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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Some diurnal properties of clouds over the Martian volcanoes

The diurnal properties of cloud systems over Martian volcanoes observed by the Viking Orbiter spacecraft are discussed. Photographic sequences of diurnal cloud development are presented for clouds in the vicinity of Elysium Mons and Ascraeus Mons, and the rapid growth of cloudiness starting at 11.23 LT is noted. The low-lying fogs and convective afternoon clouds observed are characterized as water ice clouds, while the cirrus-type clouds may be composed of CO2. The diurnal development of the clouds is then explained in terms of local atmospheric stability and circulation as influenced by surface topography and thermal properties. Consideration is also given to possible reasons for the pronounced seasonal variations in cloudiness.

Hunt, G. E.↗
NASA NTRS1980

Top inlet system feasibility for transonic-supersonic fighter aircraft applications

Top inlet flow field and inlet performance data are presented which provide preliminary insight into the feasibility of upper-fuselage mounted inlet systems for transonic-supersonic fighter aircraft. Presented data span the Mach 0.2 to 2.0 envelope and enable evaluation of the influence of key aircraft configuration variables - inlet location, wing position, wing leading-edge extension (LEX) planform area, and variable incidence canards - on top inlet performance. The viability of this concept relative to more conventional inlet/airframe integrations is assessed via comparative evaluation of top and conventional inlet flow field parameters at transonic and supersonic speeds. It is shown that the action of the wing LEX vortex system produces a significant improvement in top inlet performance. Currently available transonic-supersonic data indicate that top inlet systems pose a viable configuration option for fighter aircraft requiring moderate angle of attack capability. However, recently acquired data indicate that increased angle of attack capability may be obtained by increasing wing leading-edge sweep angle.

Williams, T. L.↗
NASA NTRS1980

Scattering and absorption properties of CO2 ice spheres in the region 360-4000 kaysers

The results of Mie calculations for CO2 ice particles of radius a = 0.1, 1 and 10 microns in the region 360-4000 kaysers are presented. Since CO2 possesses a very small imaginary refractive index, the larger particles behave as conservative scatters. This is quite different from the equivalent water ice particles. The results presented in this study will be useful for investigation of the Martian atmosphere and surface.

Hunt, G. E.↗
NASA NTRS1979

Progress on the Dow Corning process for solar-grade silicon

The Dow Corning approach to increasing the resistivity of solar-grade silicon from about 0.04 ohm-cm (40 ppma B) to greater than 0.1 ohm-cm (10 ppma B) involves the use of high-purity raw materials carbothermically reduced in a specially designed electric arc furnace. Final purification occurs during Czochralski crystal growth of a polycrystalline ingot. This small-scale purification technology has resulted in silicon that has been fabricated into solar cells with a maximum AM1 conversion efficiency of 13.4%.

Hunt, L. P.↗
NASA NTRS1979

Solar silicon via the Dow Corning process

Technical feasibility for high volume production of solar cell-grade silicon is investigated. The process consists of producing silicon from pure raw materials via the carbothermic reduction of quartz. This silicon was then purified to solar grade by impurity segregation during Czochralski crystal growth. Commercially available raw materials were used to produce 100 kg quantities of silicon during 60 hour periods in a direct arc reactor. This silicon produced single crystalline ingot, during a second Czochralski pull, that was fabricated into solar cells having efficiencies ranging from 8.2 percent to greater than 14 percent. An energy analysis of the entire process indicated a 5 month payback time.

Hunt, L. P.↗
NASA NTRS1980

Aerothermal environment in chordwise gaps between split elevons at Mach 6.8

A large scale model representing a wing elevon junction on a shuttle-type entry vehicle was aerothermally tested in the Langley 8 foot high temperature structures tunnel with a turbulent boundary layer on the wing and elevon. The flow pattern between elevons was studied, and the pressure and heat load were determined within the chordwise gaps formed by adjacent elevons and by the stub fairing which separates the elevons. Model angle, elevon deflection angle, and gap widths were varied. Heating in the gaps was generally proportional to windward surface heating and inversely proportional to gap width. Maximum heating between the elevon and stub was 36 percent of the windward wing surface for a 0.18 cm wide elevon stub gas, and maximum heating between elevons was 30 percent of the heating on the windward elevon surfaces for a 7.7 cm wide elevon gap.

Hunt, L. R.↗
NASA NTRS1980

Variable stream control engine for advanced supersonic aircraft design update

The updating of the engine concept for a second-generation supersonic transport, the variable stream control engine (VSCE), in terms of mechanical design definition and estimated performance is discussed. The design definition reflects technology advancements that improve system efficiency, durability and environments were established. The components unique to the VSCE concept, a high performance duct burner and a low noise coannular nozzle, and the high temperature components are identified as critical technologies. Technology advances for the high temperature components (main combustor and turbines) are also discussed. To address the requirements in this area, the technical approach for undertaking a high temperature validation program is defined. The multi-phased effort would include assorted rig and laboratory tests, then culminate with the demonstration of a flight-type main combustor and single-stage high pressure turbine at operating conditions envisioned for a VSCE.

Hunt, R. B.↗
NASA NTRS1981

Top-mounted inlet system feasibility for transonic-supersonic fighter aircraft

The more salient findings are presented of recent top inlet performance evaluations aimed at assessing the feasibility of top-mounted inlet systems for transonic-supersonic fighter aircraft applications. Top inlet flow field and engine-inlet performance test data show the influence of key aircraft configuration variables-inlet longitudinal position, wing leading-edge extension planform area, canopy-dorsal integration, and variable incidence canards-on top inlet performance over the Mach range of 0.6 to 2.0. Top inlet performance data are compared with those or more conventional inlet/airframe integrations in an effort to assess the viability of top-mounted inlet systems relative to conventional inlet installations.

Williams, T. L.↗
NASA NTRS1980

Thermal structure and dynamics of the Jovian atmosphere. 2: Visible cloud features

Voyager IRIS data reveal strong similarities among a broad range of features which differ considerably in visual appearance. The atmosphere above anticyclonic features, including the major white ovals, the Great Red Spot, and a zone, are cold relative to the immediate surroundings in the upper troposphere and tropopause region. These results are consistent with upwelling and divergence in this part of the atmosphere. A hot spot and a barge, which are localized cyclonic features, are found to be warm relative to their surroundings, implying subsidence with accompanying convergence. In all cases, the thermal wind shear associated with the features indicates a decay of the vorticity with height in the upper troposphere and lower stratosphere. Vertical velocities inferred from the observed temperature perturbations imply an upper limit of vertical mixing times near the tropopause of approximately 20 years. Temperatures in the upper stratosphere above the anticyclonic features show considerable variation, but in most cases are found to be relatively warm.

Conrath, B. J.↗
NASA NTRS1980

First Voyager view of the rings of Saturn

Voyager 1 imaging data of the Saturn rings, taken at a resolution of 1000 km/line pair between September 3 and October 13, 1980 are discussed. It is pointed out that as the spacecraft approached Saturn, finer radial structure in the rings between and within the major divisions became apparent, together with extensive azimuthal structure in the B ring. It is shown that the fine structure observed in the rings cannot, for the most part, be attributed to classical resonances with the known inner satellites. Preliminary model calculations of ring brightness based on photometry data indicate that the particles of the A and B rings are characterized by a greater degree of diffuse backscattering ability than previously suspected, behaving like Lambert spheres, while those of the C ring are either darker or more highly forward scattering than the A or B ring particles.

