Tandem-wing Airplanes

"Morgans" wrote in
:


"Bertie the Bunyip" wrote

Nope, it's a pisitive stagger biplane.

That's strange. Every positive stagger biplane I have looked at had
the top wing with a couple degrees more incidence than the lower wing.
Know why it is like the opposite?


Nope, almost never, in fact. The reason being that the bottom wing's
flow is affected by the top's. I'm guessing you thought they had the top
wing at a higher incidence probably because you heard that the top wing
should stall first to ensure a stable stall, which is patly true, but
that doesn't factor in the airflow in the "slot" between the wings,
which effectively lowers the angle of attack of the lower wing even
though it's incidence is higher than the top. Likewise the stab is
affected, and though a negative angle of attack is required for
stability, the airflow around the tail is affected by the wings and a
bit of down stabiliser is called for. Most guys find that the incidence
on the plans isn't enough, in fact.


Well, some guys have done this, but I'm not that crazy about the
piper jackscrew system in an airplane that will be turned up side
down. The plan is to have it hinged at the rear as you suggest, and
then have a attachment at the front that's shimmable and get it right
that way.

You could do it without using a jackscrew, I would think. How about
something like a cam on each side, with a shaft turning a cam on each
side, and a belcrank to turn the shaft. You could limit the range of
motion possible, so that even if something broke, it would be flyable.
I understand not wanting to trust a jackscrew.

It would probably add some complexity and weight, though, but it would
be an advantage for top speed, I would think.


What 86 instead of 85? Nah, weight is all impertant in this airplnae
since the power will be low. Also simplicity. The bits for the
adjustable incidence are already in place, anyway.. Never head of a cam
system before. Should work ok, though, once no slop was allowed.
In any case this is a traditional airplane using all traditional
materials. The only concessions to modernity I can think of are the disc
brakes and the nylon rags. Aside from that, it's a 1930 airplane in
every way.


Bertie