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At least 613 records · Page 34

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Aspect system for HEAO-B

The aspect system for the HEAO-B Observatory provides the necessary absolute referencing of the Observatory coordinates to the celestial sphere with a precision of one arc second. In addition, it provides realtime data to the Spacecraft to permit pointing of the Observatory to one arc minute. The system is composed of three star trackers with associated shades, a pair of bright object detectors and a fiducial light system for referencing the experiment X-ray axis to the star tracker axes.

Koch, D.↗

NASA NTRS1978

Additional aspects of elastohydrodynamic lubrication

Elastohydrodynamic lubrication (EHL) for materials of low elastic modulus is considered. Engineering applications in which EHL is important for low-elastic-modulus materials include seals, human joints, tires, and elastomeric-material machine elements. Theoretical solutions of the problem of fully flooded line contacts in the case of low-elastic-materials are discussed. The equation regarding dimensionless minimum film thickness for fully flooded elliptical contacts for low elastic modulus is compared with the corresponding equation for materials of high elastic modulus. The powers of the dimensionless speed parameter U are quite similar in both equations, but the power of the dimensionless load parameter W is much more significant for low-elastic-modulus materials. Attention is given to aspects of dimensionless grouping, the isoviscous rigid regime, the viscous rigid regime, the isoviscous elastic regime, and the viscous elastic regime.

Hamrock, B. J.↗

NASA NTRS1978

Properties of aspect-ratio-4.0 rectangular jets in a subsonic crossflow

A series of wind-tunnel and laboratory tests were conducted at the NASA Langley V/STOL tunnel facility to determine both the detailed structure and the induced effects of aspect-ratio-4.0 rectangular jets both in a subsonic crosswind and in quiescent conditions. Wind-tunnel tests were conducted on both blunt (nozzle major axis normal to free stream) and streamwise (nozzle major axis parallel to free stream) nozzle orientations for jet injection angles ranging from 15 to 90 degrees at jet-to-crossflow velocity ratios of 4, 8, and 10. Results indicate that the blunt nozzle induced effects are more significant than those produced by comparable streamwise-oriented jets and that both the flow-field structure and induced effects of streamwise-oriented rectangular jets are quite similar to those created by round jets. Additionally, it is shown that significant differences exist in the vortex flow fields generated by the same rectangular nozzle mounted in two different test hardware configurations.

Thames, F. C.↗

NASA NTRS1978

Performance of single-stage axial-flow transonic compressor with rotor and stator aspect ratios of 1.19 and 1.26, respectively, and with design pressure ratio of 1.82

The overall and blade-element performance of a low-aspect-ratio transonic compressor stage is presented over the stable operating flow range at 70, 90, and 100 percent design speeds. At design speed the rotor and stage achieved peak efficiencies of 0.872 and 0.845 at pressure ratios of 1.875 and 1.842, respectively. The stage stall margin at design speed was 21.8 percent.

Reid, L.↗

NASA NTRS1979

Materials and structural aspects of advanced gas-turbine helicopter engines

The key to improved helicopter gas turbine engine performance lies in the development of advanced materials and advanced structural and design concepts. The modification of the low temperature components of helicopter engines (such as the inlet particle separator), the introduction of composites for use in the engine front frame, the development of advanced materials with increased use-temperature capability for the engine hot section, can result in improved performance and/or decreased engine maintenance cost. A major emphasis in helicopter engine design is the ability to design to meet a required lifetime. This, in turn, requires that the interrelated aspects of higher operating temperatures and pressures, cooling concepts, and environmental protection schemes be integrated into component design. The major material advances, coatings, and design life-prediction techniques pertinent to helicopter engines are reviewed; the current state-of-the-art is identified; and when appropriate, progress, problems, and future directions are assessed.

Freche, J. C.↗

NASA NTRS1979

Study of blade aspect ratio on a compressor front stage aerodynamic and mechanical design report

A single stage compressor was designed with the intent of demonstrating that, for a tip speed and hub-tip ratio typical of an advanced core compressor front stage, the use of low aspect ratio can permit high levels of blade loading to be achieved at an acceptable level of efficiency. The design pressure ratio is 1.8 at an adiabatic efficiency of 88.5 percent. Both rotor and stator have multiple-circular-arc airfoil sections. Variable IGV and stator vanes permit low speed matching adjustments. The design incorporates an inlet duct representative of an engine transition duct between fan and high pressure compressor.

Burger, G. D.↗

NASA NTRS1979

Meteorological and operational aspects of 46 clear air turbulence sampling missions with an instrument B-57B aircraft. Volume 1: Program summary

The results of 46 clear air turbulence (CAT) probing missions conducted with an extensively instrumented B-57B aircraft are summarized. Turbulence samples were obtained under diverse conditions including mountain waves, jet streams, upper level fronts and troughs, and low altitude mechanical and thermal turbulence. CAT was encouraged on 20 flights comprising 77 data runs. In all, approximately 4335 km were flown in light turbulence, 1415 km in moderate turbulence, and 255 km in severe turbulence during the program. The flight planning, operations, and turbulence forecasting aspects conducted with the B-57B aircraft are presented.

Davis, R. E.↗

NASA NTRS1979

Influence of optimized leading-edge deflection and geometric anhedral on the low-speed aerodynamic characteristics of a low-aspect-ratio highly swept arrow-wing configuration

An investigation conducted in the Langley 7 by 10 foot tunnel to determine the influence of an optimized leading-edge deflection on the low speed aerodynamic performance of a configuration with a low aspect ratio, highly swept wing. The sensitivity of the lateral stability derivative to geometric anhedral was also studied. The optimized leading edge deflection was developed by aligning the leading edge with the incoming flow along the entire span. Owing to spanwise variation of unwash, the resulting optimized leading edge was a smooth, continuously warped surface for which the deflection varied from 16 deg at the side of body to 50 deg at the wing tip. For the particular configuration studied, levels of leading-edge suction on the order of 90 percent were achieved. The results of tests conducted to determine the sensitivity of the lateral stability derivative to geometric anhedral indicate values which are in reasonable agreement with estimates provided by simple vortex-lattice theories.

Coe, P. L., Jr.↗

NASA NTRS1979

Performance of two-stage fan having low-aspect-ratio first-stage rotor blading

The NASA two stage fan was tested with a low aspect ratio first stage rotor having no midspan dampers. At design speed the fan achieved an adiabatic design efficiency of 0.846, and peak efficiencies for the first stage and rotor of 0.870 and 0.906, respectively. Peak efficiency occurred very close to the stall line. In an attempt to improve stall margin, the fan was retested with circumferentially grooved casing treatment and with a series of stator blade resets. Results showed no improvement in stall margin with casing treatment but increased to 8 percent with stator blade reset.

Urasek, D. C.↗

NASA NTRS1979

Study of the feasibility aspects of flight testing an aeroelastically tailored forward swept research wing on a BQM-34F drone vehicle

The aspects of flight testing an aeroelastically tailored forward swept research wing on a BQM-34F drone vehicle are examined. The geometry of a forward swept wing, which is incorporated into the BQM-34F to maintain satisfactory flight performance, stability, and control is defined. A preliminary design of the aeroelastically tailored forward swept wing is presented.

Mourey, D. J.↗

NASA NTRS1980

Performance of single-stage axial-flow transonic compressor with rotor and stator aspect ratios of 1.19 and 1.26 respectively, and with design pressure ratio of 2.05

The overall and blade-element performances of a low-aspect-ratio transonic compressor stage are presented over the stable operating flow range for speeds from 50 to 100 percent of design. At design speed the rotor and stage achieved peak efficiencies of 0.876 and 0.840 at pressure ratios of 2.056 and 2.000, respectively. The stage stall margin at design speed was 10 percent.

Moore, R. D.↗

NASA NTRS1980

Simulation of electromagnetic aspects of lightning

Electromagnetic processes peculiar to the direct-strike case are reviewed with respect to their implications for lightning electromagnetic simulation. At low frequencies (quasistatic) there are important surface-charge-density and corona effects in addition to the surface-current-density effects. At resonant frequencies the frequency-spectral content of the excitation and properties of the arc (attachment, detachment, time history, spatial distribution, resistance, etc.) are significant. Of great complexity in all this are nonlinear aspects of the arc and corona around the system of interest. The complexity of these various processes requires rigor in the simulator design. Potential simulation concepts are presented and their relative merits are discussed.

