Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “tilt”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

State reversals of optically induced tilt and torsional eye movements

Alternations of the state of apparent self-motion during observation of a large visual display rotating about the line of sight are associated with alternations in the magnitude of induced tilt and torsional eye rotation. In one experiment, shifts in visually induced tilt during these state alternations are found to be in the opposite direction to corresponding shifts in induced ocular torsion. In a second experiment, the reversals of self-motion perception are shown to be an intravisual phenomenon, independent of competing inputs provided by the vestibular system. These results emphasize the importance of distinguishing between visual and vestibular processes in tilt perception and ocular rotation during human orientation to gravitational vertical.

Finke, R. A.↗
NASA NTRS1979

Effect of image tilt of a virtual image display on simulated transport touchdown performance

An evaluation of the visual effect of image tilt of a refractive lens display system is presented. The system was used to present a rudimentary computer generated out the window scene to the pilot of a flight simulator during approach, flare, and touchdown. Comparisons are made of sink rate at touchdown and performances for untilted and tilted displays. Sixty four landings with each condition for a total of 128 touchdowns were made by 3 subjects. Performance measures, such as the flare and touchdown footprints, were recorded and analyzed. The visual effect of the image tilt was investigated for a terrain model board scene.

Parrish, R. V.↗
NASA NTRS1978

Variation of solar cell sensitivity and solar radiation on tilted surfaces

An empirical study was performed (1) to evaluate the validity of various insolation models used to compute solar radiation incident on tilted surfaces from global data measured on horizontal surfaces and (2) to determine the variation of solar cell sensitivity to solar radiation over a wide range of atmospheric condition. Evaluation of the insolation data indicates that the isotropic sky model of Liu and Jordan underestimates the amount of solar radiation falling on tilted surfaces by as much as 10%. An anisotropic-clear-sky model proposed by Temps and Coulson was also evaluated and found to be deficient under cloudy conditions. A new model, formulated herein, reduced the deviations between measured and predicted insolation to less than 3%. Evaluation of solar cell sensitivity data indicates small change (2-3%) in sensitivity from winter to summer for tilted cells. The feasibility of using such global data as a means for calibrating terrestrial solar cells as done by Treble is discussed.

Klucher, T. M.↗
NASA NTRS1979

Eye torsion and visual tilt are mediated by different binocular processes

Viewing a large, patterned field rotating about the line of sight produces two measurable effects; cyclotorsion of the eyes (torsion) and a perceived displacement of vertical and horizontal (tilt). Experiments examining binocular interaction for these effects show: (1) both effects demonstrate summation in normal individuals and thus both involve a binocular process; (2) the process for tilt is different than for torsion, since summation for torsion is spared in stereodeficient individuals while that for tilt is eliminated.

Wolfe, J. M.↗
NASA NTRS1980

The relation between tilt table and acceleration-tolerance and their dependence on stature and physical fitness

A group of 12 highly trained athletes and a group of 12untrained students were subjected to passive changes of position on a tilt table and positive accelerations in a centrifuge. During a 20 min tilt, including two additional respiratory maneuvers, the number of faints and average cardiovascular responses did not differ significantly between the groups. During linear increase of acceleration, the average blackout level was almost identical in both groups. Statistically significant coefficients of product-moment correlation for various relations were obtained. The coefficient of multiple determination computed for the dependence of acceleration tolerance on heart-eye distance and systolic blood pressure at rest allows the explanation of almost 50% of the variation of acceleration tolerance. The maximum oxygen uptake showed the expected significant correlation to the heart rate at rest, but not the acceleration tolerance, or to the cardiovascular responses to tilting.

Klein, K. E.↗
NASA NTRS1980

Investigations of tilt measurements using shallow borehole tiltmeters

An array of shallow borehole tiltmeters has been operated at Pinon Flat Observatory since early in 1977. The data from this array are examined for coherence between the individual instruments and compared with the corresponding data from three 732-m laser strainmeters. In general, there is no significant coherence between the signals from the tiltmeters outside the microseismic and tidal bands even though they are spaced as closely as 10 m apart. Comparisons with the strain records show that the observed tilt noise power exceeds the strain noise power by 25-40 dB over the band from 0.000001 to 1 Hz. Analysis of the coherence estimates establishes the necessity for an unacceptably large (approximately 1000) array of instruments in order to determine the common tectonic signals. The observed secular tilt rates are from 40 to 450 times the observed secular strain rates for the same period. The theoretical noise power limit of the tilt transducer renders the instrument incapable of recording background noise at a quiet site over the band from 0.0001 to 0.1 Hz.

