manifold pressure and rpm

J

JordanD

Here so I don’t get fined
I know the basic principles of how the prop governor works and all that on engines with constant speed props, but I have w little trouble understanding the relationship between manifold pressure and rpms during some stages. For example, say you're going to do a full power stationary runup, with the prop lever, full forward, does pushing the throttle forward actually make the engine turn faster and then the prop governor kicks in and takes control of the the rpm?
 
You're confusing yourself because you're thinking about ground operations. The prop blades have a fixed range of angles they can turn at, usually about 18-24 degrees. With the prop lever full forward and the throttle at idle, the governor pushes the blades to the lowest possible pitch for the fastest speed.

Basically, the prop lever says "I want 2700" and the prop says "Sorry dude, but all you're gonna get is 800 until the engine starts doing some work!"

The governor starts becoming effective at (usually) about 2000 RPM. If you pull the prop lever halfway back at idle, nothing will happen. If you pull the prop lever halfway back during a full-power runup, it should slow down.

If you're airborne in a complex single and you push the throttle forward rapidly, you'l hear the prop blade angles change as the governor tries to set the speed again.
 
adk said:
You're confusing yourself because you're thinking about ground operations. The prop blades have a fixed range of angles they can turn at, usually about 18-24 degrees. With the prop lever full forward and the throttle at idle, the governor pushes the blades to the lowest possible pitch for the fastest speed.

Basically, the prop lever says "I want 2700" and the prop says "Sorry dude, but all you're gonna get is 800 until the engine starts doing some work!"

The governor starts becoming effective at (usually) about 2000 RPM. If you pull the prop lever halfway back at idle, nothing will happen. If you pull the prop lever halfway back during a full-power runup, it should slow down.

If you're airborne in a complex single and you push the throttle forward rapidly, you'l hear the prop blade angles change as the governor tries to set the speed again.
Click to expand...
Gotcha. Ground operations was really what I was curious about, since when you're stationary on the ground the prop doesn't have a lot of forward airflow to work with, if that makes sense. Just a curiosity thing. I always start to think outside the box on the stuff the books don't really go into detail on.
 
Go read all the John Deakin powerplant-related articles at Avweb...they're great reading, and you'll treat the engines a lot better once you're done with them.
 
adk said:
You're confusing yourself because you're thinking about ground operations. The prop blades have a fixed range of angles they can turn at, usually about 18-24 degrees. With the prop lever full forward and the throttle at idle, the governor pushes the blades to the lowest possible pitch for the fastest speed.

Basically, the prop lever says "I want 2700" and the prop says "Sorry dude, but all you're gonna get is 800 until the engine starts doing some work!"

The governor starts becoming effective at (usually) about 2000 RPM. If you pull the prop lever halfway back at idle, nothing will happen. If you pull the prop lever halfway back during a full-power runup, it should slow down.

If you're airborne in a complex single and you push the throttle forward rapidly, you'l hear the prop blade angles change as the governor tries to set the speed again.
Click to expand...

Good explanation
 
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