloc/msg61203/#msg61203

extremely simple, give it 3 deg anhedral [see image]

Fro Speed of Sound and its relationship with temperature and how it varies with height , read this
http://www.rcindia.org/chatter-zone/sound-density-and-temperature/

Sir,
Will the dutch roll reduce if i increase the vertical stabilizer area?

Do both give it a little anhedral as well, Vertical fin is required for directional stab too, apart from its contribution in lateral stability

anhedral vs dihedral - that should be an interesting topic...

twist in the prop RpM and Forward speed, read this
http://www.rcindia.org/rc-general-topics/behaviour-of-propellor-in-rest-and-motion/msg62055/#msg62055

Why do pylon racers have wings like this ???

1. It is because of the Drag, Drag depends on wing in section and in planform. In section it needs to have low Thickness to Chord ratio (See Image 1) needs to be Straight in planform (See Image 2), both these put together will give profile cleanliness to the aeroplane, and therefore low Drag consequently Higher speed for given power.

2. In fact where the fuse joins the wing , the fuse needs to be waisted, this is to achieve a ideal body of revolution. called Area Ruling, this is to reduce the interference drag. (Aeroplane Shown above is not Area Ruled)

3. You will ask me if i sweep back the drag should be less, because all high speed aeroplane is swept back, the answer is they are designed to travel at transonic and supersonic speeds, so their Critical Drag Rise mach number needs to be high. (See Image). However at low RC Speeds Swept Wing has more drag than the straight wing

Any more Doubts ? Shoot


Next Topic is Gurney Flap

Waisting or Area Ruling (See Images) Self Explanatory

First of all, these models are called F5D models and they are relatively new, 1990 onwards. The wing tip is elliptical because it will lead to lesser induced drag than square tipped planes whose effect becomes more prominent at higher speeds. Also higher aspect ratio will lead to reduced drag, but making the model more difficult to control.They use the MH airfoil whose transition is much later on the wing. Transition is the change from laminar to turbulent flow, laminar is what you want.

But all that can be achieved with an elliptical wing tip, but these planes have a very peculiar tip. PFA pic.

From what I understand, the stream of air on the lhs wing tip leaves it much later after the wing, where vortices will be formed, on the other hand the stream of air on the rhs will leave sooner leading to vortice being created very near to the wing.

Sorry for the shady drawing, but explains it. Experts correct me if im wrong.

Sweet!
Thanks a lot Augustinev and Husein. Will rep++ whenever I can :bow:

This was bugging me for so long. I feel much better now :)

Good to see the reputation system being put to good use :) Over the coming years, this should be helpful to everyone.

Let me answer this question in two parts (a) Why Does a Vortex form (b) How can it's effect be minimised

(a) Wing Produces Lift agreed . in straight and level flight this lift needs to equal weight. This lifting force will translate to low pressure on top of the wing and high/not so low pressure on the bottom of the wing. This pressure differential for a given weight has to be same irrespective of the wing shape that means the vortex will remain same, because when air leaves the wing has to come back to neutral pressure

(b) how do you minimise its effect. Answer is simple instead of one big vortex, create multiple small vortex and one not so big vortex. advantage in this setup will be the core low pressure of the big vortex in case two will be less and consequently the loss (Also called the tip spillage) will be slightly less, HOWEVER the effect is only 10-12% overall, because of the pressure differential remaining same

A tip shaped like left wing of SLS's image will have multiple small vortex and one big vortex. Right wing will have one big vortex with much lower core pressure.

like the vg's we r using on the addiction x  :headscratch:

VGs induce Small vortex airflow which prevents separation of airflow at high angle of attack (Basically low speeds) because a turbulent flow is thick , has more energy and sticks to the surface longer (See image), VGs induce turbulent flow so that the flow doesn't separate at laminar stage itself. Thats how low speed handling of our addiction X is good. yeah small vortex by VGs analogy is bang on


Also read
http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg44317/#msg44317

Exact scaling of an aircraft, for testing purposes, isnt just scaling down the size, coz thats just static scaling. For dynamic scaling a lot of factors would have to be taken into account, Reynolds no., Froudes no., moment of inertia etc. I had read about this in a book called Modelling Flight, how do you go about this physically i.e. make a model that takes all this into consideration.

This is called Scale Effect, it is simply because of the relationship of forces vis-a-vis the size of the aircraft. if lift =CL ½ σ V² S. if i halved 'S' (Surface area, read post http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg41421/#msg41421) to see the same effect i need to adjust 'σ' and 'V'.this is where our dimensionless quantity called Reynolds number comes in. read more on Reynolds Number here (http://en.wikipedia.org/wiki/Reynolds_number)

Read for runway Orientation , downwind landing etc this whole thread

http://www.rcindia.org/chatter-zone/runway-traffic-90-minutes-compressed-into-230-minutes/msg64098/#new

Sirs,

I had read a book recently. "Flight without formulae" by A.C. Kermode. It deals with all the basic concepts of Flight/Aerodynamics.
Hope it will be a very useful to some beginers here. :)

try "Mechanics of Flight" by AC Kermode even that is good one!

Thank you Sir.
I will search for the book in my college libraray, once my college reopens.

As a beginner i kept wondering why do twin engine planes have propellers rotating in opposite directions  :headscratch:

found the answer here .....

http://www.aerospaceweb.org/question/dynamics/q0015a.shtml

Had the same question, & I thought I had partially the answer. The Bristol Beaufighter had a marked propensity to swerve on take off(It had propellers rotating in the same direction),whereas the P-38 lightning was given contra rotating props for improved handling.....but I knew there was more to it.thanks for the link!

The link is Inadequate , watch out for this space for prop induced swing , torque effect , ground loop etc.

Augustinev Sir,

Noticed your current total number of posts. It's 1234 ...  ;D

Yeah, he's properly taught us the '1234' of RC through all those!  ;D

Thanks! didn't notice that. I remember the 1000 th post of anwar bhai, if I am not wrong in Sushil sir post, be that as it may.
PIO( pilot induced oscillations) occurs when the aircraft lag and your control inputs match and is out of phase. There are long period oscillations called phugoid. This is not dangerous , dangerous is short period oscillations, occurs during landing. Margin of error is less. Remedy ? I case you get into oscillations (normally happens after touchdown) just hold the elev , do not move she will settle down. Happens in heli too, ESP during hover. Factors Affecting aircraft lag? Please read http://www.rcindia.org/radios-and-receivers/sanwa-the-choice-of-champions/msg72826/#new add air speed altitude and angle of attack to that list.

Now, contra rotating props and pusher props are same or different?
So if I understand correctly the difference between them, a pusher prop would throw wind forward while a normal prop would throw backwards right? In an electric setup, we often make the normal prop work as a pusher by interchanging any two leads of the motor/esc combine. How different it is from using a pusher prop?

Contra rotating props, on an aircraft, will BOTH push the air backwards (towards the tail) to make the aircraft fly forwards. One would be mounted on the port wing and the other on the starboard wing. While one would spin clockwise, the other would spin anti clockwise to negate the torque generated both by the engines. Alternately they could be both mounted on the same shaft as in the picture. Note the opposite pitch on the props.

Also, from what I know, to turn a normal prop (in an electrical setup), you not only have to interchange two wires from the ESC to the motor, you also have to mount the prop backwards on the motor shaft.

The above is my understanding and I would like to know if it is correct.

Thats exactly my point. In an twin motor electrical setup, if one is to move 'contra' then it will become a pusher. so one motor in tractor and another one in pusher configuration is not flying. PERIOD!!!
So think there is some problem in my understanding

Haha. Don't get confused. If one is tractor and the other one pusher won't they cancel each others thrust? It is just that the prop twist is so adjusted that both rotating in opposite diection still threw the air back , our man newton pushed the airplane forward, this setup cancelled each others torque reaction , but the swing is not only due to torque. It is also due to rotating mass of air and it's reaction with fin. This is a large contributor, then the question is why twin prop? The engine in this airplane though had enough did not have the adequate rpm . It could swing a larger prop but the Clearance was less. Therefore two props. That's about it.

then please answer the questions on #140. The main issue is if I am building a twin motor electric setup, how do I do it?

Not necessarily the prop should rotate anti clockwise it can rotate clockwise too, prop for that is twisted the other way, so that they both throw air backward while rotating in the opposite direction. Even for a Rc airplane such props are available.

What he means is, you put a tractor prop on one side and a pusher prop on the other side and rotate them in opposite directions. Then they will both push air in the same direction. :)

@sukurt
Thanks.... that is the answer that I can understand....

VC

Not very clear what you mean. Reversing the prop does not reverse pitch It will still remain the tractor (or pusher) it was, but with lower efficiency.

from what I know, the marking in the prop always points to the front whether the configuration is a tractor or a pusher.

Prop has something called the Helical Twist. It is CW or CCW. tractor pusher is a wrong terminology , why? Can a tractor prop be used in a pusher configuration? Of course you can , whether in front or rear , a CCW prop will rotate CCW to throw the air back , a CW prop will do the opposite,
Pankaj, you are thanking sukurt for simplifying matters? Actually he did not, there is nothing called tractor prop and pusher prop, it is very colloquially, loosely and incorrectly used terminology,

To simplify and put matters to rest
(a) viewed from front if a prop is rotating Counter Clockwise ( CCW) then it is CCW prop, it could be a tractor or it could be a pusher.
(b) viewed from front if a prop is rotating clockwise(CW) then it is a CW prop,
CW prop is used as a port inboard and starboard outboard prop ( in a two/four engine configuration, like the super Connie, this too is not a rule though, beaufighter is an example where both prop rotated to the same side, advantage was you needn't look for a spare port or starboard engine, one spare engine worked for both, ground looping landing accidents outweighed this advantage though) , also used as a pusher prop

I hope I have made myself clear. If there is still some doubt, feel free to shoot

To be more specific, the front of the motor, not the airplane.

OK I am confused.

Hobbyking does sell "pusher prop"  so not sure why they misrepresent on a 7x4 prop these are two

Pusher   http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8044
Tractor http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8011

so now as I understand, when I mount the motor in the front and facing the front, it is called a tractor and when I mount it near the tail and facing away from the nose, it it called a pusher. In the pusher arrangement, even if I mount a normal prop, the marking is towards the nose and I just change the direction of the wind by interchanging two wires connecting the motor to the esc. Aparantly,interchanging the wires makes the motor rotate anti clock wise.  In both these cases the wind travels from the nose to the tail hence the plane moves forward


So to understand the twin motor setup, both the motors have to push the wind from head to tail but one needs to move in clockwise direction while the other in anti clock wise. So how am I supposed to do this because given what I have described, one would throw wind in opposite direction to the other? Since  this is not what is supposed to be, I am sure I do not understand how the setup is to work


 

Thanks Sushil sir, there was a possibility of confusion there,

Now pankaj how do you do a contra rotating prop is a complicated, let me try to be simple.
If using same motor or engine you need a gearing mechanism which rotates outer shaft CW and the inner CCW. you can also use two engine/ motor through gearing doing the same thing.
Complication in a contra rotating prop is pitch of the rear prop, matching that without a CSU( constant speed unit, which keeps prop pitch optimum depending on flight conditions) is counter productive, in an Rc setup contra prop is optimum only for a particular speed , because the inlet velocity of the rear prop is the exit velocity of the front prop and it is a different direction. The interaction between both has something called Cascade Effect,
Bottom line contra prop in  just cosmetic in Rc, advantage accrued is far far less.

so what happens if the motor I use is not geared? direct drive brushless types?
secondly, I have not seen the EDF units being sold as pairs (as in left EDF unit being different than the right one) so aparantly they operate in the same cw or ccw direction (thats what I think) So how do they balance out?

