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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Free-jet feasibility study of a thermal acoustic shield concept for AST/VCE application-dual stream nozzles. Comprehensive data report. Volume 2: Laser velocimeter and suppressor. Base pressure data

Acoustic and diagnostic data that were obtained to determine the influence of selected geometric and aerodynamic flow variables of coannular nozzles with thermal acoustic shields are summarized in this comprehensive data report. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale-model nozzles. Aerodynamic laser velocimeter measurements were made for four selected plumes. In addition, static pressure data in the chute base region of the suppressor configurations were obtained to assess the influence of the shield stream on the suppressor base drag.

Janardan, B. A.↗
NASA NTRS1986

Modifications to the 4x7 meter tunnel for acoustic research: Engineering feasibility study

The NASA-Langley Research Center 4 x 7 Meter Low Speed Wind Tunnel is currently being used for low speed aerodynamics, V/STOL aerodynamics and, to a limited extent, rotorcraft noise research. The deficiencies of this wind tunnel for both aerodynamics and aeroacoustics research have been recognized for some time. Modifications to the wind tunnel are being made to improve the test section flow quality and to update the model cart systems. A further modification of the 4 x 7 Meter Wind Tunnel to permit rotorcraft model acoustics research has been proposed. As a precursor to the design of the proposed modifications, NASA is conducted both in-house and contracted studies to define the acoustic environment within the wind tunnel and to provide recommendations or the reduction of the wind tunnel background noise to a level acceptable to acoustics researchers. One of these studies by an acoustics consultant, has produced the primary reference documents that define the wind tunnel noise sources and outline recommended solutions.

Source record↗
NASA NTRS1986

Feasibility study of optical boundary layer transition detection method

A high sensitivity differential interferometer was developed to locate the region where the boundary layer flow undergoes transition from laminar to turbulent. Two laboratory experimental configurations were used to evaluate the performance of the interferometer: open shear layer, and low speed wind tunnel turbulent spot configuration. In each experiment, small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements were compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of 0.001 the laser wavelength. An attempt to detect boundary layer transition over a flat plate at NASA-Langley Unitary Supersonic Wind Tunnel using the interferometer system was performed. The phase variations during boundary layer transition in the supersonic wind tunnel were beyond the minimum signal-to-noise level of the instrument.

Azzazy, M.↗
NASA NTRS1986

Feasibility of generating an artificial burst in a turbulent boundary layer

Artificial bursts were generated in laminar and turbulent boundary layers. The burst-like events were produced by withdrawing near-wall fluid from two minute holes separated in the spanwise direction or by pitching a miniature delta wing that was flush-mounted to the wall. Either of these actions generated streamwise vorticity and a low-speed streak that resembled a naturally occurring one. The resulting sequence of events occurred at a given location and at controlled times, allowing detailed examination and comparison with natural, random bursts by means of flow visualization and fast-response probe measurement techniques.

Gad-El-hak, M.↗
NASA NTRS1985

Feasibility study for ergonomic analysis and design of future helicopter cockpit systems

The Army's light scout-attack helicopters (LHXs), planned for deployment in the 1990's, will fly nap-of-the-earth (NOE) missions in high threat environments, often under poor visibility and adverse atmospheric conditions, and probably with a one man crew. A procedure for the analysis of pilot workload that will identify and explicate the main characteristics of those LHX mission components holding overload potential is described. A principled, in-depth, explication of the cognitive demans of LHX piloting is essential to any effective effort to address the human factors issues. A task-analytic procedure that will yield the detail and organizstion needed to achieve these goals is examined.

Hawkins, H. L.↗
NASA NTRS1986

Feasibility experiments on time-resolved fluorosensing applied to oil slicks

The introduction of time resolved observations can provide a very penetrating tool in the practice of laser fluorosensing. The investigations have demonstrated a relevance of multispectral, time resolved analysis for oil fingerprinting. By comparative studies on a variety of crude oils and their most significant fractions, it was found that the process of time decay in a composite oil is characterized by a few steps, which are associated with specific components in the medium light range. The average decay times of these pure fractions are markedly differentiated as to absolute values and spectral spread; as a consequence, the corresponding parameters in the resultant crude are quite sensitive to the particular mixture of these components. Measurements of the time response give then a finer discrimination between oil classes, depending on the relative content of certain fractions. Experiments were pursued with an improved fluorosensor facility, in order to test the application of time resolved fluorosensing to remote samples on water.

