Date: Fri, 28 Apr 2000 09:51:14 -0400
From: "Douglas L. Dodson, Jr." <73773.1546@compuserve.com>
Subject: Flap gap
Sender: "Douglas L. Dodson, Jr." <73773.1546@compuserve.com>
To: Blind.Copy.Receiver@compuserve.com
Message-ID: <200004280954_MC2-A2CF-BD34@compuserve.com>
Mime-Version: 1.0

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>> With the flap fully extended to 40 degrees... I end up with an even
gap .... As the flap is retracted ... the upper skin LE then contacts the
back of the rear spar.

If on the other hand, I place the flaps in their fully retracted position
and then slide the upper skin into place so that the LE is just in contact
with the
rear spar, I end up with a substantial (and unsightly) gap when flaps
are dropped to 40 degrees. <<

Angier,

That tells me the radius of the forward edge of the flap is too small. 
IOW, the radius should be such that it is equal to the distance from the
hinge pin to the aft edge of the wing skin.  The fore/aft position will be
obvious then.

I had this same issue on my Glasair flaps and ailerons.

Your choices are:

1:  fill the leading edge of the upper flap skin (the curved part) until it
is "right".  Do that by placing the skin so the gap is nice with the
flaps retracted, then fill as required to close the gap across the range of
flap extension.

2:  leave the gap with the flaps down.  This will give you the best
efficiency in cruise (no or small gap).  The gap you describe may cause
some extra drag with the flaps down, but doesn't sound like it will cause
problems with flap movement or collect precipitation excessively.  Who
cares what drag you get with the flaps extended? You WANT drag then, it
aids in landing.  The only drawback is aesthetics.  If you can't stand the
way it looks, ok... but it really isn't a performance issue.  In fact,
filling the gap adds weight... always a performance issue.

I fixed the gaps on my ailerons as I described in option 1.  I left the
gap between the wing skin and the flaps alone as I describe in option 2.


 - Doug Dodson
   Glasair II-S FT
   Flight Test Engineer, CFI-A,G
   Baby Dragon IF1 Race Team
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