Mechanical & Fluid Systems

Safer Roadside Crash Walls Would Limit Deceleration

These walls would protect both vehicle occupants and bystanders.

The figure depicts the aspects of a proposed deceleration-limiting design for crash walls at the sides of racetracks and highways. The proposal is intended to overcome the dis- advantages of both rigid barriers and kinetic-energy-absorbing barriers of prior design. Rigid barriers can keep high-speed crashing motor vehicles from leaving roadways and thereby prevent injury to nearby persons and objects, but they can also subject the occupants of the vehicles to deceleration levels high enough to cause injury or death. Kinetic-energy-absorbing barriers of prior design reduce deceleration levels somewhat, but are not designed to soften impacts optimally; moreover, some of them allow debris to bounce back onto roadways or onto roadside areas, and, in cases of glancingly incident vehicles, some of them can trap the vehicles in such a manner as to cause more injury than would occur if the vehicles were allowed to skid along the rigid barriers. The proposed crash walls would (1) allow tangentially impacting vehicles to continue sliding along the racetrack without catching them, (2) catch directly impacting vehicles to prevent them from injuring nearby persons and objects, and (3) absorb kinetic energy in a more nearly optimum way to limit decelerations to levels that human occupants could survive.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Product development, Crashworthiness, Impact tests, Roads and highways

Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure

A report proposes a method of utilizing solar-radiation pressure to keep the axis of rotation of a small spin-stabilized spacecraft pointed approximately (typically, within an angle of 10° to 20°) toward the Sun. Axisymmetry is not required. Simple tilted planar vanes would be attached to the outer surface of the body, so that the resulting spacecraft would vaguely resemble a rotary fan, windmill, or propeller. The vanes would be painted black for absorption of Solar radiation. A theoretical analysis based on principles of geometric optics and mechanics has shown that torques produced by Solar-radiation pressure would cause the axis of rotation to precess toward Sun-pointing. The required vane size would be a function of the angular momentum of the spacecraft and the maximum acceptable angular deviation from Sun-pointing. The analysis also shows that the torques produced by the vanes would slowly despin the spacecraft — an effect that could be counteracted by adding specularly reflecting "spin-up" vanes.
Posted in: Briefs, TSP, Mechanical Components, Mechanics, Propellers and rotors, Attitude control, Attitude control, Sun and solar, Radiation, Spacecraft

Cable-Dispensing Cart

A versatile cable- dispensing cart can support as many as a few dozen reels of cable, wire, and/or rope. The cart can be adjusted to accommodate reels of various diameters and widths, and can be expanded, contracted, or otherwise reconfigured by use of easily installable and removable parts that can be carried onboard. Among these parts are dispensing rods and a cable guide that enables dispensing of cables without affecting the direction of pull. Individual reels can be mounted on or removed from the cart without affecting the other reels: this feature facilitates the replacement or reuse of partially depleted reels, thereby helping to reduce waste. Multiple cables, wires, or ropes can be dispensed simultaneously. For maneuverability, the cart is mounted on three wheels. Once it has been positioned, the cart is supported by rubber mounts for stability and for prevention of sliding or rolling during dispensing operations. The stability and safety of the cart are enhanced by a low-center-of-gravity design. The cart can readily be disassembled into smaller units for storage or shipping, then reassembled in the desired configuration at a job site.

Posted in: Briefs, Mechanical Components, Mechanics, Wiring, Wiring, Tools and equipment

Device for Locking a Control Knob

A simple, effective, easy-to-use device locks a control knob in a set position. In the initial application for which this device was conceived, the control knob to be locked is that of a needle valve. Previously, in that application, it was necessary for one technician to hold the knob to keep the valve at the desired flow setting while another technician secured the valve with safety wire — a time-consuming procedure. After attachment of the wire, it was still possible to turn the knob somewhat. In contrast, a single technician using the present device can secure the knob in the desired position in about 30 seconds, and the knob cannot thereafter be turned, even in the presence of harsh vibrations, which occur during space shuttle launch. The device includes a special-purpose clamp that fits around the control knob and its shaft and that can be tightened onto the knob, without turning the knob, by means of two thumbscrews. The end of the device opposite the clamp is a tang that contains a slot that, in turn, engages a bolt that protrudes from the panel on which the control knob and its shaft are mounted.
Posted in: Briefs, TSP, Mechanical Components, Mechanics, Sensors and actuators, Sensors and actuators, Tools and equipment, Fasteners, Valves

Prolonging Microgravity on Parabolic Airplane Flights

Techniques for improving the approximation of free fall are proposed.

