Fixed-Pitch Propeller/Piston Aircraft Operations at Partial Throttle

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The linearized propeller polar or bootstrap approach to e xed-pitch propeller aircraft performance is extended to include partial-throttle operations. Power setting parameter P is dee ned as the ratio of actual engine torque to maximum possible (full-throttle ) torque at the given atmospheric density. To compute quasisteady partial-throttle performance, two additional data items, beyond the nine items of the ordinary bootstrap data plate, are required: 1) brake specie c fuel consumption rate as a function of engine power and 2 ) level cruise speeds with associated engine speeds (from a e ight test at any one altitude and weight ). The latter results in a propeller chart giving advance ratio J as a function of CP/J 2 , the independent variable in the propeller polar. With that information, level cruise performance tables (similar to GAMA format, but extended with thrust and propulsive efe ciency ) can be calculated. Installed propeller charts can be constructed and expressions for partial-throttle absolute ceilings derived. Given the airplane’ s airspeed and desired e ight path, e.g., a standard rate turn descending 300 ft/min at 90 KCAS, engine rpm required for that maneuver can then readily be calculated. This partial-throttle facility rounds out the bootstrap approach, allowing full prediction of quasisteady performance of e xed-pitch propeller airplanes.