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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Progress of research to identify rotating thunderstorms using satellite imagery

The possibility of detecting potentially tornadic thunderstorm cells from geosynchronous satelite imagery is determined. During the life of the contract, we examined eight tornado outbreak cases which had a total of 124 individual thunderstorm cells, 37 of which were tornadic.These 37 cells produced a total of 119 tornadoes. The outflow characteristics of all the cells were measured. Through the use of a 2-D flow field model, we were able to simulate the downstream developmemt of an anvil cloud plume which was emitted by the storm updraft at or near the tropopause. We used two parameters to characterize the anvil plume behavior: its speed of downstream propagation (U max) and the clockwise deviation of the centerline of the anvil plume from the storm relative ambient wind at the anvil plume outflow level (MDA). U max was the maximum U-component of the anvil wind parameter required to successfully maintain an envelope of translating particles at the tip of the expanding anvil cloud. MDA was the measured deviation angle acquired from McIDAS, between the storm relative ambient wind direction and the storm relative anvil plume outflow direction; tha latter being manipulated by controlling a tangential wind component to force the envelope of particles to maintain their position of surrounding the expanding outflow cloud.

Anderson, Charles E.↗
NASA NTRS1989

Performance and loads data from an outdoor hover test of a Lynx tail rotor

A Lynx tail rotor was tested in hover at the Outdoor Aerodynamic Research Facility at NASA Ames Research Center. The test objectives were to measure the isolated rotor performance to provide a baseline for subsequent testing, and to operate the rotor throughout the speed and collective envelope before testing in the NFAC 40- by 80-Foot Wind Tunnel. Rotor forces and blade bending moments were measured at ambient wind conditions from zero to 6.23 m/sec. The test envelope was limited to rotor speeds of 1550 to 1850 rpm and minus 13 deg to plus 20 deg of blade collective pitch. The isolated rotor performance and blade loads data are presented.

Signor, David B.↗
NASA NTRS1988

A catalog of small, optically selected molecular clouds - Optical, infrared, and millimeter properties

A catalog of small, optically selected molecular clouds is presented. The relevant selection criteria were small angular size, large central opacity, and freedom from connecting opaque material. The mean ellipticity of the clouds in the catalog is 2.0, with a maximum ellipticity of 7. The position angle of the clouds is uncorrelated with the direction of the Galactic plane. About 60 percent of the cataloged clouds have associated IRAS Point Source Catalog (PSC) sources in their cores or envelopes. The likelihood of a detection of a PSC source is some 6.1 times higher for the core regions of the clouds than for the envelopes, indicating a strong association of FIR sources and Bok globules. Of a sample of 97 of the clouds observed in the J = 2-1 line of (C-12)O, 70 percent have cold gas kinetic temperatures and approximately sonic line widths. The remaining 30 percent are about equally divided between those clouds likely to be radiatively heated by nearby stars and those undergoing active protostellar collapse or outflows with no bulk gas heating.

Clemens, Dan P.↗
NASA NTRS1988

A piloted simulation investigation of yaw dynamics requirements for turreted gun use in low-level helicopter air combat

A piloted, fixed-base simulation study was conducted to investigate the handling qualities requirements for helicopter air-to-air combat using turreted guns in the near-terrain environment. The study used a version of the helicopter air combat system developed at NASA Ames Research Center for one-on-one air combat. The study focused on the potential trade-off between gun angular movement capability and required yaw axis response. Experimental variables included yaw axis response frequency and damping and the size of the gun-movement envelope. A helmet position and sighting system was used for pilot control of gun aim. Approximately 340 simulated air combat engagements were evaluated by pilots from the Army and industry. Results from the experiment indicate that a highly-damped, high frequency yaw response was desired for Level I handling qualities. Pilot preference for those characteristics became more pronounced as gun turret movement was restricted; however, a stable, slow-reacting platform could be used with a large turret envelope. Most pilots preferred to engage with the opponent near the own-ship centerline. Turret elevation restriction affected the engagement more than azimuth restrictions.

Decker, William A.↗
NASA NTRS1988

The origin of scattering in the inner Galaxy

It is argued that the enhanced scattering of radiowaves observed at low Galactic longitude and latitude is caused by the low-density outer envelopes of H II regions in the inner 8 kpc of the Galaxy. A simple phenomenological theory is developed to estimate the strength of density fluctuations in a turbulent medium and apply the theory to the H II envelopes, using the densities and sizes determined from a recent 325-MHz recombination-line survey. The predicted values are in good agreement with the observations.

Anantharamaiah, K. R.↗
NASA NTRS1989

Stationary nonlinear Alfven waves and solitons

Stationary solutions of the derivative nonlinear Schroedinger equation are discussed and classified by using a pseudopotential formulation. The solutions consist of a rich family of nonlinear Alfven waves and solitons with parallel and oblique propagation directions. Expressions for the envelope and the phase of nonlinear waves with periodic envelope modulation, and 'hyperbolic' and 'algebraic' solitons are given. The propagation angle for the slightly modulated elliptic, periodic waves and for oblique solitons is evaluated.

