One of the reasons that we don't often talk about or compare propeller
efficiency is that almost all modern props score around 82 to 85%
efficiency -- it's very very tough to improve on that. In fact the Wright
brothers did most of the essential design work on props, and one of the
reasons they beat Langley and the Euro experimenters so soundly is that they
built props with 70% efficiency (according to modern testing -- they
themselves thought they had 66%). So the past century has produced only
about a 25% improvement in prop efficiency, and I suspect very little of
that bump has happened since WWII.

See http://www.fluent.com/about/news/new...i2_fall/a2.htm
for a very cool summary of this issue.

Seth
Comanche N8100R

"Robert M. Gary" wrote in message
ups.com...
I don't know about that, I always thought there was a lot of science
behind props. I also drive a Mooney but never noticed my prop having
longer cord than others. However, other than ground clearance (my
Mooney has 13 inches but looks like 2" ) I would imagine that the
cord of the prop would be just like different cord's on wings. Don't
most props include an efficiency index? Perhaps I'm over thinking it
though...

-Robert