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/Propeller
http://www.epi-eng.com/propeller_tec..._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. ;-)