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At least 271 records · Page 15

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NASA NTRS1972

Effect of environmental torques on short-term attitude prediction for a rolling-wheel spacecraft in a sun-synchronous orbit

A numerical evaluation and an analysis of the effects of environmental disturbance torques on the attitude of a hexagonal cylinder rolling wheel spacecraft were performed. The resulting perturbations caused by five such torques were found to be very small and exhibited linearity such that linearized equations of motion yielded accurate results over short periods and the separate perturbations contributed by each torque were additive in the sense of superposition. Linearity of the torque perturbations was not affected by moderate system design changes and persisted for torque-to-angular momentum ratios up to 100 times the nominal expected value. As these conditions include many possible applications, similar linear behavior might be anticipated for other rolling-wheel spacecraft.

Hodge, W. F.↗

NASA NTRS1972

Determination of angles of attack and sideslip from radar data and a roll-stabilized platform

Equations for angles of attack and sideslip relative to both a rolling and nonrolling body axis system are derived for a flight vehicle for which radar and gyroscopic attitude data are available. The method is limited to application where a flat, nonrotating earth may be assumed. The gyro measures attitude relative to an inertial reference in an Euler angle sequence. In particular, a pitch, yaw, and roll sequence is used as an example in the derivation. Sample calculations based on flight data are presented to illustrate the method. Results obtained with the present gyro method are compared with another technique that uses onboard camera data.

Preisser, J. S.↗

NASA NTRS1972

Effect of carbide size, area, density on rolling-element fatigue

A carbide parameter that can be used to predict rolling element fatigue life was developed.The parameter is based on a statistical life analysis and incorporates the total number of particles per unit area, particle size, and percent carbide area. These were determined from quantimet image analyzing computer examinations of random samples selected from eight lots of material previously tested in rolling fatigue. The carbide parameter is independent of chemical composition, heat treatment, and hardening mechanism of the materials investigated.

Chevalier, J. L.↗

NASA NTRS1972

A new criterion for predicting rolling-element fatigue lives of through-hardened steels

A carbide factor was derived based upon a statistical analysis which related rolling-element fatigue life to the total number of residual carbide particles per unit area, median residual carbide size, and percent residual carbide area. An equation was experimentally determined which predicts material hardness as a function of temperature. The limiting temperatures of all of the materials studied were dependent on initial room temperature hardness and tempering temperature. An equation was derived combining the effects of material hardness, carbide factor, and bearing temperature to predict rolling-element bearing life.

Chevalier, J. L.↗

NASA NTRS1972

Hot press and roll welding of titanium-6-percent-aluminum-4-percent-vanadium bar and sheet with auto-vacuum cleaning

Hot press butt welds were made in 0.5 in. diameter bar, and roll lap welds were made in 0.060 in. thick sheet of Ti-6A1-4V. For hot press welds made after auto-vacuum cleaning at 1800 F for 2 hours, weld strength and ductility equaled the parent metal properties. Only 5 minutes of pressing time were needed at 1800 F and 200 psi to make the hot press welds. Roll welds were made in sheet at 1750 F with only 10 percent deformation. The welds in the bar and sheet were metallurgically indistinguishable from the parent material.

Holko, K. H.↗

NASA NTRS1971

Roll angle detector.

Description of a roll angle detector system under development that is designed to measure the relative roll angle of two independent bodies to a high degree of precision. The system involves the imaging of a very small aperture by an optical system on one body onto the surface of the other. A review of the underlying mathematical principle, is followed by an optical-mechanical and electrical description of the system and a listing of several important sources of measurement errors. The ultimate achievement of an accuracy of plus or minus 5 arc seconds is expected.

Lowen, I.↗

NASA NTRS1972

Rolling-element fatigue life of silicon nitride balls: Preliminary test results

Hot pressed silicon nitride was evaluated as a rolling element bearing material. The five-ball fatigue tester was used to test 12.7 mm (0.500 in.) diameter balls at a maximum Hertz stress of 800,000 psi at a race temperature of 130 F. The fatigue spalls in the silicon nitride resembled those in typical bearing steels. The ten-percent fatigue life of the silicon nitride balls was approximately one-eighth to one-fifth that of typical bearing steels (52100 and M-50). The load capacity of the silicon nitride was approximately one-third that of typical bearing steels. The load capacity of the silicon nitride was significantly higher than previously tested ceramic materials for rolling element bearings.

Parker, R. J.↗

NASA NTRS1972

A new criterion for predicting rolling-element fatigue lives of through-hardened steels.

A carbide factor was derived based upon a statistical analysis which related rolling-element fatigue life to the total number of residual carbide particles per unit area, median residual carbide size, and percent residual carbide area. An equation was empirically determined which predicts material hardness as a function of temperature. The limiting temperatures of all of the materials studied were dependent on initial room temperature hardness and tempering temperature. An equation was derived combining the effects of material hardness, carbide factor, and bearing temperature to predict rolling-element bearing life.

Chevalier, J. L.↗

NASA NTRS1973

Are penumbral filaments convection rolls.

The occurrence of strong magnetic fields in dark filaments in sunspot penumbrae is shown to be only marginally consistent with the hypothesis of penumbral convection rolls. Convection rolls are not permitted if the field in dark filaments exceeds that in bright filaments by more than 2%. The upper limit to this excess may be as small as 0.8% if not in fact negative.

