[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: REFLECTOR: Kevlar Vs. Carbon fiber vs. E-glass



Being the lucky person that I am a good friend that closed dow his race car
building business gave me a fair amount of carbon, Kevlar,  and some
interesting bid made of alternating strands of carbon & Kevlar.

I reinforced my overhead with a longitudinal 12" 2 bid carbon layup that Y's
to the to heavy engine mount layups in the rear, across the top at the
carbon door beams and down the window posts about 6 " onto the lower
fuselage.  It is full width at the door openings up to the windscreen and
back to the carbon beams.  The natural curve of the top gives a nice arch to
the carbon to make it more beam like.  I then covered the carbon with one
Kevlar bid to contain the pieces should it be over stressed to the point
that the carbon shatters.  This is a good use for Kevlar especially when
free.  I also have two Kevlar bid under the seats for penetration resistance
if I put it in the trees.  My hinge areas are very stiff and the
longitudinal beam being tied into the heavy layups at the rear, carbon beams
and  he front window pillars distribute the loads along the entire length of
the lower fuselage.

As far as cutting the Kevlar I have a heavy duty pair of carpet sheers that
when properly sharpened cuts the Kevlar with no problem.

Jim

Alan Shaw wrote:

> David Dotty,
>
> > Kevlar is very strong in tension and very weak in compression.
> >
> > Kevlar is also good for scraping, and is often put along canoe keels
> > for that reason (scraping on rocks and river banks). Might be great
> > along the lower edges of the winglets or the belly of a retract.
>
> Thank-you David....so true.  When ever people speak of Kevlar in
> structuralapplications a big red flag pops up in my head.
>
> Armada fibers (Kevlar) have five times the tensile strength of stainless
> steel but less than half the compression strength of fiberglass.   This
> is compounded by the fact that the fibers have to be "scrubbed" rough
> before weaving so they will get some bond to the matrix.  They still
> delam easy especially with secondary bonds.  Hand layups are so resin
> rich they are not much lighter than glass anyway.  For the same reason
> hand layups in carbon don't save weight but they do impart rigidity were
> needed.  Cutting and sanding Kevlar just produces fuss which can only be
> rid of by high speed sanding with fresh 400 grit.
>
> If you want to save weight here are a few tips:
>
> -minimize the use of micro glass filler...are you using it were foam or
> micro ballon is OK?
> -Tape glass should not be oversized or sloppy.    Try pre-wets on
> plastic both layers at once in a big rectangle then cut into neat
> strips, lay in place, besure and peel out plastic then lay peel ply down
> good.
> -new Velocity kits have many high tech flanged parts.  These are bonded
> in with adhesive which is much stronger than laminating resin.  Tape
> glassing over the outside of these flanges after bonding is a waste.  If
> you can reach the inside a very narrow tape will increase the strength a
> little but in most cases is not needed considering the bond strength of
> these adhesives.
> -West systems 410 micro lite filler and Urethane primers are much
> lighter and easyer for finishing than glass bubbles and epoxy primers.
> -most Velocities are over weight and the customers needed more resin to
> complete the kit..I wonder why?  Dan built one that weighed 1100 lbs.!
>
> Kevlar is lighter and cheaper than carbon and more rigid than glass.
> The ultra light cowling on my own V-300 is a tri-hybid.  First a fine
> glass was laid in the mold then a coarse Kevlar which was trimmed short
> of all the edges.  Then a double coarse carbon was taper laid around all
> the edges for stiffening and attachment.  The Kevlar/glass combo when
> co-laminated under pressure is actually lighter than carbon and cheaper
> too.  It is weaker in compression but in this application what I like is
> that it won't rip apart for how thin it is.
>
> Kevlar comes in #49 and #29 one is for structures with normal flat weave
> or knit and the other is a tight canvas like weave for ballistics.  The
> latter may be handy in the fuselage and on the fuel strakes depending on
> were you live and/or if you are in the wrong business.  Fortunately the
> Velocity is the wrong design for STOL and stealth so I'm not worried
> about any of our customers in that respect.
>
> Alan Shaw

--
//------10--------20--------30--------40--------50--------60--------70--------80

// James F. Agnew
// Tampa, FL
// Velocity 173 FG Elite ( http://www.VelocityAircraft.com/ ) under
construction