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At least 685 records · Page 38

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NASA NTRS1987

Circumstellar radio molecular lines

Radio molecular lines appear to be useful probes into the stellar environment. Silicon oxide masers provide information on the physical conditions in the immediate vicinity of the stellar photosphere. Valuable information on the physics operating in the envelope of IRC + 10216 was recently obtained by high sensitivity observations and detailed theoretical analyses. Infrared speckle interferometry in the molecular lines and in the continuum is helpful in the investigation of the inner region of the envelope. These techniques are discussed in terms of late-type star mass loss.

NGUYEN-QUANG-RIEU↗

NASA NTRS1985

Handling qualities of a wide-body transport airplane utilizing Pitch Active Control Systems (PACS) for relaxed static stability application

Piloted simulation studies have been conducted to evaluate the effectiveness of two pitch active control systems (PACS) on the flying qualities of a wide-body transport airplane when operating at negative static margins. These two pitch active control systems consisted of a simple 'near-term' PACS and a more complex 'advanced' PACS. Eight different flight conditions, representing the entire flight envelope, were evaluated with emphasis on the cruise flight conditions. These studies were made utilizing the Langley Visual/Motion Simulator (VMS) which has six degrees of freedom. The simulation tests indicated that (1) the flying qualities of the baseline aircraft (PACS off) for the cruise and other high-speed flight conditions were unacceptable at center-of-gravity positions aft of the neutral static stability point; (2) within the linear static stability flight envelope, the near-term PACS provided acceptable flying qualities for static stabilty margins to -3 percent; and (3) with the advanced PACS operative, the flying qualities were demonstrated to be good (satisfactory to very acceptable) for static stabilty margins to -20 percent.

Grantham, William D.↗

NASA NTRS1988

Annoyance caused by advanced turboprop aircraft flyover noise: Single-rotating propeller configuration

Two experiments were conducted to quantify the annoyance of people to advanced turboprop (propfan) aircraft flyover noise. The objectives were to: (1) determine the effects on annoyance of various tonal characteristics; and (2) compare annoyance to advanced turboprops with annoyance to conventional turboprops and jets. A computer was used to produce realistic, time-varying simulations of advanced turboprop aircraft takeoff noise. In the first experiment, subjects judged the annoyance of 45 advanced turboprop noises in which the tonal content was systematically varied to represent the factorial combinations of five fundamental frequencies, three frequency envelope shapes, and three tone-to-broadband noise ratios. Each noise was presented at three sound levels. In the second experiment, 18 advanced turboprop takeoffs, 5 conventional turboprop takeoffs, and 5 conventional jet takeoffs were presented at three sound pressure levels to subjects. Analysis indicated that frequency envelope shape did not significantly affect annoyance. The interaction of fundamental frequency with tone-to-broadband noise ratio did have a large and complex effect on annoyance. The advanced turboprop stimuli were slightly less annoying than the conventional stimuli.

Mccurdy, David A.↗

NASA NTRS1987

Extinction and abundance properties of Alpha Scorpii circumstellar grains

The UV extinction and element depletions in the circumstellar envelope Alpha Sco are investigated using IUE, Copernicus, and AS data of Alpha Sco B which can be seen in absorption through the cool-star envelope. The circumstellar reddening, depletions, and spectral extinction toward Alpha Sco B are estimated. Evidence is presented which suggests that the circumstellar grains are large and siliceous.

Snow, Theodore P., Jr.↗

NASA NTRS1987

The dust coma of comet P/Halley - Measurements on the Vega-1 and Vega-2 spacecraft

Measurements obtained with the Dust Counter and Mass Analyzer instruments on the Vega 1 and 2 spacecraft are used to study properties of the coma of comet P/Halley. Well-defined envelope boundaries for the inverse square dependence of flux with distance from the nucleus are found, and regions of enhanced fluxes above these R exp -2 baselines inside these boundaries are identified as dust jets. The mass spectrum of the giant flux enhancement noted near the closest approach of Vega 1 is shown to be similar to the preencounter spectra. The data suggest the emission from the nucleus of large conglomerates of small particles which disintegrate as they travel outward, explaining the 10 to the -13th g particles observed beyond the envelope boundaries.

Simpson, J. A.↗

NASA NTRS1987

Uranus satellites - Densities and composition

Homogeneous and core-differentiated silicate/ice models of the Uranian satellites Miranda, Ariel, Umbriel, Titania, and Oberon are examined in the light of imaging observations and mass and density determinations obtained during the Voyager 2 encounter with Uranus in January 1986. The data and model predictions are compared in extensive tables and graphs and discussed in detail. The mass fractions of silicates in Oberon and Titania are found to be between 0.42 and 0.65, about the same as the average for the satellites of Jupiter and Saturn but significantly higher than that for the smaller Saturnian satellites or that predicted by current solar-nebula models. It is suggested that the satellites formed by accretion of material from their primary planets' outer envelopes. The observed rock/ice fractions are attributed to solar-nebula CO and solid-organics abundances and to preferential dissolution of H2O in outer-envelope planetesimals.

Johnson, Torrence V.↗

NASA NTRS1989

An indirect method for numerical optimization using the Kreisselmeir-Steinhauser function

A technique is described for converting a constrained optimization problem into an unconstrained problem. The technique transforms one of more objective functions into reduced objective functions, which are analogous to goal constraints used in the goal programming method. These reduced objective functions are appended to the set of constraints and an envelope of the entire function set is computed using the Kreisselmeir-Steinhauser function. This envelope function is then searched for an unconstrained minimum. The technique may be categorized as a SUMT algorithm. Advantages of this approach are the use of unconstrained optimization methods to find a constrained minimum without the draw down factor typical of penalty function methods, and that the technique may be started from the feasible or infeasible design space. In multiobjective applications, the approach has the advantage of locating a compromise minimum design without the need to optimize for each individual objective function separately.

Wrenn, Gregory A.↗

NASA NTRS1989

Computer-aided design of bevel gear tooth surfaces

This paper presents a computer-aided design procedure for generating bevel gears. The development is based on examining a perfectly plastic, cone-shaped gear blank rolling over a cutting tooth on a plane crown rack. The resulting impression on the plastic gear blank is the envelope of the cutting tooth. This impression and envelope thus form a conjugate tooth surface. Equations are presented for the locus of points on the tooth surface. The same procedures are then extended to simulate the generation of a spiral bevel gear. The corresponding governing equations are presented.

Shuo, Hung Chang↗

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↗