Bill, well said. Anybody who has spent any time at all flying low ceiling
gliders knows that flappers are a major performance improvement!
Speaking of which, do you guys sand the top or the bottom of the wing on
your cat I flappers? It looks like Kurt's plans indicate taper and airfoil
shape sanded on both sides. Kurt?
Also, how much mean camber do you think is optimum for a cat I glider? My
best glider for our 36" site has only about 5/32" of undercamber, so mean
camber is likely around 3/16".
Thanks
Don
-----Original Message-----
From: Indoor_Construction_at_yahoogroups.com
[mailto:Indoor_Construction_at_yahoogroups.com] On Behalf Of Bill Gowen
Sent: Sunday, February 11, 2007 5:23 PM
To: Indoor_Construction_at_yahoogroups.com
Subject: Re: [Indoor_Construction] IHLG Flappers
Gary
I tried for several years to equal the Cat 1 records with very light weight
built up gliders. I never broke 40 seconds until I built my first Slow
Poker. The Poker airfoil is very thin and has a lot of undercamber. My
gliders with similar airfoils on fixed wings were a lot like trying to
launch a parachute. With flatter airfoils altitude was not a problem but the
sink rate was too much.
A couple of years ago I had my best contest day with gliders by breaking 80
seconds in Cat 1 in all 3 classes. The Slow Poker did it in HLG and UCLG and
a similar shrunken version did it in Standard class.
Regardless of how hard the flap function is to analyze, they definitely do
work.
----- Original Message -----
From: dgbj_at_aol.com
To: Indoor_Construction_at_yahoogroups.com
Sent: Sunday, February 11, 2007 6:37 PM
Subject: Re: [Indoor_Construction] IHLG Flappers
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.
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Received on Sun Feb 11 2007 - 16:38:54 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:44 CET