Blast-tube cooling for aircraft generators

BLAST cooling has been a major factor in obtaining the phenomenal outputs of modern aircraft generators from a small weight of material. This subject, in spite of its importance, seems to have been neglected in technical literature and, as a result, the fundamental principles do not seem to be at all well understood. Because of this lack, the subject has often appeared to be more involved than it actually is. It is generally understood that the amount of air flowing through a given generator depends upon the pressure differential available across the generator, and it is also well understood that the amount of pressure available from the blast tube depends upon the amount of air drawn by the generator. Because of this mutual interdependence, flight tests are today generally taken with a specific generator and blast tube, and it seems to be generally felt that it is necessary to test each different combination of generator and blast tube. Just as Ohm´s law enormously simplified the calculation of electric circuits, so can the calculation of blast cooling be simplified by the use of similar concepts, which will be defined, explained, and used in this paper. This line of attack clarifies the fundamental principles involved, makes it necessary to run only one series of tests on any given blast tube, and one series of tests on any one given generator. It is not necessary to test each and every combination of generator and blast tube. This line of attack also makes it possible to write specifications which simultaneously accomplish a number of purposes: