How to decide MP and RPM settings

MAKG1 said:
How do you measure torque on an airplane engine installed in the aircraft?

That strain gauge you're talking about would depend on a calibrated engine mount (strain gauges measure distortion, not force or torque), and measures thrust, not torque. You can apply a lot of torque to a prop spinning at 5000 RPM, but it won't make much thrust if the prop is stalled.

If you truly want to know peak torque, it's rather precisely peak RPM for a fixed pitch prop. For a constant speed prop, the best measure is related to energy production (EGT), calibrated by the airspeed indicator. I.e., find the EGT that gives you the best indicated airspeed. If you relate it to peak EGT, it will be less sensitive to remaining variables like OAT and altitude.
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With strain gauges in the mounts.
 
The best way really to set power in your engine is by sound. It tells you everything you need to know about how much stress your engine is under. The residue in your exhaust pipe will tell you how your valves, seats, prison top, and ring lands look. Black soot is a bad sign. White dust means you're as clean inside as it gets.
 
the best indicator of torque is the airspeed indicator . . . .
 
My head hurts. Maybe it's from reading this thread or maybe it's from pounding my head on my desk. But in either case it's from reading this thread! :)

Whatever it takes to clear the trees. Everything after that is gravy.
 
You could get horsepower from fuel flow, then divide by rpm (theres a constant in there too).

I wonder what rpm to use is best to warm up my engine? 1000? 1500? 2000? Should I use the prop knob and slow it down?
 
The car companies have done stuff like this at their test track. Hold everything the same on 10 cars. Vary one thing. Then put 100,000 miles on them and see if there is any difference.
 
coloradobluesky said:
You could get horsepower from fuel flow, then divide by rpm (theres a constant in there too).

I wonder what rpm to use is best to warm up my engine? 1000? 1500? 2000? Should I use the prop knob and slow it down?
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Only if you are LOP. Once you are ROP horsepower is limited by airflow, not fuel flow. You'll hit peak power at about 75°ROP. Any fuel flow added after that will have no, then eventually a negative, affect on power.
 
coloradobluesky said:
You could get horsepower from fuel flow, then divide by rpm (theres a constant in there too).

I wonder what rpm to use is best to warm up my engine? 1000? 1500? 2000? Should I use the prop knob and slow it down?
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Not if throttle and fuel can be adjusted independently.

That might work in your car, but airflow is a whole lot easier to measure, and it's done anyway in order to meter the fuel.
 
Henning said:
With strain gauges in the mounts.
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Umm, no. Strain gauges measure strain. Strain is not a force, it is a distortion and comes in distance units (or more commonly in dimensionless units, normalized to an undistorted distance).

If you could have a stress gauge, like a spring, and you could arrange it sensibly, you could measure torque, but torque is really not directly relevant to airplanes. It's thrust you care about. Thrust need not be easily related to torque, and maximum thrust can be measured more directly with the airspeed indicator.
 
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MAKG1 said:
Not if throttle and fuel can be adjusted independently.

That might work in your car, but airflow is a whole lot easier to measure, and it's done anyway in order to meter the fuel.
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You need to accurately meter both air and fuel to determine power by consumption parameters. If you want that, buy a Continental FADEC engine, then you get all sorts of information as well as knock detection IIRC. With the systems currently in use in GA, it's pretty much impossible. The only way we have to reliably determine power is TAS entered into tables of known tested values. If you want to do better, it takes reasonably expensive instrumentation.
 
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