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Roberts, L.

Publications and source records attributed to Roberts, L..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Interaction of a turbulent vortex with a lifting surface

The impulsive noise due to blade-vortex-interaction is analyzing in the time domain for the extreme case when the blade cuts through the center of the vortex core with the assumptions of no distortion of the vortex path or of the vortex core. An analytical turbulent vortex core model, described in terms of the tip aerodynamic parameters, is used and its effects on the unsteady loading and maximum acoustic pressure during the interaction are determined.

Lee, D. J.↗
NASA NTRS1985

A simplified model of the turbulent microburst

A simple model was developed to describe the low altitude shear associated with a microburst (or small downburst) in the atmosphere. Such microbursts are thought to be the cause of convective radial flows near the ground which represent potentially hazardous conditions to aircraft during approach and landing. Closed form solutions are presented for the equations of mass, momentum, and thermal energy to give the spreading rate of the microburst and the velocity and temperature decay due to turbulence. An analysis of the impact of the microburst and its radial spreading over the ground is given and illustrated examples are provided. The solution for the downward and outward wind velocities are given in terms of simple dimensionless algebraic parameters which can be computed readily in realtime during a piloted simulation of an aircraft flying through a microburst.

Roberts, L.↗
NASA NTRS1984

Viscous-inviscid aerodynamic analysis of two-dimensional thrust augmentors

A theory for the computation of two-dimensional thrust augmentor performance is developed. The flow field is assumed to be incompressible, of uniform density and statistically steady. The flow in and around the augmentor is assumed to consist of an outer, inviscid part and an inner, viscous part. The outer field is calculated analytically and then matched with the inner, viscous field, which is computed by means of integral methods. This form of analysis leads to a simple and economical approach, particularly useful for conducting parametric studies. The theoretical results are compared with recently acquired experimental data.

Tavella, D. A.↗
NASA NTRS1982

Recent progress in VSTOL technology

Progress in vertical and short takeoff and landing (V/STOL) aircraft technology, in particular, during the 1970 to 1980 period at Ames Research Center is discussed. Although only two kinds of V/STOL aircraft (the helicopter and the British direct lift Harrier) have achieved operational maturity, understanding of the technology has vastly improved during this 10 year period. To pursue an aggressive R and D program at a reasonable cost, it was decided to conduct extensive large scale testing in wind tunnel and flight simulation facilities, to develop low cost research aircraft using modified airframes or engines, and to involve other agencies and industry contractors in joint technical and funding arrangements. The STOL investigations include exploring STOL performance using the rotating cylinder flap concept, the augmentor wing, upon initiation of the Quiet Short Haul Research Aircraft program, the upper surface blown flap concept. The VTOL investigations were conducted using a tilt rotor aircraft, resulting in the XV-15 tilt rotor research aircraft. Direct jet lift is now being considered for application to future supersonic fighter aircraft.

Roberts, L.↗
NASA NTRS1981

V/STOL aircraft and fluid dynamics

The impact of military applications on rotorcraft and V/STOL aircraft design is summarized with respect to fixed-wing aircraft. The influence of the mission needs on the configurational design of V/STOL aircraft, the implications regarding some problems in fluid dynamics relating to propulsive flows, and their interaction with the aircraft and the ground plane, are also considered. Additional research in fluid dynamics that can contribute to an improvement in performance of V/STOL aircraft is suggested.

Roberts, L.↗
NASA NTRS1981

Recent progress in V/STOL aircraft technology

Recent results from wind-tunnel and flight-tests investigations for V/STOL aircraft were reviewed. Primary emphasis is given to technical results relating to three types of subsonic aircraft: a quiet STOL aircraft; a tilt rotor aircraft, and a turbofan V/STOL aircraft. Comparison and correlation between theoretical and experimental results, and between wind-tunnel and flight-test results, is made. The quiet STOL aircraft technology results are primarily those derived from the NASA/Boeing Quiet Short Haul Aircraft (QSRA) program. The tilt rotor aircraft technology results are those obtained from the NASA/Army/Navy/Bell (XV-15-TRRA) aircraft flight investigations. The turbofan V/STOL aircraft technology results are from static ground facility and wind-tunnel investigations of a NASA/Navy/Grumman full-scale lift/cruise fan aircraft model, which features two tilting nacelles with TF-34 engines.

Roberts, L.↗
NASA NTRS1981

Recent Progress in V/STOL Aircraft Technology

Results from wind tunnel and flight tests investigations for V/STOL aircraft are reviewed. Primary emphasis is given to technical results relating to three types of subsonic aircraft: a quiet STOL aircraft; a tilt rotor aircraft; and a turbofan V/STOL aircraft. Comparison and correlation between theoretical and experimental results and between wind tunnel and flight test results, is made. The quiet STOL aircraft technology results are primarily those derived from the NASA/Boeing Quiet Short Haul Technology (QSRA) program. The QSRA aircraft uses an upper surface blown flap and develops a usable engine-out landing approach lift coefficient of 5.5 and landing distances less than 1,000 ft. The tilt rotor aircraft technology results are those obtained from the NASA/Army/Navy/Bell (XV-15-TRRA) aircraft flight investigations. The TRRA is a twin rotor research aircraft capable of vertical takeoff and landing and cruise speeds of 300 knots. The turbofan V/STOL aircraft technology results are from static ground facility and wind tunnel investigations of a NASA/NAVY/Grumman full scale lift/cruise fan aircraft model, which features two tilting nacelles with TF-34 engines.

