Constant Speed prop

[WHBM]

Can someone please give me a straight little paragraph or two on the concepts behind a Constant Speed propeller control. Because while I know (apparently) how to handle the blue lever and to watch manifold pressure and RPM in combination, and adjust the prop accordingly, I would be grateful to actually know what it's doing and can't find a good reference, despite looking.

It is obviously not an actual propeller pitch lever, as the CSU changes the prop pitch itself while the lever stays fixed. I understand the lever changes the governor on the CSU. What's being governed ? It can't be RPM because otherwise it would be calibrated with RPM.

[plugster]

Try this:
Constant Speed Propeller FAQ (http://www.hariguchi.org/flying/info/prop.html)

[bfisk]

I understand the lever changes the governor on the CSU. What's being governed ? It can't be RPM because otherwise it would be calibrated with RPM.

Perhaps I don't get your question here, but this is exactly what happens. You are governing the prop RPM. The CSU increases or reduces pressure in the hub to change the pitch of the propeller blades so that the propeller balances the engine torque thus producing a fixed (constant) RPM....

:confused:

[seilfly]

Well.. technically you are mechanically governing the tension of a spring in the governor, against which the centrifugal forces of the flyweights have to work. The more tension on that spring, the more RPM you are demanding since higher RPM gives more centrifugal force to work against that spring.

So if you demand more RPM by increasing the tension of that spring by advancing your prop levers to full forward, the tension becomes higher. At that point the RPM is lower, and the springtension overcomes the current centrifugal force which allows the pilot-valve to move and give way to the hydraulic fluid (oil) into the propeller-dome, which in turn drives the prop towards finer pitch; which in turn gives LESS DRAG, which in turn gives higher RPM - which in turn... gives higher centrifugal force acting on the flyweights until this centrifugal force counters the tension of the spring you initially set.

If that is what you asked for; exactly what you do with your prop levers? You "Govern" the springtension and the governor governs the "RPM" as it seeks to equal the springtension and centrifugal force by adjusting the RPM by adjusting the pitch.

Did I repeat myself 3 times now? :O

An animation - somewhat interactive: Propeller and Governor Operation (http://ehflyers.com/AeroLaulima/animations/links/propAndGovernor.html)