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This paper is an overview of the status of lift fan transport technology. Selected results of recently completed NASA in-house and contractual research investigations are included within the general areas of lift fan transport design: propulsion, acoustics, integrated propulsion/airframe/aircraft control systems, piloted moving-base simulation, and aircraft aerodynamics. On-going NASA lift fan transport research is briefly summarized, and a possible next step in the overall program is suggested.

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.

The noise goal of 95 PNdB for STOL aircraft imposes severe technology demands on propulsion systems. Effects of this goal on the design of the propulsion system are reviewed. Results from recent development programs associated with STOL noise reduction, such as high bypass fan tests, 25 PNdB acoustic suppression tests, sonic inlets, and powered lift system noise tests, are presented. Integrated propulsion system designs for the blown flap and augmentor wing powered lift systems capable of meeting the noise goal are shown and the performance, installation, and economic penalties assessed.

The joint development of an augmentor wing jet STOL research aircraft by NASA and the Canadian Government Department of Industry, Trade, and Commerce has progressed to the point that the design of the modifications to the de Havilland C-8A Buffalo are complete and the engines are being tested. The predicted performance shows that the airplane will be able to take off and land in less than 1500 ft. Simulation studies indicate that the handling qualities of the airplane, with stability augmentation, will be acceptable for STOL research missions.

This paper summarizes the results and findings of a program to design, develop, and evaluate actuator rod seals for use in advanced aircraft high-temperature hydraulic systems. The rod seals are intended to function efficiently and reliably for 3000 hr in the temperature range of -40-500 F. Preliminary studies of various material and design combinations showed that a polyimide low-pressure second-stage V-seal in a two-stage configuration had the greatest potential in long-term duty cycle testing in a simulated actuator test system. Modifications of this seal that provided for improved fatigue life and more efficient loading met the test objectives of 20 X 106 short-stroke cycles of operation at 500 F. Severity of this testing was equivalent to 3000 hr of duty cycle operation. The validity of design techniques used to achieve performance goals was shown.

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.

NASA, in cooperation with the FAA, is evaluating the two-segment approach as a routine procedure for reducing aircraft noise. The program calls for separate flight evaluations using a 727 and a DC-8, and an extrapolation of these results to determine the adaptability of the technique to the rest of the fleet. After a review of the total program, this paper presents (i) the profile and procedures developed and the noise reduction achievable, (ii) the vortex characteristics behind an aircraft on a two-segment path, and (iii) cost estimates for retrofitting aircraft with two-segment avionics.