1938-01-01

Flight-Testing with an Engine Torque Indicator 380124

A TORQUE indicator, in which the reaction forces of the fixed gear in the propeller reduction gearing are measured, has been developed and flight-tested by Pratt & Whitney Aircraft Division of United Aircraft Corp.
In this device the reaction forces are balanced by two hydraulic pistons, thus producing an oil pressure under these pistons which is proportional to the engine torque. The pressure of the oil, measured by an ordinary pressure gage in the cockpit, in conjunction with the engine speed and a suitable factor, gives the actual brake horsepower developed by the engine under all operating conditions of positive torque. Using a constant-speed propeller, it has been possible to make complete engine calibrations of power versus manifold pressures at various engine speeds at several altitudes between sea level and 20,000 ft.
Fuel consumptions, induction-system temperatures and pressures at several points from the carbureter inlet to the intake port, cylinder temperatures, airplane speeds, miles per gallon, and other data were obtained in flight. The effect of mixture strength on power, airplane speed, cruising range, and on general engine operation has been evaluated. The differences in air speed and engine power between an uncowled engine with short exhaust stacks and the same engine with cowling and collector are shown. Very illuminating results are shown as to the effects of cowl flap opening on engine power, airplane speed, drag coefficient, and fuel consumption in miles per gallon although the data on the study of range under cruising conditions are meager at present.
The torque indicator has shown itself to be very free from trouble during 150 hr. of flying and is an aid to the pilot in regulating mixture strength, in checking ignition, adjusting carbureter preheat, and, primarily in controlling the engine power. The added weight is about 20 lb.

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