On Wed, 31 Mar 2004 23:09:43 GMT, "x" wrote:

"Corky Scott" wrote in message
...
On Wed, 31 Mar 2004 19:51:59 GMT, "x" wrote:

Anyone care to comment on using one of MT's composite blade props with
electric pitch control?

Eggenfellner seems to really want you to use this prop with his Subaru
setup.

I'm a bit concerned both with a composite prop and an electric pitch
control.


I don't think there's anything wrong with a properly made composite
prop, and MT is one of better known prop manufacturers. They make
LOTS of props, many of them for certified airplanes.

What's your specific concern?

Corky Scott

I don't know anything about using composite construction for a propeller. I
do know a little about fiberglass and carbon fiber composite, just from an
"educated layman" point of view. So bearing that in mind, I would be
worried about:

1) Would continual flex/unflex cause fatigue and how would you detect it if
it's internal? (I think in the research environment they basically CAT scan
parts to look for internal fatigue?)
2) How could you tell a trivial rock ding from a potentially disastrous one
(again, hard to see what's inside)?

Again, I'm not all all claiming these things happen, I just am asking if
people know of any gotchas. Of course, there are lots of testimonials that
basically say "I've had mine for X years and it hasn't broken yet", but
that's not really data.

There are a number of businesses making composite props in the world
today, some of them making props for extreme aviation endeavors. MT
and Hoffman make composite props that are used in unlimited aerobatic
competitiions. In the world of props, metal props are the most
dangerous in that they can and do vibrate in sympathy with the engine
harmonics and can rapidly fatigue and fail. Some conditions are so
dangerous that the airplane/engine/prop combination has a plackard
requiring that the pilot avoid operations at a specific rpm. Wooden
props are at the other end of the spectrum, they actually deaden
vibrations. Composite props are somewhere in between those two
extremes. MT and Hoffman are big time players in the world of
certified and experimental props, and their prices reflect that.

Secondly, does the electric system work automatically (so that you don't do
anything), or is there a control that works like manifold pressure (i.e.
"governed" so that changes in RPM cause automatic changes in blade pitch),
or is there just a blade pitch control? Why would it be better/worse than
hydraulic?

Does anyone out there have one who can ring in on this?

Electrically controlled props may or may not also be governed. Some
just adjust pitch, others adjust pitch and govern rpm. If you have an
electric adjustable prop in mind, the best thing to do would be to ask
the vendor what it's designed to do.

Corky Scott