Fixed Pitch Prop and Manifold Pressure

[TMAN]

I have a Grand Rapids EIS 4000 in my airplane. Somewhere in their literature they mentioned using a manifold pressure gauge in fixed pitch prop operations, but it did not go into detail how to use this. I am completely aware of the MP/RPM settings in a constant speed prop application, but in the dark about the benefit of MP with fixed pitch prop. Anyone have any incite on this issue?? I have a fixed pitched prop and just wondering if it is worthwhile to have the MP feature on my EIS or just continue using the Tach. TMan

 

[Glen Lewis]

You will need MP for % HP calculations. I have a fixed pitch and that's all I use my MP pressure for.

 

[Mel]

Manifold is very handy with F/P prop. It allows you to adjust your power settings more quickly than having to wait until the RPM settles down.

 

[Kevin Horton]

Manifold is very handy with F/P prop. It allows you to adjust your power settings more quickly than having to wait until the RPM settles down.

One of the flight test engineers I work with is in a partnership with a fixed pitch RV-6. He did a bunch of cruise perf testing in smooth air at various altitudes, setting various MP, and seeing what the rpm was once everything stablized. He then figured out the percent power for each of those conditions, and plotted percent power vs MP for each desired altitude. He created a table of power settings, giving the required MP for various percent power at typical cruise altitudes. He reports that it works extremely well, as you can set the target MP and it stays essentially constant, even though the rpm varies around the mean as the speed varies in the bumps.

 

[jclark]

Which Engine???

One of the flight test engineers I work with is in a partnership with a fixed pitch RV-6. He did a bunch of cruise perf testing in smooth air at various altitudes, setting various MP, and seeing what the rpm was once everything stablized. He then figured out the percent power for each of those conditions, and plotted percent power vs MP for each desired altitude. He created a table of power settings, giving the required MP for various percent power at typical cruise altitudes. He reports that it works extremely well, as you can set the target MP and it stays essentially constant, even though the rpm varies around the mean as the speed varies in the bumps.

Kevin,

Any chance this was for a 160HP O-320?? (Please, please!! )

Regarding the question of the thread ... I too use the MP to get a quick and consistent power setting. This comes in very handy for flight testing, formation lead, various calibrations, etc.

James

 

[Kevin Horton]

Kevin,

Any chance this was for a 160HP O-320?? (Please, please!! )

Yeah, it was for a 160 hp O-320, but his data wouldn't be of any use to anyone else. Any small change in aircraft drag, or engine power, or prop pitch would change the relationship between MP and rpm, which would change the relationship between MP and percent power.