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At least 757 records · Page 42

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NASA NTRS1982

A doublet lattice method for the determination of rotor induced empennage vibration airloads. Analysis description and program documentation

An efficient state-of-the-art method was developed to determine the unteady vibratory airloads produced by the interaction of the main rotor wake with a helicopter empennage. This method was incorporated into a computer program, Rotor Induced Empennage Vibration Analysis (RIEVA). The program requires the main rotor wake position and the strength of the vortices locates near the empennage surfaces. A nonlinear lifting surface analysis is utilized to predict the aerodynamic loads on the empennage surfaces in the presence of these concentrated vortices. The analysis was formulated to include all pertinent effects such as suction of the interacting vortices and the shed vorticity behind the empennage surfaces. The analysis employs a time domain solution. The output of the program consists of chordwise and spanwise airload distributions on the empennage surfaces. The airload distributions are harmonically analyzed and formulated for input into the Coupled Rotor/Airframe Vibration Analysis.

Gangwani, S. T.↗

NASA NTRS1982

X-ray illumination of globular cluster puzzles

Globular clusters are thought to be among the oldest objects in the Galaxy, and provide, in this connection, important clues for determining the age and process of formation of the Galaxy. The present investigation is concerned with puzzles relating to the X-ray emission of globular clusters, taking into account questions regarding the location of X-ray emitting clusters (XEGC) unusually near the galactic plane and/or galactic center. An adopted model is discussed for the nature, formation, and lifetime of X-ray sources in globular clusters. An analysis of the available data is conducted in connection with a search for correlations between binary formation time scales, central relaxation times, galactic locations, and X-ray emission. The positive correlation found between distance from galactic center and two-body binary formation time for globular clusters, explanations for this correlation, and the hypothesis that X-ray sources in globular clusters require binary star systems provide a possible explanation of the considered puzzles.

Lightman, A. P.↗

NASA NTRS1983

Autonomous navigation using lunar beacons

The concept of using lunar beacon signal transmission for on-board navigation for earth satellites and near-earth spacecraft is described. The system would require powerful transmitters on the earth-side of the moon's surface and black box receivers with antennae and microprocessors placed on board spacecraft for autonomous navigation. Spacecraft navigation requires three position and three velocity elements to establish location coordinates. Two beacons could be soft-landed on the lunar surface at the limits of allowable separation and each would transmit a wide-beam signal with cones reaching GEO heights and be strong enough to be received by small antennae in near-earth orbit. The black box processor would perform on-board computation with one-way Doppler/range data and dynamical models. Alternatively, GEO satellites such as the GPS or TDRSS spacecraft can be used with interferometric techniques to provide decimeter-level accuracy for aircraft navigation.

Khatib, A. R.↗

NASA NTRS1982

Bubble motion in a rotating liquid body

The behavior of a single gas bubble inside a rotating liquid-filled sphere has been investigated analytically and experimentally as part of ground-based investigations aimed at aiding in the design and interpretation of Shuttle experiments. In the analysis, a quasi-static description of the motion of a bubble was developed in the limit of small values of the Taylor number. A series of rotation experiments using air bubbles and silicone oils were designed to match the conditions specified in the analysis, i.e., the bubble size, sphere rotation rate, and liquid kinematic viscosity were chosen such that the Taylor number was much less than unity. The analytical description predicts the bubble velocity and its asymptotic location. It is shown that the asymptotic position is removed from the axis of rotation.

