Hi Randy,
Flappers are tricky to get right. I only had
success with flaps made from A grain wood. The flap
needs to be flexible enough to bend and straighten out
during the launch. For a 40 ft ceiling I think you
want the flap to straight out when a 45-50 MPH wind is
going across the wing. Some time ago before I got the
feel I would do testing by mounting the gliders
outside of my car and drove down the road measuring
when the flap lifted. Only about 10 MPH more after a
flap lifts does it starts to flutter. Then a couple
MPH more and the wing starts destroying itself.
So too stiff of a flap, you have too much drag and
you don't get much height. Too weak of a flap and it
flutters, again not much height. It needs to be just
right and is a function of the launch velocity and the
height your hoping to achieve.
I hope this helps, good luck.
Kurt
--- rreyno2001 <rreyno_at_earthlink.net> wrote:
> I have been tinkering with my flappers under our
> 37-39' ceiling and
> I'm certain I don't have them shaped correctly. If
> I build lightly
> at 6-7 grams, I can't get them anywhere near the
> ceiling but I can
> with 9-11gm versions. These are 21-24" gliders.
>
> Isn't the theory that under launch conditions the
> flaps will flatten
> out due to air pressure and drop down as the
> airspeed decreases? If
> so this gives a pretty good undercambered airfoil
> and a resultant
> slow minimum sinkrate glide, all things being in
> trim.
>
> It is likely that flaps need to be very, very limber
> in the hinge
> area and this likely requires balsa with very few
> hard grain lines
> so that the material is pretty much homogeneous. In
> addition, I
> think I work that area much too thick for the flap
> to actually
> respond properly.
>
> So here is my question: How do you make the flap as
> flexible as it
> needs to be and is there a way to judge that? I
> notice on Kurt's
> website that the airoil detailed there has a top
> curvature that is
> continuous whereas the undercamber has been carved
> into the front
> section and it transitions up to a very thin flap.
>
> So if I build this airfoil such that the flap is
> very thin and
> flexible will it help get a lighter glider to the
> roof?
>
> Thanks, Randy
>
>
Kurt Krempetz
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Received on Sat Feb 10 2007 - 18:46:04 CET