Closer to drag line this effect is less in a edf unit.

I guess I am getting confused in two aspects.
1) the direction of rotation of the motor
2) the direction of the prop.

so if I understand correctly, a prop is like a screw you turn in one direction it goes in and turn in the opposite direction it comes out. Now if a standard screw would go in while turning clockwise and suppose there was a screw with threads such that it goes in anti-clock wise then this might be similar to the twin motor setup -right?

Bingo, that's why da vinchi called it and even now it is called airscrew

read this post for insight into Flaps

http://www.rcindia.org/rc-general-topics/flaps-up-or-down/msg77245/#msg77245

Back to the drawing board.

Made a pusher 50" span the wing is polyhyderal, shapped like this \______/. The flat part is 30". The elevated portions are 10" each and have ailerons. Chord is 7".
The horizontal stab is about 20% of the wing area (7x50) and the vertical fin is about half the stab.
CG checked at less than 1/3 the chord length.
Motor is 1400Kv with a 7x4 pusher prop.


The moment the bird takes to air, it kind of has a very erratic behavior. It banks sharply on left even with a full aileron trim. It goes up and down like a tail heavy bird, but I suspect CG is not the issue here.

So the question is what should be checked? I know it may not be possible but - any suggestions?

The symptoms indicate a warped wing :-\

polyhedral if not made well will always give you trouble, few things i need to check please post some pics

hi,

your specs match mine. i have built a pusher with 50" wing span, 7" chord.
the wing is tip dihedral the same which you showed.
i have set it up for 3 channels, with a 1400kv motor, 18A esc and a 6x4 prop.

flys very stable. infact tested with a 2200mah lipo and the model was nose heavy would not glide
when motor was turned off. surprisingly flies with a 1300 mah bat and glides also very well. the CG seems to be at 50% wing chord. i wonder how  :headscratch:

pls see pics below.

There seems to be a lot of Doubt of Descend that's why this post, i urge all of you who want to know about descend to please read carefully

Knowing this is important, i have seen many people on engine cut pull back (They call"Saar i gave max up elevator yet i crashed ") and crash, GLIDING , SLOPE SOARING, LANDING BACK AFTER A CUT, for all of these this topic will be useful, please read carefully.

Angle / Rate of Descent in Glide

17.   As the aircraft descends on a steady glide path, it forms a finite angle with respect to the horizontal. This angle is called the Gliding Angle.  While gliding at a steady speed, the aircraft would also have a finite rate of descent, which will be proportional to its gliding angle and the speed of gliding.

18.   An aircraft in glide may be flown at any speed by choosing the angle of descent of the aircraft, i.e. by steepening the descent. The aircraft may be flown at a higher speed with a correspondingly higher rate of descent or it may be possible to fly the aircraft at speeds as low as its stalling speed. From the pilot’s point of view, lowering the nose of the glider may not necessarily mean that the rate of descent would increase and the range of glide reduce. Similarly, slowest speed during glide neither means the shallowest angle of descent nor does it mean the slowest rate of descent. To understand the mechanics of a gliding descent let us understand the forces that act in a glide as indicated in Fig
 
Forces in a Glide

19.   The four forces in flight are Lift, Weight, Drag and Thrust. Since there is obviously no thrust available in a glide, the balance of forces of the remaining three forces is as follows:

(a)   Weight is balancing the lift as well as drag, however the addition is not ‘algebric’ but ‘vectoral’. From the Fig 16-6, it can be seen that the total (aerodynamic) reaction obviously is balanced by the only available force, that is ‘Weight’.
(b)   The drag accordingly, is being balanced by a component of weight  i.e.   W sin θ.
(c)   The lift is being balanced by another component of weight i.e.  W cos θ.

The Lift continues to be at right angles to the flight path and Drag continues to be along the flight path in the reverse direction of flight.  The only source of energy to do the work, which is being done against the drag, is the potential energy of the aircraft, which is being slowly traded off as the height of the aircraft is reducing.

Gliding for Endurance (For Slope Soaring)

20.   Gliding for ‘endurance’ means gliding for maximum time in air.  Obviously, from a specified commencement height, an aircraft with the least rate of descent would stay afloat in air longest.  

21.   In Fig we can see that for minimum rate of descent, V sin θ must be minimum.  From balance of forces in a glide:

D   =    W sin θ

Multiplying the equation with velocity V

DV    =    W sin θ.V   OR
Vsin θ    =    D.V                  
       W

From Fig  we know that

ROD    =    V sin θ

Therefore, from equation , for the ROD to be minimum, the value of D.V/W should be minimum.  Assuming the weight to be constant, the minimum ROD and hence maximum endurance of the aircraft would be achieved at the speed requiring minimum power.

22.   when flying at the endurance speed least ROD is required above and below this speed (Min power speed) the ROD would increase.

Gliding for Range When engine Cuts  :banghead:

23.   Gliding for range means gliding in a fashion so as to cover maximum distance by the time the aircraft touches down on ground. From Fig , for a given commencement height, the maximum range would mean a point farthest on the ground from the point vertically below the commencement point.  This in turn would mean the smallest gliding angle or the ‘flattest’ glide.  For example, a TB 20 aircraft has approximately an angle of glide of 4.7 degrees and the CAP 232 aircraft has an angle of glide of about 12.95 degrees when flying at respective best L/D angles of attack.

24.   From Fig , the triangle formed by Lift, Drag and Total reaction is geometrically similar to that formed by Distance, Height and Glide-path.  Now, if distance is to be maximum, gliding angle must be minimum.  θ is minimum when Cot θ is maximum or  Tan θ is minimum.  From the balance of forces, since L  =  W . Cos θ  and D = W . Sin θ,   Cot θ  = L / W.  Therefore θ is maximum when     L / D is maximum.  Further, in most aircraft the gliding angle is quite shallow, being less than 15 degrees hence the lift can be safely assumed to be equal to weight. For the more mathematically inclined reader, truly speaking the lift will be equal to Cos function of the gliding angle, which in case of a glide angle of 15 deg works out to be L  X  Cos 15 = L X  0.9659 i.e. less than 2% error, which will be even lesser at lesser glide angles.

25.   Therefore best (smallest) angle of glide depends on maintaining an angle of attack that gives the best lift/drag ratio. Since lift is assumed to be equal to the weight and hence constant, best L/D ratio would correspond to the ‘minimum drag’ condition. For the mathematician, like mentioned earlier, in case of steeper gliding angles, the lift would be lesser than the weight by a factor of cos θ. In case the aircraft is equipped with an angle of attack indicator, the pilot needs to just maintain the same angle of attack as earlier; however if the aircraft does not have the AOA indicator and the pilot has to go by the EAS, he would have to reduce gliding speed by a factor of √cos θ to continue to maintain the optimum angle of attack for best range.

PS
For some of you initial reading might sound confusing, i do urge you to read and understand, shoot questions after you have done so

What is this? How to check?

Another thing is that this is my third pusher. First one was 3 channel setup - flew very well, the next two I tried with ailerons ( one dihedral and one ppolyhydral). Same uneven flight characteristic noted on both wings. So was wondering if something special needs to be done for putting in ailerons on pushers - specially for scratch builds

hi,

ever wondered why the easystar does not have ailerons. it flies best with rudder only.

even the axn floater requires rudder input alongwith ailerons. i am mixing rudder with the ailerons on the axn.

as per my experience. slow flying planes fly best with rudder only.

for speed models ailerons are the best.

my current pusher is 3ch and it flys beautifully. hence no intention of putting ailerons. infact all my students like to fly it.

regds
sandeep

AFAIK this has nothing to do with speed of the plane, i have a super slow easyglider which almost refuses to turn without any aileron input. On the other hand Amar has a super fast easystar which he flies like a pylon racer just on rudder.

I doubt that this is the reason of uneven flight characteristics. Only thing to remember is with sufficient dihedral/polyhydral you wont need ailerons. Ailerons are not very effective for turning if the wing has dihedral/polyhydral and rudder is not very effective for turning if the wing does not have enough dihedral/polyhydral. Augustinev is the best person to explain dynamics of this but before that you should post pictures of your wing.

About warped wing; its when one wing "twists" out of symmetry from the other wing. PFA a picture worth many words :)
image source (http://www.rcgroups.com/forums/showpost.php?p=5298623&postcount=1509)

i didn't want to take the path that about to take now, the reason for me to go a deep into it is that, there appears to be a great deal of doubt amongst even senior aeromodellors on the theory aspect, especially  of turn performance (Since theory  is lacking they are exhibiting the same in teaching and building models).well here it for you,


Axes of Movement of an Aircraft

1.   Lateral Axis.    The lateral axis is a straight line through the CG, normal to the plane of symmetry, rotation about which is termed pitching.  This axis may also be known as the pitching or looping axis.  If any component of the forward flight velocity acts parallel to this axis the subsequent motion is called sideslip or skid.

2.   Longitudinal Axis.    The longitudinal axis is a straight line through the CG, fore and aft in the plane of symmetry, movement about which is known as rolling.  This axis is sometimes called the roll axis.

3.   Normal Axis.    The normal axis is a straight line through the CG at right angles to the longitudinal axis, in the plane of symmetry, movement about which is called yawing.  This axis can be referred to as the yawing axis.

4.   Fixed Relationship.     The three axes are fixed relative to the aircraft irrespective of its attitude.  Fig below shows the major axes and the possible movements about them.

Now imagine a yaw (Caused by applying only rudder) in an aircraft the outer wing will travel faster than the inner wing this will cause the aeroplane to roll, this roll will tilt the lift vector which now supports the weight and also gives necessary centripetal force for the aeroplane to turn

If If, lateral stability of a model is good and directional stability poor (High winger, High Dihedral, small fin) , this yaw induced roll will corrected by the lateral stability and the aeroplane will right itself back, to turn with rudder if you apply more rudder she will do a kind of an unbalanced skidding turn (Evident by the way where if you have to push down on elevator to avoid the aeroplane to climb)

At last it is all the interaction of movement of aeroplane on one axis with an another (Including aerodynamic and inertial forces, do not discount inertial forces especially in a model aeroplane inertial forces play a large role)

Do not ever jump to conclusion without reading about it, it can be dangerous to the model and you

For an aircraft to turn, centripetal force is required to deflect it towards the centre of the turn.  By banking the aircraft and using the horizontal component of the now inclined lift force, the necessary force is obtained to move the aircraft along a curved path.

1. If the aircraft is banked, keeping the angle of attack constant, then the vertical component of the lift force will be too small to balance the weight and the aircraft will start to descend.  Therefore, as the angle of bank increases, the angle of attack must be increased progressively by a backward movement of the control column to bring about a greater total lift.  The vertical component is then large enough to maintain level flight, while the horizontal component is large enough to produce the required centripetal force.

Effect of Weight

2.   In a steady level turn, if thrust is ignored, then lift is providing a force to balance weight and a centripetal force to turn the aircraft.  If the same speed and angle of bank can be obtained, the radius of turn is basically independent of weight or aircraft type.  However not all aircraft can reach the same angle of bank at the same speed.

