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At least 397 records · Page 22

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NASA NTRS1984

Computer study of a jet flap ASTVOL 'Harrier'

A study of the costs/benefits trade-off was conducted for an Advanced Supersonic Short Takeoff and Vertical Landing (ASTOVL) aircraft incorporating a jet flap. The data used were the theory of jet flaps and high aspect ratio nozzles, experience with a V/STOL aircraft study performed for NASA Ames Research Center in February 1982, and a high performance aircraft-synthesis program (ACSYNT). The methodology was to accurately model the supersonic Harrier V/STOL aircraft design on ACSYNT, and then modify the design by both adding high aspect-ratio nozzles in place of the rear (core-flow) nozzles on the Pegasus-type turbofan engine, and integrating these nozzles on each wing's trailing edge, thus creating a jet flap. The predicted performance advantages (increase in maximum lift coefficient with flap deflection and horizontal thrust recovery) were traded off against the disadvantages (additional weight and thrust loss due to ducting) on two representative missions.

Wilson, S. B., III↗

NASA NTRS1988

Development Of A Digital Flight-Control System

Feed-forward control path includes inversion of model of the aircraft. Report describes concept, development, tests of digital flight-control system for vertical-attitude-takeoff-and-landing aircraft. System based in airborne digital computer. Combines control of attitude and thrust in unified system for operation over full coupled ranges of velocity, altitude, attitude, and acceleration.

Smith, G. Allan↗

NASA NTRS1988

A review of technologies applicable to low-speed flight of high-performance aircraft investigated in the Langley 14- x 22-foot subsonic tunnel

An extensive research program has been underway at the NASA Langley Research Center to define and develop the technologies required for low-speed flight of high-performance aircraft. This 10-year program has placed emphasis on both short takeoff and landing (STOL) and short takeoff and vertical landing (STOVL) operations rather than on regular up and away flight. A series of NASA in-house as well as joint projects have studied various technologies including high lift, vectored thrust, thrust-induced lift, reversed thrust, an alternate method of providing trim and control, and ground effects. These technologies have been investigated on a number of configurations ranging from industry designs for advanced fighter aircraft to generic wing-canard research models. Test conditions have ranged from hover (or static) through transition to wing-borne flight at angles of attack from -5 to 40 deg at representative thrust coefficients.

Paulson, John W., Jr.↗

NASA NTRS1988

STOVL acoustic fatigue technologies

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.

Groen, David S.↗

NASA NTRS1990

Analysis of internal flow in a ventral nozzle for STOVL aircraft

Short takeoff and vertical landing (STOVL) aircraft are planned for possible future development. For these aircraft, the same propulsion system will provide power for lift, hover, and horizontal flight. To accomplish this, many designs include a ventral nozzle to provide part of the vertical thrust required. Understanding and predicting the internal aerodynamic flow caused by a single exhaust duct opening are highly desirable in assessing this concept. A numerical simulation of a ventral nozzle is presented and the results are compared with experimental data. Comparisons include visualizations of the flow along the ventral duct walls and in the tailpipe plane of symmetry. Performance calculations are also compared with measured values.

Smith, C. Frederic↗

NASA NTRS1990

Analysis of internal flow in a ventral nozzle for STOVL aircraft

Smith, C. Frederic↗

NASA NTRS1991

Integrated flight/propulsion control design for a STOVL aircraft using H-infinity control design techniques

Results are presented from an application of H-infinity control design methodology to a centralized integrated flight propulsion control (IFPC) system design for a supersonic Short Takeoff and Vertical Landing (STOVL) fighter aircraft in transition flight. The emphasis is on formulating the H-infinity control design problem such that the resulting controller provides robustness to modeling uncertainties and model parameter variations with flight condition. Experience gained from a preliminary H-infinity based IFPC design study performed earlier is used as the basis to formulate the robust H-infinity control design problem and improve upon the previous design. Detailed evaluation results are presented for a reduced order controller obtained from the improved H-infinity control design showing that the control design meets the specified nominal performance objectives as well as provides stability robustness for variations in plant system dynamics with changes in aircraft trim speed within the transition flight envelope. A controller scheduling technique which accounts for changes in plant control effectiveness with variation in trim conditions is developed and off design model performance results are presented.

Garg, Sanjay↗

NASA NTRS1991

Small-scale experiments in STOVL ground effects

A series of tests was completed in which suckdown and fountain forces and pressures were measured on circular plates and twin-tandem-jet generic STOVL (short takeoff and vertical landing) configurations. The tests were conducted using a small-scale hover rig, for jet pressure ratios up to 6 and jet temperatures up to 700 F. The measured suckdown force on a circular plate with a central jet was greater than that found with a commonly used empirical prediction method. The present data showed better agreement with other sets of data. The tests of the generic STOVL configurations were conducted to provide force and pressure data with a parametric variation of parameters so that an empirical prediction method could be developed. The effects of jet pressure ratio and temperature were found to be small. Lift improvement devices were shown to substantially reduce the net suckdown forces.