Collins, S.A.↗
NASA NTRS1980

A 5.57 hr modulation in the optical counterpart of 2S 1822-371

A periodic 5.57 hr modulation has been observed in the optical counterpart of the X-ray source 2S 1822-371. Two alternative periods are consistent with the data: P = 0.232114d and P = 0.232191d, with statistical uncertainties of 0.000015d in each case. Minimum light occurred at JD 2,444,105.668 + or - 0.005. The amplitude of the modulation is about 1 mag, independent of UBV color, and no variability exceeding the 2% level other than the 5.57 hr effect is found on time scales down to a few seconds. The light curve of the star can be understood in terms of a highly inclined close binary system which contains a relatively large, luminous accretion disk that is periodically occulted by a companion star and an associated gas stream. On the assumption that the companion is a main-sequence star, the distance of the system is found to be more than 600 pc, based on the absence of color variations commensurate with the 5.57 hr intensity cycle.

Mason, K. O.↗
NASA NTRS1981

Observations of Uranus, Neptune, and Titan by the International Ultraviolet Explorer

The ultraviolet spectra of Uranus, Neptune, and Titan do not reveal absorption features at 7-A resolution from 2100 to 3200 A. Upper limits of from 1 to 3 A are set for the equivalent widths of narrow absorptions, which corresponds to a CO/H2 mixing ratio less than 2 x 10 to the -4th in the case of Uranus. The slopes of the continuum reflectivities of Uranus and Neptune are consistent with the semi-infinite Rayleigh-Raman scattering model of Cochran, while the absolute levels are matched only if solar photometry is modified within acceptable limits. An alternative, but less satisfactory explanation of the new data is that the UV reflectivities of both Uranus and Neptune are depressed uniformly by a continuum absorber. The suggestion by Savage et al (1980) that the albedo of Uranus decreases by approximately 20% from 2200 to 1800 A is not confirmed. For Titan, the albedo decreases monotonically toward shorter wavelengths down to 2300 A. New limits are set for the pressure level in the atmosphere of Titan up to which the real, but presently unidentified, UV absorber there must extend, and for the fraction of Titan that must be covered by this absorber

Caldwell, J.↗
NASA NTRS1981

Line parameters of methane from 2385 to 3200/cm

A list of new methane line parameters for the 2385-3200 cm region included in the Air Force Geophysical Laboratory's compilation of molecular line parameters is presented. Line positions were determined by computer computations from Fourier transform spectrometer data using a Kitt Peak subroutine. With the exception of class IV lines, all line strengths were determined by the method of equivalent widths. Additional line strengths were measured from spectra taken at cold sample temperatures so that lower state transition energies could be determined experimentally. Observed line positions and strengths are given for 8076 absorptions with strengths greater than 3.3 x 10 to the -24 cm/molecule.

Toth, R. A.↗
NASA NTRS1980

NASA/FAA flight-test investigation of helicopter microwave landing system approaches

The helicopter Microwave Landing System flight-test investigations, conducted by a joint NASA/FAA effort in order to gather statistical data for establishing terminal instrument procedures criteria, and to provide a performance data base for developing advanced MLS guidance concepts, are presented. The specific flight-test objectives were to: (1) develop acceptable angle-only MLS approach profiles; (2) determine tracking errors; (3) determine altitude loss during missed approach; (4) evaluate guidance display sensitivities; and (5) evaluate pilot acceptability. Fourteen pilots flew 140 manual (without stability augmentation) dual-pilot simulated instrument approaches in a UH-1H helicopter. The flight profiles flown included 3-, 6-, and 9-degree glideslope, centerline approaches to decision heights of 50, 100, and 150 ft, respectively. The angular guidance display sensitivities and the data acquisition system are also described. Eight major conclusions are made, and include the following: (1) the use of pitch attitude to control airspeed and collective to control glideslope was the preferred pilot technique for the steep glideslope approaches, and (2) angular guidance deviation indicator sensitivity requirements for helicopter MLS approaches to STOLports and heliports have been found to be significantly different from standard ILS sensitivities.

