Wing Sweep Dihederal Effect, Pros/Cons

[Butch777]

I like scratch building aerobatic parkflyer for smaller areas.
It seems to me, that wing sweep adds some stability and unlike dihederal, works both right side up and inverted.

But I don't see alot of real planes using much sweep in aerobatic planes.
The Ultimate Biplane has some sweep, but it seems like I read it was for other reasons than stability.

So what are the pros and cons of sweep?

And at what sweep angle does it make things worse?

Thanks for any help, Butch

[BMatthews]

It takes a lot of sweep angle to do the same as just a couple of degrees of dihedral. biplanes with sweep angle in the upper wing do it so the wing's lift can be moved back slightly while keeping the center section forward enough to let the pilot easily get in and out and provides a better view upwards from the cockpit. We do it on the models either for scale reasons or just because it looks cool. But the 3 or 4 degrees that are used on biplanes provides so little roll effect that it's not worth mentioning. You actually need to use more than 10 degrees of sweep angle before it'll have a noticable dihedral like effect.

[JetPlaneFlyer]

For serious aerobatic ships you don’t really want any lateral stability from dihedral or sweep. Dihedral (or sweep) produces a yaw/roll couple (i.e. the model rolls when you apply rudder) which is undesirable for aerobatics.

The aim for most aerobatic ships, either full scale or model is neutral stability, so mid wing and no dihedral or sweep is prevalent.

Steve

[HerkS]

There are a lot of factors at work - besides sweep, but of the six 3D park flyers that I am currently flying, the ones with sweep handle the transition to ultra high AOA much better than the ones with straight wings. Even a modest amount of sweep seems to make a difference. This one will do a very slow transition to hover with no wing-walking or wobbling at all. I really like the way it handles.

This is purely subjective - experience -- no science implied.

[BMatthews]

Ah yes... but post stall behaviour is a whole other issue Herk. I won't even try to guess at the why's and wherefore's of this bit of success and choice but it's certainly got very little to do with sweep acting as dihedral.

Your picture is making me itch to run out and buy some Depron..... :D

On a more general note it stands to reason that if some sweep to the wing provides a slight dihedral effect either way up then when flying knife edge it would have no effect since the wing ideally isn't providing any lift. Or if you want to look at it a different way it's in transition from positive to negative lift.

[Iso Octane]

Oooh I like the Balsa one! :cool: