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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Wind-tunnel roll-damping measurements of a winged space shuttle configuration in launch attitude

Ground-wind load studies were conducted on three model configurations to assess the importance of aeroelastic instabilities of erected space shuttle vehicles. Roll damping was measured on a fuselage-alone model, which had a D cross section, and a fuselage and tail surfaces in combination with either a clipped-delta wing or a low-sweep tapered wing as the primary lifting surface. The largest negative roll-damping coefficients were measured with the fuselage-alone configuration and were a function of wind azimuth. At the wind azimuths at which the wing-fuselage configuration was unstable, the negative roll-damping coefficients were a function of reduced frequency.

Hess, R. W.↗
NASA NTRS1974

Method of making rolling element bearings

A method is described of making rolling elements by forming low mass cores having either hollow centers or being of a low mass material. The low mass cores are plated and heat treated to provide hard surfaces on the rolling elements. After grinding to the proper diameter the rolling elements are assembled between races to form a hearing.

Parker, R. J.↗
NASA NTRS1975

Experimental pitch-, yaw-, and roll-damping characteristics of a shuttle orbiter at Mach number 8

Wind tunnel tests were conducted to measure the pitch-, yaw-, and roll-damping characteristics of a modified 089B shuttle orbiter. These tests were conducted for NASA-Langley at the von Karman Gas Dynamics Facility of the Arnold Engineering Development Center. Data were obtained utilizing the small amplitude forced-oscillation technique at angles of attack of -4.9 to 26.5 deg at Reynolds numbers, based on model length, of 1,180,000 to 4,820,000. The orbiter was dynamically stable in pitch, yaw, and roll, and the pitch derivatives were dependent on Reynolds number, while the roll derivatives were independent of Reynolds number.

Uselton, B. L.↗
NASA NTRS1975

Effect of starvation on film thickness and traction under elastohydrodynamic rolling and sliding conditions

Traction measurements under starved elastohydrodynamic conditions were obtained for a point-contact geometry. Simultaneous measurements of the film thickness and the location of the inlet lubricant boundary were made. Optical interferometry was used to measure film thickness. The thickness of a starved film for combined rolling and sliding conditions varies with the location of the inlet boundary in the same way as previously found for pure rolling conditions. When the fluid velocity distribution is calculated in the inlet region by a Reynolds lubrication analysis, backflow is seen to occur over a portion of the inlet region. Backflow is essential for the establishment of a flooded condition. The location of certain fluid velocity conditions within the inlet region, as suggested in the literature, does not adequately describe the onset of starvation. For the same slide-roll ratio a starved film was observed to possess greater traction than a flooded film. Traction measurements under starved conditions were also compared with those under flooded conditions for equivalent shear rates in the Hertzian region. When the shear rates within the Hertzian region were low and the film was severely starved, the measured tractions were lower than expected. This may be due to large shear stresses developed by the large pressure gradients that are generated in the inlet region when it is severely starved.

Wedeven, L. D.↗
NASA NTRS1977

Effect of double vacuum melting and retained austenite on rolling-element fatigue life of AMS 5749 bearing steel

AMS 5749 steel combines the tempering, hot hardness, and hardness retention characteristics of AISI M-50 steel with the corrosion and oxidation resistance of AISI 440C stainless steel. The five-ball fatigue tester was used to evaluate the rolling-element fatigue life of AMS 5749. Double vacuum melting (vacuum induction melting plus vacuum arc remelting, VIM-VAR) produced AMS 5749 material with a rolling-element fatigue life at least 14 times that of vacuum induction melting alone. The VIM-VAR AMS 5749 steel balls gave lives from 6 to 12 times greater than VIM-VAR AISI M-50 steel balls. The highest level of retained austenite, 14.6 percent, was significantly detrimental to rolling-element fatigue life relative to the intermediate level of 11.1 percent.

Parker, R. J.↗
NASA NTRS1978

Rolling element fatigue testing of gear materials

Rolling element fatigue lives of nine alloys were evaluated in Rolling Contact (RC) rigs. Test conditions included a Hertzian stress at 4,826 MPa (700 ksi), a rolling speed of 6.23 m/sec (245 in/sec.). Tests were run with a Type I oil (MIL-L-7808G) at room temperature. B-10 lives (10% failure rate) of alloys were compared versus reference alloys, VIM-VAR AISI M-50 and VAR AISI 9310. Six case carburizing alloys (AISI 9310, CBS600, CBS1000M, EX00014, Vasco X-2 and EX00053) and three through-hardening alloys (AISI M-50, VascoMax 350 and Vasco Matrix 2 evaluated, showed RCF performance inferior or equivalent to that of AISI 9310 and AISI M-50. It was also found that the effects of vacuum melting processes, different tempering temperatures, freezing cycle during heat treating, shot peening, gold plating and chrome plating employed in the present investigation did not significantly affect RCF life.

