Propeller Pitch and Aerodynamic Forces
Asked by: vne147 5536 views Aerodynamics, Aircraft Systems, Commercial Pilot
Hello everyone. I'm studying for my comm/instrument multi-engine add-on and I've found what appears to be conflicting information. I'm hoping someone can give me some clarification on a nuance of constant speed propellers. Specifically, with respect to the aerodynamic forces acting on a rotating propeller and whether or not those forces tend to twist the blade towards the low pitch (high RPM) or high pitch (low RPM) position.
I understand the that the aerodynamic forces are not the only forces acting to twist the blade one way or the other and, I understand how single engine and multi-engine airplanes differ in how the propeller reacts to a loss of engine oil pressure. However, in my reading one text says the aerodynamic forces act to push the blade to low pitch and another place I looked says the opposite.
It all boils down to the location of the center of pressure of the blade, is it forward or aft of the propeller's central axis? If it's aft (what I would expect) the blade would get pushed towards the low pitch setting by the aerodynamics forces, if it's forward, the opposite would occur. I have always thought the blade gets pushed towards low pitch (high RPM) but this other possibly incorrect source confused me.
So, which is it? Is it always one way or does it depend on the specific propeller? Does anyone have a reliable source of information they can point me to?
Thanks in advance for your help.
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