oggers:
This equation [propulsive efficiency] is very useful for many cases, but you should see a problem in that as your velocity goes to zero, no matter how much thrust you're producing, your efficiency goes to zero. So how do you know how good your prop is doing at low speeds or statically? Well, there's another term that can be used, Figure of Merit, which is Induced Power divided by Power Available, or how much of your power is going into accelerating the air...
I don't disagree with anything he said!
I hope you realize that he also agreed with what I said!
Like he says, you don't know how good your prop is doing at making thrust by analyzing THP. And he's saying that "Figure of Merit" will show you how efficiently the propeller makes thrust. That has nothing to do with THP!
So how does this 'prove' me wrong?
Induced power is the same as thrust horsepower.
NO. IT. IS. NOT!
THP = Thrust x aircraft velocity
Induced power = Thrust x (aircraft velocity + induced velocity at the propeller)
I just taught my nephew the other day (who is 5 years old) that if a word isn't spelled the same,
it's not the same! He seemed to understand that right away.