# Not so constant-speed prop?



## nincomp (Apr 20, 2013)

I know that P-38 pilot were told to reduce RPM's and increase manifold pressure to maximize range. How did pilots set the "constant speed props" to a lower RPM?
Was there a lever that allowed the pilot to set the "constant speed" to a lower RPM, or did he need to manually control the propeller pitch?


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## bobm4360 (Apr 28, 2013)

A constant-speed prop maintains the engine rpm at whatever speed the pilot sets it. This can be a lever control or a 2-way switch. Either type is connected to a governor that varies the blade pitch to keep the engine speed constant. The throttle controls the power going to the prop and is indicated by the manifold pressure gauge.

Regards,
Bob


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## gumbyk (Apr 28, 2013)

What Bob said...
Just think of it like the gearbox in a car:
High prop speed for take-off and climb (equal to low gear in a car, for starting and up hills)
Low prop speed for cruise (high gear in a car for cruise)

Just like using top gear in a car will improve gas mileage, so too does a lower prop speed in an aircraft (to a point).


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