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During low power settings, low throttle setting and prop full during taxi, the blade angle will be at its finest pitch. As we increase the throttle for take-off, will the blade angle remain in its finest pitch to cater for increasing RPM ? Will the propeller be at its finest pitch at full throttle & full prop setting ?

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Prop full forward means fine pitch, so when the throttle is pushed full open the engine can spool up to its maximum rated RPM and thereby develop maximum power for takeoff. The fine pitch stop is set so as to prevent the engine from overspeeding at full throttle conditions.

With the throttle still wide open, deepening the pitch angle (pulling back on the prop control) will increase the torque load on the engine and cause it to slow down.

With the engine thus slowed down to a lower RPM setting and the throttle still wide open, pulling back on the throttle will cause the prop governor mechanism to decrease the prop pitch, so as to automatically maintain that RPM setting.

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At stand still, maybe, but more likely no. At rotation, almost surely no. Depends on aircraft.

Moving forward reduces the angle of attack of the blades for the same pitch, and it is the angle of attack that determines how much force the blade is converting to thrust.

When you advance the prop lever, the blades will be full fine (low incidence) so they produce less thrust and there is excess torque to accelerate the propeller to the target RPM. But

  • When the target RPM is reached, the governor will increase the incidence to convert the excess torque to power and stop accelerating the propeller.
  • When the forward speed increases, the governor will increase the incidence to compensate for the decrease in angle of attack due to speed to keep the thrust, and torque constant, otherwise the prop would again accelerate (a fixed one does).

At stand-still, the engine might or might not be able to reach the full RPM. But the maximum power the engine can produce is proportional to the RPM, and you want to have full power for take-off, so using a propeller that does not allow the engine to reach the full RPM before or just after the aircraft starts moving is a design mistake. And as we said, once the RPM is reached, the pitch starts increasing.

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