Power Settings


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Many people have asked about the YAK 52 and M14 power charts contained in both the aircraft and engine manuals and the POH.  The following is an explanation of that power chart along with some helpful hints on maximizing speed vs. economy.  If you'd like to download a copy, click here.

Understanding the M14P Power Chart

This is the power chart from the M14P manual. Iíll try to "translate" it into something that you may find helpful. Recently added is the fuel consumption in gallons and liters per hour and the actual manifold pressures as read on the gauge.  This should help with flight planning.

Rating

HP

RPM

%

Fuel Consumption
Grams/HP/Hour

Fuel Consumption
Gallons/Liters per hr.

Blower Outlet Pressure (mmHg)

Take Off

360

2900

99%

285-315

37.7- 41.7 Gal
141.7 - 157.9 Liters

125 - 15 (surplus)
885 - 870 mmHg

Nominal I

290

2400

82%

280-310

29.8 - 33.0 Gal
112.8 - 124.9 Liters

95 -15 (surplus)
855 - 840 mmHg

Nominal 2

240

2050

70%

265-300

23.4 - 26.5 Gal
88.6 - 100.3

75 -15 (surplus)
835 - 820 mmHg

Cruise 1

.75 of N2

1860

64%

210-230

13.9 - 15.2 Gal
52.6 - 57.6 Liters

735 mmHg +/-15 (absolute)

Cruise 2

.6 of N2

1730

59%

215-235

11.4 - 12.4 Gal
43.2 - 46.9 Liters

670 mmHg +/-15 (absolute)

To convert grams per horsepower/hour, first convert grams to pounds/HP (1 gram = .0022046 pounds).

Thus 285 grams * .0022046 = .628311 pounds * 360HP = 226.2 pounds/hour / 6 pounds per gallon = 37.7 gallons per hour. 315 grams * .0022046 = .694449 pounds * 360HP = 250.0 pounds/hour /6 pounds per gallon = 41.7 gallons per hour.

The Blower Outlet Pressure (boost) is always confusing.  What they mean by "surplus" is that pressure OVER standard atmospheric pressure, which at sea level on a standard day is 760 mmHg (29.92" of Hg).  So add 125 mm (the max SURPLUS) to the 760 = 885 mmHG.  The minus 15 would be 870 mmHg.  Therefore the manifold pressure at max takeoff power or 2900 RPM will be between 885 and 870 mmHg as read on your manifold pressure gauge on a standard day at sea level. 

Converting 885 to 870 mmHg at sea level on a standard day (29.92" Hg) = 34.95 inches to 34.35 inches of Hg.  Thus the Blower (boost) increases the manifold pressure over standard atmospheric pressure at this power setting approximately 5 inches of Hg. 

Now lets look at Nominal 2.  Same thing applies as above, but the fuel consumption is 265 * .0022045 = .5842 * 240HP = 140.2 pounds/hour / 6 = 23.37 to 26.54 gallons per hour.  The Blower boost is 760 +75 or 835 mmHg to 820 mmHg (-15).  You can do the conversion to inches.

At the Cruise I power setting is where you can expect to achieve your best speed and fuel economy.   The ".75 of Nominal 2 (240 HP)" = 180 HP at 64% RPM.  Fuel consumption at this rating is 210 to 230 grams/hp/hour or 13.88 to 15.21 gallons per hour.  That's with a manifold pressure setting of 735 +/- 15 absolute or 720-750 mmHg.    So, as a veteran WWII B17 Bomber pilot told me a long time ago, to get the best cruise speed with the best fuel economy, run the engine "oversquare" or make the engine turn the prop and not the prop turn the engine.  ie: Lower rpm (in this case 64%) and higher manifold pressure (720 to 750 mmHg).  In cruise flight, try setting the power to 65% and 70mmHg.  I think you will be quite pleased with the results.

Unfortunately, this is not a perfect world, nor is our own individual airplanes.  There are many other factors which will affect power and fuel consumption.  But as a baseline, this is as good as it gets.

Dennis Savarese
December 8, 2003