Marvin Kaye wrote:

Putting the outlets under the stab on a Lancair 2-seater would be a real
trick... the fuselage width back there is only about 4-5" and the rudder
actuator cables and elevator pushrod would be right in the way.  I think
we're doomed to dumping the cooling air out the bottom of the fuselage.
There is already some controversy about the potential for tail flutter with
the MKII (larger cf) tail, and it seems to me that modifying that structure
back there in any way without a detailed FEA would be courting disaster.
I'm sure there is more to it than just adding a couple layers of cf BID and
hoping that nothing else has been adversely affected in the process.  Just
IMHO.

   <Marv>

At 12:03 AM 2/16/99 -0800, you wrote:

BTW If you have a composite airplane like the
Lancair and you want to take advantage of the
low pressure area under the horz stab for radiator
air outlets don't forget to beef up the holes.
The sides of the fuselage in that area provides material
that carries a large sheer load due to the downforce on the
tail.

Not just "bid" Marvin. Carbon fiber bid.

It is your call Marvin. That is the way it should be. Its 
your life on the line.

Never-the-less ten total layers of three inch wide
bid carbon fiber all around a five by five inch hole is a lot stronger 
and stiffer than 4 layers of glass with one quarter inch of PVC foam. 

If you doubt that make up a test sample of the current aft fueslage
material and a sample of the carbon fiber and load both samples
in shear and measure the deflection in shear.

Has anybody beefed it up back there with carbon fiber yet.
If not why not?

Glass is a rubber band compared to carbon fiber. The shear modulas on 
glass is less than one million as I recall.  Carbon fiber
has a stiffness comparable to steel. Klaus cut  big holes both sides 
in his Variez fuselage for windows and did this trick to reinforce 
the holes. If your interested I may be able to do a simple equavalent 
analysis based on some data in Bruhn on the subject of window holes 
in airliner fueslages.

Finally has anyone measured the torsional stiffness of the aft fuselage
yet? It is not that big a deal. We used to do it all the time with
our composite race car chassis. You clamp down the wing spars 
and apply a small torque to the stab spar and measure the twist angle
as a function of the torque applied. The torsional resonence freq. will
be a function of the stiffness and the inertia of the tail.
 
Paul Lamar
 
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