Planes Unlimited.

The article reports on the progress of aircraft development in the U.S. and the economic, engineering problems facing designers. Design elements considered are structures, engines, pitch propellers and wing loading, and there are three factors to determine the utilization of bigger airplanes for airline operation. Domestic trunk line operators chose the four-engine Douglas DC-4 and DC-6 in planning their postwar equipment programs. Also being developed are the Lockheed Constellation, Boeing C-97 two-story plane and adaptations of the Mars flying boats.