and doesn't the prop on the outside of the circle see a lower AoA (when the nose is flat)?
But what if the nose is up by two degrees ;-) ?
A short time back, I posted about using the Advance Ratio to understand some aspects of propellers. The advance of a propeller is just how far forward the plane moves in one revolution of the prop. One definition of the Advance Ratio is just this distance divide by the diameter of the prop. This is similar to the P/D ratio (pitch divided by prop diameter) that we often speak of. The advance of a propeller is just:
Airspeed / (prop angular speed)
In usual units: advance = air speed (inches/minute) / prop rpm
One can calculate the angle of the prop blade at each radius using the pitch of the prop:
tan(angle) = pitch / (2pi x radius).
One can calculate a similar angle using the advance, A :
tan(advance angle) = advance / (2pi x radius).
The advance angle is the apparent angle of the air as seen by the prop blade at each radius.
Since the pitch angle is the angle of the prop blade, the difference between the pitch angle and the advance angle is the angle of attack (at each radius):
AoA = arctan (pitch angle) – arctan(advance angle)
I hope this answers your question. Post if this is too confusing or if you have other related questions.
Leo
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:48 CET