Message-Id: <3.0.3.32.19980926131733.00725a28@mail.digital.net>
Date: Sat, 26 Sep 1998 13:17:33 -0400
To: lancair.list@olsusa.com
From: John Cooper <heyduke@digital.net>
Subject: Carbon vs. Glass
In-Reply-To: <199809252044_MC2-5AB8-AE02@compuserve.com>
Mime-Version: 1.0

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Guy--

Thanks for the numbers. They were more useful than the ones I was using,
since they apparently reflected the "layed-up" condition rather than just
the strength of the fibers themselves.

I am assuming that "msi" means "million pounds per square inch", right?

Also, I just got back from the hangar where I was working on the center
console "lids". I remeasured the distance from the engine CG to the main
spar and it was 52", not 40". I reverified that the longeron-to-spar
distance was in fact 17" (to the bottom of the spar).

So the 52" dimension makes the stress in the longerons 900# per G, not 706#
as in my previous post. 450# per longeron per G...

Using your Young's Modulus numbers:

spruce=1.57mpsi
glass=2.42mpsi
carbon=9.97mpsi

the ratios normalize to 1 : 1.54 : 6.35 instead of the figures that I used
in the last post, which were 1 : 7 : 21

Recalculating using my original areas, I get:

AE(spruce) = 1 x 0.56
AE(glass) =  2.42 x 0.12 = 0.29
AE(carbon) = 9.97 x .12 = 1.20
sum of above = 2.05

So therefore the percent of load carried by each material is:

Spruce .56/2.05 = 27%
Glass .29/2.05 = 14%
Carbon 1.20/2.05 = 59%

For the original configuration (without carbon fiber):

Spruce = .56/0.85 = 66%
Glass = .29/0.85 = 34%