Difference in airfoil?

[GreenAce92]

Ok can anyone break it down easy enough to explain how a flying wing's airfoil works and how its different. Also how to calculate all the wing specs and CG on a flying wing. Is there any know unstable designs that anyone should stay away from?

Thanks

[dimadee]

Flying Wing airfoils have what is called a positive pitching moment. They have an 'S' shaped camber line and an amount of reflex with the elevons to effectively create an up elevator effect. The C of G for wings is normally around 20-25%. Within reason, you can get most airfoils to work as a wing, but there are some optimised sections especially designed for maximum efficiency.

A really good website is www.b2streamlines.com (http://www.b2streamlines.com) - Bill & Bunny are passionate about flying wings, and are always helpful with questions. You could also try www.twitt.org (http://www.twitt.org) (The Wing Is The Thing).

I recently built a conventional depron plane with a very low aspect ratio wing, powered by a GWS geared (A gears) 350 motor with an 8x6 prop on 2S LiPo. I have plenty of brushless options, but really wanted to play with the GWS geared setup. It turned out really well, but flew just OK. After staring at it for a while, I cut the tail off of it and made it into a flying plank - it now flies absolutely fantastic. It has a great speed range, is very aerobatic, and flies inverted with minimal down elevator. I have only flown it a couple of times, but it is a definite keeper. It slows right down, and remains totally stable - sometimes, it just all comes together :tc:

I have attached a couple of pics if it helps.

[GreenAce92]

Thats a pretty cool design. Question for you... how did you cut the wings without making chips or flaws and is that bluecore you used?

So basically.... the end part of a flying wing's airfoil where it curves up acts as the tailwing on regular planes with the tailwing? And these flying wings fly straight and nice right?

[dimadee]

Thanks for your kind words.

The wing is hollow. I made up a spar which comprised of 2 pieces of 6mm balsa with a piece of 6mm depron sandwiched between them. I then developed a profile for the front of the airfoil and cut some formers from 6mm depron. These were glued to the front of the spar and in turn this D box frame was glued to the bottom surface of the wing skin (made from 3mm depron). I then wrapped & glued the skin around the frame, and finally glued the trailing edge togther. I used a broom handle for the leading edge radius, and then pre formed the LE of the wing skin using the broom handle and a heat gun. The final step was to cap the ends with some depron to close up the structure. The wing is stiff, and has excellent torsional rigidity. I used foam friendly CA and kicker on every joint.

The RTF plane with a 2S 1300mAh LiPo weighs about 360g (12.7oz) from memory. This gives a wing loading of about 5.6 oz/sq. ft. This is very light, but my intention was to build something I can fly at the park, so it needed to have the ability to fly slowly, and have a good glide angle in case I lose power and need to glide it home.

Yes, you are correct about the elevon setting - the slight reflex at the trailing edge acts like the elevator in a conventional aircraft. The other thing which is critical is making sure you have enough fin area to keep the plane directionally stable. You need to keep the fin as far back as possible on the plane, and the sweep I have used pushes it back even further.

This plane flies as straight and true as any other plane I own (I have a couple! ;-) ).

[GreenAce92]

cool. Thats a pretty neat idea. I might try that myself later.
Glad it flies well, I always hate it when you build somethin nice and it doesnt fly. I have another question again. Some friends of mine have given me this walmart plane and i was going to gut it and use the parts for another. Is there a simple design thats very stable and can glide for this? and also because some walmart planes are cheap like this one it uses motor differential thrust control.and also how do i mount the motor on, and what angle to mount it if its a pusher.