A large number of tests were made in the altitude laboratory of the Bureau of Standards, using aircraft engines. The complete analysis of these tests was conducted under the direction of the Powerplants Committee of the National Advisory Committee for Aeronautics. Many of the engines were of the same make, differing in compression ratio or dimensions. The testing program included determinations of the brake-horsepower at various speeds and altitudes, or air densities, and the friction power, or the power required to operate the engine with no fuel or ignition at various speeds and air densities, with normal operating conditions of oil, water and the like. Some tests included determination of the effect of change of mixture ratio and of air temperature, and of different oils.
The difficulties caused by the necessity of using indirect methods to ascertain the effect of various factors are outlined. The test analyses and curves are presented. Results from many tests were analyzed and the relation between speed, air density and friction torque expressed as mean effective pressure, was studied. Running comment is made on the analyses and charted results, including consideration of pumping loss, variation of friction-horsepower with speed, the effect of change of air density upon the indicated power and the foot-pounds of indicated work obtained per pound of gasoline supplied.
Heat balance and losses are considered in considerable detail, the conclusion being that an increased utilization of the energy supplied in fuel must be obtained by an increase of compression ratio and the efficiency of combustion, as it seems almost impossible to reduce the jacket losses to an appreciable extent.