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The AV-8B Harrier II V/STOL strike aircraft for the U.S. Marine Corps features an advanced design, limited authority digital Stability Augmentation and Attitude Hold System (SAAHS). Utilization of this single channel electronic flight control system required an extensive self-test and monitoring system. New techniques to detect failures were based on extensive simulation, Iron Bird and flight test results. Self-test capabilities are provided for maintainability as well as safety. SAAHS monitoring is implemented in three primary categories: hardware, software monitor of hardware, and software monitor of performance. Total system health is determined in a comprehensive preflight Built-in-Test (BIT). System performance during flight is continuously monitored by In-Flight-Monitoring (IFM).

In the field of powered lift there is a long history of collaboration between the USA and the UK. The most obvious manisfestation of this is the Harrier/AV8 aircraft series which was preceded in the 1950's by the original Hawker P1127 Kestrel experimental aircraft. The capability of that aircraft series has now been greatly extended by the development of the AV8B/Harrier GR5, with its new wing, uprated engine and other improvements. This latest version of the concept that originated in the Kestrel is, however, still a subsonic aircraft. The operational advantages of short take-off and vertical landing combined with supersonic performance and high agility in a future combat aircraft are very attractive to both the US and UK. This interest has led to the latest US/UK powered lift collaboration designated Advanced Short Take-off and Vertical Landing (ASTOVL). This collaboration was formalised in January 1986 by a government to government Memorandum of Understanding (MOU).

Helicopters have been under active development for the last 50 years. The earlier years were characterized by configuration development and demonstration of capabilities, and the latter 25 years have been characterized more by pressing against the fundamental barriers of ideal performance, compressibility, and materials. This paper reviews the trends that have preceded today's status and concludes that helicopter technology still has opportunity for significant growth ahead.

Advanced subsonic vertical and short takeoff and landing (V/STOL) aircraft configurations offer new transportation options for civil applications. This paper describes a range of vehicles from low-disk to high-disk loading aircraft, including high-speed rotorcraft, V/STOL aircraft, and short takeoff and landing (STOL) aircraft. The status and advantages of the various configurations are described. Some of these configurations show promise for relieving congestion in high population density regions and providing transportation opportunities for low population density regions.

The X-Wing is a lifting surface with four blades geometrically arranged in an X shape that provides the capability for an aircraft to be configured in flight as a fixed wing or a rotary wing vehicle. This lifting device requires a compressed air source which provides air to the leading and trailing edges of each rotor blade as demanded by a flight control system. This controlled blowing utilizes the Coanda Effect to augment the lift on each of the blades such that either uniform lift or pitching or rolling moments can be generated. In 1983, NASA and DARPA embarked on a joint program to investigate the X-Wing concept with the goal of developing the critical technologies necessary to support the development of a prototype vehicle. The subject of this paper is to report the current status of that program.

Experiments were performed to simulate jet plume effects associated with VTOL aircraft in takeoff and cruise modes. A water facility was used to investigate the influence of inclination angle and separation distance on the three-dimensional fountain flowfield generated by two impinging jets operating at a jet Reynolds number of 250,000. Substantial differences in the flow features were observed for different spacings between the jets. Plume effects in cruise mode were simulated by a supersonic unheated jet parallel to a wall. Variation of the distance between the wall and the edge of the plume is shown to have a major controlling effect on the supersonic screech instability.

This paper assesses the state of the art in acoustic fatigue technologies as applied to an advanced supersonic short takeoff and vertical landing (STOVL) aircraft. The topics covered include advanced materials, fatigue, acoustic loads prediction, and stress response prediction. Advanced materials are compared from the standpoints of fatigue resistance and fatigue data availability. State of the art acoustic load prediction techniques are evaluated. Subsonic and supersonic jet noise generation mechanisms, axisymmetric and two-dimensional nozzles, and noise suppression methods are covered. Stress response prediction methods for acoustic, thermal, and maneuvering loads are addressed and the necessity of structural analysis with all three loading types applied simultaneously is assessed.

