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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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Tandem wheel drop-leg device provides a semitrailer with fore and aft mobility that allows it to be moved without a prime mover. The modified drop-legs have trunnion dual wheels and an adjustable brace.
System employs synchronous motor driven by deflection waveform of TV and connected directly to color filter wheel to phase lock wheel to deflection unit. Innovation stabilizes color response of small TV cameras and allows for small, lightweight installations. Problems associated with motor phase changes are cited.
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.
An engineering model of a momentum wheel is described that is suspended by magnetic bearings. It consists of a mechanical assembly on the right, and associated electronics on the left. The momentum wheel is mounted at the center of the rotor shaft and the magnetic bearings are on each end. The rotor is magnetically suspended so there is no physical contact between the rotor and the support structure. The system, therefore, can operate directly in the vacuum environment without lubrication; and it has virtually unlimited operating lifetime, independent of speed.
The sealing techniques are studied for existing aircraft wheel-tire designs to meet the hard vacuum .00001 torr and cold temperature -65 F requirements of space travel. The investigation covers the use of existing wheel seal designs.
The study included material selection and trade-off for the structural components of the wheel and brake optimizing weight vs cost and feasibility for the space shuttle type application. Analytical methods were used to determine section thickness for various materials, and a table was constructed showing weight vs. cost trade-off. The wheel and brake were further optimized by considering design philosophies that deviate from standard aircraft specifications, and designs that best utilize the materials being considered.
The development of light weight wheel and brake systems designed to meet the space shuttle type requirements was investigated. The study includes the use of carbon graphite composite and beryllium as heat sink materials and the compatibility of these heat sink materials with the other structural components of the wheel and brake.
The design and fabrication of a dual spin gas bearing reaction wheel are discussed. Numerical analyses, data, and conclusions from performance tests are reported. The unique feature of the reaction wheel is the dual gas bearing concept in which two sets of self-acting hydrodynamic bearing are used to obtain stictionless operation and low noise around zero speed and to accommodate the momentum range from plus 6.8 N-m-s to minus 6.8 N-m-s with the potential for long life inherent in gas bearings.
Results are described of a study program in which the characteristics of a magnetically supported reaction wheel are defined. Tradeoff analyses are presented for the principal components, which are then combined in several reaction wheel design concepts. A preliminary layout of the preferred configuration is presented along with calculated design and performance parameters. Recommendations are made for a prototype development program.
The failure of high speed emergency braking is discussed for railroad wheels and track. It is shown that high compressive residual stresses exist in the rims of new wheels which generate excessive heat, reducing the stress levels. Thermal stresses that build up in continuous lengths of welded track are reported and nondestructive methods of measuring stresses in thick steel are presented for identification, replacement, or adjustment before hazardous failures occur.
An engineering model of a magnetically suspended momentum wheel was designed, fabricated, and tested under laboratory conditions. The basic unit consisted of two magnet bearings, a sculptured aluminum rotor, brushless dc spin motor, and electronics. The magnet bearings, utilizing rare-earth cobltrat-samarium magnets were active radially and passive axially. The results of the program showed that momentum wheels with magnetic bearings are feasible and operable, and that magnetic bearings of this type are capable of being used for applications where high capacity, high stiffness, and low power consumption are required. The tests performed developed criteria for improved performance for future designs.
The fabrication and testing of three reaction wheels with associated drive and system monitoring electronics and brushless dc spin motors are discussed; the wheels are intended for use in a teleoperator simulator. Test results are included as graphs.
Engineering details, project status, system design and specifications, and test results are presented on a powered-wheel drive system based on the Dynavector rotary actuator. The design and operation of the Dynavector system (with positive displacement very-low-inertia nonrotating vane motor) are reviewed. Feasibility studies, contract data, and findings of braking tests are described. Exploded diagrams of Dynavector details are displayed. Success in using powered wheels in lieu of aircraft main engines for on-ground movements should bring benefits in energy conservation, noise abatement, reduced pollution, and alleviated congestion in the terminal area.
An experimental investigation was conducted at the Langley aircraft landing loads and traction facility to study the braking and cornering response of a slip ratio controlled aircraft antiskid braking system with ground speed reference derived from an unbraked nose wheel. The investigation, conducted on dry and wet runway surfaces, utilized one main gear wheel, brake, and tire assembly of a DC-9 series 10 airplane. During maximum braking, the average ratio of the drag force friction coefficient developed by the antiskid system to the maximum drag force friction coefficient available was higher on the dry surface than on damp and flooded surfaces, and was reduced with lighter vertical loads, higher yaw angles, and when new tire treads were replaced by worn treads. Similarly, the average ratio of side force friction coefficient developed by the tire under antiskid control to the maximum side force friction coefficient available to a freely rolling yawed tire decreased with increasing yaw angle, generally increased with ground speed, and decreased when tires with new treads were replaced by those with worn treads.
Continuing efforts to improve the University of San Francisco/NASA toxicity screening test method have included the addition of exercise wheels to provide a different measure of incapacitation, and oxygen replenishment to offset any effect of oxygen depletion by the test animals. The addition of exercise wheels limited the number of animals in each test and doubled the required number of tests without any significant improvement in reproducibility. Oxygen replenishment appears to have an effect on survival in the last 5 minutes of the 30-minute test, but the effect is expected to be similar for most materials.
One type of azimuth bearing for a large ground antenna (100 m) will consist of steel wheels, mounted at four corners of the alidade, rolling on a circular flat rail which provides the vertical restraints; a radial constraining bearing at the center of the alidade provides the horizontal restraints. One important design feature is the compressive stresses in the grout or concrete foundation under the wheel-rail load. A finite element analysis check was made of a particular design that consists of a steel rail resting on a concrete foundation. Symmetry was assumed as much as possible in order to minimize the models, but meaningful element sizes were used. Recently developed isoparametric hexahedron elements available in the NASTRAN computing program, which minimizes the number of elements required while maintaining the accuracy of the computed stresses, were used with two versions of NASTRAN. Test cases to check with the analytical solutions were made. A side loading was also applied to calculate the increase in the concrete stresses.
A flexure strut wheel suspension system is described which keeps a wheel flat against the track and maintains a small interface moment. Equations are presented for the evaluation of this moment. A comparison of the flexure strut system is made with a rigid link design containing pivot bearings.
Magnetic bearings used for the suspension of momentum wheels provide conclusive advantages: the low friction torques and the absence of abrasion allow the realization of lightweight high speed wheels with high angular momentum and energy storage capacity and virtually unlimited lifetime. The use of actively controlled bearings provides a magnetic gimballing capability by applying the external signals to the two servo loops controlling the rotational degrees of freedom. Thus, an attitude control system can be realized by using only one rotating mass for 3-axis active satellite stabilization.