Paul,

I usually like to "do things myself" and building a composite prop is one of
the things I would like to attempt.  My goal is to build a 3 blade constant
speed prop similar to the construction method that Hoffman and MT use.  I've
seen a cut-away drawing of MT's construction and was wondering if you or
someone on your E-mail list might be familiar with some of the terminology
used.  For the root of the blades, they use "compressed" beechwood that is
glues to the spruce blade blank using a tapered joint.  What do they mean by
compressed?  Also, they show a series of 11 lag bolts which have been
referred to as "special lag bolts".  Any idea what is "special" about them?
As far as the tapered joints are concerned I think that any typical glued
joint would work.  Instead of using the beechwood-spruce combination, I
might just go with hardrock maple for the entire blade.  Thank you.

David Kuc

These are some important issues with blade retention. I suspect compressing beechwood
is an impregnation and done at very high pressure. The "lag bolts" are probably
a custom thread and machined from high strength steel. For a homebuilder
carbon fiber and high temp epoxy would be safer I think. The drawing is of
the MT or Hoffman and the picture is a threaded machined steel prop hub for bonding
on a carbon fiber blade with a combination of axial and circumferencial fibers.

Paul Lamar
 
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