"..." wrote:

I think the best way is to use thick carbon fibber skins laid up in

female

moulds  and bond them together at leading and trailing edges. Clamp

them back

in the mold and inject them under pressure with syntactic
foam. Syntactic foam

Paul, Far and away better is to wrap the prepreg around a rubber form,

(hollow)

place it in a female mould with clearance to trail the fibre out the

trailing edge.

Then close the mould pressurize the rubber form and heat the whole mess.

The resultant

blade has a "single sheet" strength the trailing edge is trimmed and you

are done.

The layers of the trailing edge are clamped together and the leading

edge is continuous.

My $.02. If I'm making the molds that is how I'll do it.
Bill Jepson

That sounds like a less labor intensive way of doing it.
What do you use for the rubber bladder Bill? How closely must it be

shaped

to the final planform of the prop blade? Can a section of bicycle inner

tube

be used?

Send me some sketches on this process. Would it help if a flat wood

insert

was placed in the rubber bladder the shape of the prop blade plan form?

Paul Lamar

Sounds like an interesting process if the blade is thick and hollow,
like the LAEV prototype blades. However, I think that blade was made too
thick. The beauty of carbon fiber is the blade can be made very thin
like a metal blade. Thinner blades give better performance, and it shows
in my computer prop simulations. My fan blades are also very thin, and
almost solid carbon fiber.

--
Perry Mick
Custom Composite Props
mick@bridgingworlds.com
http://www.ductedfan.com

 Making Composite props

Hi Perry,
Paul has just put me on the Newsletter list, I am new here, wow what a lot
of interesting and stimulating discussions.
I will send you this as I see Paul will be away for a few days, I will also
send it to Paul.

The rubber bladder process is best for larger  hollow mouldings but I am not
sure it is the best way to make prop blades as the tips and the trailing
edges of the blades might be too thin for the bladder. ( vehicle tyres are
made this way)

Some of the first carbon blades were for the fan on RB211 engine developed
by RR, they were compression moulded, which I think is the way most of the
smaller composite blades are produced.
I hope I am not telling you all things you already know, compression
moulding is use to produce parts from mixtures of heat curing resins which
contain a filler which might be chopped glass fiberes,kevlar,glass
beads,chopped carbon fibre or other fillers depending on the application of
the component.

The material is put in the mould in the form of semi prepared component or
prepreg it is then compressed in a press and heated for a predetermined time
to cure the resin.

This way you have control over the moulding process and the quality of the
finished product which is most important in this case.
I hope I am not tell grandmother how to suck eggs,( do you know that
one?)you may have been through all this before.
Is there an archive for the newsletter?
I look forward to your comments
Geoff

We have a CD. Check the web site below.

Paul Lamar
 
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