On Sep 5, 5:44*pm, Jim Logajan wrote:
a wrote:
On Sep 5, 12:02*pm, Leviterande Leviterande.
wrote:
the todays propellers didnt differ *from the ones used 100
years ago btw...

[...]
Would you care to cite a reference supporting your claim tha efficiencies
have not improved?

Barging in...

I don't know about 100 years ago, but many airship propeller efficiencies
were measured at over 65% efficient in 1920s. The reference I have is Table
13 from "Airship Design" by Charles P. Burgess (1927) [Still in print,
btw.] While there are some low "outliers" under 50% efficient, the bulk of
the 26 table entries show propeller efficiences between 55% and 65%. These
were prop efficiences at maximum speed and horsepower.

The airships LZ-120, LZ-121, Bodensee, and Nordstern appear to have had the
highest efficient props at 66%.

For more recent props, according to these sources:

http://en.wikipedia.org/wiki/Propell..._propeller.htm

current props peak around 87% efficient under optimum conditions.

If the average efficiency in the 1920s was ~60% and now is ~85% then that
is a an improvement of ~45%. On the other hand, no one will ever be able to
double on the efficiencies they were already getting over 80 years ago. ;-)

Yeah, it'll take some magic to convert rotary power into throwing air
backwards hard enough to improve efficiency very much, at least for ga
airplanes. A big fluted duct to take advantage of ram air induction
might help, but any back of the envelope sketches doesn't show much
room for other things, like pilots, and hauling around ducts adds
weight too. I'm not expecting to see many breakthroughs, but if they
are coming we'll probably see it in a home built at Oshkosh one of
these years.