A presentation of the results of previous RAND studies concerned with variations in the density of air cargo and the effects of these variations on aircraft design, aircraft capacity estimates, airlift operations, and airlift costs. The Memorandum presents methods of comparing costs of airlifting different commodities, which take into account the densities of the commodities and the characteristics of the transporting aircraft. Attention is drawn to implications of the fact that air cargo varies in density and rarely, if ever, adheres to the average values that are usually computed. Generalized radar concepts with the use of array antenna.