Re: REFLECTOR: Carbon fiber vs. E-glass

[Alan Shaw <wingco@iu.net>]

Al Gietzen wrote:

>   carbon
>   a waste of money.

  I could not disagree more.  The problem here is rigidity.  The model "T" Ford
had this twisting around the doors problem and Henry fixed it on the model "A"
by putting large steel box frames around the doors and members across the roof.
(he also got rid of the "Mags"!.....yes as Dan Maher put it our "modern"
airplanes are stone age)

90% of all structural problems are compression so tensile strength has very
little to do with it.  In real life carbon is much higher in compression than
glass because it is so rigid that it doesn't start to buckle.  It also takes off
axis loads much better because of this rigidity.  Any kind of carbon across the
roof between the four hinges does wonders to the rigidity by completing the load
path started by the carbon side beams.  I put heavy carbon on the whole roof
area above the doors.

You can make test coupons with EZ-poxy of glass and of carbon and test
deflection and twist for your self.  This matrix (resin) works to make a very
rigid part with carbon.  Carbon lams also take higher temps even with the same
resin system.

Carbon makes a stronger lighter airplane and cost far less than labor, engines
and equipment.  It is the best bargain in your airplane.  Buy 12K (heavy) not 6K
or 3K(fine) carbon it is less $$ per pound and less layers to put in.  12K uni
with sticky string works great in many areas and will not fracture on impact if
a glass fine bid on a bias is layed over it.

All carbon airplanes are glassed together with fiberglass so as to not fracture
at the intersections.  Assembling fiberglass airplanes with carbon is supposed
to be a no-no but I've done it and crashed it and it held together.  Strange.
Don't use carbon for tape glass because it may just peel out over flexing glass
but heavy carbon reinforcements hybridized with glass stay put.  Study load
paths and remember carbon is so rigid that it will always try to carry the whole
load when put with glass.  Either fan out the load into fiberglass or tie it
into more carbon continuing on....ie the top of the door post.

Carbon is dangerous to work with.  You should always use a dust mask even when
just cutting it with scissors small particles fly up into your lungs causing the
miners black lung disease.  Always wash your hands after touching the dry cloth
and don't touch your face.  Use peel ply too make it lay down better, help
prevent those invisable(stealth) air bubbles and save some dangerous tough
grinding.  If a splinter breaks off under your skin get it out because it is
organic, it WILL get infected and fester.      Great stuff!

As our planes get faster and bigger and equipment more and more expensive using
fiber glass does not make much sense.  It is heavy and like rubber.  Making a
expensively equipped airplane out of fiberglass makes about as much sense as
making a sailing yacht that has a titanium mast and Kevlar sails out of ferro
cement.

Al and Simon this is a hot topic.  Thanks for bringing it up.  Pultrusions of
Boron make the best spar caps and hardware should be titanium not steel or
aluminum.  Molds should be made bigger so more can be made monolithic under
pressure with less final assembly and weight.  Powerplants should have only one
moving part...a high-by-past turbo fan.   Landing gear should be just a simple
cushion of air.  Were does it stop? Good thing Dan and Duane have kept their
thumb on me all these years or I would have pushed the Velocity R&D and kit cost
through the roof and out of the market with high tech.  The key is the right
compromise that we call medium tech.

Back to building mostly fiberglass wings.

Alan Shaw