Annamalai, P.↗

NASA NTRS1983

Computer graphics applications to crew displays

Astronauts are provided much data and information via the monochrome CRT displays on the orbiter. For this project two areas were investigated for the possible introduction of computer graphics to enhance and extend the utility of these displays. One involved reviewing the current orbiter displays and identifying those which could be improved via computer graphics. As an example, the tabular data on electrical power distribution and control was enhanced by the addition of color and bar charts. The other dealt with the development of an aid to berthing a payload with the Remote Manipulator System (RMS). This aid consists of a graphics display of the top, front and side views of the payload and cargo bay and point of resolution (POR) position and attitude data for the current location of the payload. The initial implementation was on an IBM PC clone. The demonstration software installed in the Johnson Space Center Manipulator Development Facility (MD) was reviewed. Due to current hardware limitations, the MDF verision is slow, i.e., about a 40+ seond update rate and, hence, not real-time. Despite this fact, the evaluation of this additional visual cue as an RMS operator aid indicates that this display, with modifications for speed, etc., can assist the crew. Further development is appropriate.

Wyzkoski, J.↗

NASA NTRS1986

Speculations on nature and extent of Archean basement in Labrador as indicated by SR, ND and PB isotopic systematics of proterozoic intrusives

The Sm-Nd and Rb-Sr isotopic compositions of mid to late Proterozoic (approximately 1.6 to 1.1 Ga) massif-type anorthosites and mafic intrusives in the eastern Canadian shield are correlated with geographic location. Complexes in the Grenville province have positive epsilon sub Nd values and initial Sr-87/Sr-86 (I sub Sr) generally less than 0.703, suggesting derivation from depleted mantle. In Labrador, similar complexes close to or northwest of a line roughly corresponding to the Grenville Front have negative epsilon sub Nd values and I sub Sr 0.703. This contrast was intrepreted as reflecting either enriched mantle under the Nain Province, or contamination of the Nain intrusives with older crustal components. Lead isotopic compositions, however, favor the latter. The possibility of using these Proterozoic intrusives as tracers to characterize the nature and extent of older basement types in Labrador is discussed.

Ashwal, L. D.↗

NASA NTRS1987

Emergency-Radio Modulation Would Identify Type of Vehicle

New emergency beacon similar to conventional one, except modulation interrupted periodically while unmodulated carrier is transmitted. Modulation scheme for emergency radio beacons aids searchers by indicating kind of vehicle in distress. Transmitted signal similar to present standard signal of emergency locator transmitters (ELT's) and emergency position-indicating radio beacons (EPIRB's) but also includes periods of unmodulated carrier.

Wren, Paul↗

NASA NTRS1986

Formationkeeping of Spacecraft via Differential Drag

This paper examines the use of differential drag in the formationkeeping of spacecraft. In many future space missions one satellite will be required to fly in a specific position with respect to another satellite; this action is referred to as formationkeeping. In this study, differential drag is the difference in drag between the two satellites. Reasons to use differential drag as an actuator for formationkeeping include the avoidance of jet plume impingement effects on closely spaced satellites and possible fuel savings. The equations of relative motion between the two satellites are derived and a mathematical transformation is made to reduce the formationkeeping problem to the simultaneous solution of a double integrator and a harmonic oscillator. A two-part control law is developed that simultaneously and dependently solves the double oscillator and harmonic integrator. Results are presented of eight test cases being driven to a target position; two different simulations are used. The validity of assumptions made in the derivation of the control law is examined in the comparison of similar test cases run through different simulations. The control law developed can drive a satellite from an initial position to a target position and maintain the satellite at that location.

Leonard, Carolina Lee↗

NASA NTRS1987

Linear baroclinic instability in the presence of large scale topography

The effect of a planetary-scale, wavenumber 2 topography on baroclinically active disturbances is investigated for a channel domain in a two-layer, quasi-geostrophic context. When the lower-layer zonal velocity is nonzero, the topography influences the disturbances by forcing a stationary wave, and the topography and the forced wave influence the growth rates and the spatial structures of the time-dependent solutions. The case of zero zonal velocity in the lower layer was also investigated, for which no forced wave exists. Asymptotic forms of the equations, valid when the topographic effect (governed by the ratio of the nondimensional topographic height to the rotational Froude number) is small, are used to obtain both the stationary and time-dependent solutions. The latter are also obtained using a numerical approach, in which is determined the eigenvalues and eigenfunctions of a matrix representing the dynamical equations. Agreement is good between the two approaches. Recent laboratory experiments with a baroclinic annulus in which there is a false bottom with wavenumber 2 topography, are used to select governing parameters. The simultaneous presence of a stationary forced wave of wavenumber 2 and a time-dependent baroclinic wave of wavenumber 4, which has wavenumber 2 and 6 sidebands due to the topography, yields a flow field that exhibits some principal features of the laboratory experiments. The position of the forced wave and the location of an excursion in latitude of the storm track show qualitative resemblance to those features observed in the atmosphere.

