--- Mark Jones <flyk...@wi.rr.com> wrote:
1/8" will provide superior strength. 1/16" just did
not sit well with me as I could see it bending under
loads.
Mark,
I think you are still on the "overkill" side, even
with .060.
It would weigh: (@.125 thk =4.25 lbs)
(@.060 thk =2.04 lbs)
Consider this:
6061-T6 has a Tensile Strength of 42 KSI
7075-T6 has a Tensile Strength of 78 KSI
So probably .040 thick 7075-T6 would be more than
adequate. The 7075-T6 is as much as 80% stonger than
the 6061-T6(when comparing same loads and
thicknesses).
Add stiffening angles to get the required stiffeness
needed to handle panel buckling. You can achieve
expotentially higher stiffeness by adding angles, than
you could ever hope to gain by simply making the part
thicker.
Use solid rivets to attach the piano hinge and
stiffening angles. Commercial, hardware store "pop"
rivets are for non-flight applications. Don't use them
on your airplane. The material they are made from is
hardly airworthy to begin with (I do not wish to get
into some big debate over this issue, so please don't
even go there!).
Probably 5/32nds spaced at 6 to 8 D (.96 to 1.28)would
suffice to attach the stiffening angles to the speed
brake panel. That means probably 8, 5/32nd fasteners
per stiffener. This would give the attachment
capability of each stiffener approximately 4600 lbs of
shear.
Probably 5 angles minimum to break up the panel, and
hemming the edge couldn't hurt either.
This would "break-up" the 9 x 36 inch panel into 4,
9 x 9 panels. Much smaller area when considering panel
buckling.
The stiffening angles should be (obviously) positioned
longitudinally to reduce drag when the speed brake is
in the stowed position.
The stiffening angles probably only need to be about
.50 inch tall and attach with a .75 inch flange.
Again, probably more than overkill. The good news is
that it would only weigh approximately 1.60 lbs.
Bottom line? 1.6 lbs vs 4.25 lbs, A much lighter, and
many times over stiffer panel.
Another suggestion: make the Speed Brake with a couple
of plys of BID, and co-cure some stiffening angles
onto
the speed brake panel. This would weigh about half of
the .040 7075-T6 version.
=====
Scott Cable
KR-2S # 735
Wright City, MO
s2cab...@yahoo.com
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