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Pulse-Tube Refrigerator for Liquid Hydrogen

An unusually high operating frequency enables reductions of size and weight. An improved closed-loop, two-stage pulse-tube refrigerator provides 4 W of cooling power at a temperature of 15 K. The original intended application of this refrigerator is in preventing boiloff of liquid hydrogen from a propellant tank aboard a spacecraft. The basic refrigerator design can also be adapted to terrestrial applications like cooling superconducting electronic devices.

Posted in: Machinery & Automation, Briefs, TSP

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Fail-Safe, Continue-to-Operate Concept for Jackscrews

Redundant nut increases reliability and facilitates inspections. A fail-safe, continue-to-operate design concept for machine jackscrews calls for the incorporation of a redundant follower nut that would assume the axial jack load upon failure of the primary nut. Heretofore, the way to design for increased reliability of jackscrews has been to provide for multiple jackscrews operating in unison. The present fail-safe, continue-to-operate design concept offers an alternative for preventing catastrophic failures in jackscrews, which are used widely in aeronautical, aerospace, and industrial applications.

Posted in: Machinery & Automation, Briefs

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Ultrasonically Induced Fountains and Fogs

Diverse visual effects could be produced in computer-controlled displays. Experiments have demonstrated the feasibility of generating fountains and fogs over a body of water (see Figure 1) by utilizing high-intensity ultrasound to induce acoustic streaming, cavitation, and atomization. The transducer used in the experiments had a 10-cm diameter and a 10-cm focal length, was immersed in water at a depth approximately equal to its focal length, and was excited at various amplitudes and at various frequencies from 100 kHz to 2 MHz. It was observed in the experiments that the fountain and fog effects depend on the amplitude and frequency of excitation.

Posted in: Mechanics, Briefs, TSP

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Control Derivatives of the F-18 Airplane

These derivatives will be used in designing an active-aeroelastic-wing control system. Flight data gathered by use of the F-18 System Research Aircraft (SRA) based at Dryden Flight Research Center have been used to estimate stability and control derivatives for a baseline F-18 airplane. The data were obtained in the high-dynamic-pressure range of the F-18 flight envelope in an experiment performed in support of a future F-18 program to be devoted to the concept of the active aeroelastic wing (AAW). The AAW technology is intended to integrate aerodynamics, active controls, and aeroelasticity in such a way as to maximize the performance of the airplane. More specifically, the goal of the AAW project will be to maximize the contribution of a reduced-stiffness F-18 wing to roll-rate performance.

Posted in: Mechanics, Briefs

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Computational Test Cases for Oscillating Clipped Delta Wing

These data can be used to test computational simulations of aerodynamic behavior. Computational test cases have been selected from archived sets of data acquired some years ago in wind-tunnel experiments on a clipped delta wing equipped with a hydraulically actuated trailing-edge control surface. In some of the experiments, the wing was subjected to pitching oscillations and control-surface oscillations. (The wing was stiff and thus did not undergo appreciable elastic oscillations; instead, it was mounted in such a way as to enable it to oscillate as a rigid torsionally sprung body.) The data obtained in the experiments included the static pressures and the real and imaginary parts of the first harmonics of dynamic pressures at a number of points on the upper and lower wing surfaces.

Posted in: Mechanics, Briefs, TSP

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Magnetostrictive Motor and Circuits for Robotic Applications

Notable features include power-factor correction, speed control, and high position resolution. A magnetostrictive motor and its drive circuit and control system have been designed to be especially suitable for robotic applications in which there are requir- ements for precise, high-force linear actuators. The motor includes a laminated armature made of the magnetostrictive alloy Tb0.27Dy0.73Fe0.2. The armature is sandwiched between two double-layered, three-phase stators, which are energized to make the armature move linearly in “inchworm” fashion. The total range of linear motion is 25 mm. Like other magnetostrictive motors, this motor offers the advantages (relative to geared-down conventional motors) of reduced weight, extreme ruggedness, fewer moving parts, greater reliability, and self braking when power is not applied.

Posted in: Machinery & Automation, Briefs, TSP

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Advances in Cooperative Transport by Two Mobile Robots

Two mobile robots move in formation while transporting a long payload. Special gimbal mech- anisms and algorithms that implement decentralized compliant control have been developed for use in research on the sensors, the actuators, and the design and functional requirements for systems of multiple mobile robots cooperating in site-clearance and construction operations. The gimbal mechanisms and control algorithms were designed, in particular, to enable two robotic exploratory vehicles (i.e., rovers) to transport a long payload while moving along the ground in a commanded formation. Although these developments are parts of a continuing effort to develop robotic capabilities for exploration of Mars, the same robotic capabilities could be expected to find application on Earth.

Posted in: Machinery & Automation, Briefs, TSP

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