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  • 1
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    An improved calibration technique for wind tunnel model attitude sensors (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Aerodynamic wind tunnel tests at NASA Langley Research Center (LaRC) require accurate measurement of model attitude. Inertial accelerometer packages have been the primary sensor used to measure model attitude to an accuracy of +/- 0.01 deg as required for aerodynamic research. The calibration parameters of the accelerometer package are currently obtained from a seven-point tumble test using a simplified empirical approximation. The inaccuracy due to the approximation exceeds the accuracy requirement as the misalignment angle between the package axis and the model body axis increases beyond 1.4 deg. This paper presents the exact solution derived from the coordinate transformation to eliminate inaccuracy caused by the approximation. In addition, a new calibration procedure is developed in which the data taken from the seven-point tumble test is fit to the exact solution by means of a least-squares estimation procedure. Validation tests indicate that the new calibration procedure provides +/- 0.005-deg accuracy over large package misalignments, which is not possible with the current procedure.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: International Instrumentation Symposium, 39th, Albuquerque, NM, May 2-6, 1993, Proceedings (A93-54351 24-35); p. 89-102.
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  • 2
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    Evaluation of the prototype dual-axis wall attitude measurement sensor (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A prototype dual-axis electrolytic tilt sensor package for angular position measurements was built and evaluated in a laboratory environment. The objective was to investigate the use of this package for making wind tunnel wall attitude measurements for the National Transonic Facility (NTF) at NASA Langley Research Center (LaRC). The instrumentation may replace an existing, more costly, and less rugged servo accelerometer package (angle-of-attack package) currently in use. The dual-axis electrolytic tilt sensor package contains two commercial electrolytic tilt sensors thermally insulated with NTF foam, all housed within a stainless steel package. The package is actively heated and maintained at 160 F using foil heating elements. The laboratory evaluation consisted of a series of tests to characterize the linearity, repeatability, cross-axis interaction, lead wire effect, step response, thermal time constant, and rectification errors. Tests revealed that the total RMS errors for the x-axis sensor is 0.084 degree, and 0.182 degree for the y-axis sensor. The RMS errors are greater than the 0.01 degree specification required for NTF wall attitude measurements. It is therefore not a viable replacement for the angle-of-attack package in the NTF application. However, with some physical modifications, it can be used as an inexpensive 5-degree range dual-axis inclinometer with overall accuracy approaching 0.01 degree under less harsh environments. Also, the data obtained from the tests can be valuable for wind tunnel applications of most types of electrolytic tilt sensors.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-109056 , NAS 1.15:109056
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  • 3
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    Enhanced reduction of velocity data obtained during CETA flight experiment (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A newly developed technique for enhanced data reduction provides an improved procedure that allows least squares minimization to become possible between data sets with an unequal number of data points. This technique was applied in the Crew and Equipment Translation Aid (CETA) experiment on the STS-37 Shuttle flight in April 1991 to obtain the velocity profile from the acceleration data. The new technique uses a least-squares method to estimate the initial conditions and calibration constants. These initial conditions are estimated by least-squares fitting the displacements indicated by the Hall-effect sensor data to the corresponding displacements obtained from integrating the acceleration data. The velocity and displacement profiles can then be recalculated from the corresponding acceleration data using the estimated parameters. This technique, which enables instantaneous velocities to be obtained from the test data instead of only average velocities at varying discrete times, offers more detailed velocity information, particularly during periods of large acceleration or deceleration.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-4460 , L-17168 , NAS 1.15:4460
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  • 4
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    Enhanced data reduction of the velocity data on CETA flight experiment (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A newly developed technique for enhanced data reduction provides an improved procedure that allows least squares minimization to become possible between data sets with an unequal number of data points. This technique was applied in the Crew and Equipment Translation Aid (CETA) experiment on the STS-37 Shuttle flight in April 1991 to obtain the velocity profile from the acceleration data. The new technique uses a least-squares method to estimate the initial conditions and calibration constants. These initial conditions are estimated by least-squares fitting the displacements indicated by the Hall-effect sensor data to the corresponding displacements obtained from integrating the acceleration data. The velocity and displacement profiles can then be recalculated from the corresponding acceleration data using the estimated parameters. This technique, which enables instantaneous velocities to be obtained from the test data instead of only average velocities at varying discrete times, offers more detailed velocity information, particularly during periods of large acceleration or deceleration.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: International Instrumentation Symposium, 39th, Albuquerque, NM, May 2-6, 1993, Proceedings (A93-54351 24-35); p. 353-370.
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  • 5
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    Evaluation of electrolytic tilt sensors for measuring model angle of attack in wind tunnel tests (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The results of a laboratory evaluation of electrolytic tilt sensors as potential candidates for measuring model attitude or angle of attack in wind tunnel tests are presented. The performance of eight electrolytic tilt sensors was compared with that of typical servo accelerometers used for angle-of-attack measurements. The areas evaluated included linearity, hysteresis, repeatability, temperature characteristics, roll-on-pitch interaction, sensitivity to lead-wire resistance, step response time, and rectification. Among the sensors being evaluated, the Spectron model RG-37 electrolytic tilt sensors have the highest overall accuracy in terms of linearity, hysteresis, repeatability, temperature sensitivity, and roll sensitivity. A comparison of the sensors with the servo accelerometers revealed that the accuracy of the RG-37 sensors was on the average about one order of magnitude worse. Even though a comparison indicates that the cost of each tilt sensor is about one-third the cost of each servo accelerometer, the sensors are considered unsuitable for angle-of-attack measurements. However, the potential exists for other applications such as wind tunnel wall-attitude measurements where the errors resulting from roll interaction, vibration, and response time are less and sensor temperature can be controlled.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-4315 , L-16938 , NAS 1.15:4315 , International Conference on Instrumentations for Aerodynamic Simulation Facilities; Oct 28, 1991 - Oct 31, 1991; Rockville, MD; United States
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  • 6
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    Evaluation of electrolytic tilt sensors for wind tunnel model angle-of-attack (AOA) measurements (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The results of a laboratory evaluation of three types of electrolytic tilt sensors as potential candidates for model attitude or angle of attack (AOA) measurements in wind tunnel tests are presented. Their performance was also compared with that from typical servo accelerometers used for AOA measurements. Model RG-37 electrolytic tilt sensors were found to have the highest overall accuracy among the three types. Compared with the servo accelerometer, their accuracies are about one order of magnitude worse and each of them cost about two-thirds less. Therefore, the sensors are unsuitable for AOA measurements although they are less expensive. However, the potential for other applications exists where the errors resulting from roll interaction, vibration, and response time are less, and sensor temperature can be controlled.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ICIASF ''91 - International Congress on Instrumentation in Aerospace Simulation Facilities; Oct 27, 1991 - Oct 31, 1991; Rockville, MD; United States
    Format: text
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