Effect of Thrust (See my MiG 29 Video you will realise what i am talking about)

3. as far the effect of thrust on level turns has been ignored.  However, the thrust, or lack of thrust, may be the determining factor as to whether the optimum speeds for turn i achieved.  Even in level flight it can be seen clearly with some aircraft that a component of thrust is acting in the same direction as lift due to the inclination of the thrust line from the horizontal.  This effect becomes more pronounced as the critical angle of attack is approached (see image).  The thrust component assists lift so that either less lift is required from the wing  or the turn can be improved beyond that indicated by simple theory.  Just as lift was split into two components in turn fig, one to oppose weight and one to provide centripetal force, so the component of thrust that acts in the same direction as lift can also be split into two similar components.  This is the reason for the remarkably  mall radius of turn of which some high performance aircraft like the Mig-29 and SU-30 (using thrust vectoring) are capable of. 

4.   It should be realized that many trainer glider aircraft do not have sufficient thrust to reach and sustain the optimum speed thrust assisted turn.

Sandeep
See easy star two's flying chrac, same aerofoil see the difference


That is because of excessive lateral stability, even high performance fighter jet requires rudder (Because high sweep increases lateral stability, but high sweep is required evil for supersonic flight, so it is all about lateral stability and directional stability and how harmonious the airplane is )

Not a true statement at all, read the reps above, it is all the interaction of lateral stability to directional stability both static (the initial response) and dynamic (What happens after a while, to put it in a layman's term)

Does the longitudinal stability has anything to do with the size of the stabilizers (horizontal and/or vertical)?
Does the distance between the GC point on the wing and the hinge of rudder/elevator  has anything to do with stability?

Tailplane and Elevator.    The function of a tailplane is to supply any force necessary to counter residual pitching moment arising from inequalities in the two main couples, i.e., it has a stabilizing function.  This is achieved most commonly by fixing a hinged flap behind the tailplane by which the direction of force being generated, as well as its magnitude can be varied.  The force on the tailplane is positioned some distance from the CG means that it can apply a large moment to the aircraft (see fig). For this reason the area and lift of the tailplane is small compared with the mainplane.

Additional Information on the Tailplane

(a)    Design.    The tailplane may be required to produce either an upload or a download. Therefore the tailplane is usually (Not always) symmetrical in design.

(b)   Tailplane Flight Longitudinal Dihedral.    In most conventional aircraft, the tailplane operates in the downwash of the mainplane. The downwash reduces the effective angle of attack of the tailplane (usually the tailplane operates at half the angle of attack of the main plane). The reduced angle of attack of the tailplane is termed as the Tailplane Flight Longitudinal Dihedral.

(c)    Tailplane Riggers Dihedral.    In order to offset the reduction in angle of attack due to mainplane downwash, the angle of incidence of the tailplane is usually rigged to some positive incidence relative to the main plane. This is referred to as Tailplane Riggers Dihedral.

(d)    Trim Drag.   (Very Important fro RC Flying, if your aeroplanes nose is too heavy you will add to apparent weight to the aeroplane in terms of trim drag) In order to maintain straight and level flight, the tailplane is required to produce an up/down force to counter any imbalance between the thrust - drag and lift - weight couples. If the tailplane has to provide a downward force, this additional force adds to the effective weight of the aircraft. The increase in weight has to be countered by increasing lift (by increasing speed or angle of attack). The additional drag generated in this process is called trim drag.

(e)    Case of Reducing Speed and Stabilized Low speed.    When speed is being reduced, the stick is being brought back, i.e., the elevator is deflected upwards, implying that the tailplane is generating downward force (lift). However, this is a transient phase. In a stabilized low speed condition of level flight, the center of pressure has moved up (as the angle of attack is higher) and the nose down lift-weight couple is reduced. This would cause the nose down pitch to reduce. Now, to maintain straight and level flight, the force being produced by the tailplane is less downward. The converse occurs in a case of increasing speed and stabilized High Speed.

f.    Variation of Speed in Level Flight.    For level flight the lift must equal the weight. From the lift formula (L= CL ½ ρ V2 S) it can be seen that, for a given aircraft flying at a stated weight, if the speed factor is decreased, then the lift coefficient (angle of attack) must be increased to keep the lift at the same value as the weight.

g.    Aircraft Attitude in Level Flight.     At low speed the angle of attack must be high, while at high speed only a small angle of attack is needed to obtain the necessary amount of lift. Since level flight is being considered, these angles become evident to the pilot as an attitude, which will be nose-up at low speeds and nose lower at high speeds. The difference between low and high-speed attitudes is most marked on aircraft having sweptback or unswept wings of low aspect ratio,

 ???
 ??? :headscratch:

 {:)} :salute: :bow: :hatsoff:

:rofl:

Augustinev,
What about the vertical stabilizer's size? How does it effect the stability?

Directional Stability, (Most of the times it is the limiting factor manoeuvring at high angles of attack) and as an offshoot lateral stability (If the fin is dorsal then it contributes positively to lateral stability and if the fin in ventral then negatively

Two questions.
1) The stabs and the fins have a ratio to the wing area. for example, in a high winger tractor, the stab should be about 15-20% of the wing area. While if it is less, then it may not provide necessary stability, but what happens if it is more?

2)While scratch building I have noticed that it is nearly impossible to make the wings/stabs parallel to each other, nor for that matter the fin would be exactly perpendicular to the stab. There exists a difference even if it is less than a degree in angle or 1mm in distance. The materials that we use for models is soft. Sometimes due to storage or due to faulty constructions or due to repeated hard landings, these angles/measurements changes. How do these variations effect an RC model (not the real plane).

Not answering the questions just suggesting that while you are thinking about stab sizes you should also consider the movement arm length. Refer image posted by Augustinev on reply #174.

ps: this is my favorite thread on RCIndia :)

Arm length part is almost similar to a basic lever ( effort - fulcrum - load). So that part I can relate to :D

Well,
These questions are pushing me to cover issues which will scare away guys  :banghead:

There are two terms called Decalage and Longitudinal Dihedral

Decalage When two airfoils have different angles of incidence, (from the French word for “shift” or “offset”)  The more wing to tail decalage you have, the more vigorously the airplane will oppose any attempted deviation from its preferred angle of attack. +ve decalage is + ve responce by the model, -ve decalage is -ve response from the model (If you watch carefully the model while it is flying is slight wind condition , without your input when hit by a small gust of air see what it does (See Image), if updraft of air and the nose comes down it is +Ve and nose goes up it is -ve, there are theories of where the centre of mass is etc which i am not going into presently)

The Angular between the angles of incidence of the wing and tailplane is called Longitudinal Dihedral. Positive if the wing incidence is greater. it is like the Dihedral you give for lateral stability, while scratch building give slightly more positive incidence for the main wing and have a different and less incidence in the tailplane, aeroplane will be longitudinally stable as well

See image for Balance of forces using Rainfall Analogy to make things clear (As brought out by SLS)

Like I said, in simplistic terms, I am able to understand the wt x distance from the fulcrum needs to be same on both sides of the fulcrum ( CG /NP ). So what this means is that if the stab area is more, then not only the effect of rainfall is more pronounced, but as the weight of the tail also increases, it would mean additional weight on the nose. In theory as far a stab and wings are concerned, this is understood (did I understand correctly?).

What about the vertical fin? how does this get represented on the rainfall/level theory? The simple stuff on the above diagram is that the lift produced by the stab and the wing are the two loads. While this is understood for pitch movement, on the Yaw front, the tail fin appears to be the only load so what is it balancing against?

Are my questions making sense?

bigger tail will have more tail lift , nose will pitch down

Fin maintains direction and contributes slightly to lateral stability as well

not always because some planes have inverted airfoil for tail so that nose pitching is reduced. So if the nose is heavy it can be compensated by an inverted airfoil for the tail

in the design consideration inverted aerofoil (Like the Dornieir 228) is for completely different purpose. We will only complicate the matter. at RC Level let us keep it simple

ya i agree its not used for this purpose.
i just wanted to put up the point.
i had a problem with a heavy nose once and tried out and it worked out well. the only thing is it decreases the speed of the plane.
and sure it complicates things a bit.

The simple moment figures are clear.

Now, If the CG resides just below the wing lift point ( one arm length = 0), so there is no need of stabilizer,

and

if the CG goes left (As per Pic right arm length = -ve), one moment should be in opposite to other theriotically to stabilize and stabilizer force should be downward insted of upward.

A simple MOMENT Calculation only (Recall Strength of materials). :D

Am I Right? Is this related or useless?

? about centre of mass? how will aeroplane behave? that's why i said let's leave it at that

Augustinev,

Please look at the problem in post #24 of this thread http://www.rcindia.org/electric-planes/scratch-build-powered-glider/new/#new

Look at this HK model... http://www.hobbyking.com/hobbyking/store/__8472__Hobby_King_Piaget_EPP_CF_3D.html

Seems to have a tail fins type of assembly on the wing as well. Does this serve any purpose?

Chato Read this
http://en.wikipedia.org/wiki/Wingtip_device

Read this thread and the reply for some insight into 'V' tail config

http://www.rcindia.org/self-designed-diy-and-college-projects/coro-whistling-racer/msg84898/#msg84898

Basic points that could be considered while designing scratch built glider (Some more reading on the subject will be required)
http://www.rcindia.org/electric-planes/scratch-build-powered-glider/msg83934/#msg83934

Flaps, Spoileron & Crow/Butterfly

I will try and keep it as simple as i can,

Flaps

1. what lifts the wing is the angle that leading edge  of the wing and the trailing edge of the wing makes with the path that the aeroplane follows,
2. when you lower flaps what happens is the trailing edge of the wing is lowered and the aeroplane without changing the position of the nose and the speed gets a boost in the lift. also the camber increases.
3. what happens in take off is that it is able to lift off at a lesser speed and at a lesser runway length, but the drag also increases
4. that is why after take off the flap is raised and the wing now becomes clean and produces less of drag ,
5. same thing happens in landing with increase in lift the aeroplane is able to, and at a lesser speed make landing easy and reducing the landing roll.


1. Flaperon in RC parlance is when you you use a full length aileron, also as flaps


2. for reducing the landing roll you can use it like a flap and aileron, increased lift can be used for not only landing you can use it to fly the aeroplane at very less speed with stalling (Wing dropping) some use it even in a rolling harrier. in real life aeroplane too you use it, in fact hawker hunter had flaps at 15°, 23°,30°, 38°, 45° & 60°, initial couple of positions of the flaps were called Combat Flaps used during the low speed regimes of the combat so that aeroplane had adequate lift and does not spin or stall

Spoileron rolls and yaws the ailerons, not by differential lift ,  by dumping lift on one side, in RC, it is used to negate cross coupling, however in real life it is used in a short span wing where this method is more effective than aileron , in a sweeping wing (Like the F-14, MiG 23 & MiG 27 ) at the fully swept back position spoileron is used, it is also used in long wing where aileron can cause twisting moment and break the wing or negate the differential lift due to twist caused by the aileron.

crow/butterfly flaps is when ailerons go up and flaps go down. works quite like an airbrakes, to reduce speed

wash out/ Wash-in Due to Flexure

Disclaimer (This discussion pertains to RC aeroplanes and esp foamies, therefore aeroelastic tailoring has been left out of the discussion)

When a swept back wing flexes due to less of torsional rigidity the incidence at the wing tip reduces , effective lift production is concentrated inboard  of the wing (See image) wing tip therefore looses lift, the centre of pressure moves forward and aeroplanes pitches up, if the tip lift loss is high, she will pitch up and yet loose altitude  :banghead:

How does this happen (You need to have some imagination  8-), easier way is to fold a paper and see)

When a swept back wing flexes under load, all chordwise points at right angles to the main spar are raised to the same degree,  see image two, the points A and B rises through the same distance and the points C and D rise through the same distance but through a greater distance than A and B.Thus C rises further than A and there is a consequent loss in incidence at this section. This effect is termed, ‘washoutdue to flexure’, and is obviously greatest at the wing tips. It is most noticeable during high g manoeuvres when the loss of lift at the tips and the consequent forward movement of the centre of pressure causes the aircraft to tighten up in the manoeuvre. (very applicable on foamies).

