flying wings

[zerop51]

i am working on an engineering project.
we have to design or improve something. i would like to improve on flying wings but i dont know if you can. anyways i need some help.
can you tell me what kind of airfoil is used and anything else like that. i am trying to make a glider that has separate elevator and aileron control. i would like to know some of the principles behind a flying wing.

if this is in the wrong area please move it.

thanx,
zerop51

[Sparky Paul]

A good place to start..
"The Wing is the Thing"
http://www.twitt.org/

[BMatthews]

A lot depends on what planform of flying wing you're working with. A simple rectangular or "plank" style wing relies on the shape of the camber line to provide the positive stability. These airfoils have the high point relatively forward with a strong reflex in the last part of the curve.

Swept flying wings are a bit different. In this planform you sort of "cheat" by using the rearward tip portion of the wings to act as the stabilizer. Since the tips are to the rear of the MAC you could say that the tips ARE the stabilizer for a simple swept wing. Due to the twist required for the swept wings the span wise lift distribution starts high at the center, tapers to nothing at some point between 1/2 and 3/4 of the span and is negative at the tips. So you've replaced the fuselage with the wing to hold the stabilizer in place.

Because the CG placement and wing reflex or twist are so dependant on each other you need to know what the CG will be and design the amount of twist to corelate.

For swept wings that rely on twist the Panknin twist formula is a very handy tool. The ultimate swept flying wing would be one with a variable CG and variable twist flexible wing so that the model could be tuned to optimum for all flight modes. Controls for the swept wings are pretty much elevon only. It's just not practical to have separate ailerons and elevator in the tip sections where they would fight for placement. The elevator needing to be as far back as possible and the ailerons as far out as possible. That's at the tips for a flying wing.

For plank wings I prefer elevons so that minor changes can be made in flight to the controls to alter the reflex. Such changes can be added on the ground to a model with separate ailerons and elevator via the control linkages. It's important that the neutral elevator and aileron trims line up or the one part of the wing will be fighting the other...... another plus to elevons.

PS: Sparky is right. That's one of the better sites for wing info. But do a Google on "flying wing" if you haven't already. There's tons of stuff out there about it. As for airfoils if you go to the Martin Hepperle site you'll find a bunch of "flying wing airfoils". Be aware that some of those are intended for planks and those are more reflexed than the others that are only LOW pitching moment airfoils rather than fully POSITIVE pitching moment airfoils that are needed for plank wings. The low Pm types are good for swept wings but no good for planks

[biber]

Bruce, that's a quite good comprehension, but only at high speeds you will get a negative lift coefficient at the tip of swept tailless. At average speeds mostly positive lift can be maintained even at the tips. And both, plank and swept wing aswell can be designed to provide an elliptical lift distribution. But separated elevator and ailerons are as mentioned in many cases not first choice.

biber

[Ollie]

http://www.b2streamlines.com/OTW.html
http://www.b2streamlines.com/Culver.html
http://www.aerodesign.de/english/profile/profile_s.htm
http://www.mh-aerotools.de/airfoils/index.htm

[e-sailpilot86]

Bill Kuhlman is a regular at the flying field and club I go to. If you want even more details on flying wing design, I'm sure he'd be able to give you an extraordinary amount of information. His E-mail is on the b2streamlines website. Very very big on flying wings, that's almost all he flies at the field, and his knowledge of their design extends well beyond what most people get to see. Check out his books on designing airfoils for wings and designing them in general. Trust me, it'd be extremely hard to improve on the designs he's made, unless you intend on flying it at a different range of speeds. I've seen his 6 foot creations that have something like a 2 or 3 foot chord approach from 500 feet away, and about 12 feet off the deck at that distance, land at his feet. I've never seen something with such a cool thermaling ability and ground effect for such an off-beat design. Once he tells you what's going on with the plane, it makes sense why it's such a perfect design! Must be fun to fly, someday I'll build one... :)