The subject of high lift systems is extremely broad and therefore must be restricted in order to be tractable. For the purposes of this paper, it is felt to be sufficient to consider four-engine M = 0.8 turbofan aircraft with about 1800-ft FAA field length capability. Even with the foregoing limitations on scope, it is only possible to present what are felt to be the essential concepts at the edge of the propulsion, aerodynamic, and design elements of the subject.
The analysis indicates that:
When there is a need for turbofan STOL aircraft capable of operation from 1800-ft fields, this need can be satisfied by aircraft that are similar in size and proportions to current conventional aircraft. Propulsion developments in process are expected to yield engines with excellent thrust matching between low-speed and high-speed requirements. The weights and noise of these engines are expected to be completely acceptable. Efficient cascade-type thrust deflectors suitable for the resulting high-bypass engines also appear possible.
In order to use conventional wing loadings and aspect ratios, maximum lift coefficients must approach the theoretical limit of circulation lift. Projected developments in variable-geometry, blowing BLC leading edge slats, combined with blowing BLC trailing edge flaps, are expected to provide the needed improvements.
The propulsion and aerodynamic trends that could result in a family of 24 possible high lift systems appear to contain only three acceptable members. The one acceptable first-generation concept provides a basis for evolution to the two possible second-generation systems, possibly with a common airframe.