Corsiglia, Victor R.↗

NASA NTRS1990

Aeroacoustic environment of an advanced STOVL aircraft in hover

The near-field aeroacoustic environment of a 6.02 pct scale advanced short takeoff and vertical landing aircraft is investigated in proximity to a simulated ground plane. The screech and impingement-tone characteristics of twin supersonic round and rectangular plumes are shown to be highly dependent on nozzle geometry and height above the ground plane. Shadowgraph and laser-sheet flow visualization are used to clarify the flowfield mechanisms responsible for time-dependent loads due to screech, impingement tones, and unsteady impingement of the upwash on the fuselage undersurface. Detailed dynamic pressure measurements from an array of transducers on the fuselage confirms that fountain impingement is responsible for the greatest unsteady loading.

Wlezien, Richard W.↗

NASA NTRS1990

Small-scale experiments in STOVL ground effects

A series of tests has been completed in which suckdown and fountain forces and pressures were measured on circular plates and twin-tandem-jet generic STOVL (short takeoff and vertical landing) configurations. The tests were conducted using a small-scale hover rig, for jet pressure ratios up to 6 and jet temperatures up to 700 F. The measured suckdown force on a circular plate with a central jet was greater than that found with a commonly used empirical prediction method. The present data showed better agreement with other sets of data. The tests of the generic STOVL configurations were conducted to provide force and pressure data with a parametric variation of parameters so that an empirical prediction method cold be developed. The effects of jet pressure ratio and temperature were found to be small. Lift improvement devices were shown to substantially reduce the net suckdown forces.

Corsiglia, Victor R.↗

NASA NTRS1991

STOVL Hot Gas Ingestion control technology

A comprehensive wind tunnel test program was conducted to evaluate control of Hot Gas Ingestion (HGI) on a 9.2 percent scale model of the McDonnell Aircraft Company model 279-3C advanced Short Takeoff and Vertical Landing (STOVL) configuration. The test was conducted in the NASA-Lewis Research Center 9 ft by 15 ft Low Speed Wind Tunnel during the summer of 1987. Initial tests defined baseline HGI levels as determined by engine face temperature rise and temperature distortion. Subsequent testing was conducted to evaluate HGI control parametrically using Lift Improvement Devices (LIDs), forward nozzle splay angle, a combination of LIDs and forward nozzle splay angle, and main inlet blocking. The results from this test program demonstrate that HGI can be effectively controlled and that HGI is not a barrier to STOVL aircraft development.

Amuedo, K. C.↗

NASA NTRS1990

Aircraft automatic flight control system with model inversion

A simulator study was conducted to verify the advantages of a Newton-Raphson model-inversion technique as a design basis for an automatic trajectory control system in an aircraft with highly nonlinear characteristics. The simulation employed a detailed mathematical model of the aerodynamic and propulsion system performance characteristics of a vertical-attitude takeoff and landing tactical aircraft. The results obtained confirm satisfactory control system performance over a large portion of the flight envelope. System response to wind gusts was satisfactory for various plausible combinations of wind magnitude and direction.

Smith, G. A.↗

NASA NTRS1992

Automatic Flight Controller With Model Inversion

Automatic digital electronic control system based on inverse-model-follower concept being developed for proposed vertical-attitude-takeoff-and-landing airplane. Inverse-model-follower control places inverse mathematical model of dynamics of controlled plant in series with control actuators of controlled plant so response of combination of model and plant to command is unity. System includes feedback to compensate for uncertainties in mathematical model and disturbances imposed from without.

Meyer, George↗

NASA NTRS1991

Aircraft Ship Operations

The interest in the use of shipborne aircraft is widespread among NATO countries. Major weapons systems like aircraft carriers with conventional fixed-wing aircraft, VSTOL aircraft or helicopters embarked, are operated by the United States, the United Kingdom, France, Italy and Spain. Nearly all NATO countries employ various classes of smaller ships as helicopter platforms for amphibious assault, anti-submarine warfare or search and rescue. The deployment of aircraft on board ships presents unusual and difficult technical and operational problems. Considering the multi-national interest in aircraft/ship operations it was considered meaningful and timely for the Flight Mechanics Panel to sponsor a symposium on this topic. This symposium considered problems of mutual interest connected with fixed and rotary wing aircraft operations from ships, and the application of new technology to enhance such operations. The Symposium reviewed and assessed the current problems and possible future progress in: - The ship environment in terms of wind, temperature, precipitation, turbulence and deck motion. - Guidance, Controls and Displays, primarily in the approach and landing phase. - Flight Test and Simulation Techniques. - Launch, Recovery and Handling Systems Developments. - Operational/Pilot Views. - Future Developments.

