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Considerable research on large-scale high-performance, lift-engine, V/STOL configurations has been conducted at Ames Research Center. The exhaust gas reingestion characteristics, lift-engine inlet total-pressure recovery and distortion, and engine-airframe induced effects were measured in the 40 × 80 ft wind tunnel both in and out of ground effect over a wide range of transition flight conditions. The results of these investigations show that the lift-engine configurations studied may have severe operational constraints placed upon them during transition.

A practical procedure for the optimum design of low-speed airfoils is demonstrated. The procedure uses an optimization program based on a gradient algorithm coupled with an aerodynamic analysis program that uses a relaxation solution of the in viscid, full-potential equation. The analysis program is valid for both incompressible and compressible flow, thereby making optimum design of high-speed, shock-free airfoils possible. Results are presented for the following three constrained optimization problems at fixed angle of attack and Mach number: (i) adverse pressure-gradient minimization, (ii) pitching-moment minimization, and (iii) lift maximization. All three optimization problems were studied with various aerodynamic and geometric constraints.

Recent applications of numerical optimization to the design of advanced airfoils for transonic aircraft have shown that low-drag sections can be developed for a given design Mach number without an accompanying drag increase at lower Mach numbers. This is achieved by imposing a constraint on the drag coefficient at an off-design Mach number while the drag at the design Mach number is the objective function. Such a procedure doubles the computation time over that for single design-point problems, but the final result is worth the increased cost of computation. The ability to treat such multiple design-point problems by numerical optimization has been enhanced by the development of improved airfoil shape functions. Such functions permit a considerable increase in the range of profiles attainable during the optimization process.

This paper addresses the three questions: “Is V/STOL capability economically viable for business aircraft, and if so, how does the viability depend on the aircraft concept?”; “How is a V/STOL concept chosen to match a given mission, and what are some of the promising V/STOL concepts for future business aircraft?”; and “What unique operational requirements are likely to be imposed on users of future V/STOL business aircraft?” A cost-benefit analysis is presented which indicates that a VTOL business aircraft would be more viable economically than a contemporary turbine-powered business aircraft. The combinations of traveler's time value and trip distance for which each aircraft dominates is shown. A discussion is presented on the significance of disc loading as it relates to V/STOL concept application. Preliminary design configuration studies for three different business-aircraft-sized V/STOLs, using three concepts covering a range of disc loading, are presented as examples.