Effect of Altitude on Ventilation and Rating of Aircraft Electric Machines

Fundamental problems involved in the cooling and rating of aircraft electric machinery at medium and high altitudes are discussed in this paper, primarily to assist users in the application of such equipment, and to assist builders in designing equipment to meet the requirements. In addition flight tests are reported which confirm in part the blast-tube theory developed in a previous paper. For blast-cooled generators, an equation has been developed to show the maximum permissible output in terms of entering-air temperature and density, ramming-head pressure, and winding temperature For motors curves of total winding temperature at rated load have been plotted as a function of altitude; these curves were plotted for selected values of sea-level temperature rise. Specific conclusions are drawn as to: 1. Permissible generator output as a function of altitude and sea-level rise. 2. Limiting sea-level temperature rises for motors on the basis of constant or reduced life at altitude. This paper presents a qualitative method of analysis rather than a definitive solution of the problems involved.