Now washout is structurally not dangerous, because wing tip is unloaded of high lift

Wash-in Due Flexure on a swept forward wings (Like su-47 berkut)

In a swept forward wings if you see the image above due to flexure the wing tips will produce more lift, this will overload wing tips and it will break away clean . The image i have put here is from the rcgrops (http://www.rcgroups.com/forums/showpost.php?p=15309060&postcount=9), you can see how cleanly it has broken, if you see the thread he has attributed it to flutter, it is not, it is due to wash in due to flexure

read a little bit more about berkut here

http://www.rcindia.org/electric-planes/su-47-berkut-tomhe-plans-build-and-fly-log/msg91398/#msg91398

Why are Flaps required ? here
http://www.rcindia.org/electric-planes/using-ailerons-as-flaps/msg96159/#msg96159

Adverse Aileron drag (I have talked about it earlier) and why should you setup aileron differential



For years,  modelers often used 'Y' cables for ailerons and offset servo output arms Very rarely in India though) to achieve differential aileron movement. Today, however, using separate aileron servos and the aileron differential program menu in your radio has greatly simplified the task. Before we take a closer look, let’s first check out the Aerodynamics  >:D of our model during a turn or a roll to understand why aileron differential is important.

Adverse Aileron Drag

Typically, most models are set up with equal amounts of elevator (pitch up and down) and rudder (yaw left and right) control surface movements. But when it comes to ailerons, equal amounts of up and down (roll left and right movement), can cause the model to yaw in the wrong direction. Reason: When the ailerons are at their neutral positions, the lift and drag produced by each wing panel is equal and the model tracks straight ahead. But when a model has ailerons that move in equal amounts both up and down, the amount of drag (and lift) created by the wing panel with the down aileron becomes greater than the one with the up aileron. The panel with the aileron pointing downward moves up because it creates more lift. The opposite panel goes down (less lift) and causes the model to back toward the up aileron. Because of the increased drag caused by the upward motion, that down aileron wing panel also slows down; this causes the model’s nose to yaw in the opposite direction of the roll. The model yaws nose right in a left-hand bank/turn  :banghead: . This condition is known as adverse yaw. Without aileron differential, most airplanes require a certain amount of coordinated rudder to prevent, or at least minimize, adverse yaw while the model is banking through a turn. For sport and scale planes, this can be done manually or with a program mix-however, it won’t work in all types of flight conditions. in some high performance ARF like the CARF Yak 55 Sp and in real life aeroplanes we have something called the frise aileron (More about it later). This adverse yaw thing is also an important consideration while flying aerobatic planes. Aerobatic pilots need to set up their models to react in pure yaw, roll and pitch motions. During a roll (whether it’s executed on a horizontal or vertical line), the model must roll axially without its nose yawing or wandering off the straight line of flight. Aileron differential helps keep the model’s tracking straight.

Symptoms of a an Adverse Yaw
 
1. The model skids through turns.
2. The tail drops during a turn.
3. The nose swings out of the turn.
4. It’s very difficult to roll your model in a straight line.

Using your radio’s programming is the easiest way to get the job done.

Radio Programming

Assuming you have dual aileron servos (One or more servo / aileron). One connected to the aileron receiver port and the other in the Aux.1 port (Typically Ch 6). Make sure the aileron servo moves in the proper direction.

Activate the flaperon wing type or, depending on your radio system, the dual aileron function.

Start with 30% to 40% differential (down going aileron 30 or 40% less than up going aileron).

If differential mix is backwards (more down than up), reverse the servo connections by switching the aileron and Aux. 1 servo leads.

Adjust the differential percentage after flying the model (You need to watch it carefully). Land the model before making adjustments and test fly again.

Happy Differentialling  {:)}

thanks for the great knowledge Sir.. :salute:

Ah, this thread is a boon for guys like me who don't like reading thick books!
Thanks so much for explaining it so clearly and plainly Gusty sir!   :)

Waaaaaaaaa.... :'(...I am totally out of my depth. :headscratch:. :banghead:You can always say: 'Leave out if u can't follow.' But how can I ?  :-\ My technical knowledge is next to NIL. Now I have to learn the hard way. Otherwise, how to interpret the results of structural modifications I incorporated in to the model if I am scratch-building and experimenting? Gusty, man, you are taking me by the collar to think n learn.  :salute: I used to think that all I have to do is get a model, assemble it, put in electronics, power it up and fly. :giggle:  But I still enjoy learning things, though most of these things you all are discussing are bouncers, going over n above my head. My situation is just like the man trying to walk forward n always back to square one, just like the figure of the man in SWAPNIL'S post. >:(.
Thanks, any way.
eaaaargee.

Haha! Actually that figure symbolizes the amazing nature of curiosity.
The more knowledge you acquire, the more curious you get. The more curious you get, the more mysteries you ponder upon. The more mysteries you ponder upon the more you study and acquire knowledge! And on and on it goes...it's a mystical cyclic process!

So the more forward the man walks, the more mysteries he stumbles upon and the more he enjoys it!

It's just shows how you perceive life...
For those who see acquiring knowledge and solving mysteries as difficult and pointless and do things just for looking 'cool', life is just a dull one way trip! 
For the curious and knowledge hungry folk life is a beautiful adventure!

This is why I respect Gusty sir and his knowledge sharing so much!  :salute:

yes..great sharing of knowledge.. :salute:

Thirukural Couplet 396

தொட்டனைத் தூறு மணற்கேணி மாந்தர்க்குக்
கற்றனைத் தூறும் அறிவு

meaning

In sandy soil, when deep you delve, you reach the springs below;
The more you learn, the freer streams of wisdom flow

I strive to keep it simple :)

 :salute: :salute: :salute:

Gusty bhaiya, I have a silly question regarding camber line. Well it is simply the line that is equidistant from the upper and lower surfaces. Now, the problem is how do I obtain these mean points because if I draw a line from the top surface to the bottom surface on the cross-sectional plane and then I find the center of that line, someone else might draw a line that is slightly skewed to the line that I have drawn and so his center will different from mine. Therefore, there must be standard lines whose centers which when joined will give the camber line.

This is the first semester that I am having aerodynamics and I am really enjoying it. My favorite portion currently is shock waves. Thank You so much for your help(I hope you remember why!!). And thanks also to JD Anderson!

You are talking about Camber line and it joins the Centre of the Curvature of the LE and TE Radius, equidistant from Top and Bottom surface and it has to be drawn mathematically, there are plenty of tools, at NASA you have foilsim, foilsim 1.1 on joukowski aerofoil had my contribution, if you decompile the Java Class file should see one Flt Lt MJ Augustine :)

the book i gave was written by me, who is Mr Anderson ? is he from Matrix  :)

Any help on Shock Waves, do PM, Theoretically known it, practically seen it (Yeah when in clouds or high Humidity condition you can see it)

Check the attached picture. I basically want to know, the center of which line to consider when drawing the camber because as you see the center of all these 3 lines will be different even though they originate from the same point. So, if I have to plot the center from the upper surface at that point, which of these three lines will I choose?

Oh! I didn't know that. That is really brilliant!  :hatsoff:

I also follow Anderson's books, they are very good.

Though I am BLUNT in aerodynamics, I think, it is the line generated by the CG of smaller area towards x-axis when the smaller area pieces having length of dx.
And, hope the angular shifting of x-axis will not differ the line generated with the camber line when dx=>0.

But the axis should be taken parallel to the wind flow always. And hence the lines are perpendicular to flow directions.

Line joining the tangents

Right! So, I did guess that correctly! Thank You  :hatsoff:

Aerodynamics by LJ Clancy is good, esp the Chapter on stability, Momentum theory of Lift, M Cdr, etc, in fact i recommend it for all RC Pilots too, further reading will help you fly better , scratch build better

Sandy and I got discussing about his scratch built Bandit (EDF Jet), then it occurred to me i need to clear the cobwebs on Air Intakes and Duct Flow, for :-

(a)  To understand EDFs
(b)  To Scratch build EDFs
(c) this is the a common subject with the jets , therefore a link of this goes into Jet Engine thread as well

Airflow through Ducts

Before considering intakes in any more detail, the behaviour of airflow through a duct, and the consequent affect the cross sectional area has on the pressure, temperature, and velocity need to be understood.

With steady continuous airflow through a duct, the mass flow rate at any cross section must be the same, i.e. mass = Air Density (Density is less at altitudes than at sea level) x Area x Velocity.  It follows therefore that at a minimum cross sectional area the velocity is highest, and at a maximum cross sectional area the velocity is lowest. (However the limiting factor is the backpressure and choking of the intake)

Because of the change in velocity there is also an effect on the pressure and temperature of the airflow at these points.  Where the velocity is highest, the static temperature and pressure are lowest, and where the velocity is lowest, the static temperature and pressure are highest (See Image).

The above paragraph can be expressed using a modified version of Bernoulli’s equation, representing the total pressure of the airflow.  The first term (pressure) is often referred to as the static pressure, and is the pressure of the surrounding air, whereas the second term (½RhoV2) is referred to as the dynamic pressure and represents the kinetic energy of the airflow.

   P     +   ½   rho  V2   =   Constant
   Where      P   =   Static Pressure
         rho   =   Density
         V   =   Velocity

   and from the Pressure law:   P   =   Constant
               T
   Where   P   =   Static Pressure
         T   =   Temperature

So that at constant density, any increase in velocity will cause a decrease in static pressure, and will be accompanied by a decrease in static temperature.  Conversely any decrease in velocity will cause an increase in static pressure, and therefore an increase in static temperature


Note:    At low speeds air density also decreases as velocity increases, but the effect is not very significant.

How much of aerodynamic - specially in terms of lift and drag actually affects the RC model?

I mean while the thrust to weight ratio of a normal plane is some where around 1/3, we are keeping a T/W to almost 1 in even the basic cases. So apparently, we should be able to cover up the ill affects of poor aerodynamics with the extra thrust available. Is this not the case?

to some extent yes, still, aeroplane flies due to interaction of the air (a) because the aerofoil (b) for example stall for a 12% T/C symmetrical aerofoil with no LE radius will occur at 12 deg alpha, whatever is the engine. the attitude it will occur will certainly depend on the engine. obvious question why  ? because air's interaction with the aerofoil has nothing to do with the engine.

PS

Above discussion pertains to EDF

http://www.rcindia.org/electric-planes/sky-surfer-from-rc-bazaar-build-and-fly-log/msg98379/#msg98379

read this and the subsequent thread for technique to launch high mounted engine glider

thanks for the guidance Sir.. :salute: :salute: :salute:

To add to what Gusty bhaiya has said,
                   density at stagnation point/ local density = [1 + (gamma-1)/2 M^2]^(1/gamma-1) 
                   Gamma = 1.3 for air. (It is the ratio of specific heat at constant pressure to specific heat at constant value)
If the local density of air during flight is within 5% of the density of air at stagnation point(velocity of the flow and dynamic pressure =0), the change in density is ignored and we consider the flow to be in compressible and therefore Bernoulli's principle can be applied.
And if substitute the value in the above equation we get M(Mach number)=0.3 . So if the local Mach number is below 0.3 the flow is considered incompressible, above which the density change is significant and has to be taken into account.
     

