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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Interpretation of tails of X-ray bursts

Four reasons for ruling out the Alcock and Hatchett (1978) proposal concerning the tails of X-ray bursts are advanced. This proposal suggests that the tails of X-ray bursts observed during burst decay are due to the small-angle scattering of the original pulse of X-rays on interstellar dust grains; grains with a typical size of approximately 3 microns are assumed. The arguments against this theory involve differences in burst tail sizes sometimes observed for bursts from the same source; the different kinds of bursts emitted by MXB 1730-335 (rapid burster); an indication that MXB 1730-335 bursts have tails less than 2 s long; and the lack of correlation between relative strength of burst tails and the interstellar absorption.

Van Paradijs, J.↗
NASA NTRS1979

On the average configuration of the geomagnetic tail

A statistical study of the geomagnetic tail has revealed large scale variations in the field configuration both in N-S and E-W directions. The largest value of the B(z) component of the field was observed near the midplane of the tail. Results, such as the discovery of more depolar fields near the flanks of the tail can be incorporated into more realistic models, which should lead to a better understanding of tail behavior. The observed dependence of the tail on interplanetary sector structure may be interpreted in terms of models linking interplanetary field lines to those of the earth.

Fairfield, D. H.↗
NASA NTRS1979

On the size of the cometary tail magnetic field

Ershkovich's (1978) criticism of previous arguments in favor of magnetic fields of approximately 100 gammas in cometary plasma tails are shown to be unjustified. It is argued that the folding velocity of tail streamers indicates a substantial tail magnetic field and that much of Ershkovich's disagreement stems from the choice of completely different models for a comet's plasma tail. It is concluded that the use of growth rates or phase-velocity information obtained from a dispersion relation to interpret large-amplitude disturbances, such as those in comet tails, is categorically incorrect.

Mendis, D. A.↗
NASA NTRS1980

Effect of wing location and strakes on stability and control characteristics of a monoplanar circular missile with low-profile tail fins at supersonic speeds

A wind tunnel test was conducted at Mach numbers from 1.70 to 2.86 to extend the aerodynamic data base for wing tail effect on stability and control characteristics of monoplanar missiles. The results are summarized to show the effects of tail fin dihedral angle, wing location, and nose body strakes. The results indicate that an increase in tail fin dihedral angle produces positive increments in directional stability that allow greater trimmed lift coefficient values (maneuver potential) to be obtained. An increase in wing tail gap for the Mach number range reduces the aerodynamic center travel and produces reductions in directional stability at the lower angles of attack. A change in wing height (vertical location) strongly influences the angle of attack at which pitch up and the most directional stability occur. The addition of strakes to the baseline configuration increases directional stability, which allows a significant increase in stable trimmed maneuver capability. The tail fins of the baseline configuration are effective in producing roll and yaw control that are accompanied by favorable yaw and roll, respectively.

Blair, A. B., Jr.↗
NASA NTRS1983

Effect of tail-fin span on stability and control characteristics of a Canard-controlled missile at supersonic Mach numbers

An experimental wind-tunnel investigation was conducted at Mach numbers from 1.60 to 3.50 to obtain the longitudinal and lateral-directional aerodynamic characteristics of a circular, cruciform, canard-controlled missile with variations in tail-fin span. In addition, comparisons were made with the experimental aerodynamic characteristics using three missile aeroprediction programs: MISSILE1, MISSILE2, and NSWCDM. The results of the investigation indicate that for the test Mach number range, canard roll control at low angles of attack is feasible on tail-fin configurations with tail-to-canard span ratios of less than or equal to 0.75. The conards are effective pitch and yaw control devices on each tail-fin span configuration tested. Programs MISSILE1 and MISSILE2 provide very good predictions of longitudinal aerodynamic characteristics and fair predictions of lateral-directional aerodynamic characteristics at low angles of attack, with MISSILE2 predictions generally in better agreement with test data. Program NSWCDM provides good longitudinal and lateral-directional aerodynamic predictions that improve with increases in tail-tin span.

Blair, A. B., Jr.↗
NASA NTRS1982

On the flaring of cometary plasma tails

Assuming that hypersonic pressure balance with the solar wind governs the shape of plasma tails, it is found that the gas pressure of tail ions and the magnetic field strength at the flanks of the ionopause control the flaring state. The gas pressure exhibits the larger effect: for constant pressures above a certain critical value, the tail flares essentially without limit, while for smaller values the tail flares only near the head (becoming cylindrical at greater distances). The influence of the magnetic field is that the tail flares to larger distances the higher the field strength at the flanks of the ionopause. The observed variability in flaring (and the implied differences in gas pressure and magnetic field) are throught to be the result of changes in the position and shape of the sunward cometary ionopause. Insertion of reasonable comet and solar wind parameters into the pressure balance equations is found to give good agreement with the observations.

