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At least 91 records · Page 5

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NASA NTRS1937

Maximum Forces Applied by Pilots to Wheel-type Controls

Measurements were made of the maximum push, pull, and tangential forces that could be applied to airplane wheel-type controls for a wide range of fore-and-aft positions of the wheel. The measurements were conducted with several sizes of wheels and several heights of the center of the wheel above the seat. Various one and two-hand grips with pilots both secure and free were studied for each of the two pilots used in the investigation.

Mcavoy, William H↗

NASA NTRS1937

The Rolling Friction of Several Airplane Wheels and Tires and the Effect of Rolling Friction on Take-Off

This report presents the results of test made to determine the rolling friction of airplane wheels and tires under various conditions of wheel loading, tire inflation pressure, and ground surface. The effect of wheel-bearing type was also investigated. Six pairs of wheels and tires were tested including two sizes of each of the types designated as standard (high pressure), low pressure, and extra low pressure. The results of calculations intended to show the effect of variations in rolling friction on take-off are also presented.

Wetmore, J W↗

NASA NTRS1954

Contribution to the theory of tail-wheel shimmy

A basic theoretical and experimental investigation is made of the shimmy behavior of a swiveling landing gear, the experimental tests being conducted with a small wheel mounted over a continuous belt. Effects of wheel loading, rolling velocity, rearward position of the wheel with respect to the swivel axis, tire elasticity, and torsional flexibility of the fuselage are investigated both experimentally and theoretically. A major theoretical conclusion is that the motion of a landing gear moving in a straight line without fuselage elasticity is stable for a sufficiently large rearward position of the wheel behind the swivel axis, and this conclusion is well verified quantitatively by the experimental data.

LOADS, LANDING - GROUND-RUN, LAND↗

NASA NTRS1994

Dither Helps Compensate For Friction In Reaction Wheel

Dither control and generator unit incorporated into reaction-wheel attitude-control system to help compensate for error caused by friction in reaction-wheel bearings at and near zero speed of wheel. Reaction-wheel attitude-control system designed primarily to maintain desired orientation of spacecraft but also useful in maintaining desired orientation of terrestrial antenna, optical instrument, or other device on aircraft, ship, land vehicle, or other moving platform. Alternating torque sufficient to overcome static friction applied at low speed.

Stetson, John B., Jr.↗

NASA NTRS1995

Automated Verification Of Small Parts In Turbine Wheels

Automated visual-inspection system determines whether turbine wheel assembled in correct positions. Includes two subsystems; part manipulator and control-and-analysis subsystem. Video camera having fixed focal length held stationary while part manipulator rotates turbine wheel to discrete angles so camera views specified positions on wheel. Control-and-analysis subsystem controls rotary table, processes image data acquired by camera, and makes record of inspection. Automated inspection of turbine wheel containing many small parts eliminates tedium and occasional error in repetitive visual and manual inspection by human technicians, enabling technicians to concentrate on nonroutine inspection problems.

Gutow, David A.↗

NASA NTRS1996

Development of a Large Scale, High Speed Wheel Test Facility

Draper Laboratory, with its internal research and development budget, has for the past two years been funding a joint effort with the Massachusetts Institute of Technology (MIT) for the development of a large scale, high speed wheel test facility. This facility was developed to perform experiments and carry out evaluations on levitation and propulsion designs for MagLev systems currently under consideration. The facility was developed to rotate a large (2 meter) wheel which could operate with peripheral speeds of greater than 100 meters/second. The rim of the wheel was constructed of a non-magnetic, non-conductive composite material to avoid the generation of errors from spurious forces. A sensor package containing a multi-axis force and torque sensor mounted to the base of the station, provides a signal of the lift and drag forces on the package being tested. Position tables mounted on the station allow for the introduction of errors in real time. A computer controlled data acquisition system was developed around a Macintosh IIfx to record the test data and control the speed of the wheel. This paper describes the development of this test facility. A detailed description of the major components is presented. Recently completed tests carried out on a novel Electrodynamic (EDS) suspension system, developed by MIT as part of this joint effort are described and presented. Adaptation of this facility for linear motor and other propulsion and levitation testing is described.