Nahm, A. H.↗
NASA NTRS1978

Surface temperature measurements in rolling and sliding EHD contacts

In this study, moving surface temperature measurements in rolling and sliding EHD point contacts were made using an available infrared technique. Film thickness and traction have also been measured. Slide-to-roll ratios of -2 to +2 have been studied. By using a different kinematic configuration, stationary surface temperatures have also been measured. It has been shown that, while surface temperature rises in the low slip region are relatively small, stationary surface temperatures are significantly higher than the moving surface temperatures. Flash temperature theory has been extended to cover the combined rolling and sliding conditions. Correlation between the predicted and the measured values has also been performed.

Nagaraj, H. S.↗
NASA NTRS1978

Roll tracking effects of G-vector tilt and various types of motion washout

In a dogfight scenario, the task was to follow the target's roll angle while suppressing gust disturbances. All subjects adopted the same behavioral strategies in following the target while suppressing the gusts, and the MFP-fitted math model response was generally within one data symbol width. The results include the following: (1) comparisons of full roll motion (both with and without the spurious gravity tilt cue) with the static case. These motion cues help suppress disturbances with little net effect on the visual performance. Tilt cues were clearly used by the pilots but gave only small improvement in tracking errors. (2) The optimum washout (in terms of performance close to real world, similar behavioral parameters, significant motion attenuation (60 percent), and acceptable motion fidelity) was the combined attenuation and first-order washout. (3) Various trends in parameters across the motion conditions were apparent, and are discussed with respect to a comprehensive model for predicting adaptation to various roll motion cues.

Jex, H. R.↗
NASA NTRS1978

An experimental wind-tunnel investigation of a ram-air-spoiler roll-control device on a forward-control missile at supersonic speeds

A parametric experimental wind-tunnel investigation was made at supersonic Mach numbers to provide design data on a ram-air-spoiler roll-control device that is to be used on forward-control cruciform missile configurations. The results indicate that the ram-air-spoiler tail fin is an effective roll-control device and that roll control is generally constant with vehicle attitude and Mach number unless direct canard and/or forebody shock impingement occurs. The addition of the ram-air-spoiler tail fins resulted in only small changes in aerodynamic-center location. For the ram-air-spoiler configuration tested, there are large axial force coefficient effects associated with the increased fin thickness and ram-air momentum loss.

Blair, A. B., Jr.↗
NASA NTRS1980

Experimental determination of pure rotary stability derivatives using curved and rolling flow wind tunnel

The technique of using a curved and rolling flow wind tunnel to extract pure rotary stability derivatives is presented. Descriptions of the curved flow and the rolling flow test sections of the Virginia Tech Stability Wind Tunnel are given including methods for obtaining the proper velocity profiles and correcting the data acquired. Results of testing current fighter configurations in this facility are presented with particular attention given to comparing pure rotary derivatives with combined rotary and unsteady derivatives obtained by standard oscillation tests. Also the effect of curved and rolling flow on lateral static stability derivatives is examined.

Lutze, F. H.↗
NASA NTRS1980

Effect of tangential traction and roughness on crack initiation/propagation during rolling contact

Rolling fatigue tests of 0.45 percent carbon steel rollers were carried out using a four roller type rolling contact fatigue tester. Tangential traction and surface roughness of the harder mating rollers were varied and their effect was studied. The results indicate that the fatigue life decreases when fraction is applied in the same direction as that of rolling. When the direction of fraction is reversed, the life increases over that obtained with zero traction. The roughness of harder mating roller also has a marked influence on life. The smoother the mating roller, the longer the life. Microscopic observation of specimens revealed that the initiation of cracks during the early stages of life is more strongly influenced by the surface roughness, while the propagation of these cracks in the latter stages is affected mainly by the tangential traction.

Soda, N.↗
NASA NTRS1981

Static and yawed-rolling mechanical properties of two type 7 aircraft tires

Selected mechanical properties of 18 x 5.5 and 49 x 17 size, type 7 aircraft tires were evaluated. The tires were subjected to pure vertical loads and to combined vertical and lateral loads under both static and rolling conditions. Parameters for the static tests consisted of tire load in the vertical and lateral directions, and parameters for the rolling tests included tire vertical load, yaw angle, and ground speed. Effects of each of these parameters on the measured tire characteristics are discussed and, where possible, compared with previous work. Results indicate that dynamic tire properties under investigation were generally insensitive to speed variations and therefore tend to support the conclusion that many tire dynamic characteristics can be obtained from static and low speed rolling tests. Furthermore, many of the tire mechanical properties are in good agreement with empirical predictions based on earlier research.

