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mstram
20th Apr 2002, 16:59
If a hypothecal aircraft was built as follows, what would the flying characterics be like ?

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.
Uniform thickness. (I.E. a BOARD !)
No dihedral (is there any on a real Extra 300 ?)

Tail surfaces - also replaced with flat boards. No camber, etc.

From what I've read, the boundary layer would seperate very quickly, causing lots of drag ??? Therefore much more power would be required ?

I'm guessing it's gonna stall at a higher speed, and pretty violently / un-predictably ?

With no dihedral (is there any on aerobatic planes), I'm guessing it would be very unstable laterally ???

Mike

Groundgripper
22nd Apr 2002, 22:34
Uncambered, flat boards for wings? Hmm, don't think you'll get much lift out of those, the only difference more power will make is the speed at which you hit the fence at the far end of the runway!

criticalmass
23rd Apr 2002, 05:17
Sounds like this one is gonna be stalled at any speed!

My guess is it will handle like a brick with the flaps down and engine out. Would some aerodynamicist like to put the appropriate model parameters into the computer and tell us how bad this thing really is?

Assume the flat boards are hollow rather than solid and the thing is fitted with some powerplant capable of delivering enough thrust through a fixed-pitch airscrew of Wright-Flyer efficiency to actually get it moving.

Gonna handle like a dog, all the same. Its bite will definitely be worse than its bark!

BayAreaLondoner
23rd Apr 2002, 06:06
Sort of on-topic... but only if the topic is "weird planes", you may be interested in this account of a 65% sized flying replica of a 1932 "Stipa-Caproni ducted-fan-technology demonstrator", which if you've seen if, will be more likely to be known as the "flying barrel".
Info and a picture here (http://www.landings.com/evird.acgi$pass*44980054!_h-www.landings.com/_landings/pacflyer/apr7-2002/An-74-Stipa-Caproni.html).

Volume
23rd Apr 2002, 07:00
You can produce some ammount of lift with a flat plate wing, some popular planes like the PA18, Aviat Husky or Christen Eagle use them on the horizontal tail and it produces enough lift to maintain moment equilibrum and allows control of the airplane.
But why should you use such a wing ? Where is the benefit ?(besides ease of structural design and reduction in tooling costs, making this one a perfect homebuild :D )
Biggest problem might be the extreme hysteresis in the CL-alpha-curve, you might reach Cl max of about .8 if the leadng edge is rounded propperly, but youŽll have to reduce alpha to essentially zero to achive reattachment of the airflow once you are stalled. Additionally CL max will depend highly on leading edge contamination, making the flight characteristics of such a plane suitable for suicidal purpose only because you never know your stall speed when landing.
By the way, the Extra 300 has no dihedral, no camber and no twist like most of the aerobatic planes.

mstram
23rd Apr 2002, 09:21
This was purely a theoretical question.

I've been doing some reading about aircraft design, and have started to understand some of the *very basics*.

The Foilsim program is a good tutorial for very basic concepts.
On the other end of the spectrum, I've downloaded Xfoil, and found some other web sites on airfoil design.

Volume:

You sound like you have some knowledge in this area :)

>By the way, the Extra 300 has no dihedral, no camber and no twist like most of the aerobatic planes.

I guessed that an aerobatic wing would not have dihedral, as you really don't want it to be stabile.

I've been looking on the web for specs of wings like the Extra or other aerobatic aircraft. Just found a l ink re: the "One Desgin" http://www.eaa1000.av.org/technicl/onedesaf/1desaf.htm#Design_Considerations

Genghis the Engineer
23rd Apr 2002, 20:58
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