propeller check

[baobab72]

Hello everyone
maybe this topic has been treated in the past however i can not find it with the search function.
I would like to know what is that you check when performing a prop check in a single engine fitted with a constant speed propeller like the piper arrow, during the runup?

My educated guess that since in a sep oil pressure is used to increase the blade pitch angle, as the prop control is retarded towards the high pitch-low rpm position, you should notice a decrease in oil pressure as pressurized oil is fed into the governor; that the prop rpm's drop as the prop control is retarded as the pitch blade angle is increased resulting into an increase in aerodynamic load and thus in a decrease in rpm, and what else?

why do you set the rmp's to 1800-2000rpm's?

Many thanks

Baobab72

[AdamFrisch]

You're correct. You'll see a drop in oil pressure, a rise in manifold pressure and a drop in rpm as you coarse the pitch (move them towards feather). The reason you're on a higher rpm is that because below a certain rpm the props no longer increase/decrease pitch and behave just like a fixed pitch prop (when they're against their stops). They're designed to do this, or else they'd try to compensate for the dropping rpm by going to ever finer and finer pitch.

[baobab72]

many thanks for your prompt answer
can you please explain better the reason why the map decreases as the propeller lever is retarded?

many thanks for your willingness

baobab72

[Pilot DAR]

MP will increase as RPM decreases (propeller control move back), if the throttle is not touched. The MP has a relationship to the torque required to turn the propeller, if you coarse the blades, the torque goes up.

Cycling the prop during the run up, or while taxiing out, just assures that warm oil is in the propeller hub, and the governor will be able to coarse the blades, and thus prevent an overspeed at the point of takeoff. If you cycle the prop, and the RPM reduces, MP increases, and you hear a "whoosh", you're all set...

I would not fixate on the oil pressure indication, you might not see a change with prop motion. As long as the prop works, you're all set. Assure oil pressure is adequate for engine operation before take off - for the engine's sake.

[Radix]

............

[AdamFrisch]

Manifold pressure in a stopped engine is always the same as they ambient pressure outside. So in effect, you're alway carrying a barometer around in the aircraft with you. So if you can't get an altimeter reading and for some bizarre reason don't know the field elevation, the MP needles will tell you and you can set the altimeter to that. They're not very accurate, but will do in a pinch.

Due to reasons beyond my knowledge, and in no small part to Bernoulli, the MP decreases as you start the engine as the flow increases. It's a bit like a wing - the higher speed above it decreases ambient pressure and vice versa.