Kondoleon, Anthony↗

NASA NTRS1996

Mars Pathfinder: The Wheel Abrasion Experiment

NASA Lewis Research Center's Wheel Abrasion Experiment (WAE) will measure the amount of wear on wheel surfaces of the Mars Pathfinder rover. WAE uses thin films of Al, Ni, and Pt (ranging in thickness from 200 to 1000 angstroms) deposited on black, anodized Al strips attached to the rover wheel. As the wheel moves across the martian surface, changes in film reflectivity will be monitored by reflected sunlight. These changes, measured as output from a special photodetector mounted on the rover chassis, will be due to abrasion of the metal films by martian surface sand, dust, and clay.

Source record↗

NASA NTRS2008

Three Axis Control of the Hubble Space Telescope Using Two Reaction Wheels and Magnetic Torquer Bars for Science Observations

The Hubble Space Telescope (HST) is renowned for its superb pointing accuracy of less than 10 milli-arcseconds absolute pointing error. To accomplish this, the HST relies on its complement of four reaction wheel assemblies (RWAs) for attitude control and four magnetic torquer bars (MTBs) for momentum management. As with most satellites with reaction wheel control, the fourth RWA provides for fault tolerance to maintain three-axis pointing capability should a failure occur and a wheel is lost from operations. If an additional failure is encountered, the ability to maintain three-axis pointing is jeopardized. In order to prepare for this potential situation, HST Pointing Control Subsystem (PCS) Team developed a Two Reaction Wheel Science (TRS) control mode. This mode utilizes two RWAs and four magnetic torquer bars to achieve three-axis stabilization and pointing accuracy necessary for a continued science observing program. This paper presents the design of the TRS mode and operational considerations necessary to protect the spacecraft while allowing for a substantial science program.

Hur-Diaz, Sun↗

NASA NTRS2013

Characterizing the Performance of the Wheel Electrostatic Spectrometer

Insulators need to be discharged after each wheel revolution. Sensor responses repeatable within one standard deviation in the noise of the signal. Insulators may not need to be cleaned after each revolution. Parent Technology- Mars Environmental Compatibility Assessment/Electrometer Electrostatic sensors with dissimilar cover insulators Protruding insulators tribocharge against regolith simulant Developed for use on the scoop for the 2001 Mars Odyssey lander Wheel Electrostatic Spectrometer Embedded electrostatic sensors in prototype Martian rover wheel If successful, this technology will enable constant electrostatic testing on Mars Air ionizing fan used to neutralize the surface charge on cover insulators . WES rolled on JSClA lunar simulant Control experiment -Static elimination not conducted between trials -Capacitor discharged after each experiment Charge neutralization experiment -Static elimination conducted between trials -Capacitor discharged after each experiment. Air ionizing fan used on insulators after each wheel revolution Capacitor discharged after each trial Care was taken to roll WES with same speed/pressure Error bars represent one standard deviation in the noise of e ach sensor

Johansen, Michael R.↗

NASA NTRSDate not supplied

Parametric Optimization of Rigid Wheels for Planetary Surface Mobility Applications

Design-Build-Test approaches for spaceflight hardware are time and cost intensive, which can result in suboptimal mechanism designs. Optimization-based approaches that utilize high-fidelity models and physics simulation could overcome these limitations while simultaneously speeding up the mechanical design process and reducing cost. In this work, we present a toolchain that enables the multi-objective optimization of rigid rover wheels for planetary surface mobility applications. The toolchain uses Chrono’s Continuous Representation Model (CRM) functionality to simulate granular soil and performs multi-objective parametric optimization on candidate rover wheels to meet a desired performance criterion. The resulting wheel design is then evaluated experimentally using a single-wheel testbed. We end with a discussion of how the toolchain can be extended to simultaneously co-optimize other system parameters, such as system power consumption and feedback control gains.

Optimization↗

NASA NTRS2024

Thermal Sensitivity Study of Lunar Terrain Vehicle Wheels

Since the early development of lunar vehicles for the Apollo program, designing a wheel capable of functioning in the harsh equatorial lunar environment was identified as a uniquely difficult engineering challenge. The Lunar Terrain Vehicle (LTV) must contend with many of the same challenges encountered during the Apollo missions, but with the addition of colder, more complex thermal environments at the lunar south pole and longer Artemis mission timelines. A full thermal assessment of LTV wheels should capture these and other details to assess heat leak through the wheels and extreme hot and cold temperatures. The goals of this study are to provide bounding lunar south pole thermal environments; to define sensitivity to interactions between the wheel and the lunar surface in different operation modes, such as parked and traversing; and to identify thermal performance concerns related to the use of shape memory alloys.

