Tech Briefs

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.

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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.

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Cloverleaf Vibratory Microgyroscope With Integrated Post

Modifications should lead to greater unit-to-unit consistency. A modified design and fabrication sequence has been devised to improve the performance of a cloverleaf vibratory microgyroscope that includes an axial rod or post rigidly attached to the center of the cloverleaf structure. The basic concepts of cloverleaf vibratory microgyroscopes, without and with rods or posts, were described in two prior articles in NASA Tech Briefs, Vol. 21, No. 9 (September 1997): "Micromachined Planar Vibratory Microgyroscopes" (NPO-19713), page 68 and "Planar Vibratory Microgyroscope: Alternative Configuration" (NPO-19714), page 70. As described in more detail in the second-mentioned prior article, the cloverleaf-shaped structure and the rod or post are parts of a vibratory element that senses rotation via the effect of the Coriolis force upon its vibrations.

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Cryogenic Temperature-Gradient Foam/Substrate Tensile Tester

Tensile strengths are measured under more nearly realistic conditions. The figure shows a fixture for measuring the tensile strength of the bond between an aluminum substrate and a thermally insulating polymeric foam. The specimen is meant to be representative of insulating foam on an aluminum tank that holds a cryogenic liquid. Prior to the development of this fixture, tensile tests of this type were performed on foam/substrate specimens immersed in cryogenic fluids. Because the specimens were cooled to cryogenic temperatures throughout their thicknesses, they tended to become brittle and to fracture at loads below true bond tensile strengths.

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Slat Heater Boxes for Thermal Vacuum Testing

Slat heater boxes have been invented for controlling the sink temperatures of objects under test in a thermal vacuum chamber, the walls of which are cooled to the temperature of liquid nitrogen. A slat heater box (see Figure 1) includes a framework of struts that support electrically heated slats that are coated with a high-emissivity optically gray paint. The slats can be grouped together into heater zones for the purpose of maintaining an even temperature within each side.

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Electrical-Impedance-Based Ice-Thickness Gauges

Compact, inexpensive gauges provide early warnings of accretion of ice. Langley Research Center has developed electrical- impedance- based icethickness gauges and is seeking partners and collaborators to commercialize them. When used as parts of active monitoring and diagnostic systems, these gauges make it possible to begin deicing or to take other protective measures before ice accretes to dangerous levels. These gauges are inexpensive, small, and simple to produce. They can be adapted to use on a variety of stationary and moving structures that are subject to accumulation of ice. Examples of such structures include aircraft, cars, trucks, ships, buildings, towers, power lines (see figure), power-generating equipment, water pipes, freezer compartments, and cooling coils.

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System for Testing Thermal Insulation of Pipes

Thermal and flow conditions are carefully controlled to minimize errors. An apparatus and method have been developed for measuring the rates of leakage of heat into pipes carrying liquids, the purpose of the measurements being to quantify the thermal performance of the insulation system. The apparatus is designed primarily for testing pipes used to carry cryogenic liquids, but can also be used for measuring the thermal performance of other insulated pipes or piping systems.

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