Ershkovich, A. I.↗
NASA NTRS1982

The curvature of radio jets and tails in the intracluster media of Abell 1446 and 2220

X-ray observations are reported for two rich clusters which contain prominent tailed radio galaxies. These X-ray data are used as probes of the cluster gas to explore mechanisms which may distort radio jets and tails. A nonrelativistic hydrodynamic flow model is invoked to examine the plasma beam parameters needed to bend the radio streams in a manner consistent with the radio and X-ray data. Within the context of this model, the wide-angle tailed radio structure of 1159 + 583 in A1446 is explained by a combination of a buoyancy pressure gradient in the cluster gas and dynamic pressure arising from slow galaxy motion (200 km/sec). The second cluster observed, A2220, contains a clumped X-ray structure with peaks near two dominant galaxies. The strongly bent radio jets of 1638 + 538 (associated with one of the bright galaxies) are consistent with about 1000 km/sec motion, possibly in a binary orbit, through the X-ray emitting cluster gas; a curved feature in the northern tail, however, may be attributable to buoyancy forces. These X-ray data also suggest that the radio jets and tails are thermally confined by the hot intracluster media.

Burns, J. O.↗
NASA NTRS1984

An evaluation of the relative merits of wing-canard, wing-tail, and tailless arrangements for advanced fighter applications

Two sets of wind tunnel tests were performed to examine the relative merits of wing-canard, wing-tail and tailless configurations for advanced fighters. Both sessions focused on variable camber using automated, prescheduled leading and trailing edge flap positioning. The trials considered a modified F-16 tail and canard configuration at subsonic, transonic and supersonic speeds, a 60 deg delta wing sweep, a 44 deg leading edge trapezoidal wing at subsonic and supersonic speeds, vortex flow effects, and flow interactions in the canard-wing-tail-tailless variations. The results showed that large negative stabilities would need to be tolerated in wing-canard arrangements to make them competitive with wing-tail arrangements. Subsonic polar shapes for canard and tailless designs were more sensitive to static design margins than were wing-tail arrangements. Canards provided better stability at supersonic speeds. The static margin limits were a critical factor in control surface selection. Finally, a tailless delta wing configuration exhibited the lowest projected gross take-off weight and drag values.

Nicholas, W. U.↗
NASA NTRS1984

Plasma entry into the distant tail lobes - ISEE-3

ISEE-3 measurements indicate that a broad mantle-like boundary layer plasma often exists within the distant geomagnetic tail lobes at all latitudes, directly adjacent to the tail magnetopause. The presence of this boundary layer at large tail distances indicates that plasma from the magnetosheath often crosses the magnetopause locally along much of the length of the tail, and is evidence that the tail is 'open'.

Gosling, J. T.↗
NASA NTRS1985

Magnetic field properties of Jupiter's tail at distances from 80 to 7500 Jovian radii

The results of a detailed study of the magnetic field data on the near and distant Jovian magnetotail from both Voyager 1 and 2 are presented. The spacecraft trajectories and the data are reviewed, and four distant tail encounters are examined and compared with the corresponding Voyager 1 interplanetary data sets. A power spectral analysis of both the near and distant tail intervals is given, and some of the differences between the tail encounters and the power spectra of these control data sets are discussed. Two solar wind or magnetosheath data sets obtained when Voyager 2 was not in the distant tail are analyzed. These more 'normal' solar wind conditions are contrasted with those reflected in both the Voyager 2 distant tail encounters and the conditions monitored by Voyager 1 farther downstream.

Goldstein, M. L.↗
NASA NTRS1986

Aerodynamic characteristics of several current helicopter tail boom cross sections including the effect of spoilers

Aerodynamic characteristics were determined of three cylindrical shapes representative of tail boom cross sections of the U.S. Army AH-64, UH-60, and UH-1H helicopters. Forces and pressures were measured in a wind-tunnel investigation at the Langley Research Center. Data were obtained for a flow incidence range from -45 to 90 deg and a dynamic pressure range from 1.5 to 50 psf. These ranges provided data representative of full-scale Reynolds numbers and the full range of flow incidence to which these helicopter tail boom shapes would be subjected at low flight speeds. The effects of protuberances such as tail rotor drive-shaft covers and spoilers were evaluated. The data indicate that significant side loads on tail booms of helicopters can be generated and that the addition of spoilers can beneficially alter the side loads. Although an increase in vertical drag occurs, the net effect through reduction of tail rotor thrust required can be an improvement in helicopter performance.

Wilson, J. C.↗
NASA NTRS1985

Runaway tails in magnetized plasmas

The evolution of a runaway tail driven by a dc electric field in a magnetized plasma is analyzed. Depending on the strength of the electric field and the ratio of plasma to gyrofrequency, there are three different regimes in the evolution of the tail. The tail can be (1) stable with electrons accelerated to large parallel velocities, (2) unstable to Cerenkov resonance because of the depletion of the bulk and the formation of a positive slope, (3) unstable to the anomalous Doppler resonance instability driven by the large velocity anisotropy in the tail. Once an instability is triggered (Cerenkov or anomalous Doppler resonance) the tail relaxes into an isotropic distribution. The role of a convection type loss term is also discussed.