Lunar Terrain Vehicle↗

NASA NTRS1928

Wheel brakes and their application to aircraft

The advantages to be gained from braking have not been ignored, and in the search for a suitable method many schemes have been suggested and tried. Some of the methods discussed in this paper include: 1) increasing the height of the landing gear; 2) air brakes of various forms; 3) sprags on tail skid and axle; and 4) wheel brakes. This report focuses on the design of wheel brakes and wheel brake controls.

BRAKES↗

NASA NTRS1955

Reduction of the shimmy tendency of tail and nose-wheel landing gears by installation of specially designed tires

Shimmy of tail and nose wheels may be eliminated by installation of dampers and use of large trail; however, this produces construction and operational disadvantages. It is more favorable to employ, instead of the customary tail-wheel tires, tires with lesser shimmy tendency. A description of the best possible form for these tires follows: furthermore, a few general concepts regarding the effects of the condition of the tire, of the type of rolling motion, and of the landing, are discussed.

WHEELS, TAIL - SHIMMYING↗

NASA NTRS1952

Analytical study of shimmy of airplane wheels

The problem of shimmy of a castering wheel, such as the nose wheel of a tricycle gear airplane, is treated analytically. The flexibility of the tire is considered to be the primary cause of shimmy. The rather simple theory developed agrees rather well with previous experimental results. The author suggests that shimmy may be eliminated through a suitable choice of landing gear dimensions in lieu of a damper.

LOADS, LANDING - GROUND-RUN↗

NASA NTRS1968

Shock-absorbing caster wheel is simple and compact

Compact shock-absorbing caster wheel mitigates or absorbs shock by a compressible tire which deforms into a cavity between its inner edge and the wheel hub. A tee-shaped annular ring embedded in the tire distributes loads more uniformly throughout both wheel and tire.

Kindley, R. J.↗

NASA NTRS1972

The motion and stability of a dual spin satellite during the momentum wheel spin-up maneuver

The stability of a dual-spin satellite system during the momentum wheel spin-up maneuver is treated both analytically and numerically. The dual-spin system consists of: a slowly rotating or despun main-body; a momentum wheel (or rotor) which is accelerated by a torque motor to change its initial angular velocity relative to the main part to some high terminal value; and a nutation damper. A closed form solution for the case of a symmetrical satellite indicates that when the nutation damper is physically constrained for movement (i.e. by use of a mechanical clamp) the magnitude of the vector sum of the transverse angular velocity components remains bounded during the wheel spin-up under the influence of a constant motor torque. The analysis is extended to consider such effects as: the motion of the nutation damper during spin-up; a non-uniform motor torque; and the effect of a non-symmetrical mass distribution in the main spacecraft and the rotor. An approximate analytical solution using perturbation techniques is developed for the case of a slightly asymmetric main spacecraft.

Bainum, P. M.↗

NASA NTRS1973

The motion and stability of a dual-spin satellite during the momentum wheel spin-up maneuver.

The stability of a dual-spin satellite system during the momentum wheel spin-up maneuver is treated both analytically and numerically. The dual-spin system consists of a slowly rotating or despun main body, a momentum wheel (or rotor) which is accelerated by a torque motor to change its initial angular velocity relative to the main part to some high terminal value, and a nutation damper. A closed-form solution for the case of a symmetrical satellite indicates that when the nutation damper is physically constrained from movement (i.e., by use of a mechanical clamp) the magnitude of the vector sum of the transverse angular velocity components remains bounded during the wheel spin-up under the influence of a constant motor torque. The analysis is extended to consider such effects as the motion of the nutation damper during spin-up, and the effect of a nonsymmetrical mass distribution.

Sen, S.↗

NASA NTRS1975

Magnetically suspended reaction wheels

Magnetic suspensions offer several advantages over conventional bearings, arising because of the contactless nature of the load support. In application to spacecraft reaction wheels, the advantages are low drag torque, wearfree, unlubricated, vacuum-compatible operation, and unlimited life. By the provision of redundancy in the control electronics, single-point failures are eliminated. The rational for selection of a passive radial, active axial, dc magnetic suspension is presented, and the relative merits of 3-loop and single-loop magnetic suspensions are discussed. The design of a .678 N-m-sec (.5 ft-lb-sec) reaction wheel using the single loop magnetic suspension was developed; the design compares favorably with current ball bearing wheels in terms of weight and power.

Sabnis, A. V.↗