Mechanical & Fluid Systems

Bearing-Seal System for Safe Motion Transfer in Deep Submersible Pressure Vessels

Elastomeric bearings permit leak-free transfer of rotary motion through the hull.Designers of deep submersibles are reluctant to use conventional shafts and seals to penetrate the hulls of deep sub- mersible, pressure vessels fearing seal failure under extreme pressures. The unique design of this patented system, designated LAMIFLEX®, incorporates elastomeric bearings in order to achieve an absolute hermetic seal and permit leak-free transfer of rotary motion up to at least 15 degrees through the hull of these highly pressurized vessels. External functions, such as control surface deflection, can be driven internally with inherent safety and backup. There are no sliding surfaces (packings, lip, or face seals) that could fail. It also exhibits a smooth spring-like reaction and limited shaft movement without friction. The new designs have been implemented and tested at pressures of 10,000 psi for more than a million cycles at ±15 degrees with no leakage.

Posted in: Briefs, Mechanical Components, Mechanics, Elastomers, Bearings, Seals and gaskets, Performance tests, Marine vehicles and equipment


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, 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, 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, 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, Microelectromechanical devices, Navigation and guidance systems, Vibration


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