Reynolds, Nathaniel Dunton↗

NASA NTRS1988

Signal Restoration of Non-stationary Acoustic Signals in the Time Domain

Signal restoration is a method of transforming a nonstationary signal acquired by a ground based microphone to an equivalent stationary signal. The benefit of the signal restoration is a simplification of the flight test requirements because it could dispense with the need to acquire acoustic data with another aircraft flying in concert with the rotorcraft. The data quality is also generally improved because the contamination of the signal by the propeller and wind noise is not present. The restoration methodology can also be combined with other data acquisition methods, such as a multiple linear microphone array for further improvement of the test results. The methodology and software are presented for performing the signal restoration in the time domain. The method has no restrictions on flight path geometry or flight regimes. Only requirement is that the aircraft spatial position be known relative to the microphone location and synchronized with the acoustic data. The restoration process assumes that the moving source radiates a stationary signal, which is then transformed into a nonstationary signal by various modulation processes. The restoration contains only the modulation due to the source motion.

Babkin, Alexander S.↗

NASA NTRS1989

Laser Rayleigh-Scattering During Space Shuttle Entry

Report presents detailed study of capabilities and requirements for equipment of proposed ultraviolet Rayleigh-scattering instrument to be carried aboard Space Shuttle. Density of atmosphere around flightpath measured. With accuracy and resolution, measurements adequate for detection of small-scale meteorological structure affecting analysis of flight dynamic data of reentering spacecraft. Also discusses extensions of concept to measurements of location of, and density as function of position in, shock wave of Space Shuttle. Measurements provide baseline data for verification of computer models of high-enthalpy hypersonic, nonequilibrium, and viscous conditions.

Mckenzie, Robert L.↗

NASA NTRS1992

Test of an orbiting hydrogen maser clock system using laser time transfer

We describe a joint Smithsonian Astrophysical Laboratory/National Aeronautics and Space Administration (SAO/NASA) program for flight testing a atomic hydrogen maser clock system designed for long-term operation in space. The clock system will be carried by a shuttle-launched EURECA spacecraft. Comparisons with earth clocks to measure the clock's long-term frequency stability (tau = 10(exp 4) seconds) will be made using laser time transfer from existing NASA laser tracking stations. We describe the design of the maser clock and its control systems, and the laser timing technique. We describe the precision of station time synchronization and the limitations in the comparison between the earth and space time scales owing to gravitational and relativistic effects. We will explore the implications of determining the spacecraft's location by an on-board Global Position System (GPS) receiver, and of using microwave techniques for time and frequency transfer.

Vessot, Robert F. C.↗

NASA NTRS1993

Development of a large space robot - A multi-segment approach. I

A concept of multisegment robot (of a class of large space cranes) is developed for use in space-based construction operations. The robot consists of a collection of segments, which are pinned together to form a snakelike configuration, with a single degree of freedom representing rotation being retained at each pinned connection and with reaction flywheels suspended within each segment for the control necessary to position each body segment. Algorithms are developed for positioning this serpentine robot to a prescribed location and orientation. A multibody dynamics simulation is used to investigate the behavior and interactions of the robot, demonstrating its viability.