Tanner, J. A.↗
NASA NTRS1982

The dynamics of fibril magnetic fields. III - Fibril configurations in steady flows. IV - Trapping in closed convective rolls

The present investigation has the objective to provide an illustration of the equilibrium form of a hypothetical fibril field beneath the surface of the sun. Equilibrium fibril paths in static and moving atmospheres are considered. The provided examples are related to horizontal flows in an atmosphere in which the two anchor points of the arched fibril lie along the flow direction relative to each other. A brief introduction to the subject of the motion of horizontal fibrils in convective rolls is also presented, taking into account some implications for the sun. The equations of motion for a slender, buoyant flux tube extending horizontally along a closed convective roll are solved to illustrate the motion of the flux tube relative to the fluid, and attention is given to theoretical possibilities for the escape of flux tubes from a large horizontal convective roll in the sun.

Parker, E. N.↗
NASA NTRS1982

Development of closed loop roll control for magnetic balance systems

This research was undertaken with the goal of demonstrating closed loop control of the roll degree of freedom on the NASA prototype magnetic suspension and balance system at the MIT Aerophysics Laboratory, thus, showing feasibility for a roll control system for any large magnetic balance system which might be built in the future. During the research under this grant, study was directed toward the several areas of torque generation, position sensing, model construction and control system design. These effects were then integrated to produce successful closed loop operation of the analogue roll control system. This experience indicated the desirability of microprocessor control for the angular degrees of freedom.

Covert, E. E.↗
NASA NTRS1983

Subsonic roll oscillation experiments on the Standard Dynamics Model

The experimental determination of the subsonic roll derivatives of the Standard Dynamics Model, which is representative of a current fighter aircraft configuration, is described. The direct, cross and cross-coupling derivatives are presented for angles of attack up to 41 deg and sideslip angles in the range from -5 deg to 5 deg, as functions of oscillation frequency. The derivatives exhibited significant nonlinear trends at high incidences and were found to be extremely sensitive to sideslip angle at angles of attack near 36 deg. The roll damping and dynamic cross derivatives were highly frequency dependent at angles of attack above 30 deg. The highest values measured for the dynamic cross and cross-coupling derivatives were comparable in magnitude with the maximum roll damping. The effects of oscillation amplitude and Mach number were also investigated, and the direct derivatives were correlated with data from another facility.

Beyers, M. E.↗
NASA NTRS1983

A helicopter flight investigation of roll-control sensitivity, damping and cross coupling in a low altitude lateral maneuvering task

A helicopter in-flight simulation was conducted to determine the effects of variations in roll damping, roll sensitivity, and pitch and roll rate cross-coupling on helicopter flying qualities in a low altitude maneuver. The experiment utilized the UH-1H helicopter in-flight simulator, which is equipped with the V/STOLAND avionics system. The response envelope of this vehicle allowed simulation of configurations with low to moderate damping and sensitivity. A visual, low level slalom course was set up, consisting of constant speed and constant altitude S-turns around the 1000 ft makers of an 8000 ft runway. Results are shown in terms of Cooper-Harper pilot ratings, pilot commentary, and statistical and frequency analyses of the lateral characteristics. These results show good consistency with previous ground simulator results and are compared with existing flying qualities criteria.

Corliss, L. D.↗
NASA NTRS1984

Models for the Effects of G-seat Cuing on Roll-axis Tracking Performance

Including whole-body motion in a flight simulator improves performance for a variety of tasks requiring a pilot to compensate for the effects of unexpected disturbances. A possible mechanism for this improvement is that whole-body motion provides high derivative vehicle state information whic allows the pilot to generate more lead in responding to the external disturbances. During development of motion simulating algorithms for an advanced g-cuing system it was discovered that an algorithm based on aircraft roll acceleration producted little or no performance improvement. On the other hand, algorithms based on roll position or roll velocity produced performance equivalent to whole-body motion. The analysis and modeling conducted at both the sensory system and manual control performance levels to explain the above results are described.

Levison, W. H.↗
NASA NTRS1985

The generation of rolling moments with the superconducting solenoid model

The superconducting solenoid model is a pilot model core for levitation in a wind tunnel magnetic suspension system. This type of core would replace the ferromagnetic core typically installed in the model fuselage. For suspension purposes, the solenoid is operated upon by a set of electromagnets surrounding the wind tunnel which are to support and restrain the model at required positions and orientations under the influence of powerful aerodynamic disturbances. The subject of providing sources of magnets rolling moment for use when spanwise magnets, which can be used for winged models, are not available is covered. Several methods have emerged for generating a rolling moment based on the use of additional superconducting loops or magnetic poles positioned around or within the solenoid. Predictions of the moment capacities of superconducting loops in models sized for a large wind tunnel are presented. An existing prototype superconducting model proved a suitable vehicle for demonstrating and calibrating, at a smaller scale, some of the other roll elements based on magnetic pole devices. Calibration data are included.

Goodyear, M. J.↗