Rohit K.I.S.S

Lol! Yes I know I crossed the line.
BTW Clancy is a very good book for beginners, was reading it the other day. Thanks for recommending.

here is the very basic discussion on control throws, Exponential and dual rates

 http://www.rcindia.org/radios-and-receivers/how-to-increase-throws-of-rudder-and-elevator-flysky-th9x/msg99684/#msg99684  (http://www.rcindia.org/radios-and-receivers/how-to-increase-throws-of-rudder-and-elevator-flysky-th9x/msg99684/#msg99684)

I saw a senior one aeromodellor entered the spin and for recovery opened power and continued pulling back and crashed, another, in a wall recovery,  flick and crash, on discussion with these people i understood, most people do not understand spin, its mechanics and recovery, subsequent posts are dedicated for Spin

Phases of the Spin,    The spin manoeuvre can be divided into three phases:

(a)   The incipient spin.
(b)   The fully developed spin.
(c)   The recovery.

The Incipient Spin.    A necessary ingredient of a spin is the aerodynamic phenomenon known as autorotation.  This leads to an unsteady manoeuvre which is a combination of:

(a)   The ballistic path of the aircraft, which is itself dependent on the entry attitude.
(b)   Increasing angular velocity generated by the rolling and yawing moment.

The Steady Spin.    The incipient stage may continue for some 2 turns after which the aircraft will settle into a steady stable spin.  There will be some sideslip and the aircraft will be rotating about all three axes.  that is it will yaw pitch and roll (see image)

The Recovery.    The recovery is done by  first opposing the autorotation (Taking off the applied rudder) and then reducing the angle of attack (Moving the stick forward),  so as to unstall the wings.  The aircraft may then be recovered from the ensuing steep dive by increasing speed and pulling out.

If you are technically challenged you can skip the subsequent post, where i have explained the nuances of spin

While rotating, the aircraft will describe some sort of ballistic trajectory dependent on the entry manoeuvre. aircraft settles down into a stable spin with steady rate of descent and rotation about the spin axis.  This will occur if the aerodynamic and inertia forces and moments can achieve a state of equilibrium.  The attitude of the aircraft at this stage will depend on the shape of the aircraft, the position of the controls and the distribution of mass throughout the aircraft.


If for some reason the angle of attack is increased by a nose-up change in the aircraft’s attitude (By pulling back on stick, quite noticeable on a 3D aeroplane where you can vary spin path by stick and throttle), the rate of descent will decrease .   spin radius will decrease  rate of spin will increase, and recovery will be that much delayed. if you are in a flat spin pull back further and see the fun. (Remember flat spin takes long time to recover and height loss is more)

 :salute: :salute: :salute: great sharing of knowledge Sir..

Gusty,
On reply #70 you briefly touched on the topic of v-tail vs t-tail. Would like some more information on why one is better than the other. Secondly does it make much of a difference whether the horz stab and elevator is mounted on the below the vertical stab or above it ( as in T or reverse)?

V tail is aerodynamically cahllenging to make and there is undesirable cross coupling that happens when you apply elevator or rudder, however advantage of v tail are (a) wt reduction (b) lesser control surface therefore less of drag (c) easy entry into spin and recovery. it is still not a prefered version because of cross coupling issues. so you rarely see them except in UAVs (For completely different reasons)

T tail is conventional config. the fin above is called dorsal fin and fin below is called ventral fin . Dorsal fin adds to lateral stabilty (roll stability) whereas ventral fin reduces it. most modem aeroplane has both.

Question
why both fins ? don't hesitate or google just shoot you answers

read this for torque and torque compensation on a fixed wing

http://www.rcindia.org/beginners-zone/query-regarding-counter-twist-force/msg101090/#msg101090

info on servo tab , could be useful in RC Flying too
http://www.rcindia.org/chatter-zone/a-plane-preserved-for-seventy-years/msg101343/#msg101343

Is there a RC plane around that can take of vertically and then move forward like the F35???
http://www.youtube.com/watch?v=Xm7_PPE-8nk
Wud luv a link on it!

We can discus on VTOL, sure, all quads, heptrs are VTOL, here is one
http://www.youtube.com/watch?v=bCJ70Fr1umA

Anton Flettner, the guy who developed Servo Tab was a RC Pilot, that is something. Here read on

http://en.wikipedia.org/wiki/Anton_Flettner

PS
Give shot at what is Anti-Servo Tab, why is it required ?

the ventral fin might be to give undisturbed & streamlined flow over the slab tail & the vertical height of the fin might be decided considering the max. angle through which the slab tail is deflected.
The ventral fin will prevent vortex generation at the area of slab tail & the exhaust. in case that fin was not present the air at that area would be turbulent, since there's a gap (as seen in pic1...rafale i guess). so in order to give a streamlined flow of air over the slab tail that fin is used.
The principle might be same as that used for flow streamliners used below the wing.

very close and a good attempt vikalp

Two reasons

(a) at high alpha the dorsal fin is partly in some cases completely masked by the wing wake, reducing the directional stabilty and some case reversing it completely. this leads to departure, ventral fin in on the other hand is not masked and maintains directional stabilty

(b) second reason is complicated, a sweep back adds to lateral (i.e Roll) stability, ball park, 10 deg sweep equals 1 deg on dihedral, say a 50 deg swept wing will have an effect of 5 deg of dihedral which is helluva lot (Trainer aircraft have only 2-3 deg) so by reducing the dorsal fin  size and puttting a ventral fin in effect reduces this excessive lateral stiblity caused by the sweep back (Because a fin surface above (i.e Dorsal fin) adds to lateral stability and fin surface below (i.e ventral fin) reduces it.)

Thanks Gusty for these additional information!
Are you an aeronautical engineer? & what is your profession?

Sir.. its precious knowledge.. opened eye.. a lots..  :salute: :salute: :salute:

http://www.rcindia.org/rc-people/augustine-from-kerala-and-my-hangar/

here is some stuff from steve

Amazingly simple STOVL F-35 Parkjet:
http://www.youtube.com/watch?v=YYVifFwBg7w

We’ve all seen the dozens of different Short TakeOff & Vertical Landing (STOVL) attempts people have made with the F-35 Parkjet concept over the past few years were basically a tricopter with an F-35 shape, these could accomplish vertical takeoff but took several motors and were quite complex. here is one successful VTOL 'Vertigo'

The Vertigo uses a pivoting ducted fan in the center with wind vanes mounted on the ducted fan unit just behind it.  When the model is taking off vertically, the wind vanes underneath the motor provide pitch and roll control.  There is no yaw control for VTOL takeoff, the plane relies on slight forward speed for yaw stability.  

Tip 1: Keep up the Thrust to Weight Ratio.

First, VTOL designs rely on a better tha 1:1 thrust to weight ratio to takeoff.  Thrust ratio is determined by dividing the total thrust provided by the power system on the plane by the flying weight of the plane.  If a plane weighs 1.8 kgs but the motor produces 1.6 kgs of thrust, that is a less than 1:1 thrust to weight ratio, where if the thrust was higher than 1.8 kgs you would have a better than 1:1 thrust to weight ratio.

http://www.youtube.com/watch?v=bCJ70Fr1umA

Tip 2: Center of Gravity Balancing.

If you look closely at the video, you’ll notice there’s a boom on the back of the F-35.  it’s there to make sure the center of gravity is placed exactly where the fan is so the plane takes off straight up. This is a way less than ideal situation, it means there is dead weight on the plane that is being used for just the purpose of balance.  In every situation you can, adjust the CG by moving the battery or getting a heavier/lighter battery.  Using dead weight should be the VERY last method you use to balance the plane.  In the case of the model in the video, more thought out placement of electronics would have probably provided better balancing options.  Keep this in mind when you build your models, you want the MOST freedom possible with your battery placement. (My Pylon Racer designed for .25 has a .40 engine on it, and the batt is below the fin in the tail section, no extra weight, think out of the box)

Tip 3: If You’re Trying Something New, Use Established Concepts.

Notice that the builder of this VTOL model has let much of his work be done by others, which is a smart way to do it! First, he’s using the Vertigo VTOL concept.  It’s a previously established, well tested and well used design.  So the “guess work” here was minimal, he could setup the vertigo layout almost exactly on the F-35 and get 90% to the STOVL performance he was after. Secondly, if you look closely it appears he’s using a pre-molded F-35 kit.  It’s likely he purchased the kit from HobbyKing, Nitroplanes, or some other similar online store and just modified it with the Vertigo system.  Genius.

Now that Subbu has started Fanwing (http://www.rcindia.org/self-designed-diy-and-college-projects/fanwing-aircraft-build-log/) there is a need to explain circulation theory of lift (I wanted to avoid getting into these complication, however these lads of today are ahead of us, forcing us to get into things RC fliers detested for a long time, getting into theory part of it)

there are two theories (Both being essentially same) with which lift is produced. One is called the momentum theory of lift (Shear momentum with which the wing is lifted) and the other is the circulation theory of lift

Look at image

to a normal air flow, if you induce a wing with a circulation, then the resultant airflow produces lift. (white solid arrow)

Not easy as it sounds, for this to occur, imagine Two lover  :giggle: molecules reached the leading edge of the wing and they had to go separate ways, one went on top of the wing and the other to the bottom portion of the wing. the top one (Possibly the male :giggle:) ran faster so as to reach his lover who went the other way to meet at the same time at the trailing edge so that they can be together again. when this occurs 'Kutta condition' (Not the Indian Kutta 'The dog'  8-)) is said to exist (Kutta was a east European scientist I guess)

In doing so, the flow on the top wing had higher speed, following Bernoulli's theorem the pressure on the top wing had to reduce to keep the mass flow constant, this difference in pressure lifted the wing

Now this is the layman's explanation. if you are mathematically challenged you must skip the subsequent post

The aerodynamicist's way of trying to understand the lift produced by a lifting surface is called the "circulation theory of lift. This is how it works. even if you are challenged read it twice thrice you will get it.

(http://www.onemetre.net/design/downwash/Circul/Circul1.gif)

First, we need to see what is meant by "circulation".  The idea is that, if a fluid is "circulating" around some object, the speed of some particle in the fluid is proportional to the distance to the centre of the circulation.  For a given amount of "circulation", the further away the circulating particles, the slower they move.  The amount of circulation is said to be the speed of the particles times the length of their circulation path.  Suppose their path is a circle.  The amount of circulation, called gamma, is given as 2 pi r, the circumference of the circle, times w, the speed of the circulating particles at some distance r from the centre.

Imagine we have gamma = 12.  This means that, at a distance of 1 from the centre, the particles are circulating with a speed of 12.  At a distance of 2, they circulate with a speed of 6.  At a distance 3, with a speed of 4, at a distance 4, with speed 3, and so on.  All of this is given when we say, the amount of circulation is 12.

Here is a diagram of a foil moving through a fluid at a speed of V.  If we look at the rectangular path around this foil, which is "h" units high and "k" units long, and ask about the amount of circulation  we see, we can calculate it by multiplying the speed of the particles at each point around the rectangle and adding this up.

