Fast glass biplanes

On Tue, 18 Nov 2003 23:31:56 -0800, "C J Campbell"
wrote:


I believe his was the fifth Lionheart completed and the fourth to crash.

Wow. What's going on here? Too much airplane for too little
experience?

Corky Scott

My take on this is that while it is true that both surfaces on a canard or
tandem wing design are lifitng surfaces, the canard cannot use all of the
available lift from the main wing - if you want the stall protection - and thus
the main wing needs to be made much larger than needed for cruising flight if
one is to expect a reasonable landing speed.

In the case of my Quickie the Eppler main wing stalls at a fairly high angle of
attack but it's peak Cl is not that good. The result is that during landing
the canard is doing more than it's share of the work. Some Quickies (all
Quickies are single seat - the 2 seaters are Q-2/200's) land as fast as the
much maligned BD-5.

Another factor to consider is just because the little wing is in the back it
must not necessarily be providing down force. It can also lift and still be
part of a pitch stable plane.


props.. Flat out, the Glasair was faster, but only slightly -- 215
vs. 210
mph.

Even this surprises me, I had been led to understand
that the canard design is inherently more efficient
because the canard wing, besides its basic function
as a stabiliser, also helps to generate lift; wheras
the stabiliser in a conventional design must push down.
So that for every 100 lbs of weight, the main wing in
a conventional design carries 110 lbs, in a canard only 90.

I'm not enough of an aviation know it all/historian so the only example I can
site off the top of my head is the Quickie, Q-2/200, Dragonfly, Flying Flea
family.

While the "little wing in the rear" isn't so little the physics are the same.
As long as the moment of the 2 "wings" move aft with an increasing angle of
attack, and forward with decreasing pitch the plane will be pitch stable at one
particular speed. This can be done simply by having the tail provide a down
force, but by properly selecting the airfoils so that the lift of the rear wing
increases faster than the front with increasing angle of attack you get the
same result.

I'm not a professional aerodynamisist, maybe even a poor amateur, and not a
very good teacher - so if your just learning about all of this in your PPL
ground school it might be a bit simpler to forget all about anything but
"conventional" airplanes for a while...........or find someone that can explain
it better than me.......which shouldn't be hard.

If you really want some interesting pitch stability mental exercise think about
a flying wing with negative sweep..........


Well well I am learning again.
My PPL ground school certainly disagrees with you!
Do you have any example of such a design?

TIA,
Karel