IO 360-A1A and Constent speed Prop

[nmontei]

Ok this might sound dumb, but I have a io-360-A1A and a constant speed prop, How do I figure out the numbers for running the engine? 75% power and all. I only have 10 hours in a constant speed prop aircraft and that was 3 years ago, Yes I know I need a few hours refresher time, and this might be blatantly obvious to me, but anyway.

thanks

[Aden Rich]

As a rule of thumb, add the Manifold pressure plus RPM to get 48 and that's close to 75% power. So 24"/2400rpm= 48=75%. Be aware of the prop rpm limitation. The HC-2YK-1BF/7666-4 has limitation from 2000-2250 rpm running cont. in this range. You can as go to Lycoming on the web and they have charts for the engine.

[Ironflight]

Actually, the "Lycoming Operators Manual"....assuming that you can find the right chart in the back (no small task, given the plethora of engine models), it will show you the relationships between rpm, MAP, fuel flow, and % HP. Well worth it!

Paul

[az_gila]

Originally Posted by nmontei

Ok this might sound dumb, but I have a io-360-A1A and a constant speed prop, How do I figure out the numbers for running the engine? 75% power and all. I only have 10 hours in a constant speed prop aircraft and that was 3 years ago, Yes I know I need a few hours refresher time, and this might be blatantly obvious to me, but anyway.

thanks

Check your PM ... gil A

[Kevin Horton]

Originally Posted by Aden Rich

As a rule of thumb, add the Manifold pressure plus RPM to get 48 and that's close to 75% power. So 24"/2400rpm= 48=75%. Be aware of the prop rpm limitation. The HC-2YK-1BF/7666-4 has limitation from 2000-2250 rpm running cont. in this range. You can as go to Lycoming on the web and they have charts for the engine.

A lot of folks claim that this works, and that a sum of 45 gives 65%, and 42 gives 55%. But these rules only get you within about 10% power, as they don't account for the effect of altitude (if you keep the rpm and MP the same, the power increases with altitude), they don't account for non-standard temperatures, and they don't account for non-linearity in the power vs rpm curve. For example, on the IO-360-A series engines,

Sum of 48:
Sea level, 30 deg C, 2100 rpm and 27" gives 66.7% power
Sea level, 15 deg C, 2100 rpm and 27" gives 68.4% power
Sea level, -15 deg C, 2100 rpm and 27" gives 72.3% power

8000 ft, ISA + 10 deg C, 2500 rpm and 23" gives 75.5% power
8000 ft, std temp, 2500 rpm and 23" gives 76.9% power
8000 ft, ISA - 10 deg C, 2500 rpm and 23" gives 78.4% power

Sum of 45:
Sea level, 15 deg C, 2100 rpm and 24" gives 58.7%

10,000 ft, std temp, 2700 rpm and 18" gives 63.0%

If you care about what power you are setting, you should either create your own power chart using the horrible Lycoming graph, or copy a power chart from the POH of a type-certificated aircraft with this engine, or make a power chart using the Excel spreadsheet that I created. The spreadsheet isn't perfect, but it matches the Lycoming power chart fairly closely.

Or, if you have a calibrated fuel flow indicator, you can get a pretty good idea of the power if you are leaned. Assume about 0.45 lb/hr per hp. So, if you want 75% (150 hp), that means a fuel flow of 67.5 lb/hr, or about 11.2 USG/hr.