Roberts, L.↗
NASA NTRS1980

An acceptable role for computers in the aircraft design process

Some of the reasons why the computerization trend is not wholly accepted are explored for two typical cases: computer use in the technical specialties and computer use in aircraft synthesis. The factors that limit acceptance are traced in part, to the large resources needed to understand the details of computer programs, the inability to include measured data as input to many of the theoretical programs, and the presentation of final results without supporting intermediate answers. Other factors are due solely to technical issues such as limited detail in aircraft synthesis and major simplifying assumptions in the technical specialties. These factors and others can be influenced by the technical specialist and aircraft designer. Some of these factors may become less significant as the computerization process evolves, but some issues, such as understanding large integrated systems, may remain issues in the future. Suggestions for improved acceptance include publishing computer programs so that they may be reviewed, edited, and read. Other mechanisms include extensive modularization of programs and ways to include measured information as part of the input to theoretical approaches.

Gregory, T. J.↗
NASA NTRS1978

Recent progress in rotorcraft and powered-lift research

The paper reviews some of the recent technological developments in the United States in the field of rotorcraft and powered-lift research, with primary emphasis on the compound helicopter and the augmentor thrust approaches to vertical flight. The last several years have seen significant developments in the state of the art through the combined use of wind tunnels, simulators, and research aircraft. The results of several representative studies are discussed to demonstrate the improvements that have been made in several of the important vehicle-related parameters. The prospect for further advances is also discussed.

Roberts, L.↗
NASA NTRS1977

Toward a new V/STOL generation

While many V/STOL problems are now better understood and technology has progressed to the point where higher thrust/weight ratios and greater stability augmentation are achievable, a number of still existing insufficiencies provide a sobering reminder that learning in ground testing and simulation, and careful methodical planning, are a prerequisite for any research and development program. The present paper is centered on the major technical problems for the Navy Type multimission V/STOL aircraft. The aircraft's configurations with and without forward lift fan are discussed, along with the propulsion systems, testing techniques, controls, displays, flight dynamics, and ground/flow field interactions.

Roberts, L.↗
NASA NTRS1977

Directions in civil aviation 1980-2000

The following future directions in civil aviation are considered: (1) greater economy and efficiency in passenger and cargo air service at subsonic speeds, and improved utility and safety for general aviation, (2) greatly improved short haul air transportation using turbofan or turboprop aircraft, and subsequently, rotorcraft and V/STOL aircraft, and (3) supersonic, and ultimately hypersonic, air transportation for transoceanic long range flight. Attention is also given to new directions in research and technology.

Roberts, L.↗
NASA NTRS1977

The technical challenge of air transportation - A Government view

This paper reviews the research and technology that must be conducted, and the facility investments that must be made, in order to assure that the United States is adequately prepared to meet the challenges that air transportation will provide in the future. The technical focal points for the next decade are reviewed in the context of the emerging pattern of air transportation needs for the remainder of the Century and the prospects for satisfying these needs are discussed. Particular attention is given to the responsibility that the Government must assume in aviation R&T and to the relationship that must be encouraged between the Government, the Industry and the University Community.

Roberts, L.↗
NASA NTRS1976

Technology outlook for aviation

Growth projections for aviation technology are put forth for a quarter-century ahead. Three main trends envisaged are towards: great efficiency and economy and longer range and endurance for subsonic aircraft; new generations of short-range fixed-wing craft and rotorcraft with versatile applicability; supersonic and hypersonic speeds. Improvements in lift/drag ratio, specific fuel consumption, structural weight factor, aerodynamic improvements (laminar flow control, increased wing aspect ratio, drag reduction for specified lift, propulsion efficiency, higher bypass ratios, composite structures) are discussed along with V/STOL, controllable twist rotors, circulation control rotors, variable-cycle engines, and higher structural efficiencies.

Roberts, L.↗
NASA NTRS1976

Persistence and decay of wake vorticity

Some recent research relating to the nature of the lift-induced vortex wakes behind large aircraft was reviewed and the scaling laws that permit a comparison of results from ground facilities with those from flight test were provided. The maximum rotational velocities in the wake are shown to depend on a span loading shape parameter and on a characteristic length of persistence behind the aircraft. The effects of Reynolds number are also shown.

Roberts, L.↗
NASA NTRS1976

Directions in civil aviation 1980-2000

This paper attempts to summarize the future directions and opportunities in aeronautics, and to characterize the research and technology that should be conducted in the next decade in order to permit the timely development of civil aviation for the remainder of the Twentieth Century. The paper is based on a recent study undertaken by NASA, entitled The Outlook for Aeronautics.

Roberts, L.↗
NASA NTRS1975

On wake vortex alleviation

Research within NASA relating to the nature of lift-induced vortex wakes behind large aircraft and the means whereby the hazard they represent to smaller aircraft can be alleviated is reviewed. The research, carried out in ground based facilities and in flight shows that more rapid dispersion of the wake can be effected by several means and that the modification of span-loading by appropriate flap deflection holds promise of early practical application.

Roberts, L.↗
NASA NTRS1975

Curriculum for modern aeronautics

Methods for improving the university training of aeronautical engineering students are discussed. Specific topics considered are: (1) the kind of students which should be developed through aeronautical engineering education, (2) to what extent should aerospace engineering be prepared for diversity and change, (3) to what extent should theory be emphasized as compared with practical engineering and design, and (4) a suggestion for NASA/Industry/University collaboration.

Roberts, L.↗