LYCOMING OPERATOR’S MANUAL SECTION 3
O-235 AND O-290 SERIES OPERATING INSTRUCTIONS
USING CURVE TO FIND ACTUAL HORSEPOWER
The following is an example of how to use the Sea Level and Altitude Performance curves, printed on
these pages, to determine actual horsepower being delivered by the engine for given altitude, RPM,
manifold pressure and air inlet temperature. This example (using figures from curve on opposite page is for
illustration purposes only.
1. Determine equivalent full throttle horsepower on altitude performance curve for observed manifold
pressure and RPM (Example – At 2400 RPM and 23.8 in. Hg. located Point “A”).
2. Repeat above procedure on sea level performance curve (Example – Point “B”).
3. Transfer value obtained in Step 2 to the altitude performance curve (Example – Point “C”).
4. Connect point “A” and point “C” with a straight line.
5. Read horsepower on line “CA” from given altitude (Example – At 1800 feet with a power setting of
2400 RPM and 23.8 in. Hg. horsepower is 99.5, Point “D”).
6. Correct power approximately 1% for each 10° variation in intake air temperature from the standard
altitude temperature shown below. Add corrections for temperatures below standard, subtract for
temperature above standard. (Example – With an air inlet temperature of 22°F at an altitude of 1800
feet, 52°F - 22°F = 30°F variation. 1% for each 10° variation is 3%. 3% of 99.5 horsepower is
approximately 3 horsepower. Since temperature is below standard, add correction: 99.5 + 3 = 102.5
horsepower, Point “E”).
STANDARD ALTITUDE TEMPERATURES IN DEGREES F.
Pressure Altitude
(Thousands) SL 2 4 6 8 10 12 14 16 18 20 22 24
Standard Altitude
(Temperature °F) 59 52 45 38 31 23 16 9 + 2 -5 -12 -19 -27
3-25
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