questions on multi-wing planforms

"flybynightkarmarepair" wrote in message
oups.com...

pTooner wrote:
Firstly, I am new here although I've been reading for a few days. For
anyone with more knowledge than I, I keep considering building a small 4
wing aircraft. Not stacked, but two up front and two in the rear. I
have
read frequently of problems supposedly resulting from interference of the
airflow between wings, but I can't seem to find anything very specific.
I'm
fairly confident that interference between the front wings (or rear) can
be
minimized by reasonable spacing and differing dihedral. I'm not sure
what
the effect of the airflow coming off the front wings will have on the
rear
set. I don't know whether I could remove most of the problem by having
one
set considerably higher (how much?) than the other set or if it is
reasonable to have them on more or less the same height. The reason for
the concept is trying to get a wingspan small enough to fit into a normal
garage and conceivably take off and land from streets and highways. I
visualise something in a two place plane that would fall into something
of
the appeal category of a motorcycle or small sports car. Any thoughts
would
be appreciated.

Gerry

John Roncz called a 3 surface airplane he participated in the design of
"the aerodynamicists full employment act"!

You will, with optimization of all the variables. be lucky to get 40%
of the lift/drag ratio of an equivalent conventional planform.

Can you elaborate? I don't see why this should be true.

But the bigger problem will be control. Pitch stability, in and out of
ground effect, will be a formidable problem, as will stall
characteristics. Compromises needed to make the handling acceptable
may make the efficiency even worse.

Well, most tandem wing aircraft are designed to make normal stall
impossible. (the rutan designs for instance) Pitch stability is a problem
that I thought had been pretty well handled by airfoil design in canard
aircraft years ago. My thoughts (I wouldn't call it a design) are simply
two sets of biplane wings mounted fore and aft. Biplane wings don't
normally present much of an efficiency problem except for the bracing which
isn't stricly necessary (The hyperbipe was a pretty efficent design) I
certainly agree that handling especially in the pitch axis is the major
challenge, but I don't see why it should present a much bigger problem than
the flying flea family of aircraft where it was eventually solved
satisfactorily.

I agree with Ernst - a low aspect ratio delta/lifting body makes more
sense. Perhaps a 2 seat Facetmobile with the outer portions folding
inward like a Dyke Delta.

Perhaps, but it's been tried many times and with very limited success. I
know of NO attempt to build the 4 wing system that I envision. That seems
strange when you consider that about every imaginable combination has been
tried at one time or another. Didn't someone finally build an operable
ornithopter?


But have you looked at all the wires around most roads? Not an area I
would want to use for landing and takeoff.

Good point, but they aren't everywhere. ;-)

Gerry