Actions for Individual Blade Pitch Control (IBC) for Vibration Reduction of Lift-offset Coaxial Rotor Vehicles with Auxiliary Propulsion

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Individual Blade Pitch Control (IBC) for Vibration Reduction of Lift-offset Coaxial Rotor Vehicles with Auxiliary Propulsion

Author
Beyer, Jessica
Published
[University Park, Pennsylvania] : Pennsylvania State University, 2023.
Physical Description
1 electronic document
Additional Creators
Pritchett, A.
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Open Access.
Summary
The combination of a lift-offset coaxial main rotor with auxiliary propulsion results in a compound rotorcraft with both low-speed maneuverability and high-speed capabilities beyond 250 knots. In high-speed edgewise flight, the stiff rotor blades used for the coaxial main rotor generate severe vibratory loads which necessitate advanced vibration reduction techniques to limit aircrew and airframe fatigue. The present study examines the hub vibratory load reduction potential of individual blade pitch control (IBC) for a lift-offset coaxial main rotor. The present study investigates the high-speed aeromechanics of the XH-59A. This investigation expands upon previous simulations using the Rotorcraft Comprehensive Analysis System (RCAS). Parametric sweeps with varying lift-offset values and rotor RPM demonstrated a significant impact on rotor performance and hub vibratory loads. The ideal lift-offset value to minimize vibrations and maximize performance was shown to vary with the flight conditions. The lift-offset value minimizing the hub vibratory loads increased from 0.2 at 80 knots to 0.4 at 240 knots. At 200 knots, decreasing rotor RPM from 100% to 90% increased rotor performance by 20% but also increased hub vibratory loads by 60%. Open-loop, single harmonic IBC sweeps of varying amplitude, phase, and harmonic are conducted at several forward flight speeds to quantify the effects of IBC on the hub vibration index and rotor effective lift-to-drag ratio. Applying a 4/rev 1° periodic pitch input at 0° phase to both rotors decreased hub vibrations by 64% at 200 knots and only decreased rotor performance by 2%. Single harmonic IBC retained its vibration reduction potential with varying flight speed with a maximum 56% decrease at 160 knots and a 69% decrease at 240 knots. IBC inputs with increased pitch amplitude demonstrated increased vibration reduction as forward flight speed increased. Analysis of the sine and cosine components of the vibratory hub loads with IBC applied demonstrated the dependence of the vibration reduction potential on the periodic pitch amplitude and input phase. Offsetting the IBC input phase angle between the upper and lower rotors increased the vibration reduction potential of open-loop 3/rev, 2° amplitude single harmonic IBC by 32% by decreasing the 3/rev hub vertical force by 84%. The results of the present study demonstrate the potential for significant reduction of high-speed rotor vibratory loads using individual blade pitch control for a lift-offset coaxial main rotor. This conclusion is consistent with recently published results by other investigators.
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Dissertation Note
M.S. Pennsylvania State University 2023.
Technical Details
The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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