(http://www.onemetre.net/design/downwash/Circul/Circul2.gif)

Starting at the top of the rectangle, we see that the particles are travelling at a speed V, and they do so over the distance k;  the circulation here is "Vk". Down the right-hand side, the particles now show an average downwash speed w, along a distance h;  circulation here is "wh". Along the bottom, the speed of the particles is -V (relative to the direction of the path we are following), and they travel at this speed for the distance k, so circulation here is "-Vk".  Finally, up the left-hand side, we see that none of the particles are moving up or down, so their speed vertically is zero, 0.  The length of the path over which they travel at, er, zero speed is h, and so the circulation here is "0h".  Add up these regions of circulation, and we find that gamma, the overall amount of circulation is simply "wh".  The amount of circulation around the foil is given by the amount of downwash times the distance over which we consider the downwash to be operating.

That's it, that is circulaton theory without a lot of maths ! read on for more ! there are beautiful animated  :headscratch: websites on the net

some insight into High KV Low KV motors and their config

http://www.rcindia.org/electric-planes/my-first-build-and-crash/msg107948/#msg107948

Thumb Rule on stick and controls movement

http://www.rcindia.org/rc-general-topics/query-on-simulator-and-control-surfaces-9765/msg108001/#msg108001

Adverse Yaw Caused by Aileron Drag
The design of the glider like aeroplane with its long wings with ailerons out near the tips gives rise to this significant handling effect. When aileron is applied, the down going one increases its camber and angle of attack to the relative airflow, thereby generating lift to lift the wingtip and roll the glider while at the other wingtip the upgoing aileron is reducing camber and angle of attack, reducing the local lift and allowing roll towards it. As more lift is generated by the downgoing aileron, more drag accompanies it, while the opposite is happening on the upgoing aileron. This extra drag is called Aileron Drag.  The difference in drag  at the tips generates yaw…adverse yaw, away from the desired direction of turn. See image
 
Also read http://www.rcindia.org/rc-maneuvers-and-skills/ar-mixing-or-not/msg112466/#msg112466

Design Counter for adverse Aileron Yaw are two

(a) Differential Aileron (Like the FunJet, if you read the manual on throw you can co-relate)

(http://upload.wikimedia.org/wikipedia/en/thumb/3/3a/DifferentialAileron.svg/300px-DifferentialAileron.svg.png)

(b) Frise Aileron (see image) used in PA Bandit and some scale planes

(http://upload.wikimedia.org/wikipedia/en/thumb/3/3b/FriseAileron.svg/300px-FriseAileron.svg.png)

both are used in RC models

Scratch building High winger ? Which semi symmetrical  aerofoil to use  ??? this question plagues most modellers and here are some options


NACA (National Advisory Committee for Aeronautics) Numbers These are 4-digit airfoils where the 4 digit number defines the shape.  The first 2 digits define the camber amount and location.  NACA2408 has a 2% camber amount (First Number), The maximum caber location is at 40% of the chord length (second Number) and the airfoil is 8% thick at is thickest location(third Number).  

Clark-Y

The Clark-Y is an all time favorite that has been used on countless models from the J-3 Cub to Electric powered warbirds.  If you want a Semi Symmetrical airfoil, and you want to be sure, the Clark-Y it is.


NACA2408 to NACA2415

These are popular for warbirds, scale and Sport aircraft with good inverted flight capability.

Flat1, Flat2 & Flat3

These are popular Trainers Slow flier aerofoil.  2 & 3 are thinner versions of Flat-1.

Aquila

This is another Flat bottom airfoil that is used on the Aquila glider.  It is the thinnest of the Flat bottom airfoils.

Telemaster

Popular Flat Bottom airfoil for the Telemaster, a large high wing trainer for aerial  photography platform.  


E214

This is an UAV's and Aerial Photography aerofoil with thick cross section.  It is a high lift airfoil with relatively low drag.

SipKill

This is a tailless highly swept flying wings aerofoil.

SD7037

Same as E214 with thinner cross section.

S6061

Sailplanes and gliders aerofoil with a reflex camber and low drag

SD7003

Another popular glider airfoil.  The maximum thickness location is further forward than the other glider airfoils. Advantage is higher CG margin and more weight on the fuse possible

RG15

RG15 is as popular as Clark-Y in the glider world. great for glider or sailplane.

RG14

A faster version of the RG15Thinner and less camber with Less drag and less lift makes it fast glider.

An online game on Roll, Pitch & Yaw (http://www.modelaircraft.org/education/amaflightschool/pitchyawroll/index.html)

An online game on Lift, Weight & Thrust (http://www.modelaircraft.org/education/amaflightschool/principles/index.html)

While Flying Jets Nandan introduced me to a colloquial term in RC Flying called 'Kangaroo'.

Kangaroo technically is called PIO (Pilot Induced Oscillation) or SPPO (Short Period Pitch Oscillation)

To understand this we need to know there are two terms that deals with stability of an aeroplane, those are Static Stability (as the name implies) and Dynamic Stability (When it interacts with air).

To Keep it absolutely simple, when you are flying a RC Aeroplane perfectly trimmed, Flying straight and level, you just push the stick slightly and watch what happens, two things will happens (a) Pitch oscillations will dampen out (b) will continue to increase . This is LPPO (long period oscillation) or Phugoid First case is Stable, Second unstable, (See Image) both has no cause for concern because they are easily correctable by piloting

(http://adg.stanford.edu/aa241/stability/images/dynamicstab.gif)

Say you are coming into land you bounce and you push the stick forward, Aeroplane take some time to react and you and the aeroplane get out of phase with each other  :banghead:, and presence of ground/fast response of the aeroplane cuts of this amplitude and the Long Period is reduced to Short and you get into a dangerous condition called SPPO or PIO

This can damage undercarriage/destroy aeroplane and in real life can kill

A classic case of PIO you can see how the control surface, pilot and the aircraft all of them were out of phase

http://www.youtube.com/watch?v=k6yVU_yYtEc


RC PIO at 5:43
http://www.youtube.com/watch?v=cTqs7Zvzf54

A little more tech explanation on Stability (Kept it as simple as i can)

An airplane in flight is constantly subjected to forces that disturb it from its path. microbursts, turbulence, gusty   ;D winds et all. How does airplane reacts to such a disturbance from its flight attitude depends on its stability characteristics.

Stability is the tendency of an airplane in flight to remain in straight, level, upright flight and to return to this attitude, if displaced, without corrective action by the pilot.

Static stability is the initial tendency of an airplane, when disturbed, to return to the original position.

Dynamic stability is the overall tendency of an airplane to return to its original position, following a series of damped out oscillations.

Stability may be (a) positive, meaning the airplane will develop forces or moments which tend to restore it to its original position; (b) neutral, meaning the restoring forces are absent and the airplane will neither return from its disturbed position, nor move further away; (c) negative, meaning it will develop forces or moments which tend to move it further away. Negative stability is, in other words, the condition of instability. Ball and Cup Analogy is good to understand. See image

(http://t2.gstatic.com/images?q=tbn:ANd9GcS1RdD2K58tNQQTclXI51uHj1H6sN5BPuU-HKCKfM5XGt4xjDZlga-JX2Zb)

A stable airplane , may lack maneuverability.

An airplane which, following a disturbance, oscillates with increasing up and down movements until it eventually stalls or enters a dangerous dive would be said to be unstable, or to have negative dynamic stability.

An airplane that has positive dynamic stability does not automatically have positive static stability. The designers may have elected to build in, for example, negative static stability and positive dynamic stability in order to achieve their objective in maneuverability. In other words, negative and positive dynamic and static stability may be incorporated in any combination in any particular design of airplane.

An airplane may be inherently stable, that is, stable due to features incorporated in the design, but may become unstable due to changes in the position of the center of gravity (Wrong CG  :banghead:).

Stability may be (a) longitudinal, (b) lateral, or (c) directional, depending on whether the disturbance has affected the airframe in the (a) pitching, (b) rolling, or (c) yawing plane.

LONGITUDINAL STABILITY

Longitudinal stability is pitch stability, or stability around the lateral axis of the airplane. (See earlier posts on Axis)

To obtain longitudinal stability, airplanes are designed to be nose heavy when correctly loaded. The center of gravity is ahead of the center of pressure. This design feature is incorporated so that, in the event of engine failure, the airplane will assume a normal glide. It is because of this nose heavy characteristic that the airplane requires a tailplane. Its function is to resist this diving tendency. The tailplane is set at an angle of incidence that produces a negative lift and thereby, in effect, holds the tail down. In level, trimmed flight, the nose heavy tendency and the negative lift of the tailplane exactly balance each other.

Two principal factors influence longitudinal stability:

(1) size and position of the horizontal stabilizer,
(2) position of the center of gravity.
(3) Longitudinal Di-Hedral (See earlier posts)


LATERAL STABILITY

Lateral stability is stability around the longitudinal axis, or roll stability.

Lateral stability is achieved through (1) dihedral, (2) sweepback, (3) keel effect, and (4) proper distribution of weight.
Dihedral

The dihedral angle is the angle that each wing makes with the horizontal. The purpose of dihedral is to improve lateral stability. If a disturbance causes one wing to drop, the unbalanced force produces a sideslip in the direction of the downgoing wing. This will, in effect, cause a flow of air in the opposite direction to the slip. This flow of air will strike the lower wing at a greater angle of attack than it strikes the upper wing. The lower wing will thus receive more lift and the airplane will roll back into its proper position.

Since dihedral inclines the wing to the horizontal, so too will the lift reaction of the wing be inclined from the vertical. Hence an excessive amount of dihedral will, in effect, reduce the lift force opposing weight.

Some modern airplanes have a measure of negative dihedral or anhedral, on the wings and/or stabilizer. The incorporation of this feature provides some advantages in overall design in certain type of airplanes. However, it does have an effect, probably adverse, on lateral stability.

Keel Effect

Dihedral is more usually a feature on low wing airplanes although some dihedral may be incorporated in high wing airplanes as well.

Most high wing airplanes are laterally stable simply because the wings are attached in a high position on the fuselage and because the weight is therefore low. When the airplane is disturbed and one wing dips, the weight acts as a pendulum returning the airplane to its original attitude.
Sweepback

A sweptback wing is one in which the leading edge slopes backward. When a disturbance causes an airplane with sweepback to slip or drop a wing, the low wing presents its leading edge at an angle that is perpendicular to the relative airflow. As a result, the low wing acquires more lift, rises and the airplane is restored to its original flight attitude.

Sweepback also contributes to directional stability. When turbulence or rudder application causes the airplane to yaw to one side, the right wing presents a longer leading edge perpendicular to the relative airflow. The airspeed of the right wing increases and it acquires more drag than the left wing. The additional drag on the right wing pulls it back, yawing the airplane back to its original path. 10 Deg of Sweepback = 1 Deg of Dihedral is the thumbrule


DIRECTIONAL STABILITY

Directional stability is stability around the vertical or normal axis.

The most important feature that affects directional stability is the vertical tail surface, that is, the fin and rudder. Keel effect and sweepback also contribute to directional stability to some degree.

The Fin

An airplane has the tendency always to fly head-on into the relative airflow. This tendency which might be described as weather vaning is directly attributable to the vertical tail fin and to some extent also the vertical side areas of the fuselage. If the airplane yaws away from its course, the airflow strikes the vertical tail surface from the side and forces it back to its original line of flight. In order for the tail surfaces to function properly in this weather vaning capacity, the side area of the airplane aft of the center of gravity must be greater than the side area of the airplane forward of the C.G. If it were otherwise, the airplane would tend to rotate about its vertical axis.