Moghaddam-Taaheri, E.↗
NASA NTRS1986

Quasi-stagnant plasmoid in the middle tail - A new preexpansion phase phenomenon

From the analysis of ISEE 3 data it is found that a plasmoid is sometimes formed in the middle tail outside the intervals of the substorm expansion phase. This plasmoid is produced by reconnection at the X-type neutral line, which is located earthward of the distant neutral line but beyond the substorm-associated near-tail neutral line, and it is almost stagnant in that the associated flow speed is less than 300 km/s. The blocking effect of the distant neutral line is the most probable reason for the slow movement. The quasi-stagnant plasmoid is observed at x = -60 to - 100 earth radii for a duration of a few tens of minutes, and in about one half of the cases it is followed by the fast tailward streaming. The onset of this streaming tends to coincide with the onset of the substorm expansion phase, and this probably occurs when the reconnection at the middle-tail neutral line comes close to processing the last closed field line. Intensification of the dawn-to-dusk electric field that causes the mantle plasma to reach the plasma sheet boundary closer to the earth is suggested as the reason for the formation of the middle-tail neutral line earthward of the distant neutral line. The effects on the energetic particle flux and relation to the near-tail reconnection are also discussed.

Nishida, A.↗
NASA NTRS1986

Progress in tail rotor noise analysis

Helicopter tail rotor noise generated by interactions with the main rotor tip vortices and with the fuselage separation mean wake is investigated. The tail rotor blade-main rotor tip vortex interaction is modeled as an airfoil of infinite span cutting through a moving vortex. The present results are compared to the tail rotor loading and high speed thickness noise and are found to be significant. This noise mechanism is a function of the helicopter operating conditions and the location of the tail relative to the main rotor. Tail rotor self-generated noise due to turbulent vortex shedding from blunt trailing edges is also analyzed.

Chou, S.-T.↗
NASA NTRS1986

The stability of the cometary plasma tail and rays

The stability of both the main cometary plasma tail and the tail rays is considered, taking into account the coupling between the plasma and the neutrals that flow out radially from the nucleus. It is shown that this coupling has a negligible effect on wave damping. Rather, it was found that the neutral wind tends to destabilize the flanks of the main tail. On the other hand, the cometary rays are subject to both stabilizing and destabilizing effects because of the ion-neutrals drag. As a result, helical perturbations should become azimuthally asymmetric. The study predicts that the folding rays may become wavy while approaching the tail axis, whereas they should remain straight far away from the tail axis.

Ershkovich, A. I.↗
NASA NTRS1988

On the persistence of unstable bump-on-tail electron velocity distributions in the earth's foreshock

This paper presents further evidence for the persistence of bump-on-tail unstable reduced velocity distributions in the earth's electron foreshock, which contradicts the understanding of quasi-linear saturation of the bump-on-tail instability. A modified theory for the saturation of the bump-on-tail instability in the earth's foreshock is proposed to explain the mechanism of this persistence, and the predictions are compared to the results of a numerical simulation of the electron plasma in the foreshock. The results support the thesis that quasi-linear saturation of the bump-on-tail instability is modified in the foreshock, due to the driven nature of the region, so that at saturation the stabilized velocity distribution still appears bump-on-tail unstable to linear plasma analysis.

Klimas, Alexander J.↗
NASA NTRS1989

Acoustic test of a model rotor and tail rotor: Results for the isolated rotors and combined configuration

Acoustic data from a model scale main rotor and tail rotor experiment in the NASA Langley 14 by 22 Foot Subsonic Tunnel are presented for the main rotor and trail rotor in isolation and for the two rotors operating together. Results for the isolated main rotor show the importance of the rotor flapping conditions on mid-frequency noise content. High levels of main rotor retreating side blade-vortex interaction noise are shown to radiate downstream of the model. The isolated tail rotor noise results show the dominance of harmonic noise in the thrusting direction. The occurrence of tail rotor broadband noise is seen by the broadening of the tail rotor harmonics and is attributed to fuselage wake turbulence. The combined main and tail rotor data are presented to show the dominance of each rotor's different noise sources at different directivity locations.

Martin, R. M.↗
NASA NTRS1990

Effect of tail size reductions on longitudinal aerodynamic characteristics of a three surface F-15 model with nonaxisymmetric nozzles

An investigation was conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of horizontal and vertical tail size reductions on the longitudinal aerodynamic characteristics of a modified F-15 model with canards and 2-D convergent-divergent nozzles. Quantifying the drag decrease at low angles of attack produced by tail size reductions was the primary focus. The model was tested at Mach numbers of 0.40, 0.90, and 1.20 over an angle of attack of -2 degree to 10 degree. The nozzle exhaust flow was simulated using high pressure air at nozzle pressure ratios varying from 1.0 (jet off) to 7.5. Data were obtained on the baseline configuration with and without tails as well as with reduced horizontal and/or vertical tail sizes that were 75, 50, and 25 percent of the baseline tail areas.

Frassinelli, Mark C.↗