Medium Speed Flight: 100-350 MPH (Subsonic)
In order to build faster aircraft, several areas or technologies had to be improved. First, the drag had to be reduced substantially. This was accomplished largely by developing enclosed, streamlined fuselages and stronger wings that did not require external bracing. This meant the structure had to be made stronger, but hopefully not heavier. Thus, materials and structures were developed with a higher ratio of strength to weight. Next, the thrust had to be greatly increased without making engines too heavy. Thus, the engine's ratio of power to weight increased. All of these areas improved in a leapfrog manner. For example, a new engine might be developed with 50 percent more power (good!) that weighed 25 percent more (not so good!) Note that this engine has a higher power-to-weight ratio, but it also weighs more. To carry this extra weight, the fuselage would have to be stronger and heavier. The resulting aircraft might not really be faster until it could be designed to be lighter. Finally, our knowledge of aerodynamics improved through the use of new tools such as wind tunnels and a lot of basic research.
The vehicles that are found in this regime are limited by the source of the thrust and, to a lesser extent, the drag. The engines are almost all propeller types, and the wings are almost all straight and fairly thick. Vehicles in this category are propeller craft like Fokker, Junkers, Cessna and Beechcraft. The need for higher-performance aircraft during WWII accelerated the development of aircraft in this speed regime. At the same time that speed was being improved, so was the carrying capacity of aircraft.
Read Related JournalsMedium-Speed Wind Tunnel Testing for High-Lift System Performance by Steve Smith