One of the best article on "Right Thrust" and "Prop Effect" I have recently read. Written by Blucor Basher (Ben Fisher owner of 3D Hobby Shop).

http://www.3drcforums.com/content.php?216-Right-Thrust-and-Prop-Effects

Great write up there, must read

quoting the sum up verbatim
"So, to sum up:
Props are thrust producers, but they also impart a lot of other forces into our airplanes, like gyroscopic force and many others.
These forces are strongest when the prop RPM (engine power) is high.
At high airspeeds, the tail of the plane counteracts these prop forces effectively, but not at low speeds.
Therefore, at high power at low airspeed (like takeoff and hovering) we feel prop forces most.
The net effect of these forces is usually to make our aircraft turn left.
To take some work off of our left thumb, we mount our power system and prop at an angle pointing right so that at high power it balances the left turning force with a right turning force.
This angle is a compromise based upon the need for the airplane to handle well at a variety of airspeeds.
Any decent quality aerobatic ARF already has an adequate right thrust angle, changing it is only for advanced pilots.
Applying the classic test to check right thrust can be difficult on a modern 3D airplane since our planes power right past the limits used in the classic test.
So, we might need to experiment to find perfection, and this is easiest done by experimenting first with rudder to throttle mixes before taking your plane apart."

gusty sir nyc write up u have gone totally technical on them haha ;D.....wing types ..drag types ...lift to drag ratio ,types of flaps lets have it all  ;D

Gusty sir,


Why is the lift considered always behind the weight? Is it because the airflow essentially separates at the thickest aerofoil section and the weight being concentrated at CG, which mostly lies around the spar?

If that is correct, in the case of a Mugi (http://www.rcindia.org/electric-planes/mugi-1-5-size-build/msg139700/#msg139700), the weight would be at the CG, and the lift behind (where) the thickest section of aerofoil? I am unable to identify the location of the lift line so I can visualize the lift-weight couple.

Am I also correct in understanding, that in an ideal setup (practically undoable) the Thrust Drag couple should nullify each other and so should the lift weight couple?

Lift Behind weight is a stable design, whenever there is increase in lift, natural tendency of the aeroplane is to come back to the original state (like the ball in a cup),. IF the lift is ahead of the CG it will continue to depart (Like a ball on top of the cup)

(http://www.intechopen.com/source/html/22198/media/image5.jpg)


Generally, yes lift is slightly aft of the thickest portion, CG slightly ahead of the thickest portion is good enough



No! how can lift weight couple nullify each other? since they are a 'Couple of Force' there will be a residual moment, depending on the quantum of force and distance between them. since, by design lift weight is nose down, thrust drag should be nose up so that they cancel each other and there is very little work for the tail plane. remember tail plane is called Horizontal stabilser !! why, whatever is residual, it balances, what changes drastically? it is the lift weight, weight being constant lift changes due to (a) Speed (b) manourvre. Who balances this residual force ? tailpane

Ideally all the force should act on the CG, there will be no residual and no requirement of tailplane (except to initiate the disturbance) that is not possible, both theoretically and practically. Fulcrum-Load_effort ? visualise

Thanks chief. All makes sense now. I see pulleys and loads and fulcrums clearly now. Think the mugi will need a little downthrust about 2 deg, since this is a pusher, the prop shaft will be pointing upwards, but yes thrustlines make most sense now.
Many thanks
GS

 Question on Thrust....
1. Is the 2deg right & down angle applicable on all engines - irrespective whether they are electric or glow or gas?

2. How does one check the angle of the firewall - whether it is perpendicular and pointing straight or at an angle?

Very good question, i did think that one day someone will question this logic. Not to complicate the matter (as it involves complex explanation of Gyroscopic effect, Fin wing position and vertical stabilizer interaction and the mathematics to go with it)

Suffice to say NO, small prop high rpm pusher doesn't require as much compensation. (Yes it requires compensation for being a pusher and being above the drag line) as a big prop tractor does.

This general thumb rule 2 deg right and down (for a tractor) works for most models, in fact once you gain proficiency and graduate onto big gassers, you will learn how to fly and see if the compensation is adequate and how to correct the same, physically, electronically (explanation of which i guess can be avoided for now)

You say small prop pusher do not need much compensation, but the Easystar and all clones/variants like Bixler, Skysurfer etc have a very steep angle. I would think, these models could qualify for high rpm and small prop.....

Higher the mass, bigger the diameter and higher the RPM of spinning Powers system then higher the gyroscopic effect.

However having said that higher RPM is more often than not coupled with smaller dia and lesser mass to achieve high RPM so less over all gyroscopic effect.

However pusher/ high pod mounted tractor /a simple tractor need different compensations due to difference in relation between the angle of thrust- angle of CG-angle of CP.

Gusty Sir,

Please have a look:-
(Me Flying MXS-R)

Is this a PIO (Pilot Induced Oscillation) or SPPO (Short Period Pitch Oscillation) ??

http://www.youtube.com/watch?v=hU58GOXjCxM&feature=youtu.be (http://www.youtube.com/watch?v=hU58GOXjCxM&feature=youtu.be)

Tanmay..

Gusty,
A question on Lift....

For a semi-symetrical aerofoil, with increase in speed, the lift increases. So net result if the lift + thrust is greater than weight + drag, then the plane goes up?
Now the question is, if this is correct then there can only be one speed at which the plane will fly level, for all other speeds we would have to give inputs - up/down elevator. Is that so?

Reason I am asking is that I used to do scratch build, then I decided to do a kit build. On all I notice that if I give full throttle, the plane starts to climb on its own. So the problem for me is to go flat out and be level at the same time.

Pankaj

it is PIO
has two types of oscillations, Short and long period, long period isn't dangerous and some aeroplanes inherently has it and people dont even know they exist, because you have time to correct.

It is the sort period oscillation that is dangerous, because pilot, instead of control, can aid it because there is a finite time delay in you giving the control input to the time the aeroplane reacts, say nearly 0.2 secs, when this time reduces then it is not possible for the humans to perceive it and correct it, therefore he ends up aids the oscillations, the timing of this oscillation closer to the ground is reduces because the amplitude of this oscillation is cut off by the ground itself therefore frequency increases you end up bobbing up and down, this is particularly dangerous because it breaks up the aircraft and the undercarriage. Cut off the energy is the only solution, throttle back and let the beast die down

that is in a nutshell PIO, SPPO happens at supersonic speeds too, it is very violent and can have catastrophic results. aeroplane from being perfectly to completely broken up takes only seconds

mid eighties we had autopilot and auto stabilisers protecting one from this menace, (It is essentially a design compromise, for performance, a neccessary evil, like steroid)

Modern aeroplanes have fly by wire controlling it

Pankaj
Lift > weight and Thrust > Drag are the requirement for initiating a climb. It is not additive. Meaning thrust need not be (And in most cases) more than weight, that's how wright brothers flew, their engine was producing very small amount of thrust compared to the weight.

open power and she climbs is because of the couple, thrust drag couple is a nose up couple.

in steady climb and descent the lift is less than weight.

in a truly vertical climb and descent lift is zero :banghead:

think about it, we will discuss further

Some questions...
Does sweep back and dihedral produces same effect?
Where is the cg of a commercial airliner located?

Sweep back and dihedral do not produce the same effect:
Dihedral: It gives the aircraft a self correcting tendency. Dihedral causes an airplane to level out, so if you are in a slight bank and you leave the sticks, dihedral will cause your plane to level out again.

Swept Back Wing: A swept back wing is mostly used to reduce drag. When an airplane is travelling at high speed, a concept known as wave drag comes into play which is caused by air flowing over a curved surface at high speeds. This drag not only requires more power from the engines to counteract, but also causes shockwaves to form above and below the wing. Sweeping the wings at an angle reduces this drag.

The CG of commercial airliners is usually between 25-30% of the mean chord length of the wing.

I  hope this helps you. I'm sure senior members would be able to help you more (and correct me if I'm wrong).

Thanks

maahinberi, you are wrong about the sweepback


topalle and mahinberi please read the whole post

I'm sorry sir. Thank you for correcting.
Sir, could you also explain the effect of forward sweep?

Post no?

An airplane with forward sweep is unstable in yaw. Additionally there are structural problems associated with it (i don't want to get into the details). However, since the wing is swept forward, the chances of tip stall are generally low. But forward sweep is not very popular.

click on where it says "Quote from: rcpilotacro on January 24, 2013, 10:08:04 AM"

Hi Gusty, would you mind throwing some light on canards and related aerodynamics and why has it not made much headway in to the model world? Thanks.

Doc I missed this question of yours


Read my Post on Trim Drag & forces in a flight posts

http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg82364/#msg82364 (http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg82364/#msg82364)

http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg82364/#msg82364 (http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg82364/#msg82364)

Excerpt of post on Trim Drag is as follows



When it comes to Canard, for balancing forces in flight, instead of tail down (Which adds to the weight component and therby adding drag) canar provides a nose up force and thereby reducing the force on wing and reducing drag. if canard was such a great thing and has only advantages why didn't it find favour with conventionally designed aeroplanes ? that is the pertinant question to ask (Remember wright brothers envisaged canard controls and not tail mounted controls, first aeroplane was in fact a canard controlled aeroplane)

Anyone can shoot the answer (Without googling ofcourse) we will proceed with the discussion of advantages and disadvantages of canard controlled flights and why didnt it find favour post 'Flier')

Well

the simple answer is, if a tailplane stalls the aeroplane will pitch down and unstall(Both the wings and the tailplane will unstall) which is desirable, whereas if the canard stalls the aeroplane will pitchup and thereby worsening the situation

 Here is the explanation for Asymmetrical Fins and Flat Plate Aerodynamics (http://www.rcindia.org/electric-planes/scratch-built-66-alula-using-hd-thermocol-my-entry-for-sweepstakes/msg176592/#msg176592)

One Question... What are wing pods used for?

could you post a pic of which pod you are referring to

the pods in commercial aiplanes like b737 a320 etc

https://www.google.co.in/search?q=wing+pods+airbus+a320&oq=win&aqs=chrome.1.69i57j69i59.2875j0j7&sourceid=chrome&espv=210&es_sm=93&ie=UTF-8 (https://www.google.co.in/search?q=wing+pods+airbus+a320&oq=win&aqs=chrome.1.69i57j69i59.2875j0j7&sourceid=chrome&espv=210&es_sm=93&ie=UTF-8)

something like this

the second pic
in the pics displayed

Well

Pods are payloads that aeroplanes carry, they can be Podded Engines (like the pic above), Flap Guide rails encased in a pod looking aerodynamic sleek structure, Drop Tanks (External Fuel Tanks, which after empty can be dropped), Photo Reconnaissance Pods, External Guided and Unguided Bombs, Missiles (Some looks like a pod)  etc

If you google the words above, and closely see the difference you will know what i mean

Hey rcpilotacro  I have made my new great planes piper cub with OS 62 V four stroke engine and for extended flights i have put du-bro fuel tank which 950 cc. so can it fly well with this kind of fuel tank , i mean will it be able to fly ?

Please HELP
ASAP

Thanks

My piper cub is of 76 inches wing span

Please  help me in how can i manage to fly with this fuel tank as i want to fly with this fuel tank

I read ur pm and replied. Answer is no

does a polyhedral wing require washout....if yes then how will u induce washout into a wing structure

@abhishekdas11
Washout has no connection with whether the wing is straight, dihedral or polyhedral.
Washout, ie tips at a slight (say 1 degree) negative incidence compared to the root, is to reduce wing dropping tendency by delaying tip stalling.

