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« Reply #225 on: April 29, 2012, 08:36:49 PM »
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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

Forces in a spin.jpg
Re: Basic Aerodynamics for RC Flying
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« Reply #226 on: April 29, 2012, 08:46:20 PM »
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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 aircraftís 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)
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« Reply #227 on: April 30, 2012, 12:18:33 AM »
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« Reply #228 on: May 08, 2012, 11:50:12 PM »
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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)?
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« Reply #229 on: May 09, 2012, 06:37:32 AM »
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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

dors vent.jpg
Re: Basic Aerodynamics for RC Flying
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« Reply #230 on: May 10, 2012, 06:33:37 AM »
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read this for torque and torque compensation on a fixed wing

http://www.rcindia.org/beginners-zone/query-regarding-counter-twist-force/msg101090/#msg101090
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« Reply #231 on: May 12, 2012, 09:00:21 PM »
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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
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« Reply #232 on: May 12, 2012, 09:12:53 PM »
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Is there a RC plane around that can take of vertically and then move forward like the F35???

Wud luv a link on it!
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« Reply #233 on: May 12, 2012, 09:20:05 PM »
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We can discus on VTOL, sure, all quads, heptrs are VTOL, here is one
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« Reply #234 on: May 13, 2012, 07:44:57 AM »
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info on servo tab , could be useful in RC Flying too

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 ?
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« Reply #235 on: May 27, 2012, 12:52:36 PM »
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Question
why both fins ? don't hesitate or google just shoot you answers
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.
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« Reply #236 on: May 27, 2012, 02:32:13 PM »
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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.)
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« Reply #237 on: May 27, 2012, 05:45:21 PM »
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Thanks Gusty for these additional information!
Are you an aeronautical engineer? & what is your profession?
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« Reply #238 on: May 27, 2012, 11:54:38 PM »
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« Reply #239 on: May 28, 2012, 05:33:13 AM »
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what is your profession?
http://www.rcindia.org/rc-people/augustine-from-kerala-and-my-hangar/
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« Reply #240 on: June 05, 2012, 05:41:05 PM »
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here is some stuff from steve

Amazingly simple STOVL F-35 Parkjet:


Weíve 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.



Tip 2: Center of Gravity Balancing.

If you look closely at the video, youíll notice thereís a boom on the back of the F-35.  itís 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 Youíre 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, heís using the Vertigo VTOL concept.  Itís a previously established, well tested and well used design.  So the ďguess workĒ 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 heís using a pre-molded F-35 kit.  Itís likely he purchased the kit from HobbyKing, Nitroplanes, or some other similar online store and just modified it with the Vertigo system.  Genius.
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« Reply #241 on: June 09, 2012, 06:16:43 AM »
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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'  Roll Eyes) 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

circulation theory of lift.jpg
Re: Basic Aerodynamics for RC Flying
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« Reply #242 on: June 09, 2012, 06:35:36 AM »
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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
Basic Aerodynamics for RC Flying


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
Basic Aerodynamics for RC Flying


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  Head Scratching websites on the net
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« Reply #243 on: July 03, 2012, 06:47:40 PM »
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some insight into High KV Low KV motors and their config

http://www.rcindia.org/electric-planes/my-first-build-and-crash/msg107948/#msg107948
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« Reply #244 on: July 04, 2012, 06:50:12 PM »
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Thumb Rule on stick and controls movement

http://www.rcindia.org/rc-general-topics/query-on-simulator-and-control-surfaces-9765/msg108001/#msg108001
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« Reply #245 on: August 18, 2012, 05:50:41 AM »
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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 yawÖadverse 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

adverse aileron yaw.jpg
Re: Basic Aerodynamics for RC Flying
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« Reply #246 on: August 18, 2012, 05:56:54 AM »
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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
Basic Aerodynamics for RC Flying


(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
Basic Aerodynamics for RC Flying


both are used in RC models
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« Reply #247 on: September 15, 2012, 05:08:07 PM »
rcpilotacro
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Scratch building High winger ? Which semi symmetrical  aerofoil to use  Huh? 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.

semi- symmetrical aerofoils.jpg
Re: Basic Aerodynamics for RC Flying
* semi- symmetrical aerofoils.jpg (31.38 KB, 243x800 - viewed 840 times.)
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Gusty's Hangar and Introduction.

A Good pilot will practice until he gets it right,
A Great pilot will practice until he canít get it wrong.
 

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« Reply #248 on: January 19, 2013, 02:37:15 PM »
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Gusty's Hangar and Introduction.

A Good pilot will practice until he gets it right,
A Great pilot will practice until he canít get it wrong.
 

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« Reply #249 on: January 19, 2013, 02:39:41 PM »
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Gusty's Hangar and Introduction.

A Good pilot will practice until he gets it right,
A Great pilot will practice until he canít get it wrong.
 

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