Estimation of helicopter rotor loads from blade structural response

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dc.contributor.advisorSirohi, Jayant
dc.contributor.committeeMemberGoldstein, David B
dc.contributor.committeeMemberRavi-Chandar, Krishnaswa
dc.contributor.committeeMemberBennighof, Jeffrey K
dc.contributor.committeeMemberBhagwat, Mahendra J
dc.creatorUehara, Daiju
dc.date.accessioned2020-05-22T18:45:06Z
dc.date.available2020-05-22T18:45:06Z
dc.date.created2019-12
dc.date.issued2020-03-27
dc.date.submittedDecember 2019
dc.date.updated2020-05-22T18:45:06Z
dc.description.abstractMeasuring the load distribution along a helicopter rotor blade has been one of the most challenging tasks in experimental aeromechanics. Conventional loads measurements with on-blade instrumentation, such as pressure transducers for airloads and strain gages for structural loads, require the experimentalist to overcome a large number of technical barriers; for example, sensor integration to the rotor blade structure, sensor failure due to strong centrifugal forces, and influence of sensor installation on rotor blade dynamics. The goal of this dissertation is to develop a new, combined experimental and theoretical methodology to estimate helicopter rotor loads without using these conventional on-blade sensors. The rotor loads estimation methodology begins with the measurement of blade structural deformation measurements using non-contact, optical, time-resolved Digital Image Correlation (DIC). The time-resolved DIC technique successfully showed its capability of measuring the three-dimensional deformation time history of a rotating blade for both a small- and a large-scale rotor in hover. The modal properties (natural frequencies, mode shapes, damping ratios, and modal coordinates) of the blade in the rotating-frame were then extracted from the deformation time history using Natural Excitation Technique - Eigensystem Realization Algorithm (NExT-ERA) and Complexity Pursuit (CP), which are operational modal analysis (OMA) algorithms. The first three modes were identified by the OMA algorithms and well correlated with a numerical model. Rotor loads were then finally estimated based on the measured deformations and blade modal characteristics. Having validated the present approach incrementally with measurements performed on rotors at different scales, configurations, and operating conditions, the current study estimated the spanwise lift distribution and integrated thrust at the hub for a 2 m-diameter, two-bladed, isolated single rotor in hover. Due to a lack of participating modes (only the first and second flap modes), the estimated sectional lift distribution did not capture the lift loss typically observed at regions of the blade tip and induced by trailing tip vortices. Nevertheless, the mean value of the estimated thrust at the rotor hub was within 5% of the measured value for all the operating conditions
dc.description.departmentAerospace Engineering
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/2152/81345
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/8353
dc.language.isoen
dc.subjectRotorcraft
dc.subjectStructural dynamics
dc.subjectAeromechanics
dc.subjectDigital image correlation
dc.subjectForce reconstruction
dc.subjectOperational modal analysis
dc.titleEstimation of helicopter rotor loads from blade structural response
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentAerospace Engineering
thesis.degree.disciplineAerospace Engineering
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy

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