Three techniques have been proposed to prolong the intervals of time available for microgravity experiments aboard airplanes flown along parabolic trajectories. Typically, a pilot strives to keep an airplane on such a trajectory during a nominal time interval as long as 25 seconds, and an experimental apparatus is released to float freely in the airplane cabin to take advantage of the microgravitational environment of the trajectory for as long as possible. It is usually not possible to maintain effective microgravity during the entire nominal time interval because random aerodynamic forces and fluctuations in pilot control inputs cause the airplane to deviate slightly from a perfect parabolic trajectory (see figure), such that the freely floating apparatus bumps into the ceiling, floor, or a wall of the airplane before the completion of the parabola. Heretofore, free-float times have tended to be no longer than a few seconds.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Trajectory control, Aircraft operations, Education, Education and training, Fixed-wing aircraft, Spacecraft

Continuous Tuning and Calibration of Vibratory Gyroscopes

Vibrational excitation is periodically switched between orthogonal axes to derive calibration data.

A method of control and operation of an inertial reference unit (IRU) based on vibratory gyroscopes provides for continuously repeated cycles of tuning and calibration. The method is intended especially for application to an IRU containing vibratory gyroscopes that are integral parts of microelectromechanical systems (MEMS) and that have cloverleaf designs, as described in several previous NASA Tech Briefs articles. The method provides for minimization of several measures of spurious gyroscope output, including zero-rate offset (ZRO), angle random walk (ARW), and rate drift. These benefits are afforded both at startup and thereafter during continuing operation, in the presence of unknown rotation rates and changes in temperature.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Calibration, Microelectricmechanical device, Microelectromechanical devices, Navigation and guidance systems, Microelectricmechanical device, Microelectromechanical devices, Navigation and guidance systems, Vibration, Vibration

Improved Bearingless Switched-Reluctance Motor

Performance is better and design simpler, relative to a prior bearingless switched-reluctance motor.

The Morrison rotor, named after its inventor, is a hybrid rotor for use in a bearingless switched-reluctance electric motor. The motor is characterized as bearingless in the sense that it does not rely on conventional mechanical bearings: instead, it functions as both a magnetic bearing and a motor. Bearingless switched-reluctance motors are attractive for use in situations in which large variations in temperatures and/or other extreme conditions preclude the use of conventional electric motors and mechanical bearings.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Propellers and rotors, Product development, Magnetic materials, Electric motors

Compact, Pneumatically Actuated Filter Shuttle

This unit satisfies a special need for alternate observation in two spectral bands.

A compact, pneu- matically actuated filter shuttle has been invented to enable alternating imaging of a wind-tunnel model in two different spectral bands characteristic of the pressure and temperature responses of a pressureand temperature-sensitive paint. This filter shuttle could also be used in other settings in which there are requirements for alternating imaging in two spectral bands. Pneumatic actuation was chosen because of a need to exert control remotely (that is, from outside the wind tunnel) and because the power leads that would be needed for electrical actuation would pose an unacceptable hazard in the wind tunnel. The entire shuttle mechanism and its housing can be built relatively inexpensively [

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Architecture, Imaging, Imaging and visualization, Architecture, Imaging, Imaging and visualization, Pneumatic systems, Wind tunnel tests

Single-Vector Calibration of Wind-Tunnel Force Balances

Improved data quality with an order of magnitude reduction in cost and calibration cycle time over prior methods.

An improved method of calibrating a wind-tunnel force balance involves the use of a unique load application system integrated with formal experimental design methodology. The Single-Vector Force Balance Calibration System (SVS) overcomes the productivity and accuracy limitations of prior calibration methods.

Posted in: Briefs, Mechanical Components, Mechanics, Calibration, Wind tunnel tests

Microgyroscope With Vibrating Post as Rotation Transducer

Unlike in prior vibratory microgyroscopes, there is no cloverleaf structure.

The figure depicts a micromachined silicon vibratory gyroscope that senses rotation about its z axis. The rotation-sensitive vibratory element is a post oriented (when at equilibrium) along the z axis and suspended at its base by thin, flexible silicon bands oriented along the x and y axes, respectively. Unlike in the vibratory microgyroscopes described in the immediately preceding article ["Cloverleaf Vibratory Microgyroscope With Integrated Post" (NPO-20688)] and other previous articles in NASA Tech Briefs, the rotation-sensitive vibratory element does not include a cloverleaf-shaped structure that lies (when at equilibrium) in the x-y plane.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Vibration, Vibration, Test equipment and instrumentation

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