bigtime209

I was wondering how would you describe how a constant speed prop works on a checkride. Specifically, how does the prop governor and flyweights work and make the prop turn at a constant rpm? Also, how would you describe a fixed pitch prop?

Split S

Typically a constant speed prop is driven off of a "free turbine" (not mechanically connected to the compressor section). When you push the power levers forward more fuel is pushed into the combustion chamber raising heat and pressure causing both the power turbine and the compressor turbine to spin faster, as such the power turbine imparts a momentary overspeed condition on the prop which is immediately countered by the prop governor attempting to maintain constant speed. As the governor senses this overspeed it counters by increasing blade angle (typically through use of high pressure oil.) The governor senses the overspeed through the fly weights which spin at the same speed as the prop. As the fly weights seperate due to the higher centripetal force they move a pilot valve porting the oil pressure to the increase pitch side of the dome. Increase in prop pitch causes the prop to take a bigger bite of air - this does two things, slows the prop back to the onspeed and produces greater thrust which is typically why you advanced the power levers in the first place! Clear as mud yet? Different aircraft design these systems somewhat differently each with it's own advantages and disadvantages.

EvilGN

the above description works the same for props connected to the engine thru an RGB such as the P-3/C130/E-2

POPA

Wow, you guys sure do know a lot!
My guess is, he was asking about PISTON engines.