Ivo Prop on O-320

"Paul Lee" wrote in message
om...
But they cautioned against it saying the props were not suited for canard
high end
performance.so it really is shoping for the "right" prop for your
particular application.



There are applications where NO prop is a really good option. A high
horsepower
pusher with the prop in disturbed air is one of those. A small diameter
running at high prop RPM makes it even worse.

A carbon fiber prop has almost no damping. Any cyclical vibrations will just
build and build as energy is input on each cycle and not dissipated.
Eventually a warp drive prop as a pusher in a disturbed airflow (
http://beta.communities.fr.msn.ca/Ad...99668152588100 )
has failed with cracks longitudinally at the tips. That's why wood props are
popular with canards. Energy is dissipated as fast as it's input, so big
vibrations do not build up.

The problem with wood is that (at least in my experience) is not very
efficient. Everyone I know (including myself) who has switched from wood to
carbon has seen a large increase in performance.

Like I said - no good option.

That's not been my experience. Certainly carbon isn't as good at
damping as wood, but it's much closer to wood than it is to aluminum.

It's not that carbon damps better than aluminum, it's just that it's a
hellova lot stronger and lighter.It can stand up to much bigger vibrations
with no ill effects.

Cast aluminum has a very small fatigue strength. If you stress it more than
about 5KPsi, it will eventually fail. and the stuff is heavy so vibrations
have a large force behind them.

Carbon fiber has about 650 KPsi theoretical tensile strength. Even when
viewed in the worst possible light, it still has about 200 KPsi in
compression, (That's right 5 KPsi vs 200 KPsi) and it's much lighter.

So carbon doesn't break as readily as aluminum, but that is not damping,
that's because of a radical strength advantage.

On Thu, 14 Oct 2004 08:30:51 -0800, "Ron Webb"
wrote:

The problem with wood is that (at least in my experience) is not very
efficient. Everyone I know (including myself) who has switched from wood to
carbon has seen a large increase in performance.

Like I said - no good option.

How about a wood prop core, overlaid with carbon fiber? I think
that's what MT does for their props.

Best of both worlds?

Corky Scott

On Thu, 14 Oct 2004 13:28:45 -0400, Corky Scott
wrote:

On Thu, 14 Oct 2004 08:30:51 -0800, "Ron Webb"
wrote:

The problem with wood is that (at least in my experience) is not very
efficient. Everyone I know (including myself) who has switched from wood to
carbon has seen a large increase in performance.

Like I said - no good option.

How about a wood prop core, overlaid with carbon fiber? I think
that's what MT does for their props.

Best of both worlds?

Corky Scott

And in a fixed pitch prop I think prince props are wood and carbon as
well. They also claim to flex a bit to give a quasi constant speed
effect

"Bashir Salamati" wrote in message

Take wood dowl, an aluminum rod, and a piece of carbon fiber/epoxy
composite.
Suspend from a string. Tap each with a small hammer. See which one rings
longest.


Hmmm...a very interesting thought experiment.

It is obvious that the aluminum would ring like a bell, the composite might
ring a little, but not much, and the wood would go "thunk". I had not
thought of it like that. I'm not sure how much of this result would apply to
the propeller situation but on the surface at least you seem to have a
point.

I'm going to have to think about that...