ALTITUDE PERFORMANCE of High-Output Aircraft Engines 410099
THIS paper deals principally with a description of the methods used in, and a discussion of the results of, an investigation of the possible altitude performance with liquid-cooled engines of high output and consequent high ground boost.
As the first step in the investigation of altitude performance the power of the engine cylinder under all possible conditions of manifold pressure, manifold temperature, and exhaust pressure is determined. The single-cylinder laboratory employed can produce any desired exhaust suction; manifold pressures up to 150 in. hg; inlet air temperature up to 400 F; and handle engine speeds up to 5000 rpm.
Maintenance of power at altitude by means of the exhaust-driven turbo compressor, Mr. DuBois believes, affords a most convenient way out for the engine manufacturer; the troubles, if any, are transferred to the builder of the turbo and of the airplane. He considers “worthy of considerable attention” the use of a two-stage supercharger with an auxiliary engine to drive the first stage. He explains that this arrangement is especially applicable to large airplanes.
Other supercharger arrangements discussed are the single - stage geared compressor; two - speed drives; continuously variable drives; two - stage geared superchargers; and modified two-stage installations, such as two-speed both stages, bypassed first stage, and the two-speed first stage.
The two-speed first-stage method of using two stages is the most satisfactory yet considered, Mr. DuBois believes, since three steps of supercharging reduce the amount of throttling required and, therefore, improve the overall efficiency of the system.