Re: The difficulty of high-lift devices for tandem wing aircraft (long)


David J. Gall
 

Wladimir,

Your camber and toe-in numbers are incorrect. You don't want toe-in, you don't want negative camber, and you don't want anything near 3 degrees for any of these angles. Camber should be neutral to slightly positive (0-2 degrees) and toe should be neutral to slightly toe-out (0-2 degrees). Tires, depending on the tire design, will skid at angles between three and seven degrees, analogous to airfoils stalling at critical angle of attack. Mounting the tire with three degrees toe (in or out) means that the side force on that tire will be approximately 40-90% of the normal load on that tire... NOT GOOD! See an auto mechanic about tire angles for wheel alignment and you'll find them talking about angles in the range of 1/4 to 1/2 degree for camber and toe measurements....

Kraft paper makes an excessively heavy part, regardless of its suitability in other respects. Better to stick with the tried and proven. I've already commented on the remainder of your ideas so I wish you luck in your researches.


David J. Gall

----- Original Message -----
From: "Wladimir Kummer de Paula" <wladimirkummer@...>
To: Q-LIST@...
Subject: Re: [Q-LIST] The difficulty of high-lift devices for tandem wing aircraft (long)
Date: Sat, 05 Nov 2005 12:38:18 -0200


Hi,

This is my first posting...I just thought this subject so
interesting...I´ve been designing a Q type aircraft, initially monoplace
to test the concept. My approach to lowering the stall speed would be
plain and simple more wing(s) area. High lift device would tear down one
of the most beautiful aspects of this design that is simplicity. Also
I´d use a almost zero pitch down moment airfoil in the main wing so it
would not load down the canard thus allowing it to be smaller. In fact I
have this airfoil designed by myself. The canard would be rectangular
planform for ease of construction and swept back about 15 degrees. This
would make the wheels closer to the balance point. Also it would have
enough toe in (about 3degress) and negative camber (something like 5-7
degrees). The canard airfoil has a usual coefficient of moment so to
unload the wing and allowing it to be smaller. The stall speed is
dictated mostly by the canard loading and airfoil so I would adjust this
to get a reasonable stalling speed (say 55mph). Vortex generators at
the main wing would keep it flying avoiding the so feared deep stalled
condition.
The fuse could be built using alu angles/tubes riveted as the main
structure and foam/glass for final shaping. I think this is the most
crash resistant method of building and if done right....light as well.
The wing would use the proven aeromodelling/Rutan concept, but for the
spar Id use something more newer like a PVC shear web and carbon rods.
Using this the wing sheeting could be as simple (and cheap) as brown
(Kraft) paper with epoxi since this type of spar building is very very
strong and flexible. A second spar at the aileron line could account for
the torsional loads. This kind of sheeting can become as though as a
nail....In fact I´ve used this many times for my model airplanes....And
is sooo easily repaired. The ailerons and elevators are full span for
most efficiency and lower weights (no rods necessary).

Wladimir in Brazil.....

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