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Constant Speed Propeller and relation to manifold pressure setting.

Asked by: 1081 views Aircraft Systems, Commercial Pilot, Flight Instructor, General Aviation

Hello everyone,

I am currently doing my CFIA course in Arrow and let us say when we set up our cruise power at 2400RPM for good, and I noticed something strange when playing with throttle.

RPM was constant through out various manifold pressure setting(throttle), and when I decrease the throttle, the airspeed started to bleed off. Conversely with throttle pushed forward, airspeed picks up.

I understand that constant speed prop does its job maintaining constant RPM but my question is why airspeed decreases and increases at different throttle setting?

Is this because there is a change in prop pitch?

Steve.

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2 Answers



  1. EAD on Jul 03, 2016

    Chapter 11 of the Airplane Flying Handbook should have the answer you seek

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  2. Skyfox on Jul 07, 2016

    As you change the throttle, the constant speed prop will increase or decrease the blade pitch angle to maintain the set RPM. Increasing the throttle and therefore power will cause the prop to react by increasing the blade pitch, taking a larger bite out of the air and increasing airspeed without increasing RPM. Likewise, decreasing throttle will result in the prop decreasing to a shallower pitch angle, taking a thinner bite out of the air which doesn’t generate as much thrust and reducing airspeed. And of course, if the throttle is brought back far enough the prop won’t be able to get any shallower and RPM will decrease along with airspeed.

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