A model scaled test apparatus has been designed and assembled to simulate supersonic plume/aircraft structure Interaction for the cruise configuration. Preliminary results have been obtained to demonstrate the severity of the associated acoustic fatigue loads. Two rectangular supersonic nozzles with aspect ratios of 7 and 7.7 ware fabricated with internal convergent-divergent contours designed for Mach numbers of 1.35 and 2.00. A large flat plate was located beneath each nozzle at various nozzle height separations. The plate was instrumented to measure surface dynamic pressure and mean wall temperature. Phase averaged schliern measurements revealed the presence of high intensity acoustic emission from the supersonic plume above the plate and directed upstream. This radiation can be associated with the shock noise generation mechanism. Narrow band spectra of wall dynamic pressure show spectral peaks with amplitude levels as high as 1 PSI.

A full-scale aircraft crash test of the Bell ACAP developed under the U.S. Army's Advanced Composite Airframe Program was conducted at NASA Langley Research Center's Impact Dynamics Facility on August 27, 1987. The test demonstrated that the Bell ACAP was capable of meeting the U.S. Army's stringent crash survivability requirements of 50-ft/s resultant ground impact velocity (42-ft/s sink speed, 27-ft/s forward velocity, with two-thirds DGW rotor lift) at an aircraft attitude of 10° roll and 10° nose-up pitch without any apparent serious injuries to the occupants. The impact velocity is comparable to a free fall from a four-story building. The ACAP crash test represents the first time any helicopter has ever been tested to this 50-ft/s impact level with the aircraft attitudes of 10° for both roll and pitch conditions.

The possible replacement of existing Navy tactical-support air assets by a single airborne platform is being contemplated for such roles as Airborne Early Warning. Anti-Submarine Warfare, Electronic Warfare, and other secondary applications. These missins are currently performed by the E-2, S-3, and EA-6A air vehicle systems. This new multi-mission tactical aircraft is to be operated from larger carriers of the CVA-63 class with high performance catapult and arresting equipment. With this type of basing, design studies have shown that a conventional takeoff and landing (CTOL) navalized aircraft will most effectively and efficiently meet the projected requirements. However, a unique dimension in operational deployment freedom and basing flexibility could be achieved with a Short Takeoff and Vertical Landing (STOVL) aircraft under preliminary evaluation by MCAIR - the Model 276 Medium Speed Tactical Aircraft.

A variable inlet guide vane (VIGV) convertible engine that could be used to power future high-speed V/STOL and rotorcraft was tested on an outdoor stand. The engine ran stably and smoothly in the turbofan, turboshaft, and dual (combined fan and shaft) power modes. In the turbofan mode with the VIGV open, fuel consumption was comparable to that of a conventional turbofan engine. In the turboshaft mode with the VIGV closed, fuel consumption was higher than that of present turboshaft engines because power was wasted in churning fan-tip airflow. In dynamic performance tests with a specially built digital engine control and using a waterbrake dynamometer for shaft load, the engine responded effectively to large steps in thrust command and shaft torque.

A piloted simulation was conducted to: evaluate attitude response bandwidth as a predictor of V/STOL hover flying qualities, validate a unique convolution integral simulation technique (CONVO), and qualitatively assess the one-to-one motion characteristics of the Grumman Large Amplitude Research Simulator (LARS). Handling qualities ratings demonstrated good correlation with attitude response bandwidth for both attitude command and rate command response types, however, a minimum damping requirement is necessary to supplement the bandwidth requirement for attitude command responses. Formal validation of the CONVO technique was not possible due to inaccurate modeling of the Grumman V/STOL Design 698, however, CONVO fidelity for the bandwidth investigation was satisfactory. Comparisons of pilot evaluations of the Design 698 on LARS and the NASA Ames VMS show LARS evaluations to be much worse (2-3 HOR's) due to high controller sensitivity.

