Date of Award

Summer 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Onur Bilgen

Committee Member

Martin Sekula

Committee Member

Colin Britcher

Committee Member

Thomas Alberts

Call Number for Print

Special Collections; LD4331.E56 K822 2013

Abstract

The subject of this thesis is the design, analysis, and experimental assessment of active-twist rotors. These active rotors use piezoelectric actuators embedded in the skins to twist the blade to reduce vibratory loads in the fixed system. First, the design and optimization of the twist response within the geometric and structural constraints of a rotor blade is presented. A parametric analysis is conducted varying the airfoil thickness, active-material placement, and structural plies to determine the maximum static twist response. A Macro-Fiber Composite (MFC), which is a fibrous piezoelectric device is used as the active material. Analyses of the cross-section are conducted using engineering software, University of Michigan Variational Asymptotical Beam Sectional (UMWABSA) analysis, which uses a 2D finite element approach with the variational-asymptotical method to reduce geometric nonlinear 3D elasticity to a 1D initially curved and twisted beam theory, to determine the deformation induced by the MFCs.

Next, bench-top experiments on an active-twist rotor, including modal testing and frequency response measurements are discussed. A shift is observed in blade resonant frequencies with increasing actuation levels. Nonlinear actuation authority versus voltage is also observed in the blade. Comparisons of the experimental blade modal frequencies and the frequency response magnitudes with analysis are discussed as well. It is found that the analysis and experiment agree within 5% for the flap and torsion frequencies. However, the lag frequencies are predicted within 15%.

Finally, hover and forward flight testing are conducted in a wind tunnel with an R- 134a test medium. Hover frequency response is measured and compared reasonably well with analysis, which uses a harmonic balance method with nonlinear beam elements and 2D aerodynamic lookup tables with unsteady aerodynamics. Static actuation in hover is attempted to show improvement in the hover performance quantified in terms of figure of merit. However, because the change in the hover performance improvement is small the wind tunnel results prevent definitive conclusions on the effectiveness of active-twist on performance. The forward flight testing demonstrated fixed system vibration reduction, with up to 50% reduction in the normal force vibratory loads. Other fixed-system loads are significantly reduced as well at the phase angle that produced the maximum normal force vibration reduction. A decrease in the blade oscillatory flapwise bending moment loads is also observed.

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DOI

10.25777/rkrk-9q95

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