Wyatt, F.↗
NASA NTRS1981

Eye torsion and the apparent horizon under head tilt and visual field rotation

Two different experimental manipulations, namely head tilt and the viewing of a visual display rotating around the line of sight, induce torsional displacements of the eyes and a tilting of the apparent horizon. The present study examines the routes by which visual (field rotation) and otolith-proprioceptive (head tilt) sources of afference influence horizon judgments. In particular, the relationship between torsional eye movements and horizon estimates is addressed. The results indicate that visual and otolith-proprioceptive information sum directly in their influence on eye torsion, but interact more complexly in horizon estimates, indicating a dissociation of their central determinants.

Merker, B. H.↗
NASA NTRS1985

Cosmic ray intensity and the tilt of the neutral sheet

Recent publications have related long-term variations in cosmic ray intensity at the Earth with long term variations in the tilt of the neutral sheet in the inner heliosphere. The tilt of the neutral sheet from 1971 to 1974 is compared with the cosmic ray intensity at Earth, recorded by the Mt. Washington neutron monitor. The remarkable large decreases in cosmic ray intensity which occurred in 1973 and 1974 correlate well with excursions in the tilt of the neutral sheet which occurred earlier during these same two years.

Saito, T.↗
NASA NTRS1984

Simulation validation of the XV-15 tilt-rotor research aircraft

The results of a simulation validation program of the XV-15 tilt-rotor research aircraft are detailed, covering such simulation aspects as the mathematical model, visual system, motion system, cab aural system, cab control loader system, pilot perceptual fidelity, and generic tilt rotor applications. Simulation validation was performed for the hover, low-speed, and sideward flight modes, with consideration of the in-ground rotor effect. Several deficiencies of the mathematical model and the simulation systems were identified in the course of the simulation validation project, and some were corrected. It is noted that NASA's Vertical Motion Simulator used in the program is an excellent tool for tilt-rotor and rotorcraft design, development, and pilot training.

Ferguson, S. W.↗
NASA NTRS1985

A study of the cornering forces generated by aircraft tires on a tilted, free-swiveling nose gear

An experimental investigation was conducted to study the effect of various parameters on the cornering forces produced by a rolling aircraft tire installed on a tilted, free-swiveling nose gear. The parameters studied included tilt angle, trial, tire inflation pressure, rake angle, vertical load, and whether or not a twin tire configuration corotates. These parameters were evaluated by measuring the cornering force produced by an aircraft tire installed on the nose gear of a modified vehicle as it was towed slowly. Cornering force coefficient increased with increasing tilt angle. Increasing trial or rake angle decreased the magnitude of the cornering force coefficient. Tire inflation pressure had no effect on the cornering force coefficient. Increasing vertical load decreased the cornering force coefficient. When the tires of a twin tire system rotated independently, the cornering force coefficients were the same as those for the single-tire configuration. When the twin tire system was made to corotate, however, the cornering force coefficients increased significantly.

Daugherty, R. H.↗
NASA NTRS1986

Calculated performance, stability and maneuverability of high-speed tilting-prop-rotor aircraft

The feasibility of operating tilting-prop-rotor aircraft at high speeds is examined by calculating the performance, stability, and maneuverability of representative configurations. The rotor performance is examined in high-speed cruise and in hover. The whirl-flutter stability of the coupled-wing and rotor motion is calculated in the cruise mode. Maneuverability is examined in terms of the rotor-thrust limit during turns in helicopter configuration. Rotor airfoils, rotor-hub configuration, wing airfoil, and airframe structural weights representing demonstrated advance technology are discussed. Key rotor and airframe parameters are optimized for high-speed performance and stability. The basic aircraft-design parameters are optimized for minimum gross weight. To provide a focus for the calculations, two high-speed tilt-rotor aircraft are considered: a 46-passenger, civil transport and an air-combat/escort fighter, both with design speeds of about 400 knots. It is concluded that such high-speed tilt-rotor aircraft are quite practical.

Johnson, Wayne↗
NASA NTRS1986

Calculated performance, stability, and maneuverability of high-speed tilting-prop-rotor aircraft

The feasability of operating tilting-prop-rotor aircraft at high speeds is examined by calculating the performance, stability, and maneuverability of representative configurations. The rotor performance is examined in high-speed cruise and in hover. The whirl-flutter stability of the coupled-wing and rotor motion is calculated in the cruise mode. Maneuverability is examined in terms of the rotor-thrust limit during turns in helicopter configuration. Rotor airfoils, rotor-hub configuration, wing airfoil, and airframe structural weights representing demonstrated advanced technology are discussed. Key rotor and airframe parameters are optimized for high-speed performance and stability. The basic aircraft-design parameters are optimized for minimum gross weight. To provide a focus for the calculations, two high-speed tilt-rotor aircraft are considered: a 46-passenger, civil transport and an air-combat/escort fighter, both with design speeds of about 400 knots. It is concluded that such high-speed tilt-rotor aircraft are quite practical.