This paper summarizes a basic and well-controlled experimental study involving flow visualization and noise measurements to define the acoustic and flow fields of single plumes impinging on a simulated ground plane. The flow visualization was made by strobing a laser light source at the discrete frequencies generated by the impingement of the jets and measured by a nearfield microphone. This enabled visualization of instability waves generated by the interaction between the plumes and the sound generated during impingement, and also by dynamic coupling between the two plumes. These data were acquired as a function of distance between the ground and the nozzle exit. Nearfield acoustic data were acquired simultaneously. Data for nozzle diameters of 0.265 in. and 0.4 in. are described. For selected nozzles, effects of exit boundary layer characteristics and nozzle protrusion through a simulated aircraft body are also presented.

In the period from 1950 to 1970, the development of VTOL capability in fixed wing aircraft was energetically pursued in many parts of the world. The larger proportion of this effort was dedicated to machines featuring composite powerplants. In these vertical thrust was wholly or partly provided by lift engines designed for the purpose. A number of sophisticated experimental aircraft of this type were built and flown in Europe, all of which featured Rolls-Royce lift engines. Many technical problems were encountered and overcome in the field of engine design and powerplant installation. New and rigorous methods of design validation were introduced. The technology base and engineering disciplines which grew out of this experience had a strongly beneficial influence on all engine and powerplant design. The accumulated experience remains highly relevant to new aircraft projects planned with VTOL capability, where a composite powerplant provides the optimum performance.

This paper addresses the effect of bypass ratio on thrust-to-weight, fuel flow, and hover efficiency. Four selected representative tilt propulsion system aircraft are analyzed. The paper covers a quantative discussion of the issues involved in selecting a V/STOL propulsion system.

Vertical landing/takeoff candidate aircraft will require some type of Reaction Control System (RCS) for aircraft balance, control, and maneuver during jet-boume flight. Typically these systems require high pressure compressor bleed air to be discharged through nozzles located on the wing tips, nose and tail of the aircraft for hover stability. Bleed rates on the order of 10 to 20 lbs/sec could be required with the source of air from compressor interstage, compression discharge or a combination from both locations.

Supersonic capable STOVL fighter/attack aircraft can provide capabilities for close support and air superiority which will be highly desirable in the future. Previous papers in this session described the historical aspects, tradeoffs, and requirements for powered lift propulsion systems, and it is shown that propulsion technology is more key to the success of this type of aircraft than for any previous fighter/attack aircraft. This paper discusses the NASA Lewis Research Center program activities which address required propulsion technology development. Several elements of this program have been initiated which address hot gas ingestion and ejector augmenter performance and some preliminary results are shown. In addition, some additional near-term research activity plans and the new Powered Lift Facility (PLF) research capability are presented.

The Global Positioning System will become operational in the near future after years of careful planning and the expenditure of considerable resources. In the interest of efficiency its potential must be utilized as soon as it becomes available. To this end, there are a number of systems under development that exploit its unique capabilities; however, many of these systems cannot be successful without the support of carrier aircraft. This paper is written in the hope of contributing to the flexibility and efficiency of the carrier aircraft interface.

The latest generation of integrated circuit MIL-STD-1750A microprocessors lack sufficient speed for a number of system applications for which the SCI Technology, Inc. Data Acquisition and Control System could be applied. The classic co-processor and bus interface techniques do not provide an efficient approach to increasing throughput in these applications. However, the small size and low power of the latest 1750A microprocessors combined with the high density of memories now available and the integration of complex logic into a gate array, can reduce to a small single board, a processor of mini-computer capability. A number of these processors in a single system operating in parallel can produce a powerful computer that can be fully radiation hardened for space applications.

To a large degree all of us at one time or another have envisioned our “Over the Rainbow” version of a future should be. System engineers envision perfect harmony between vehicle aerodynamics and avionics integration. The program manager dreams of schedules and funding well within the projected budget. Then reality; budget constraints, backward compatibility, technology availability, schedule problems, and etc. This paper is intended to recognize the “dreamer” and at the same time offer a means of reconciliation to the real world. We will address advanced avionics architectures and a transitionary means to attain our goals and objectives. An “Avionics System Index” will be presented which defines and specifies a means of describing and partitioned avionics configuration.