Cooling rotating aircraft electric equipment

THE STEADILY INCREASING upper limits in flight speed and altitude for modern aircraft make the study of cooling systems for rotating electric equipment imperative. Experience with conventional fan- and blast∗∗∗cooling systems indicates poor cooling performance under many of the high-altitude high-speed conditions presently encountered. Several factors, such as decreasing air density at altitude which results in decreasing available pressure drop, air-weight flow, and heat transfer coefficients, contribute to equipment overheating. Further, the air pickup drag incurred in blast cooling can result in a loss of aircraft carrying capacity many times greater than the difference in weight between a blast-cooled system and a heavier system utilizing some other cooling method. For example, it is possible for some blast-cooling installations to incur drag penalties of the order of magnitude shown in Figure 1.