FlyingForFun
13th Apr 2004, 11:17
I thought I understood p-factor, until I tried explaining it, and now I've got myself confused.
So, here's what I (think I) know:
- P-factor occurs when the propellor is not facing in the same direction as the aircraft is moving, such as in slow flight, or at the start of the take-off roll in a taildragger.
- In this configuration, the down-going blade moves further than the up-going blade in each half-rotation of the propellor. This is because it moves from the rear-most position of the propellor plane of rotation at the start of the half-rotation, to the front-most position of the plane at the end of the half-rotation, whilst the up-going blade does the opposite.
- Because of this, the down-going blade produces more thrust than the up-going blade
- The extra thrust on one side of the propellor results in yaw.
But then I thought about the down-going blade. According to what I've written above, it creates more thrust because it's moving faster. But my understanding is that increasing the forward speed of a propellor (whilst leaving the blade angle and the RPM unchanged) results in a lower angle of attack, less thrust, and less torque. (Less torque, of course, results in the propellor RPM increasing if the engine power is unaltered, when we're talking about the propellor as a whole.)
So if an increase in forward speed reduces thrust, then why does the extra forward speed of the down-going blade result in more thrust being produced on that side????? :confused:
FFF
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So, here's what I (think I) know:
- P-factor occurs when the propellor is not facing in the same direction as the aircraft is moving, such as in slow flight, or at the start of the take-off roll in a taildragger.
- In this configuration, the down-going blade moves further than the up-going blade in each half-rotation of the propellor. This is because it moves from the rear-most position of the propellor plane of rotation at the start of the half-rotation, to the front-most position of the plane at the end of the half-rotation, whilst the up-going blade does the opposite.
- Because of this, the down-going blade produces more thrust than the up-going blade
- The extra thrust on one side of the propellor results in yaw.
But then I thought about the down-going blade. According to what I've written above, it creates more thrust because it's moving faster. But my understanding is that increasing the forward speed of a propellor (whilst leaving the blade angle and the RPM unchanged) results in a lower angle of attack, less thrust, and less torque. (Less torque, of course, results in the propellor RPM increasing if the engine power is unaltered, when we're talking about the propellor as a whole.)
So if an increase in forward speed reduces thrust, then why does the extra forward speed of the down-going blade result in more thrust being produced on that side????? :confused:
FFF
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