The following points, discussed in this paper, should be considered very carefully in all systems contemplating the use of lift engines for VTOL aircraft: (1) The rate of benefit to the aircraft decreases rapidly for engine thrust-to-weight ratios greatly in excess of 20:1; (2) Working relationships are available for use in the aeromechanical design phase of high thrust-to-weight ratio engines; (3) The “installed” thrust-to-weight ratio of lift engines is the most important criterion for evaluation of alternative peripheral equipment design concepts; (4) The reaction control, thrust vectoring, and induction subsystems contribute most of the degradation of lift engine “installed” thrust-to-weight; (5) The rotating cascade concept is the most promising system for deflecting lift engine exhaust flow to achieve both vehicle control and STOL capability; (6) The jetevator, vane deflectors and spherical nozzle concepts are competitive within specified deflection angle ranges; (7) Scoop-type inlets with movable vanes in the upper surface can be devised to alleviate lift engine induction losses; and (8) Significant improvements in the lift engine installed volume can be obtained by optimizing the inlet lip and engine vertical location within the fuselage or engine pod.
