Marvin Kaye wrote:

At 09:02 AM 2/16/99 -0800, you wrote:

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.

I know you mentioned cf BID, I parenthesized that in my last post to you.
We also need to remember that the entire structure is designed with a
certain amount of stiffness built into it. (The area in question, BTW, is
_not_ made up of 2-BID / 1/4" foam / 2-BID... the core is 1/4" Nomex
honeycomb.  I know, not that big a difference, but the Lancair structure
uses no foam-coared components.)  By placing a stiffening CF-BID structure
into an area made primarily of e-glass the loads will change in the entire
assembly, with large stress risers where the CF stops and the e-glass
begins.   

I have read the web site Marvin.

http://www.olsusa.com/Users/Mkaye/flutter.html.

I think you are being a wee bit too paranoid here. 
Many aircraft designers mixed CF and glass in composite designs with no
ill effects. It is not as if we are talking about fatique here.
I think the certified Lancair Columbia has carbon fiber spar caps
and glass skin and spar webs bonded on.

If it makes you feel better use ten layers of E-glass on each side
of the five inch by five inch hole instead of carbon fiber. 
Its just a weight issue. 

We are merely adding stiffness to make up for lost stiffness
by putting reinforcements around the rad exit holes in the side of 
the fuselage. The same thing is done in airliner windows.

As I said before build samples and measure the stiffeness. 

You can also use the overall
car lift test as shown on the motor mount section of
the ACRE web site to test the fuselage at 6G beyond 
the 3.75G certification requirements. 

I would even go further than that and measure
the torsional stiffness of the unmodified fuselage and
compare it to the modified version to allay your fears.
This test could take less than an hour.

Don't let me talk you  into this if you don't want to do it.

To get an efficent low drag cooling system you are going to 
have to cut into the fuselage somewhere. My contention is if you 
throughly bond it in you will wind up with a stronger and 
stiffer structure. 

Paul Lamar
 
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