Accession Number : ADA119612

Title :   Rotorcraft Blade Mode Damping Identification from Random Responses Using a Recursive Maximum Likelihood Algorithm.

Descriptive Note : Contractor rept.,

Corporate Author : MOLUSIS (JOHN A) ASHFORD CT

Personal Author(s) : Molusis,John A

PDF Url : ADA119612

Report Date : Sep 1982

Pagination or Media Count : 50

Abstract : An on-line technique is presented for the identification of rotor blade modal damping and frequency from rotorcraft random response test data. The identification technique is based upon a recursive maximum likelihood (RML) algorithm, which is demonstrated to have excellent convergence characteristics in the presence of random measurement noise and random excitation. The RML technique requires virtually no user interaction, provides accurate confidence bands on the parameter estimates, and can be used for continuous monitoring of modal damping during wind tunnel or flight testing. Results are presented from simulation random response data which quantify the identified parameter convergence behavior for various levels of random excitation. The data length required for acceptable parameter accuracy is shown to depend upon the amplitude of random response and the modal damping level. Random response amplitudes of 1.25 degrees to .05 degrees are investigated. The RML technique is applied to hingeless rotor test data from the NASA Langley Research Center Helicopter Hover Facility. The inplane lag regressing mode is identified at different rotor speeds. The identification from the test data is compared with the simulation results and with other available estimates of frequency and damping. (Author)

Descriptors :   *Damping, *Rotor blades(Rotary Wings), *Helicopter rotors, Maximum likelihood estimation, Parameters, Algorithms, Recursive functions, Wind tunnel tests, Experimental data, Rotary wing aircraft, Helicopters

Subject Categories : Aerodynamics
      Helicopters
      Theoretical Mathematics

Distribution Statement : APPROVED FOR PUBLIC RELEASE