Mullan, D. J.↗

NASA NTRS1974

Two-dimensional Gaussian processes applied to the determination of contact between lubricated rolling surfaces

The effectiveness of a lubricant film preventing metallic contact between two rolling surfaces (such as in ball bearings) as a function of surface roughness parameters was investigated. The parameters considered are the spectral moments of the two-dimensional surface obtained by superposition of the two rolling surfaces. The peak height distribution, estimation of one-dimensional profile spectral moments, and the estimation of two-dimensional surface moments from several profile measurements were considered. Also given is an asymptotic relation between the mean film thickness and contact occurrences.

Sidik, S. M.↗

NASA NTRS1974

Rolling-element fatigue life of silicon nitride balls

The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of bearing quality steel running against steel at stress levels typical rolling-element bearing application. The fatigue life of hot-pressed silicon nitride is considerably greater than that of any ceramic or cermet tested. Computer analysis indicates that there is no improvement in the lives of 120-mm-bore angular--contact ball bearings of the same geometry operating at DN values from 2 to 4 million where hot-pressed silicon nitride balls are used in place of steel balls.

Parker, R. J.↗

NASA NTRS1973

The 'rolling motion' phenomenon in galactic spiral arms

The 'rolling motion' in the spiral arms in the outer parts of the Galaxy are interpreted as only apparent motions caused by the combined effect of the bending of the galactic plane and the differential rotation. Theoretical contour maps (latitude vs velocity) are plotted in a number of directions on both sides of the Galaxy for direct comparison with observations. The velocity and density fields used in the calculations are based on a linear analysis of the three-dimensional gas motions in response to the spiral density-wave potential studied by Lin, Shu, and Yuan and by Vandervoort (1970). It is found that the combined effect under consideration is sufficient to cause an apparent rolling motion in a spiral arm.

Yuan, C.↗

NASA NTRS1974

Two-dimensional Gaussian processes applied to the determination of contact between lubricated rolling surfaces

Theoretical investigation of how effectively a lubricant film prevents metallic contact between two rolling surfaces (such as in ball bearings) as a function of surface roughness parameters. The parameters considered are the spectral moments of the two-dimensional surface obtained by superposition of the two rolling surfaces. We consider the peak height distribution, estimation of one-dimensional profile spectral moments, and the estimation of two-dimensional surface moments from several profile measurements are taken into account. Also given is an asymptotic relation between the mean film thickness and contact occurrences.

Sidik, S. M.↗

NASA NTRS1975

Silicon nitride used as a rolling-element bearing material

Rolling-element fatigue tests were conducted with hot-pressed silicon nitride to determine its ability to withstand concentrated contacts in rolling-element bearings. If hot-pressed silicon nitride is used for both balls and races, attention must be paid to fitting both shaft and bearing housing.

Parker, R. J.↗

NASA NTRS1974

Subsonic roll-damping characteristics of a series of wings

The aerodynamic damping in roll of a series of wings has been investigated in the Langley high-speed 7- by 10-foot tunnel at Mach numbers ranging from 0.2 to 0.8 by use of a forced oscillatory-roll technique. Tests were conducted on wings of aspect ratio 6 with sweep angles of 25, 35, and 45 deg and on 35 deg swept wings of aspect ratios 4 and 5.

Boyden, R. P.↗

NASA NTRS1975

A flight test investigation of the rolling moments induced on a T-37B airplane in the wake of a B-747 airplane

A flight test investigation of the B-747 vortex wake characteristics was conducted using a T-37B as a probe aircraft. The primary purpose of the program was the validation of the results of B-747 model tests which predicted significant alleviation of the vortex strength when only the inboard flaps were deflected. Measurements of the vortex-induced rolling moments of the probe aircraft showed that the predicted alleviation did occur. The effects of landing gear extension, increased lift coefficient, idle thrust, and sideslip were investigated, and all had an adverse effect on the alleviated condition as evidenced by increased induced rolling moments of the T-37B probe aircraft. Idle thrust also increased the strength of the B-747 wake vortexes with both inboard and outboard flaps extended.

Smith, H. J.↗

NASA NTRS1975

Effect of viscosity on rolling-element fatigue life at cryogenic temperature with fluorinated ether lubricants

Rolling-element fatigue tests were conducted with 12.7-mm-(1/2-in.-) diameter AISI 52100 steel balls in the NASA five-ball fatigue tester, with a maximum hertz stress of 5500 mN/m2 (800 000 psi), a shaft speed of 4750 rpm, lubricant temperature of 200 K (360 R), a contact angle of 20 deg, using four fluorinated ether lubricants of varying viscosities. No statistically significant differences in rolling-element fatigue life occurred using the four viscosity levels. Elastohydrodynamic calculations indicate that values of the lubricant film parameter were approximately 2 or greater.

Dietrich, M. W.↗

NASA NTRS1975

Velocity and rolling-moment measurements in the wake of a swept-wing model in the 40 by 80 foot wind tunnel

Measurements were made in the wake of a swept wing model to study the structure of lift generated vortex wakes shed by conventional span loadings and by several span loadings designed to reduce wake velocities. Variations in the span loading on the swept wing generator were obtained by deflecting seven flap segments on each side by amounts determined by vortex lattice theory to approximate the desired span loadings. The resulting wakes were probed with a three component, hot wire probe to measure velocity, and with a wing to measure the rolling moment that would be induced on a following aircraft. The experimental techniques are described herein, and the measured velocity and rolling moments are presented, along with some comparisons with the applicable theories.

Rossow, V. J.↗