Tord,
I think if you look you will find that carbon fiber is good in
compression and tension. Yes better in tension, but it is also good in
compression. The problem is that there are additional forces that must be
applied. The main is the bonding/resin strength that is necessary to
combine all the carbon fibers into a solid matrix. Normally this fails
before the carbon does. The carbon gets the blame...but it is the resin
that failed allowing the carbon to deflect.
As to the airplane example. GA airpnaes have specific loading scheme.
It mainly surrounds positive loading, not negative ones. Especially non
aerobatic planes. And if aluminum was better in theweight vs strength vs
stiffness...they would use it! Carbon is still better when you add weight
and stiffness into the mix.
JAson Werner
----- Original Message -----
From: "Tord" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Wednesday, July 24, 2002 5:59 PM
Subject: [RCSE] Carbon fibre
Hi,
It was me who said that carbon fibre ain't good in compression :-)!
It is very easy to make a spar structure that uses (soft) aluminium as
top spar and CF as bottom spar, while it is a wee bit difficult to
prevent Cf spars from buckling in compression.
Even a very thin CF rod is really excellent in tension, while
in compression it very easily breaks - unless it is strapped to a stiff
member, like a wooden spar. A simple CF tube are much better in
compression, while an arrow shaft (which often is a thin aluminium tube
inside a very thin CF tube) is even better, as it is even more resistant
to buckling!
So, while it is very easy to build a strong spar structure with aluminium
and CF it takes a lot of more effort to make a good one of pure CF! I think
Lancair uses twice as much CF in the top spar as in the bottom, just to
prevent the upper from buckling!
Without the aid of a vacuum system I'll keep to the mixed design,
but I know it is rare!
Tord
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