Camagni, P.↗
NASA NTRS1985

Free jet feasibility study of a thermal acoustic shield concept for AST/VCE application: Dual stream nozzles

The influence of selected geometric and aerodynamic flow variables of an unsuppressed coannular plug nozzle and a coannular plug nozzle with a 20-chute outer stream suppressor were experimentally determined. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale model nozzles. Also, aerodynamic measurements of four selected plumes were made with a laser velocimeter. The presence of the 180 deg shield produced different mixing characteristics on the shield side compared to the unshield side because of the reduced mixing with ambient air on the shielded side. This resulted in a stretching of the jet, yielding a higher peak mean velocity up to a length of 10 equivalent diameters from the nozzle exit. The 180 deg shield in community orientation around the suppressed coannular plug nozzle yielded acoustic benefit at all observer angles for a simulated takeoff. While the effect of shield-to-outer stream velocity ratio was small at angles up to 120 deg, beyond this angle significant acoustic benefit was realized with a shield-to-outer stream velocity ratio of 0.64.

Janardan, B. A.↗
NASA NTRS1986

Feasibility analysis of reciprocating magnetic heat pumps

The conceptual design selected for detailed system analysis and optimization is the reciprocating gadolinium core in a regenerative fluid column within the bore of a superconducting magnet. The thermodynamic properties of gadolinium are given. A computerized literature search for relevant papers was conducted and is being analyzed. Contact was made with suppliers of superconducting magnets and accessories, magnetic materials, and various types of hardware. A description of the model for the thermal analysis of the core and regenerator fluids is included.

Larson, A. V.↗
NASA NTRS1985

Optimal cure cycle design for autoclave processing of thick composites laminates: A feasibility study

The thermal analysis and the calculation of thermal sensitivity of a cure cycle in autoclave processing of thick composite laminates were studied. A finite element program for the thermal analysis and design derivatives calculation for temperature distribution and the degree of cure was developed and verified. It was found that the direct differentiation was the best approach for the thermal design sensitivity analysis. In addition, the approach of the direct differentiation provided time histories of design derivatives which are of great value to the cure cycle designers. The approach of direct differentiation is to be used for further study, i.e., the optimal cycle design.

Hou, Jean W.↗
NASA NTRS1986

Feasibility assessment of the Get-Away Tether Experiment

The small free-flying tether system deployable from a Get-Away Special canister is analyzed. The objectives of the GAS experiment which include demonstrating electric power generation and orbital reboost using electrodynamic technology, measuring micrometeoroid hazards to the tethers, conducting a radio propagation experiment, and measuring long wire radar-cross-section are discussed. The physical layout and components of the mother and daughter satellites are described. The command and control system of the tether system is examined. The electrodynamic experiments to be conducted after plasma contact is established and the electrodynamical capabilities of the system are considered.

Greene, M.↗
NASA NTRS1986

Folding tilt rotor demonstrator feasibility study

This study considers the modification of existing aircraft to the folding tilt rotor (FTR) design configuration, and then addresses the vehicle design requirements necessary to demonstrate the FTR concept throughout the hover/transition high-speed envelope. Three potential candidates are considered: (1) the Bell/Boeing V-22 Osprey combined with either the existing TF-34 convertible engine or a conceptual convertible engine utilizing the torque-converter-coupled fan configuration; (2) a combination of the same powerplants with a modified Lockheed S-3A Viking; and (3) the NASA/Army/BELL XV-15 airframe mated with a conceptual generic turbofan engine with a fixed-pitch fan coupled to the engine by means of a torque converter. Required aircraft modifications are identified and recommended R&D efforts for engine/rotor/airframe integration are presented.

Eisenberg, J. D.↗
NASA NTRS1987

Feasibility of observations of stratospheric trace gases using the Hubble Space Telescope

The stellar occultation method has been successfully used in the past from orbiting observatories to measure concentrations of certain trace gases in the earth's mesosphere. The greatly improved spectroscopic capabilities of the Hubble Space Telescope (HST) have prompted recent suggestions for its use to measure stratospheric C10. This possibility is examined along with that for other species relevant to the chemistry of the ozone layer. It is concluded that stratospheric (as opposed to mesospheric) observations with HST are not practical, in part because of its orbital and pointing characteristics, but primarily because the high opacity of stratospheric ozone over most of the bandpass of the HST's most suitable spectrometer will obscure observation of other trace species, such as C10, having mixing ratios of less than 0.001.