Johnson, Wayne↗
NASA NTRS1988

Improvements to tilt rotor performance through passive blade twist control

A passive blade twist control is presented in which the twist distribution of a tilt rotor blade is elastically changed as a function of rotor speed. The elastic twist deformation is used to achieve two different blade twist distributions corresponding to the two rotor speeds used on conventional tilt rotors in hover and forward flight. By changing the blade twist distribution, the aerodynamic performance can be improved in both modes of flight. The concept presented obtains a change in twist distribution with extension-twist-coupled composite blade structure. This investigation first determines the linear twists which are optimum for each flight mode. Based on the optimum linear twist distributions, three extension-twist-coupled blade designs are developed using coupled-beam and laminate analyses integrated with an optimization analysis. The designs are optimized for maximum twist deformation subject to material strength limitations. The aerodynamic performances of the final designs are determined which show that the passive blade twist control concept is viable, and can enhance conventional tilt rotor performance.

Nixon, Mark W.↗
NASA NTRS1988

Ocular torsion in upright and tilted positions during hypo- and hypergravity of parabolic flight

Four subjects considered resistant to motion sickness were tested in KC-135 parabolic flight to examine ocular torsion at hypo-gravity and hypergravity. Three of these subjects showed no significant torsion at zero G in either the upright position or when tilted 30 deg to right or left. At 1.8 G in the tilted positions, they showed greater ocular counterrolling than at 1 G. None of these three subjects became motion sick. The fourth subject showed eye torsion toward his left in all positions at zero G. This leftward bias could also be seen at 1.8 G when tilted left ear down, the side that induces rightward counterrolling. There he had less eye torsion than at 1 G. This subject became motion sick. These results support the hypothesis that asymmetry of the utricular system may be well compensated in the normal 1 G environment, but unmasked in unaccustomed gravitational situations, suggesting a possible predictive test for space adaptation syndrome.

Diamond, Shirley G.↗
NASA NTRS1989

Tilt rotor aircraft aeroacoustics

This paper studies the state of knowledge and the needed improvement in noise methodology and measurements for tilt rotor aircraft. Similarities and differences between tilt rotor aeroacoustic conditions and helicopter and propeller experience are identified. A discussion of the possible principal noise mechanisms throughout the flight envelope shows a need for further experimental and analytical investigations to develop an adequate understanding of the important sources and influencing factors. Existing experimental data from flight tests suggest terminal area noise reduction by operating within certain portions of the conversion flight envelope. Prediction methods are found to provide approximate indications only for low frequency harmonic and broadband noise for several of the tilt rotor's operating conditions. The acoustic effects of the hover case 'fountain' flow are pronounced and need further research. Impulsive noise and high frequency harmonic noise remain problems, as on helicopters, pending major improvements in wake, unsteady aerodynamics, and acoustics methodology.

George, Albert R.↗
NASA NTRS1990

Mars - Change in axial tilt due to climate?

The average tilt of Mars' equator with respect to its orbital plane may have increased significantly over the age of the solar system. Obliquity oscillations might have induced changes in the climate, which altered the mass distribution and hence the solar torque on the planet. Viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt. Earth-like effective viscosities can account for virtually the entire present obliquity of 24.4 degrees. Thus the present average tilt of Mars may not be primordial.

Rubincam, David Parry↗
NASA NTRS1988

A review of tilt rotor download research

Experimental and theoretical research on the forces on a wing immersed in the wake of a hovering rotor is reviewed, with emphasis on the tilt rotor download problem. The basic features of the rotor/wing flow field on a tilt rotor aircraft are described. The effect of important geometric and operational parameters on the wing download is assessed. The magnitude of the download for typical tilt rotor configurations is reviewed, and advanced concepts for download reduction are described. Recommendations are presented for the direction of future research efforts.

Felker, Fort F.↗
NASA NTRS1990

Intraocular pressure, retinal vascular, and visual acuity changes during 48 hours of 10-deg head-down tilt

Intraocular pressures, retinal vascular diameters, and visual acuities of nine men, were repeatedly measured while the subjects were tilted 10 deg head-down for 48 h and while they were seated before (baseline), and after the tilt. An immediate increase in intraocular pressure, measured by pneumatonometer was recorded when subjects assumed the head-down position, and diurnal variations in intraocular pressures were observed for the 48 h. The initial and final head-down intraocular pressures were not significantly different. However, when subjects resumed the sitting position, intraocular pressures fell below the initial sitting values. Computer image analysis of the retinal vasculature detected a 6 percent and 2 percent reduction in the caliber of arteries and veins, respectively, as compared with sitting baseline values. No changes in visual acuity were documented during the 48 h of head-down tilt. The data suggest that the choroidal blood reservoir increases in volume over 48 h at continuous head-down position with a compensatory decrease in aqueous volume. These findings may explain intraocular pressure changes noted in astronauts during previous space missions and in studies associated with change in body position.

Mader, Thomas H.↗