Baum, C. E.↗

NASA NTRS1980

Study of blade aspect ratio on a compressor front stage

A single stage, low aspect ratio, compressor with a 442.0 m/sec (1450 ft/sec) tip speed and a 0.597 hub/tip ratio typical of an advanced core compressor front stage was tested. The test stage incorporated an inlet duct which was representative of an engine transition duct between fan and high pressure compressors. At design speed, the rotor stator stage achieved a peak adiabatic efficiency of 86.6 percent at a flow of 44.35 kg/sec (97.8 lbm/sec) and a pressure ratio of 1.8. Surge margin was 12.5 percent from the peak stage efficiency point.

Behlke, R. F.↗

NASA NTRS1978

A computer program for calculating aerodynamic characteristics of low aspect-ratio wings with partial leading-edge separation

The necessary information for using a computer program to predict distributed and total aerodynamic characteristics for low aspect ratio wings with partial leading-edge separation is presented. The flow is assumed to be steady and inviscid. The wing boundary condition is formulated by the Quasi-Vortex-Lattice method. The leading edge separated vortices are represented by discrete free vortex elements which are aligned with the local velocity vector at midpoints to satisfy the force free condition. The wake behind the trailing edge is also force free. The flow tangency boundary condition is satisfied on the wing, including the leading and trailing edges. The program is restricted to delta wings with zero thickness and no camber. It is written in FORTRAN language and runs on CDC 6600 computer.

Mehrotra, S. C.↗

NASA NTRS1980

Some problems of human adaptation and ecology under the aspect of general pathology

The main problems of human adaptation at the level of the body and the population in connection with the features of current morbidity of the population and certain demographic processes are analyzed. The concepts of health and adaptation of the individual and human populations are determined. The importance of the anthropo-ecological approach to the investigation of the adaptation process of human populations is demonstrated. Certain features of the etiopathogenesis of diseases are considered in connection with the population-ecological regularities of human adaptation. The importance of research on general pathology aspects of adaptation and the ecology of man for planning, and organization of public health protection is discussed.

Kaznacheyev, V. P.↗

NASA NTRS1980

Statistical aspects of carbon fiber risk assessment modeling

The probabilistic and statistical aspects of the carbon fiber risk assessment modeling of fire accidents involving commercial aircraft are examined. Three major sources of uncertainty in the modeling effort are identified. These are: (1) imprecise knowledge in establishing the model; (2) parameter estimation; and (3)Monte Carlo sampling error. All three sources of uncertainty are treated and statistical procedures are utilized and/or developed to control them wherever possible.

Gross, D.↗

NASA NTRS1979

Some aspects of stratospheric chemical response to solar particle precipitations. I - Potential roles of N2/A3Sigma/ and ion-chemistry

Large amounts of long lived N2(A3Sigma) are created by the energy degradation of precipitating solar particles. Laboratory data suggest that in the stratosphere N2(A3Sigma) are efficiently converted into N2O. Through reactions with O(1D), N2O may gradually release NO and thereby influence the long term aspects of stratospheric chemical response. During the daytime, negative ions may transform an active NO(x) into an inactive HNO3. At night both negative and positive ion chemistry generate HO(x). Omission of ionic chemistry results in considerable underestimation of O3 depletion during the initial phases of solar particle events, and thereby introduces significant error in the estimation of the nature of the prompt response.

Prasad, S. S.↗

NASA NTRS1979

Operational aspects of satellite data collection systems

Operational aspects of satellite data collection systems (DCS) are discussed with consideration given to a cooperative program between the United States and France. The Tiros-N DCS is described which is a random access system providing operational capability for position location and/or data collection of 4000 to 16,000 moving and/or fixed platforms. The platform transmissions and processing of the data is designed to conform with the user needs. The position location is obtained through ground processing of Doppler measurements made by the data collection instrument on board the spacecraft.

Morakis, J. C.↗