Powered-lift Aircraft Research Articles

Application of nonlinear inverse methods to the control of powered-lift aircraft over the low-speed flight envelope

This paper presents a summary of experience in the design of velocity vector control systems for operation of short take-off and landing (STOL) and short take-off and vertical landing (STOVL) aircraft over their low-speed flight envelopes. A nonlinear inverse control method developed at NASA Ames Research Center was employed to deal with the highly nonlinear, multi-dimensional aerodynamic and propulsion system characteristics that are inherent in these aircraft. The method partitions the control system into a command element that is defined solely by the dynamic response to achieve good flying qualities, and a nonlinear inverse element that computes the aerodynamic and propulsion control effector positions required to satisfy the pilot's commands and to regulate against disturbances. Experience gained at flight evaluations with a powered-lift STOL aircraft and in piloted simulation with a STOVL aircraft design indicates that this system design approach produces the desired flying qualities over the low-sp...

Flight measurements of downwash on the Ball-Bartoe Jetwing powered lift aircraft

Flight tests were conducted with the Ball-Bartoe Jetwing powered lift technology demonstration aircraft to visualize flow angles on the fuselage surface and at selected points in the flowfield near the horizontal tail. Simple data acquisition techniques were used. The results were used to calculate the downwash near the horizontal tail and its variation with airspeed, jet deflection angle, and blowing coefficient over a range of level flight conditions. Further research is needed to broaden the database and substantiate these findings.

Flight evaluation of pursuit displays for precision approach of powered-lift aircraft

Flight experiments with NASA Ames Research Center's quiet short-haul research aircraft evaluated the influence of pursuit displays on the ability of pilots to execute precision-instrument flight operations in the terminal area, particularly approaches to and landings on a short runway. The aircraft is a powered-lift, short-takeoff and landing configuration equipped with a modern digital fly-by-wire flight control system, a head-up display, and a color head-down display that make it possible to investigate control and display concepts for full-envelope, powered-lift operations. Flight-path-oriented displays that provide status and command information in a format with minimal clutter were investigated. The pilots could fly the aircraft with the precision associated with flight-director guidance and with a high degree of situation awareness. The primary benefits of this display concept were realized when the pilot was required to execute a complex transition and approach under instrument conditions and in the presence of a wide range of wind and turbulence conditions.

The 1989 Team

Inderjit Chopra Inderjit Chopra is Professor and Acting Chairman of Aerospace Engineering at the University of Maryland. He received a B.Sc. in Engineering from Punjab Engineering College, Chandigarh^ India, in 1965; an M.E. from Indian Institute of Science, Bangalore, India, in 1968; and a Sc.D. from Massachusetts Institute of Technology in 1977. He worked at the National Aeronautical Laboratory in Bangalore from 1966 to 1974: His research there included aeroelastic wind tunnel testing of scaled models of airplanes and launch vehicles. At MJT, he worked on aeroelastic analyses of wind turbine rotors for his doctoral dissertation. In 1977, he joined NASA Ames/ Stanford University Joint Institute of Aeronautics and Acoustics, wheje he researched aeroelastic analyses of advanced rotor systems and dynamic testing of full-scale helicopters in the NASA Ames 40 x 80 ft wind tunnel. In 1981, he joined the University of Maryland. He is a major participant of the Army's Center of Rotorcraft Education and Research at Maryland. An author of over 60 articles and papers, Dr. Chopra is also an associate editor of the Journal of the American Helicopter Society and a member of the editorial advisory board of Vertica, The International Journal of Rotorcraft and Powered Lift Aircraft. He is an Associate Fellow of AIAA.

Flight evaluation of augmented controls for approach and landing of powered-lift aircraft

Flight experiments were conducted with Ames Research Center's Quiet Short-Haul Research Aircraft to evaluate the influence of highly augmented control modes on the ability of pilots to execute precision instrument flight operations in the terminal area, particularly approaches to and landings on a short runway. The aircraft is a powered-lift, short-takeoff and landing configuration that is equipped with a modern digital fly-by-wire flight control system, a head-up display, and a solar head-down display that make it possible to investigate control concepts and display format and content for full envelope, powered-lift operations. Considerable attention has been devoted in this flight program to assessing flightpath and airspeed command and stabilization modes developed using nonlinear, inverse model-following methods. The primary benefit of this control concept was realized when the pilot was required to execute a complex transition and approach under instrument conditions and in the presence of a wide range of wind and turbulence conditions.

Fuel-Conservative Guidance System for Powered-Lift Aircraft

A technique is described for the design of fuel-conservative guidance systems and is applied to a system that was flight tested on board NASA's sugmentor wing jet STOL research aircraft. An important operational feature of the system is its ability to rapidly synthesize fuel-efficient trajectories for a large set of initial aircraft positions, altitudes, and headings. This feature allows the aircraft to be flown efficiently under conditions of changing winds and air traffic control vectors. Rapid synthesis of fuel-efficient trajectories is accomplished in the airborne computer by fast-time trajectory integration using a simplified dynamic performance model of the aircraft. This technique also ensures optimum flap deployment and, for powered-lift STOL aircraft, optimum transition to low-speed flight. Also included in the design is accurate prediction of touchdown time for use in four-dimensional guidance applications. Flight test results have demonstrated that the automatically synthesized trajectories produce significant fuel savings relative to manually flown conventional approaches.