Spanos, P. D.↗

NASA NTRS1991

Optical position measurement for a Large Gap Magnetic Suspension System

This paper describes the design of an optical position measurement system which is being built as part of the NASA Langley Large Gap Magnetic Suspension System (LGMSS). The LGMSS is a five degree-of-freedom, large-gap magnetic suspension system which is being built for Langley Research Center as part of the Advanced Controls Test Facility (ACTF). The LGMSS consists of a planar array of electromagnets which levitate and position a cylindrically shaped model containing a permanent magnet core. The optical position measurement system provides information on the location and orientation of the model to the LGMSS control system to stabilize levitation of the model.

Welch, Sharon S.↗

NASA NTRS1937

Tests of related forward-camber airfoils in the variable-density wind tunnel

A recent investigation of numerous related airfoils indicated that positions of camber forward of the usual location resulted in an increase of the maximum lift. As an extension of this investigation, a series of forward-camber airfoils has been developed, the members of which show airfoil characteristics superior to those of the airfoils previously investigated. The primary object of this report is to present fully corrected results for airfoils in the useful range of shapes. With the data thus made available, an airplane designer may intelligently choose the best possible airfoil-section shape for a given application and may predict to a reasonable degree the aerodynamic characteristics to be expected in flight from the section shape chosen.

Jacobs, Eastman N↗

NASA NTRS1958

A Low-Speed Experimental Investigation of the Effect of a Sandpaper Type of Roughness on Boundary-Layer Transition

An investigation was made in the Langley low-turbulence pressure tunnel to determine the effect of size and location of a sandpaper type of roughness on the Reynolds number for transition. Transition was observed by means of a hot-wire anemometer located at various chordwise stations for each position of the roughness. These observations indicated that when the roughness is sufficiently submerged in the boundary layer to provide a substantially linear variation of boundary-layer velocity with distance from the surface up to the top of the roughness, turbulent "spots" begin to appear immediately behind the roughness when the Reynolds number based on the velocity at the top of the roughness height exceeds a value of approximately 600. At Reynolds numbers even slightly below the critical value (value for transition), the sandpaper type of roughness introduced no measurable disturbances into the laminar layer downstream of the roughness. The extent of the roughness area does not appear to have an important effect on the critical value of the roughness Reynolds number.

Von Doenhoff, Albert E↗

NASA NTRS1948

Hydrodynamic Characteristics of a Low-drag, Planing-tail Flying-boat Hull

The hydrodynamic characteristics of a flying-boat incorporating a low-drag, planing-tail hull were determined from model tests made in Langley tank number 2 and compared with tests of the same flying boat incorporating a conventional-type hull. The planing-tail model, with which stable take-offs were possible for a large range of elevator positions at all center-of-gravity locations tested, had more take-off stability than the conventional model. No upper-limit porpoising was encountered by the planing-tail model. The maximum changes in rise during landings were lower for the planing-tail model than for the conventional model at most contact trims, an indication of improved landing stability for the planing-tail model. The hydrodynamic resistance of the planing-tail hull was lower than the conventional hull at all speeds, and the load-resistance ratio was higher for the planing-tail hull, being especially high at the hump. The static trim of the planing-tail hull was much higher than the conventional hull, but the variation of trim with speed during take-off was smaller.

Suydam, Henry B↗

NASA NTRS1947

The Development of Jet-engine Nacelles for a High-speed Bomber Design

The results of an experimental investigation made for the purpose of developing suitable jet-engine nacelle designs for a high-speed medium bomber are presented. Two types of nacelles were investigated, the first enclosing two 4000-pounds-thrust jet engines and a 65-inch-diameter landing wheel and the second enclosing a single 4000-pounds-thrust jet engine. Both types of nacelles were tested in positions underslung beneath the wing and centrally located on the wing. This report summarizes the investigation which was performed at low speed for the purpose of developing entrance and body shapes of suitable form. Included are results from the high-speed portion of the investigation on the characteristics of an underslung nacelle.

Dannenberg, Robert E↗