Aircraft carriers↗

NASA NTRS1990

Supersonic STOVL propulsion technology program: An overview

Planning activities are continuing between NASA, the DoD, and two foreign governments to develop the technology and to show the design capability by the mid-1990's for advanced, supersonic, short takeoff and vertical landing (STOVL) aircraft. Propulsion technology is the key to achieving viable STOVL aircraft, and NASA Lewis will play a lead role in the development of these required propulsion technologies. The initial research programs are focused on technologies common to two or more of the possible STOVL propulsion system concepts. An overview is presented of the NASA Lewis role in the overall program plan and recent results of the research program. The future research program will be focused on one or possibly two of the propulsion concepts seen as most likely to be successful in the post advanced tactical fighter time frame.

Blaha, Bernard J.↗

NASA NTRS1992

Aircraft ship operations

Worldwide interest in the use of shipborne aircraft as a major weapons system is very broad. Many NATO countries operate fixed wing aircraft from ships. Additionally, the use of ships as helicopter platforms is extensive in the NATO community and brings another import dimension to the aircraft/ship interface issue. Thus, it seemed that both fixed and rotary wing aviation deserved equal billing in the Aircraft/Ship Interface Symposium which is the subject of this Technical Evaluation Report. This Symposium was held in Seville, Spain, from 20th to 23rd May 1991 and was the first Symposium sponsored by the AGARD Flight Mechanics Panel devoted to this topic. The Symposium contained twenty-five presentations grouped under the following topics: Keynote Addresses; Ship Environment; Guidance, Controls, and Displays; Flight Test and Simulation Techniques; Launch, Recovery, and Handling Systems Development; and Operational Views and Future Developments. The full texts of the papers presented at this Symposium are published in AGARD-CP-509.

Aircraft carriers↗

NASA NTRS1992

Preliminary dynamic tests of a flight-type ejector

A thrust augmenting ejector was tested to provide experimental data to assist in the assessment of theoretical models to predict duct and ejector fluid-dynamic characteristics. Eleven full-scale thrust augmenting ejector tests were conducted in which a rapid increase in the ejector nozzle pressure ratio was effected through a unique facility, bypass/burst-disk subsystem. The present work examines two cases representative of the test performance window. In the first case, the primary nozzle pressure ration (NPR) increased 36 percent from one unchoked (NPR = 1.29) primary flow condition to another (NPR = 1.75) over a 0.15 second interval. The second case involves choked primary flow conditions, where a 17 percent increase in primary nozzle flowrate (from NPR = 2.35 to NPR = 2.77) occurred over approximately 0.1 seconds. Although the real-time signal measurements support qualitative remarks on ejector performance, extracting quantitative ejector dynamic response was impeded by excessive aerodynamic noise and thrust stand dynamic (resonance) characteristics. It does appear, however, that a quasi-steady performance assumption is valid for this model with primary nozzle pressure increased on the order of 50 lb(sub f)/s. Transient signal treatment of the present dataset is discussed and initial interpretations of the results are compared with theoretical predictions for a similar Short Takeoff and Vertical Landing (STOVL) ejector model.

Drummond, Colin K.↗

NASA NTRS1992

Dynamic response of induced pressures, suckdown, and temperatures for two tandem jet STOVL configurations

NASA Ames Research Center has been conducting a program to improve the methods for predicting the jet-induced lift loss (suckdown) and hot gas ingestion on jet Short Takeoff and Vertical Landing (STOVL) aircraft during hover near the ground. As part of that program, small-scale hover tests were conducted to expand the current data base and to improve upon the current empirical methods for predicting jet-induced lift loss and hot gas ingestion (HGI) effects. This report is one of three data reports covering data obtained from hover tests conducted at Lockheed Aeronautical Systems, Rye Canyon Facility. It will include dynamic (time dependent) test data for both lift loss and HGI parameters (height, nozzle temperature, nozzle pressure ratio, and inlet location). The flat plate models tested were tandem jet configurations with three planform variations and variable position side-by-side sucking inlets mounted above the planform. Temperature time lags from 8-15 seconds were observed before the model temperatures stabilize. This was larger than the expected 1.5-second lag calculated from literature. Several possible explanations for the flow temperatures to stabilize may include some, or all, of the following: thermocouple lag, radiation to the model surface, and heat loss to the ground board. Further investigations are required to understand the reasons for this temperature lag.

Wardwell, Douglas A.↗