Jaramillo, M.↗
NASA NTRS1985

In-flight measurement of rotor hub drag using the RSRA - A feasibility demonstration

The Rotor Systems Research Aircraft (RSRA) is a compound helicopter that was test flown as a fixed-wing aircraft, with the main rotor blades removed and the rotor hub installed. An onboard rotor load-measurement system measured the resulting rotor hub drag and lift. Measured hub drag and lift are plotted for comparison to that predicted by full-scale and 1/6-scale model wind-tunnel tests. The success of the demonstration gives confidence that planned improvements to the RSRA will allow high-accuracy hub drag and lift measurements to be made in flight on a routine research basis.

Acree, C. W., Jr.↗
NASA NTRS1987

Repulsive force support system feasibility study

A new concept in magnetic levitation and control is introduced for levitation above a plane. A set of five vertical solenoid magnets mounted flush below the plane supports and controls the model in five degrees of freedom. The compact system of levitation coils is contained in a space 2.4 m (96 in) diameter by 1 m (40 in) deep with the top of the levitation system 0.9 m (36 in) below the center line of the suspended model. The levitated model has a permanent magnet core held in position by the five parallel superconductive solenoids symmetrically located in a circle. The control and positioning system continuously corrects for model position in five dimensions using computer current pulses superimposed on the levitation coil base currents. The conceptual designs include: superconductive and Nd-Fe-B permanent magnet model cores and levitation solenoids of either superconductive, cryoresistive, or room temperature windings.

Boom, R. W.↗
NASA NTRS1987

Investigation of the feasibility of an analytical method of accounting for the effects of atmospheric drag on satellite motion

An analytic technique for accounting for the joint effects of Earth oblateness and atmospheric drag on close-Earth satellites is investigated. The technique is analytic in the sense that explicit solutions to the Lagrange planetary equations are given; consequently, no numerical integrations are required in the solution process. The atmospheric density in the technique described is represented by a rotating spherical exponential model with superposed effects of the oblate atmosphere and the diurnal variations. A computer program implementing the process is discussed and sample output is compared with output from program NSEP (Numerical Satellite Ephemeris Program). NSEP uses a numerical integration technique to account for atmospheric drag effects.

Bozeman, Robert E.↗
NASA NTRS1988

Feasibility studies of the growth of 3-5 compounds of boron by MOCVD

Boron-arsenic and boron-phosphorus films have been grown on Si sapphire and silicon-on-sapphire (SOS) by pyrolyzing Group 3 alkyls of boron, i.e., trimethylborane (TMB) and triethylborane (TEB), in the presence of AsH3 and PH3, respectively, in an H2 atmosphere. No evidence for reaction between the alkyls and the hydrides on mixing at room temperature was found. However, the films were predominantly amorphous. The film growth rate was found to depend on the concentration of alkyl boron compound and was essentially constant when TEB and AsH3 were pyrolyzed over the temperature range 550 C to 900 C. The films were found to contain mainly carbon impurities (the amount varying with growth temperature), some oxygen, and were highly stressed and bowed on Si substrates, with some crazing evident in thin (2 micron) B-P and thick (5 micron) B-As films. The carbon level was generally higher in films grown using TEB as the boron source. Films grown from PH3 and TMB showed a higher carbon content than those grown from AsH3 and TMB. Based on their B/As and B/P ratios, films with nominal compositions B sub12-16 As2 and B sub1.1-1.3 P were grown using TMB as the boron source.

Manasevit, H. M.↗
NASA NTRS1987

The space station assembly phase: Flight telerobotic servicer feasibility, volume 1

The question is addressed which was raised by the Critical Evaluation Task Force (CETF) analysis of the space station: if a Flight Telerobotic Servicer (FTS) of a given technical risk could be built for use during space station assembly, could it save significant extravehicular (EVA) resources. Key issues and trade-offs associated with using an FTS to aid in space station assembly phase tasks such as construction and servicing are identified. A methodology is presented that incorporates assessment of candidate assembly phase tasks, telerobotics performance capabilities, development costs, operational constraints (STS and proximity operations), maintenance, attached payloads, and polar platforms. A discussion of the issues is presented with focus on potential FTS roles: (1) as a research-oriented test bed to learn more about space usage of telerobotics; (2) as a research-based test bed with an experimental demonstration orientation and limited assembly and servicing applications; or (3) as an operational system to augment EVA, to aid the construction of the space station, and to reduce the programmatic (schedule) risk by increasing the flexibility of mission operations. During the course of the study, the baseline configuration was modified into Phase 1 (a station assembled in 12 flights), and Phase 2 (a station assembled over a 30 flight period) configuration.

Smith, Jeffrey H.↗