Superaerodynamics, Mechanics of Rarefied Gases

Zahm [1] in 1934 published an article on the aerodynamics of highly rarefied gases, a branch of fluid mechanics which he called superaerodynamics. At that time, however, with the means of propulsion then available, flight at extreme altitudes did not seem to be realizable. Therefore, superaerodynamics has been considered as a subject of academic interest rather than one of practical engineering importance. With the recent perfection of the rocket as a propulsive power plant, the situation is radically changed and there should be no limit to the altitude that can be reached by an aircraft. There are even indications that the optimum flight altitude of long-range rocket airplanes is approximately 60 miles. At these and higher altitudes, the air density is so low that the fluid must be thought of as one having a coarse structure and not as a continuous medium of conventional fluid mechanics. Then concepts of superaerodynamics are needed to guide the design of such an aircraft.