Hi Gary,
I agree with Bill, ceiling under 50 ft the flapper
has a big advantage.
I will give you my observations in regards to your
questions;
1) How much force really exists on the wing? Well,
my Time Machine design is a standard glider weighing
about 2 to 2.5 grams. I have loaded the wings of this
design by putting weight at the root of the wing and
supporting the wing 1/2" from the tips on each side.
To get up 40 ft a wing needs to hold 75grams of
weight, otherwise they break on launch.
2) How much force is required to move the flap? I
just took a model out of its storage box, it took 9
grams at the root's trailing edge to straighten out
the flap.
3) What would that excess lift pull against? I
believe the excess lift pull is be countered by the
horizontal stabilizer. The loads on fuses are large
and I have broken fuses on a launch which could
support without breaking 75 grams hanging at the end.
When I test fuses I support them at the trailing edge
of the wing and hang weight at the back end of the
fuse. I believe when you see a glider bunt,
(basically looks like someone just gave the model a
little down elevator at the top of the launch
profile), what is actually happening is the fuse is
flexing. Any model that I flown; if it bunts at say
30 ft, then if you try for more height(more power) the
fuse will fail before it ever gets to 35-40 ft.
I hope some of this data can help you get a
better understanding of flappers and gliders in
general.
Kurt
--- dgbj_at_aol.com wrote:
> I've been wondering how those flaps worked ever
> since I first saw them. The
> theory is that under the increased flight loads of a
> fast launch, the flaps
> bend up, reducing the camber, the lift and the
> tendency to loop. But how
> much force really exists on the wing? With typical
> loadings, there is around
> 0.1-0.2 gram per square inch load, most concentrated
> in the forward half, less
> on the flap. How much force is required to move
> the flap? How much
> difference in lift does that flap change make? The
> lift is also not directly
> proportional to the square of the velocity. The
> excess lift will make the plane
> loop, yes, but in looping the circular airflow
> reduces both the attack angle and
> the decalage, both reducing lift and countering the
> tendency to loop.
> Somewhere the glider finds a balance, and it isn't
> at the same attack angle as in
> steady glide. What would that excess lift pull
> against? There is only 9
> grams of airplane and it only pulls back when it is
> accelerated. In a steep
> climb, most of the weight force is directed back
> toward the tail, not
> perpendicular to the wing chord. The balancing
> around the CG that establishes attack
> angle in steady glide is not at work here.
>
>
> [Non-text portions of this message have been
> removed]
>
>
Kurt Krempetz
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Received on Sun Feb 11 2007 - 17:46:22 CET