Traditional methods for inducing washout (that you may laugh at):
1. Lick the underside of the trailing edge near the tip, or blow hot breath, twist and hold. For balsa chuck gliders.
2. For stick, tissue, dope models steam the tip using a kettle/cooker, then pin to building board with shim under tip TE. Or apply a coat of thin dope and pin with shim till dry.

For foam core wings, set tip template at a slight negative incidence to root template before cutting with hot wire.

BTW, curious why you felt the need for washout!
Regards

just wanted to ask whether its required for sailplanes and gliders with larger wing span....like a mandated kind of...

The answer is 'Yes'

Gosh hw will i do it in balsa...........is there any other method other than licking and blowing breath onto balsa wood... i mean like tapering the spars chordwise or likewise strctural

@abhishekdas11

Just put a shim under the TE at the tip while building!
As the spars are spanwise, doubt if you could taper them chordwise, especially if there is only one spar ;D

If span is over 6ft, other alternatives like different sections for root and tip etc...

An 18-24" semi span wing in 8mm biofoam with no aerofoil at all will still fly quite well if the wing loading is not too high. Even without any washout!

Washout is just one of the design considerations, important but certainly not the most important.
Before washout are issues like:

- what is the wing span
- what is the chord at root/tip
- what is the wing loading
- what aerofoil section is proposed
- at what Re number range do you expect the model to fly

Abhishek, i must ask if you are diving into the deep end unneccesarily?
You can build/fly a model successfully without any of this mumbo jumbo.
Do you want to be a reasonably successful model flyer or a model airplane designer?
There is a difference between the two.

I am at your service either way. But you have to decide.
Luck!

well to b pretty frank....i am a successful structure Er... jus wana put som stuff like wash out, winglet and vortex gen onto ma SO CALLED GLIDER :-D to giv it a pro look...
wing span 66"
root chord 5"
tip chord 3"
wing loading 5.83
no idea abt reynold number

airfoil is clark Y airfoil of 70% thickness

See what you just said!

y anything wrong?

@ KK Iyer- i made a wing without ailerons to b controled ba rudder...so wt i thought ws if i incorporate a washout then my banks will be smooth and even else the airplane will just yaw and sideslip

Despite efforts unable to understand language used.
Unable to advise as no experience with 70% thick airfoils, ie, 3.5" thick at 5" root chord and 2.1"thick at 3" tip chord.

i used this online site for instant plot and print http://airfoiltools.com/plotter/index (http://airfoiltools.com/plotter/index)

Iyyer sir, its nt wt ure thinking;-)

I am a little confused regarding the relation between Thrust to Weight Ratio and Wing Loading and Climb Rate.

Case I:
Let's say I have a plane with an AUW of 1000g and a power setup which provides 750g of static thrust, thus the Thrust to Weight ratio is 0.75. (For assumption, we can assume a 40" span and 8" chord rectangular wing)

Case II:
Now, let's say I make the same plane (No change in any dimension) with an AUW of 500g. Now, the wing area remains the same, as it is the same plane, but the wing loading is lower. However, I put a power setup which gives me 375g of static thrust. Thrust to weight ratio is still 0.75.

So which of these planes will have a better climb rate. (I don't need to go vertical, just need to climb as fast as possible).
I would appreciate if anyone could help me solve this confusion.

Both will have the same rate of vertical (Y axis) climb. Level flight (X axis) will need less power in the second case as the lift is more (ASSUMING the motor has the same prop and spins at the same RPM)

Yes, but I don't want to climb straight up. Wouldn't the lower wing loading result in greater climb rate?

At the same speed, yes. But it is difficult to quantify as there are no specific values. In all probability it will just fly better

So if I want a plane that can gain height as quickly as possible, which one should I go for?

for a rapid climb.... well... the thrust to wright ratio needs to be high... extremely high... go for something like a ratio of 2: 1.  But well.... is it needed.... Sanjay Sir has tried to explain the issues in plain basic language.... it would be good if you also read a few things on thrust and weight and chapters on climb performance of aeroplanes https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2004.pdf (https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2004.pdf)  http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80t-80.pdf. (http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80t-80.pdf.)  these URLs may be of some help.  OR else lay your hand of Aerodynamics by AC Kermode..... if you really want to read about it all.....
Happy aeromodelling

Thank you.
I'll put this in context, I'm planning to attend a competition which restricts the thrust to weight ratio of an airplane at 0.75. The task is to climb as quickly as possible. Hence the question.

1. How will the judges measure thrust?  >:D >:D
2. If you make too low a wing loading, you could stall and dive....like the monkey in the well who jumps up 3 feet and slips back 2  :rofl:
3. As quickly as possible..... ie to reach a certain altitude (how will it be measured?  >:D) in the shortest time. Good clever flying can help. Climb in spirals
4. Trial and error - experiment with different set-ups of wing/motor/prop

@maahinberi: Preparing for the Aero-Dominator competition or the Aero-SAE VIT?

Not preparing yet. Saw the problem statement and went into deep thoughts of wing loading vs. Thrust to weight ratio  :P

Have you been to any of the competition before?

Nope

I had participated in 3 competitions in past held at different IIT's. The problem statement was almost the same in all, other than the one at IIT-Roorkee. The other two were same organised under Boeing Engineering Innovation Awards(BEIA).
Same were the rules there. Thrust to weight 0.75.
Round-1: Climb for 30 seconds ad then cut throttle and glide. Max. glide time was recorded. You can give throttle only in 30 seconds given after take off.
Round-2: was a bit different including passes through gates and some patterns around poles etc.

maybe a glider with a thrust to weight ratio of .75 will climb faster and glide better after the 30 sec power run.  You can try that... look for a glider like Apple Box or similar which may appear to be big in size but will fly more true due to the stability of design.  Gliders have a wing with a very high lift with very low induced drag.... a high aspect ratio wing of the glider will give you a good climb and a good glide.

What you can do is power uo the glider for 30 sec after take off and then let it glide.

Happy Flying.....

Thanks everyone.

Answer to the question posted in this thread http://www.rcindia.org/beginners-zone/prop-question-21968/ (http://www.rcindia.org/beginners-zone/prop-question-21968/)

:)

Well !! let me shed some light on it ! like i did in my earlier post on the subject in this Basic Aero dynamics thread post  (http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg47707/#msg47707)

Pitch is prop advance in one full rotation without load, there are basically three types of Pitch GMP, EMP & PP Geometric Mean Pitch, Experimental Mean Pith and Practical Pitch.

In a rotating element like a prop pitch and angle of attack on the blade depends not only on the blade basic rigging angle also on the distance from the hub BECAUSE it is a function of rotational speed as well (See Images)

Bottom line is you cannot twist the hub and reduce the pitch of the prop because the pitch of the prop becomes zero near prop tip (not always, this is a different discussion which we could defer it for some other time), by twisting hub (if you can, that is) starting from the tip of the prop the angle will start becoming negative and start producing negative thrust.

Also the helical twist (Reduction of pitch angle from the hub) depends on the basic pitch of the prop. For example if the pitch of the prop is say 10 inch and the length is 20 inch then Rate of reduction of pitch will be One inch for every inch away from the hub (this also is a complex subject, could be discussed later, just to simplify). if the Pitch of the same prop was 5 inch then the rate of change of pitch will be half an inch for every inch away from the hub

Couple of things you need to keep in mind are

1. Every Prop has a sweet spot or a sweet zone which produces max thrust, typically 20% to 65% from the Hub of the Prop

2. Tip design governs prop noise and prop loss / efficiency

3. Prop hub (Prop Shank, as it is called) is always stalled and doesnt produce any thrust at all (Area around the spinner)

4. Prop suffers from Aerodynamic and Centrifugal Twisting moments, long story short inertial (Which tends to fine the pitch) is more dominant than Aerodynamic (Which tends to coarse the pitch or increase the pitch angle)

PS

Like i said it is a very complex subject involving even supersonic flights (Yes Prop tip does go supersonic including that of model prop ;) ). i have tried to keep it simple. Shoot away your questions here or in the original thread doesn't matter

Very easy way to find the tip speed of your prop, and see if it is nearing speed of sound, if it is, it would be a major cause of prop noise . Use your high school geometry, maths and physics lessons

Thank God I found this picture. Now I know what gusty was talking about most of the time about Sukhoi Maneuvers Gusty and his favorite Kulbits :giggle: My Vocabulary was limited to only roll, cobra and loops till now  ;D.

For the benefit of Sundry

(https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-xfp1/v/t1.0-9/11880686_745599108900874_3598282130396006985_n.jpg?oh=ec0b6a36ea66efbad83697d77661bb30&oe=566DC6F5&__gda__=1450810236_f700a117ca5e65391406bd98d90f386d)

Worst feeling is to be in a Kvochur's Bell. +ve 6-7gs followed by -ve 4g, next thing you know yesterday's breakfast is in your mouth :giggle:

Posted for only to show how it works not related completely RC though.

www.youtube.com/watch?v=AiTk5r-4coc

This is the video i have taken from anwar bhai's This (http://www.rcindia.org/chatter-zone/your-favorite-online-non-rc-video/msg239527/#msg239527) post.

I have a question for all of you. If the same aeroplane flew at very low speed what will be size of the wake ? :) ;)

https://www.youtube.com/watch?v=DZcPYua8p0I (https://www.youtube.com/watch?v=DZcPYua8p0I)

@rcpilotacro,
Sir,
Wow. A real head scratcher!

Here's an attempt (without being a trained aerodynamicist) ;D.

If the query is about the size of the wake (which i presume is how far behind the vortices last), i have no clue (yet).
But presuming the query is about the size of the vortex, i made these assumptions:

1. All other things (wingtip shape/size, aspect ratio, atmospheric conditions etc) being same, the vortex size is a function of the pressure differential
2. Vortex size is inversely proportional to the pressure differential
3. Differences in drag can be ignored for simplicity

Initially i thought that in level flight, the lift must equal the weight irrespective of speed, the pressure differential must be the same at high/low speed, hence the vortices will be of the same size/dia.

But on further reflection, i think that:
1. At lower airspeed, the angle of attack is higher
2. Hence the CL is higher
3. Pressure differential is likely to be a function of CL, being higher at higher CL
4. The pressure differential is therefore higher

Hence the vortex dia will be smaller when flying slower.

If i've totally misunderstood the query, and/or my line of thought is utterly incorrect, please PM me so i can delete this post before too many members see it  ;D
Regards.

Read

Good Conventional attempt

Size of the vortex is pressure differential=Lift=weight (In level Flight)

In level flight it is only weight dependent, High speed low CL but Higher Speed=Same pressure differential, therefore the size of the vortex will remain same irrespective of the speed


:thumbsup: great attempt

@rcpilotacro,
Thanks for the kind words, even though i skipped my first answer (which was correct) in favour of my second answer (incorrect).
No one else has responded, except for rastsaurabh, whose criptic one word post 'read', was presumably for me, as it couldn't have been for you!
Hence query to saurabh,

@rastsaurabh,
Please recommend reading list...
Regards.

Iyer sir ....
Gusty is the best to suggest any reading.
If i could suggest any reading or knowledge it would be Mobile technology.
Just neglect my post. Btw it was meant that your post was seen before you could correct.

interesting discussion on funjet ultra roll charecteristics

http://www.rcindia.org/electric-planes/funjet-ultra-6s-300kmph-build-and-maiden-flight/msg244169/#msg244169

Much Appreciated