Hada, T.↗
NASA NTRS1989

Multifrequency analysis of a decametric storm observed at Voyager 1 and ground-based observatories

Observations of a Jovian decametric non-Io-A noise storm made from Voyager 1, the University of Florida Radio Observatory, the University of Texas Radio Astronomy Observatory, and the Jupiter station at Goddard Space Flight Center at frequencies of 26.3, 22.2, 20.0, and 18.0 MHz were found to be correlated. The activity observed at the ground stations occurred 68 min after the corresponding activity at Voyager 1. After correction is made for propagation time differences, this delay is reduced to 34 min. It is demonstrated that at each frequency the envelope of the individual-event beams occurring during the storm (some or all of which are associated with dynamic spectral arcs) is a quasi-constant structure that corotates with the inner Jovian magnetosphere, and that the width of this envelope beam is frequency dependent. The width increases as frequency is decreased, mainly because of the change in position of the trailing-edge beam boundary. Evidence for a relatively slow temporal change in beam geometry is also presented.

Maeda, K.↗
NASA NTRS1988

Simulation evaluation of transition and hover flying qualities of the E-7A STOVL aircraft

The generalized simulation model developed for the E-7A STOVL fighter-type aircraft configuration has attempted to define the limits of acceptibility for a vertical-to-horizontal-to-vertical flight transition envelope. An effort was also made to determine the control power required during hover and transition, and to evaluate whether the integration of flight and propulsion controls thus far effected achieves good flying qualities throughout the low-speed flight envelope. The results thus obtained furnish a general view of the acceptable transition corridor, expressed in terms of the minimum-climb capability.

Franklin, James A.↗
NASA NTRS1989

Fluctuating pressures on wing surfaces in the slipstream of a single-rotor propfan

Measurements of the fluctuating pressure levels (FPLs) induced on a Propfan Test Assessment wing by the SR-7L propfan slipstream within the airplane flight envelope were obtained as a function of propfan operating conditions. It is shown that FPLS were high over most of the flight envelope, and that the spectra were dominated by the propfan first-order blade passage frequency tone. The highest FPLs were found at the lowest aircraft test altitudes and Mach numbers and for propfan conditions of lowest rotational tip speed and highest power.

Swift, G.↗
NASA NTRS1989

Spatial structure in the color of the dust coma of Comet P/Halley

Significant spatial variations are noted in the color of the dust in Comet Halley's dust coma, out to 156,000 km from the optocenter, in the present March 1-6, 1986 narrowband CCD images. In particular, the envelope of intermediate-mass particles formed around the nucleus by solar radiation pressure is redder than the rest of the dust coma, and a strong jet noted in the March 1 images is redder than both the dust envelope and the remainder of the dust coma. A wavelength-dependence model of the Comet Halley dust's color is developed on the basis of Mie theory.

Hoban, Susan↗
NASA NTRS1989

The theoretical model for the annular jet instability - Revisited

The theoretical model of Lee and Wang (1986) for the instability of an annular jet, in which the jet's liquid layer is treated as a thin liquid sheet, is examined. It is suggested that the model should be altered so that when the envelope is closing its bottleneck during collapse, the new envelope experiences a sharp pressure pulse from its gaseous core, reversing the normal velocity of the sheet enough to maintain continuous constant gas flow. Using this improved version of the model, it is shown that if the liquid velocity is high enough and the gas velocity is greater than the liquid velocity, the bubble-formation frequency varies linearly with the difference between the two velocities, but not with their individual values.

Lee, C. P.↗
NASA NTRS1989

Observational astrochemistry - Recent results

More than 80 molecular species have now been observed in the dense interstellar clouds where stars and planets form or in the envelopes expelled by evolved stars. Elemental constituents of these compounds include all of the biogenic elements, H, C, N, O, S and P. In addition, Si is found in several molecules, and a series of metal halides have recently been detected in the outflowing envelope of a nearby carbon star. Knowledge of the chemical reservoirs for the major volatile elements and a comparison between observed molecular abundances and theoretical models are both discussed.

Irvine, W. M.↗
NASA NTRS1989

High performance linear-quadratic and H-infinity designs for a 'supermaneuverable' aircraft

Recent efforts by the National Aeronautics and Space Administration Langley Research Center have focused on expanding the flight envelope of the F/A-18 aircraft. Of particular concern has been the low speed, high angle-of-attack regime over which the conventional aerodynamic controls of the F/A-18 lose their effectiveness. In order to address this problem the F18 high alpha research vehicle was developed. This aircraft is essentially a modified F/A-18 which possesses thrust vectoring capabilities and hence increased maneuverability in this flight regime. The linear-quadratic-Gaussian with loop-transfer-recovery and H(infinity) design methodologies are used to design high performance controllers for the F18 at an operating point within the expanded envelope. In addition, how the control redundancy of the F18 can be used to maintain nominal performance, as well as nominal stability, in situations where failures occur, is shown.

