Keith:
appear to indicate that you think that if thrust is not zero then propeller efficiency cannot be zero. If you do believe this, then you are wrong (once again).
Just to be clear in case I left you in any doubt whatsoever. Yes I DO believe that if thrust is not zero then propeller efficiency is not zero. Thanks for clarifying that you don't though.
I am aware of the equation you mention. I am intensely relaxed about it. It is the obvious equation to use for an aircraft in flight. Earlier in the thread -page 4 #62 - I actually linked to a page from a prop designer who uses it . But, he is careful to point out that it cannot be used to determine the efficiency of a prop in the static thrust situation. It is - according to him - "invalid" in that situation. So, he uses a different equation for that.