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« on: December 09, 2010, 04:05:26 PM »
anwar
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Couple of years back, I had a small electric bipe (the Ultrafly Radix http://www.modelflight.com.au/ultrafly/ultrafly_radix_3d.htm ), which would fly so slow in level flight, that I could practically walk along side !  Remember that this is not in high-alpha mode, or prop-hanging mode, just in level flight.  I had a thin (and flexible) orange colored GWS prop on it, and I used to take my hands off both the sticks, and it used to slowly fly level and straight.  There is another piece between the two wings, so one can consider it as a tri-winger too.

So my question is... on a NON-WINDY day, can we build a plane that will stay PRETTY MUCH where it is IN LEVEL FLIGHT, just by putting a large dia small pitch prop, and giving it a large wing area (a bipe or even a tri-winger) ? 

In other words, if we create enough airflow of the wings, and a large enough wing loading, can we somehow defy Newton's third law ?
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« Reply #1 on: December 09, 2010, 04:19:06 PM »
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i think it is not possible if the prop is level (horizontal) and the wing is level. only possible if the prop is vertical, but then it will become a helli  Grin
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« Reply #2 on: December 09, 2010, 04:32:01 PM »
anwar
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I am not talking about being completely stationary, more like very slow walking pace.  What if the plane is really light ?
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« Reply #3 on: December 09, 2010, 04:37:11 PM »
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something like this??
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« Reply #4 on: December 09, 2010, 09:47:35 PM »
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Like i said in my thread (http://www.rcindia.org/beginners-zone/basic-aerodynamics-for-rc-flying/msg41421/#new) Lift=weight in level flight. The angle at which the wing is rigged or tilted (By your elevator action) and Velocity≤(These are the variables) that affect the lift.

In this (a) Weight is Less ∴ Lift required is less. (b) Since lift is affected at square of the velocity any reduction in weight immensely affects the reduction in speed (Square Root to be precise). It is therefore possible to reduce speed quite a lot  by reducing weight. (I flew a model which could fly by just the warmth of your palm (Micro RC))

The next discussion you brought up was once upon a time a closely guarded spark of Genius called "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).

Hanging Props (Heli/Autogyro) is a different discussion, shall we leave it for some other day ?

Did i get across? I wonder, some feedback.

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« Reply #5 on: December 10, 2010, 02:46:33 AM »
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something like this??


More like this : http://www.rcindia.org/chatter-zone/remote-control-of-a-plane-with-zero-electronics-!/msg6788/#msg6788

But I am wondering seriously how low can we go in terms of "slow but level" flight using a foamie, say one built with 3mm or even 2mm foam.  If one were to attempt this, what are the factors to consider, other than keeping the model very very light ?

« Last Edit: December 10, 2010, 01:37:29 PM by anwar » Logged

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« Reply #6 on: December 10, 2010, 02:50:37 AM »
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The next discussion you brought up was once upon a time a closely guarded spark of Genius called "Coanda Effect"

How can this be used in say a foam plane to help slow it down in level flight ?  Other than saucer shaped aircraft, I have not seen any RC aircraft that seems to use this effect.
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« Reply #7 on: December 10, 2010, 06:49:18 AM »
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"Now thats what I call Music".

We are getting deeper into complexities. if you see the equation CL Ĺ σ V≤ S. This CL (C subscript L, fondly called as CsubL) can vary from mere 0.1 to more than 1.2 (Normally, otherwise there are very high lift devices, lets leave those guys out.). Which means for all your effort, a wing may give you 10% to 120 % of what you asked for, depending on how much you pampered it. In the video you posted see the Camber of the wing under flying condition and the angle at which it is rigged. I did some math and approximated its CL more than 1. a simple Foamie ? its typically 0.2, mere 20%.

Next question? how do we increase CL? for that let us see factors affecting CL. Size, shape, Camber, Thickness/Chord ratio, Span, Wing Area, Fuselage to Wing Airflow interaction (More on this ideal body of revolution, later), these are the variables in the hands of a designer.

Practically !!, use 2 or 3 3mm corbon rods in a foamie wing to give it some camber (I am against putting one rod through the centre which only contributes to reinforcing the wing and not giving it some shape), keep the shape of the wing to near elliptical in planform(Like the Spitfire) (More on this spanwise lift distribution and Tip Stall, Later), rig the wing upward slightly, try and keep a longer chord. use canard design instead of elevator (Elevator kills lift, whereas canard adds to it? how? use your imagination and post your views).

As regards Coanda effect on a foamie? two tractor engines on the wings is better than two pusher. I remember MR Avro designed an RC called AVROCAR. there is a DIY RC using Caonda effect. see

http://www.diydrones.com/profiles/blog/show?id=705844%3ABlogPost%3A232052&commentId=705844%3AComment%3A233729&xg_source=activity

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With this kinda imagination, anwar , you should have taken up to be a aircraft designer
« Last Edit: December 10, 2010, 07:28:41 AM by augustinev » Logged

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« Reply #8 on: December 10, 2010, 07:17:48 AM »
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Wow.. that music sounds really good to my ears... thanks for all this information, keep it coming. I think I am at the right place at the right time. About your question with respect to elevators & canards... I do not have any scientific explanation but the normal daily use observation.

Take a straight edge ruler and place it on a flat surface, try to hold it from extreme back and try to lift the front portion upward... heavy? yeah it will be... now hold the front portion and try to pull it upward... feels very light. The elevators have to push the entire front to the upward and have heavy wind pressure no them wherein canards have very light pressure when compared and just change the angle of attack of the plane... not expecting 10/10 but please tell me if I sound stupid Smiley
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« Reply #9 on: December 10, 2010, 07:44:18 AM »
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Practically? bang on. Let me put it in a more complex manner.

to get the nose up (Which is what we regularly do in RC flying). in a elevator it is a Tail down force. The leading edge of the elevator goes down, thereby adding to the weight. Poor Wing has to produce little more lift to compensate that. In a canard it adds to the lift (Wings are sort of unloaded). Another factor is, a high lift wing has long chord, the elevator is closer to the center of pressure (The point on the wing through the which all the lift force is said to act). So moment arm (Fulcrum) is less. To get the same effect elevator has to press more, a canard has to push up less (Which is why canards are small).

It is only possible in RC to use canards without gyro/Fly by Wire control, not in real aeroplane. Why ?

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« Reply #10 on: December 10, 2010, 08:22:57 AM »
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I like the interactive teaching Thumbs Up

May be the advantage is acting as disadvantage here.. the same canard which require very less force to change the lift of plane could act as disadvantage and gyro help in keeping the nose in level. Talking about Mirage or Sukhoi since they are very tail heavy for easy maneuverability , we need to make sure canard keep the plane flying straight as the plane would always want to pitch up for tight turns...  Head Scratching
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« Reply #11 on: December 10, 2010, 11:01:28 AM »
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Precisely.

elevator Stalls nose will pitches down , speed increases, ac and the stabliser is unstalled. Canard stalls nose pitches up further ac enters spin, thats why Canard is with FBW (Fly by wire). FBW doesn't let that happen.
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