Tandem-wing Airplanes

"Phil J" wrote in message
...
On Feb 2, 3:21 pm, Bertie the Bunyip wrote:
Phil J wrote in news:75220ca0-969d-4a58-8dac-
:



OK. But why on the canards flying these days is the little wing in
front of the CG, and the big wing behind it. It seems like it would
be more stable in pitch if the little wing was behind the CG.

Then it wouldn't be a canard.

Putting

the little wing in front of the CG seems like it would make the
airplane inherently unstable in pitch. Looking at Rutan's designs, it
looks like he countered this by using a swept main wing. But that
would have been unnecessary if he had put the smaller wing in back.
The only reason I can think of to put the smaller wing out front would
be for pilot visibility, so maybe that's the explanation?

No, it's because he wanted a canard. I explained above that having a
lifitng stab, even a great big one, makes for a twitchy airplane. I'm
sure that could be managed if you wanted, but it's not ever going to be
a very happy airplane. The smaller "wing",on a canard is called a
canard. It's primarily a stabilsation surface that also contributes to
overall lift. It is not a wing
There are probably several reasons that Rutan elected to sweep the wing.
One, it gives good stability without sacrificing manueverability. two,
it expands the CG limits and in the case of this aricraft, allows a
shorter fuselage than would be the case if the weren't swept. .
So, tu summarise, if you put the "smaller wing" (sic) in the back, it';s
a tail unless it;s lifting. If it's lifting it needs to be fairly large
to be useful. make it large enough and you have problems with handling,
one solutuion for this problem is to reduce the sizre of the forward
wing and move the CG aft. Voila! you have a canard!

Bertie

OK, it's a canard if its primary function is stability rather than
lift. I guess Rutan's Quickie is more like what I was thinking
about. On that airplane the front wing contributes 60% of the lift,
so it's a true wing. And there you have the larger wing in front and
the smaller wing in back. I don't know much about the stall
characteristics of that airplane, but it definitely seems to be an
efficient design. With a 64-horsepower engine it has a 140-mph
cruise.

Phil