Mechanical & Fluid Systems

Formation Alignment of Multiple Autonomous Vehicles

Alignment is achieved by use of lasers, optical sensors, and rule-based controls. A table-top experiment on formation alignment of three air-levitated robotic vehicles has been performed to demonstrate the feasibility of a more general concept of controlling multiple robotic vehicles to make them move in specified positions and orientations with respect to each other. The original intended application of the concept is in the control of multiple spacecraft flying in formation, as described in “Synchronizing Attitudes and Maneuvers of Multiple Spacecraft” (NPO-20569) on page 64 in this issue of NASA Tech Briefs. In principle, the concept could also be applied on Earth to control formation flying of aircraft or to coordinate the motions of multiple robots, land vehicles, or ships.

Posted in: Mechanics, Briefs, TSP

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Ultrasonic/Sonic Vibrating/Rotating Tool Bits

Teeth are made asymmetric to induce rotation without need for rotary actuators. An easy-to-implement design concept shows promise for improving the performances of impact tool bits used in abrading surfaces, drilling, and coring of rock and rocklike materials. The concept is especially applicable to tools actuated with a combination of ultrasonic and sonic vibrations, as in the cases described in “Ultrasonic/Sonic Drill/Corers With Integrated Sensors (NPO- 20856), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. Such tools were originally intended to be used in scientific drilling and coring of rock; they might also be useful for drilling, coring, and surface grinding of rock for art and construction.

Posted in: Machinery & Automation, Briefs, TSP

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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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