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4 Answers

Constant Speed Prop.

Asked by: 4493 views Aircraft Systems

To begin, yes I know that a increase in oil pressure causes the blade angle to increase.

Recently during runup for a check out in a PA-28R (Piper Arrow) and cycling the prop. I expected to see a slight increase in on the oil pressure gauge with the prop lever momentarily in the full aft (low RPM). However, the oil pressure gauge showed a slight decrease.

I asked the instructor about this and he responded that a decrease in oil pressure is shown on the oil pressure gauge is the result that the oil system demand has increased by pumping oil from the oil system reservoir to the prop. Further adding that the oil pump is working harder and releasing oil from the engine area reservoir to another location of which is the prop.

Is the instructor's logic correct or perhaps is the oil pressure gauge not accurate/calibrated correctly?

I am ready to learn!

Thanks for the feedback.

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4 Answers



  1. Russ Roslewski on Feb 17, 2016

    Your instructor is correct and the pressure decrease you saw is a normal occurrence when pulling the prop back.

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  2. Dan Chitty on Feb 17, 2016

    Thank you Russ. I appreciate your feedback.

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  3. Parth on Feb 18, 2016

    Hi
    I have attached following link which will clear your doubt.
    http://www.boldmethod.com/learn-to-fly/aircraft-systems/how-a-constant-speed-prop-works/

    Look for animation where prop lever is pulled back. And you will see that oil will be supplied to propeller hub causing slight drop in the system since oil pressure guage takes reading of engine oil system not the oil in prop hub.

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  4. Dan Chitty on Feb 18, 2016

    Thank you Parth.

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