I have taken this small element. This has a pitch; that means, it is not in this plane, but at
an angle. You understood? A pitch is at an angle to the vertical plane. That angle we
have shown here as this phi. Phi is the pitch angle; I have drawn the diagram here. Can
you see that? This is the pitch angle. Now, the propeller is rotating in that disc, this
plane, you understand, but the element is twisted by an angle phi. So, the rotational
velocity is at an angle phi 2 pi n f. Do you get my point? Can you understand what I am
saying?
the propeller is twisted. Imagine that small element we have considered. Suppose this a
No, see the propeller is if I had all the blades flat and the propeller rotating in the same
disc and the other the tangential velocity would have been 2 pi n r in the same disc, that
is, this blade would have been flat here, you got it? If there was no pitch, but I have got
A pitch; that means the element is at an angle to that vertical plane on which the
propeller blade is rotating, you got it? And what is that angle, is the pitch angle of that
element that is phi.
propeller disc. I have got a propeller here; a small element is there