Quote:
Originally Posted by Piotrsko
Pitch is measured in distance per revolution>>>at the tips<<< As you progress towards the hub, in order to have the same thrust and prop load, pitch gets higher until its so high that part stalls. The insane pitch shown is what it takes to run that prop at the speed they want at the rpm the prop is operating at. According to Irv Culver, when the tips go sonic all that thrust is turned to noise and does not contribute to thrust. One of the multitude of reasons commercial aircraft don't fly supersonic.
Btw: on that non operating turbine, the prop is "feathered" or in low drag mode
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Pitch is the same at any diameter. The propeller blade can twist to match forward and rotational speed all the way to the hub and across, as illustrated. There is no stalled zone, but the high angle near the hub is just unable to do much work so it is often neglected, especially if it is not needed to cool the following motor, or needs more physical strength.
A variable-pitch propeller is only correct at one setting - the effective angle of attack will vary at different diameters at other settings.
It is quite common for prop tips to go supersonic during take-off, and they get loud, but they don't stall any more than supersonic aircraft fall out of the sky. That much power would create very destructive noise if it was all converted.