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« Reply #300 on: August 26, 2014, 11:19:48 PM »
abhishekdas11
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i used this online site for instant plot and print http://airfoiltools.com/plotter/index
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« Reply #301 on: August 26, 2014, 11:20:22 PM »
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Iyyer sir, its nt wt ure thinking;-)
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« Reply #302 on: September 03, 2014, 11:18:19 AM »
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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.
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« Reply #303 on: September 03, 2014, 12:17:49 PM »
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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)
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« Reply #304 on: September 03, 2014, 08:58:35 PM »
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Re:

Yes, but I don't want to climb straight up. Wouldn't the lower wing loading result in greater climb rate?
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« Reply #305 on: September 04, 2014, 07:01:54 PM »
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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
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« Reply #306 on: September 05, 2014, 03:18:05 PM »
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Re:

So if I want a plane that can gain height as quickly as possible, which one should I go for?
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« Reply #307 on: September 05, 2014, 07:57:41 PM »
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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  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
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Well I been into aeromodelling since I was in School....  had won the "WINGS Open" at "Bombay" (as it was known then) in 1985 for control line aerobatics (was doing my graduation at that time) and had received a big gold trophy....  Mr Bhivandiwala organised it and gave good awards.
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« Reply #308 on: September 05, 2014, 09:13:56 PM »
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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.
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« Reply #309 on: September 05, 2014, 09:24:52 PM »
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1. How will the judges measure thrust?  >Cheesy >Cheesy
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?  >Cheesy) 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
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« Reply #310 on: September 05, 2014, 09:37:08 PM »
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@maahinberi: Preparing for the Aero-Dominator competition or the Aero-SAE VIT?
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« Reply #311 on: September 05, 2014, 09:41:31 PM »
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Not preparing yet. Saw the problem statement and went into deep thoughts of wing loading vs. Thrust to weight ratio  Tongue
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« Reply #312 on: September 05, 2014, 09:42:51 PM »
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Have you been to any of the competition before?
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« Reply #313 on: September 05, 2014, 09:57:16 PM »
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Nope
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« Reply #314 on: September 05, 2014, 10:02:44 PM »
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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.
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« Reply #315 on: September 05, 2014, 10:48:24 PM »
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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.....
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Well I been into aeromodelling since I was in School....  had won the "WINGS Open" at "Bombay" (as it was known then) in 1985 for control line aerobatics (was doing my graduation at that time) and had received a big gold trophy....  Mr Bhivandiwala organised it and gave good awards.
Our team had won the following medals:-
1.   Gold for Control Line Aerobatics
2.   Silver and Bronze for Control line speed
3.   Bronze for Free Flight Glider
Sharma Models helped us train to win the medals
 

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« Reply #316 on: September 06, 2014, 10:10:27 AM »
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Re:

Thanks everyone.
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« Reply #317 on: July 26, 2015, 11:06:01 PM »
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Answer to the question posted in this thread http://www.rcindia.org/beginners-zone/prop-question-21968/

Smiley

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

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 Wink ). i have tried to keep it simple. Shoot away your questions here or in the original thread doesn't matter

twist.jpg
Re: Basic Aerodynamics for RC Flying
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« Last Edit: July 26, 2015, 11:26:36 PM by rcpilotacro » Logged

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« Reply #318 on: July 27, 2015, 04:17:48 PM »
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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
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« Reply #319 on: August 24, 2015, 01:03:57 AM »
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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  Grin.

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
Basic Aerodynamics for RC Flying
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« Reply #320 on: August 24, 2015, 04:27:13 PM »
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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
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« Reply #321 on: September 05, 2015, 10:15:23 PM »
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Posted for only to show how it works not related completely RC though.

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« Reply #322 on: October 07, 2015, 08:11:08 PM »
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This is the video i have taken from anwar bhai's This 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 ? Smiley Wink

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« Reply #323 on: October 07, 2015, 10:22:54 PM »
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@rcpilotacro,
Sir,
Wow. A real head scratcher!

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

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  Grin
Regards.
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« Reply #324 on: October 07, 2015, 10:26:05 PM »
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