Peach, I. L., Jr.↗
NASA NTRS1981

Subsonic/supersonic nonvectored aeropropulsive characteristics of nonaxisymmetric nozzles installed on an F-18 model

An experimental program on a model of the F-18 airplane has been conducted to determine the performance of nonaxisymmetric nozzles relative to the aircraft's baseline axisymmetric nozzle at Mach numbers from 0.60 to 2.20. The performance of a two-dimensional convergent-divergent nozzle, a single expansion ramp nozzle (ADEN) and a wedge nozzle were compared to the baseline axisymmetric nozzles. The nonaxisymmetric nozzles (except ADEN) were designed for vectoring and reversing. The axisymmetric nozzle did not have these capabilities. The comparisons presented here are for the nozzles in their full forward thrust mode and for the aircraft at zero angle of attack. The results demonstrate that nonaxisymmetric nozzles can be installed on a close-spaced twin engine fighter with equal or higher performance than the axisymmetric nozzle over the range of Mach numbers tested.

Capone, F. J.↗
NASA NTRS1981

Top-mounted inlet system feasibility for transonic-subsonic fighter aircraft applications

To inlet flow field and engine inlet performance data for an advanced fighter aircraft configuration were obtained over the Mach 0.6 to 2.0 range. The studies not only provided extensive data for the baseline arrangement, but also evaluated the effects of key aircraft configuration variables (inlet location, canopy-dorsal integration, wing leading-edge extension planform area, and variable incidence canards) on top inlet performance. In order to set these data in the context of practical aircraft systems top inlet performance is compared with that of more conventional inlet/airframe integrations. The results of these evaluations show that, for the top inlet configuration tested, relatively good inlet performance and compatibility characteristics are maintained during subsonic and transonic maneuver. However, at supersonic speeds, flow expansion over the forebody and wings causes an increase in local inlet Mach number subsequently reduces inlet performance levels. These characteristics infer that although top inlets many not pose a viable design option for aircraft requiring a high degree of supersonic maneuverability, they have distinct promise for vehicles with subsonic and transonic maneuver capabilities.

Williams, T. L.↗
NASA NTRS1981

Aerodynamic heating on the corrugated surface of a 10.2 deg half-angle blunted cone at Mach 6.7

A 10.2 deg half-angle blunted cone with corrugated surfaces was tested in the Langley 8-foot high-temperature structures tunnel to measure the aerodynamic heating of its surfaces. The tests were made in a turbulent boundary layer at angles of attack of 0 deg, 5 deg, and 10 deg. Heating of the windward side was in reasonable agreement with theoretical turbulent predictions for a smooth cone, while heating on the leeward side was between laminar and turbulent predictions as a result of local transitional flow or flow separation produced by high lee-side pressures. Localized heating measurements indicated a significant increase in heating at large cross-flow angles, with the maximum heating rates occurring where the flow reattaches on the upstream side of the corrugation crest and the minimum occurring on the downstream side where the flow is separated.

Weinstein, I.↗
NASA NTRS1982

Elastic-plastic finite-element analyses of thermally cycled double-edge wedge specimens

Elastic-plastic stress-strain analyses were performed for double-edge wedge specimens subjected to thermal cycling in fluidized beds at 316 and 1088 C. Four cases involving different nickel-base alloys (IN 100, Mar M-200, NASA TAZ-8A, and Rene 80) were analyzed by using the MARC nonlinear, finite element computer program. Elastic solutions from MARC showed good agreement with previously reported solutions obtained by using the NASTRAN and ISO3DQ computer programs. Equivalent total strain ranges at the critical locations calculated by elastic analyses agreed within 3 percent with those calculated from elastic-plastic analyses. The elastic analyses always resulted in compressive mean stresses at the critical locations. However, elastic-plastic analyses showed tensile mean stresses for two of the four alloys and an increase in the compressive mean stress for the highest plastic strain case.

Kaufman, A.↗