The annoyance of helicopter noise with impulsivity varied by phase shifting

Annoyance ratings to four digitally synthesized helicopter sounds were collected. Two were relatively impulsive; a standard helicopter‐pulse waveform produced according to the model of Schmitz and Yu (European rotorcraft and powered lift aircraft forum, France, 1977), and its cosine phase equivalent. The other two sounds were substantially less impulsive. They were low peak stimuli produced from the standard waveform by randomizing the phase relations among its Fourier components. All four stimuli had identical Fourier series amplitude spectra. The four synthesized sounds were utilized in a within‐subject factorial design with each sound presented at pulse frequencies of 10 and 20 Hz and levels of 89 and 95 dBA. The pulse trains lasted for 3 s for one group often subjects and 12.5 s for another ten subjects. In addition, another group of ten subjects with a mean age of 36 rated the sounds. All groups rated the more impulsive sounds significantly less annoying. The magnitude of this effect was 2.7, 3.5, and 4.5 dB for the three groups, respectively. This result indicates that previous studies in which the power spectra across impulsive and nonimpulsive sounds was not held constant and which found that impulsivity resulted in increased annoyance ratings may have been contaminated by this deficiency. [Work supported by NASA Langley Research Center.]

Powered-Lift Aircraft Handling Qualities in the Presence of Atmospheric Disturbances

Selected results are presented from a two-phased experimental program to investigate powered-lift aircraft handling quality degradation due to both naturally-occurring and computer-generated atmospheric turbulence. In phase I a variable stability helicopter was flown to simulate a powered-lift aircraft on final approach. In phase II a ground-based simulator with a moving cockpit and a colored visual display was used to represent the same powered-lift aircraft. During phase II a Dryden model of atmospheric turbulence was used together with actual wind profiles recorded during phase I. This paper focuses on the phase II results, which demonstrate that the Dryden model can yield optimistic ratings of airplane handling qualities in turbulent landing conditions. The model also leads to an optimistic estimate of combined pilot-vehicle performance degradation in turbulent flight.

V/STOL Aerodynamic Testing Techniques at British Aircraft Corporation

Powered-lift aircraft aerodynamic testing at the Military Aircraft Division of British Aircraft Corporation is focused on 5.5 m (18 ft) closed working section, nonreturn wind tunnel. The facility operates over a narrow freestream speed range of approximately 11-21 m/s (35-70 ft/s). Full-scale Mach number is not maintained, therefore, in the interests of drive system cost. The wide range of propulsion force coefficients required are simulated by changing the propulsion momentum while keeping the freestream momentum constant. Where possible, the propulsive forces are grounded (nonmetric), and the airframe loading due to propulsion and freestream interaction is measured with high resolution using internal strain-gage balances tailored to the expected load range. Propulsive stream flows are represented by cold compressed air taken onboard through the sting support system and used either as direct feed to jet flows or as the drive air to compressed air ejectors, for better representation of airbreathing propulsive systems. While none of these techniques are novel, together they constitute a cost-effective testing capability, ideally suited to proof of concept, preliminary project design, and basic research testing on power-lift aerodynamics.

Powered Lift and Mechanical Flap Concepts for Civil Short-Haul Aircraft

The objective of this paper is to determine various design and performance parameters, including wing loading and thrust loading requirements, for powered lift and mechanical flap conceptual aircraft constrained by field length and community noise impact. Mission block fuel and direct operating costs (DOC) were found for optimum designs. As a baseline, the design and performance parameters were determined for the aircraft using engines without noise suppression. The constraint of the 90-dB effective perceived noise level (EPNdB) contour being less than 2.6 km (1.0 mi.) in area was then imposed. The results indicate that for both aircraft concepts the design gross weight, DOC, and required mission block fuel decreased with field length. At field lengths less than 1100 m (3600 ft) the powered lift aircraft had lower DOC and block fuel than the mechanical flap aircraft but produced higher unsuppressed noise levels. The noise goal could easily be achieved with nacelle wall treatment only and thus resulted in little or no performance or weight penalty for all studied aircraft.

STOL Aircraft Flight and Landing Area Considerations

Current research to achieve a technically and socially acceptable short take-off and landing (STOL) aircraft system to help alleviate present air transportation congestion is outlined considering both flight and runway elements. The aerodynamic jet-flap propulsive-lift concept is briefly reviewed with proposed turbofan powered-lift aircraft. Short, single direction, and possibly elevated runways are considered for use in high-land-cost urban areas. Aircraft capability is being developed to enable operations under high crosswind conditions, possibly through the use of crosswind landing gears or crosswind-reducing fences erected along the sides of the runway. Techniques are being developed to insure smooth wind flow over elevated STOL ports, such as on the roofs of buildings; and emergency arresting systems are under study to contain the aircraft on the runway. Heating and grooving of the runway has been explored analytically as a method of keeping the required runway length short by guaranteeing runway friction even under ice and snow conditions.

Airworthiness Objectives for Civil Powered Lift Aircraft

THE types of powered lift aircraft which can be conceived are many and varied. Over the last 10 to 15 years a surprisingly large number of as have been tested on experimental machines, which have flown with varying degrees of success. The setbacks in terms of discarded or unproven concepts outweigh the successes in the form of erational types or of prototypes capable of commercial development; nevertheless, many valuable sons have been learnt. This evolutionary process has some way to go. The last few years have seen er new aircraft, but a proliferation of paper sibility studies, and their conclusions are as merous as their authors. However, at last a pattern beginning to emerge of the roles to be played by wered‐lift aircraft and the particular types which ty be best suited to fulfil them.