Voulgaris, Petros↗
NASA NTRS1989

Flutter Clearance of the F-18 High-angle-of-attack Research Vehicle with Experimental Wingtip Instrumentation Pods

An F-18 aircraft was modified with wingtip instrumentation pods for use in NASA's high-angle-of-attack research program. Ground vibration and flight flutter testing were performed to clear an acceptable flight envelope for the aircraft. Flight test utilized atmospheric turbulence for structural excitation; the aircraft displayed no adverse aeroelastic trends within the envelope tested. The data presented in this report include mode shapes from the ground vibration and estimates of frequency and damping as a function of Mach number.

Freudinger, Lawrence C.↗
NASA NTRS1987

Design and test of an NLF wing glove for the variable-sweep transition flight experiment

Gloves for M = 0.7 and 0.8 design points were computationally designed and analyzed at conditions over the proposed flight test envelope. The resulting computational pressure distributions were analyzed in a boundary layer stability code. These results indicate that the available pressure distributions offer a wide range of combinations of cross flow and Tollmien-Schlichting N-factors. The glove designs along with the baseline configuration were tested in an entry into the National Transonic Facility. Analysis of the force and moment data showed no significant differences in the performance and stability and control characteristics between the baseline and gloved configurations. The rolling moment constraint was met over the entire flight test envelope for the gloved configuration. Pressure distributions for the NTF test confirmed the design pressure distributions were achieved. However, it was decided that with minor modifications to the inboard region of the glove, useful available data could be significantly increased by adding another row of pressure orifices at span station 167.

Waggoner, Ed G.↗
NASA NTRS1989

Theory of gearing

Basic mathematical problems on the theory of gearing are covered in this book, such as the necessary and sufficient conditions of envelope existence, relations between principal curvatures and directions for surfaces of mating gears. Also included are singularities of surfaces accompanied by undercutting the process of generation, the phenomena of envelope of lines of contact, and the principles for generation of conjugate surfaces. Special attention is given to the algorithms for computer aided simulation of meshing and tooth contact. This edition was complemented with the results of research recently performed by the author and his doctoral students. The book contains sample problems and also problems for the reader to solve.

Gear-tooth surface↗
NASA NTRS1990

Seamless metal-clad fiber-reinforced organic matrix composite structures and process for their manufacture

A metallic outer sleeve is provided which is capable of enveloping a hollow metallic inner member having continuous reinforcing fibers attached to the distal end thereof. The inner member is then introduced into outer sleeve until inner member is completely enveloped by outer sleeve. A liquid matrix member is then injected into space between inner member and outer sleeve. A pressurized heat transfer medium is flowed through the inside of inner member, thereby forming a fiber reinforced matrix composite material. The wall thicknesses of both inner member and outer sleeve are then reduced to the appropriate size by chemical etching, to adjust the thermal expansion coefficient of the metal-clad composite structure to the desired value. thereby forming a fiber reinforced matrix composite material. The wall thicknesses of both inner member and outer sleeve are then reduced to the appropriate size by chemical etching, to adjust the thermal expansion coefficient of the metal-clad composite structure to the desired value. The novelty of this invention resides in the development of a efficient method of producing seamless metal clad fiber reinforced organic matrix composite structures.

Bluck, Raymond M.↗
NASA NTRS1990

Identification of aerodynamic models for maneuvering aircraft

Due to the requirement of increased performance and maneuverability, the flight envelope of a modern fighter is frequently extended to the high angle-of-attack regime. Vehicles maneuvering in this regime are subjected to nonlinear aerodynamic loads. The nonlinearities are due mainly to three-dimensional separated flow and concentrated vortex flow that occur at large angles of attack. Accurate prediction of these nonlinear airloads is of great importance in the analysis of a vehicle's flight motion and in the design of its flight control system. A satisfactory evaluation of the performance envelope of the aircraft may require a large number of coupled computations, one for each change in initial conditions. To avoid the disadvantage of solving the coupled flow-field equations and aircraft's motion equations, an alternate approach is to use a mathematical modeling to describe the steady and unsteady aerodynamics for the aircraft equations of motion. Aerodynamic forces and moments acting on a rapidly maneuvering aircraft are, in general, nonlinear functions of motion variables, their time rate of change, and the history of maneuvering. A numerical method was developed to analyze the nonlinear and time-dependent aerodynamic response to establish the generalized indicial function in terms of motion variables and their time rates of change.

Chin, Suei↗