Elevon aerodynamics question

[Starduster]

Hi Guys! It seems most models that use elevons for control have a swept back trailing edge. Here's my question. Picture an F-22 wing planform. Swept back leading edge, swept FORWARD trailing edge. Is there any aerodynamic reason why this wing design would not work with elevon control? Thanks for any input you may be able to offer!:)

[Andy W]

They're that way as, in most cases, when reflexed a little, it's the easiest way to design in washout without a complex wing design. They work the other way just fine also, as long as the model is stable enough to fly without washout..
..a

[Mike Taylor]

What make an elevon work as an elevator is the fact that the center of the elevon is quite a ways back from the center of the wing and the CG. This gives you a long moment arm to change the AOA.
If you sweep the wing TE forward, the control surfaces are now very near the center of the wing, the moment arm is now very short, and you have flaperons, not elevons.

[Starduster]

Thanks Andy. Suppose the wing already has some washout built into it. Will elevons still work?

[Starduster]

Thanks Mike! Ok, so it sounds like either it won't work or if it will work the plane will be very pitch sensitive. Am I heading in the right direction?

[Sparky Paul]

Originally posted by Starduster
Thanks Mike! Ok, so it sounds like either it won't work or if it will work the plane will be very pitch sensitive. Am I heading in the right direction?
.
Quite the opposite.. the closer the surface is to the c.g., the less effect it will have.
For the specific configuration noted, seperating the elevons into elevators and ailerons will be most effective.

[Starduster]

Thanks for your input Sparky. I guess my question now is would elevons work at all. I have an aircraft that is already built. I'm trying to convert it to electric. If I put the motor in the nose, the batteries end up in the tail. If I can make the plane a pusher everything seems to fall into place, except I lose the elevator. So elevons seem to be in order, but from these posts I'm still alittle confused as to whether they elevons would work. I'm expecting the plane to fly quite fast with the motor I'm installing. Would'nt want to loose her on the first flight if I can avoid it.:)

[Mark Wood]

Originally posted by Starduster
If I put the motor in the nose, the batteries end up in the tail. If I can make the plane a pusher everything seems to fall into place...Before you make this mod permanent, you might want to simply tape the equipment to the outside of the plane first. I see CG problems on the horizon.

mw

[Sparky Paul]

Star, if you think of the horizontal in its main function, a stabilizer, you'll see that rendering it inoperative (lose elevator) might not have the effect you need.
It will still be "stabilizing" the plane. Any pitch authority from the elevons will have to overcome that stability. I doubt elevons would have much more than a trimming effect in pitch.
If you remove the horizontal completely, the elevons will be effective.
Bill Evans has a Simitar version that is a trapezoidal wing, similar to a tailless F-22. Built years before there was an F-22, BTW.