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  • 1
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    Evaluation of a load cell model for dynamic calibration of the rotor systems research aircraft (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Rotor Systems Research Aircraft uses load cells to isolate the rotor/transmission system from the fuselage. An analytical model of the relationship between applied rotor loads and the resulting load cell measurements is derived by applying a force-and-moment balance to the isolated rotor/transmission system. The model is then used to estimate the applied loads from measured load cell data, as obtained from a ground-based shake test. Using nominal design values for the parameters, the estimation errors, for the case of lateral forcing, were shown to be on the order of the sensor measurement noise in all but the roll axis. An unmodeled external load appears to be the source of the error in this axis.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Rotorcraft Dynamics 1984; p 379-393
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Dynamic modelling and estimation of the error due to asynchronism in a redundant asynchronous multiprocessor system (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The use of Redundant Asynchronous Multiprocessor System to achieve ultrareliable Fault Tolerant Control Systems shows great promise. The development has been hampered by the inability to determine whether differences in the outputs of redundant CPU's are due to failures or to accrued error built up by slight differences in CPU clock intervals. This study derives an analytical dynamic model of the difference between redundant CPU's due to differences in their clock intervals and uses this model with on-line parameter identification to idenitify the differences in the clock intervals. The ability of this methodology to accurately track errors due to asynchronisity generate an error signal with the effect of asynchronisity removed and this signal may be used to detect and isolate actual system failures.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-177427 , NAS 1.26:177427
    Format: application/pdf
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  • 3
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    Estimation of dynamic rotor loads for the rotor systems research aircraft: Methodology development and validation (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Rotor Systems Research Aircraft uses load cells to isolate the rotor/transmission systm from the fuselage. A mathematical model relating applied rotor loads and inertial loads of the rotor/transmission system to the load cell response is required to allow the load cells to be used to estimate rotor loads from flight data. Such a model is derived analytically by applying a force and moment balance to the isolated rotor/transmission system. The model is tested by comparing its estimated values of applied rotor loads with measured values obtained from a ground based shake test. Discrepancies in the comparison are used to isolate sources of unmodeled external loads. Once the structure of the mathematical model has been validated by comparison with experimental data, the parameters must be identified. Since the parameters may vary with flight condition it is desirable to identify the parameters directly from the flight data. A Maximum Likelihood identification algorithm is derived for this purpose and tested using a computer simulation of load cell data. The identification is found to converge within 10 samples. The rapid convergence facilitates tracking of time varying parameters of the load cell model in flight.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-177362 , T47130 , NAS 1.26:177362
    Format: application/pdf
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  • 4
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    Inertial dynamics of a general purpose rotor (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The inertial dynamics of a fully articulated stiff rotor blade are derived with emphasis on equations that facilitate an organized programming approach for simulation applications. The model for the derivation includes hinge offset and six degrees of freedom for the rotor shaft. Results are compared with the flapping and lead-lag equations currently used in the Rotor Systems Research Aircraft simulation model and differences are analyzed.
    Keywords: AERODYNAMICS
    Type: NASA-TM-78557 , A-7731
    Format: application/pdf
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  • 5
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    Identification of a linear model of rotor-fuselage dynamics from nonlinear simulation data (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Linear regression techniques are used to obtain 9- and 12-degree-of-freedom linear rotorcraft models from the input-output data generated by a nonlinear, blade-element rotorcraft simulation in hover. The resulting models are used to evaluate the coupling of the fuselage modes with the rotor flapping and lead-lag modes at various frequencies. New techniques are proposed and evaluated to improve the identification process, including a method of verifying the assumed model structure by using data sets generated at different input frequencies.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: European Rotorcraft and Powered Lift Aircraft Forum; Sep 16, 1980 - Sep 19, 1980; Bristol
    Format: text
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  • 6
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    The use of frequency methods in rotorcraft system identification (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A new approach to model structure determination is examined. Flight data from the Rotor Systems Research Aircraft (RSRA) are transformed into the frequency domain and truncated to provide band limiting. The stepwise regression technique is then used to identify a quasistatic state-space model from the transformed data. The data processing requirements for both time domain and frequency domain identification are discussed and the results of the two techniques are compared.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 81-2386 , Flight Testing Conference; Nov 11, 1981 - Nov 13, 1981; Las Vegas, NV
    Format: text
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