If a hypothecal aircraft was built as follows, what would the flying characterics be like ?
Okay, I'll give it a go...
Low wing plane, same basic size / specs as say an Extra 300.
(or a high wing plane ... same basic specs as a 172)
Differences :
Wings - replaced by same size "flat boards'.
No camber.
Marked increase in stalling speed.
Uniform thickness. (I.E. a BOARD !)
The big player here is that presumably you are going to have square leading edges - this will give a particularly nasty pitch-down at the stall, and possibly a lot more wing drop
No dihedral (is there any on a real Extra 300 ?)
Dihedral aids lateral stability, particularly in a straight winged aeroplane. On the extra this would reduce lateral stability to very little, on the C172 you'd still have a pendular component, which would leave some lateral stability.
What does this really mean? Well, probably quite good handling in turbulence, but neutral to divergent spiral stability (this last means that the aircraft will tend to keep rolling when disturbed).
Tail surfaces - also replaced with flat boards. No camber, etc.
Good move, this will keep the effective tailplane volume co-efficient about right, and thus stability (so long as longitudinal dihedral is kept the same) should be about right if it was okay in the first place (which it certainly is for the C172 and the Extra - well fit for purpose!).
From what I've read, the boundary layer would seperate very quickly, causing lots of drag ??? Therefore much more power would be required ?
Probably not for the reason you state, the turbulence from your plank's sharp leading edge might well keep the boundary layer attached. Equally however, a less efficient lifting surface will create more drag for the same lift - so your conclusion is correct.
I'm guessing it's gonna stall at a higher speed, and pretty violently / un-predictably ?
Without a doubt if you keep sharp leading edges, if you can round them off then you'll certainly still increase the stalling speed, but might hang onto reasonable characteristics.
With no dihedral (is there any on aerobatic planes), I'm guessing it would be very unstable laterally ???
With a straight leading edge, yes this is probably true. But remember what you mean by lateral stability. Lv is rolling moment due to sideslip, so the consequence of reducing it will be...
- Negative spiral stability (constant need to keep the wings level)
- Less tendency to roll due to turbulence
- Better spin resistance.
- Tendency to lock into a spiral dive, if it's allowed to enter one.
G
Last edited by Genghis the Engineer; 23rd April 2002 at 20:03.