On the Oxalys photos, I have noticed that the trailing edge does not form a sharp edge; rather a square "step". Is there any theory behind that that someone can explain?

it's a way of getting exponential on the controls, been used in fullscale Sukhoi's for ages I believe.

Also it's aerodynamicaly (?) better to have a thicker but straight trailing edge then a sharp but wringled trailing edge. The thicker trailing edge is also more resistant to damage. It will also cause more drag, not a real problem for these planes....

They have been like that since Enigma, Evolis and Synergy all having about 4 mm thick in their wing trailing edge.

I wonder also but found no answer other than this: Is there any point for going thinner than this? In fact by having it that thick, it helps in the construction and packaging when you bring them along. Smart?

To me it seems that Oxalys has TE more than 4mm... also, I have heard that maybe there is less deflection needed for the same effect than with sharp TE... again, is that so and if yes, what is the underlying theory?

I read somewhere in a book about lift and drag (by German Hoerner I think, but not quite sure) that the portion of the wing that is cut away, (i.e. the 15-20mm that would have been there if the wing was made with a sharp trailing edge) actually adds to the lift of the surface. The "effective" chord of the wing and control surface is therefore significantly larger than it actually is, when it is cut with a blunt trailing edge. This may partly be the reason why the required deflection angles are lower. (??)
Magne

David,

By incorporating the Blunt Trailing Edge, the designer has strengthened the edge for ease of fabrication and handling, which has also been found to improve the lift characteristics of airfoils.

_________
Schpankme

"If you tell the truth, you don't have to remember anything."

This works on flat flying surfaces on small planes too. If you have a sheet stab you round the leading edge and leave the trailing edges sharp and square. This makes the plane track better.

John Schroder (top 10 Nats IMAC pilot) flies at my field. He has an early 40% Fiberclassics Extra 300. The early birds had a ruddder that tapered to a sharp trailing edge. John found that the tail wanted to waggle in straight and level flight. It was like the tail could not settle into a groove. He checked all the servos (4 JR 8411's) all the links and tillers and was still having a problem. He called Fiberclassics and they sent him two L shaped plastic strips. The told him to CA them to each side of the trailing edge so that the trailing edge was made wider. This solved the problem. All new Composite ARF kits now have a diffrent rudder trailing edge shape to eliminate this.

A thinner/sharp TE makes the surface less sensitive around neutral and has less drag. A squared off, thick TE has more drag and more sensitive around neutral.....More noticeable in around .60 size or smaller planes. If you're racing, or don't want drag, keep 'em sharp. In our aerobatic birds, going 1/8" to 1/4" depending on the model size if fine.

A sharp TE is not really any harder than a thick TE to keep straight, it'll just hurt like hell if it's really sharp :-(

Amir