Abstract
ABSTRACTThe wake vortex of lifting surfaces such as wind turbine blades or fixed-wing aircraft can heavily affect the blade aerodynamics of rotorcraft. Using blade element theory, the pilot control inputs required to mitigate such vortex effects are estimated and compared to the available control margin at the operating condition of interest. In contrast, when no pilot action is performed, the rotor blade flapping caused by the vortex is evaluated and compared to available margins. It is a safety concern when the remaining margins become zero. The influence of the vortex strength, its core radius and orientation to the rotor disk are evaluated and the effect of rotor blade characteristics (Lock number, natural frequency) is investigated.
Highlights
Vortex-rotor interactions and their impact on the flight mechanics of helicopters were first studied in the 1980s when heliports were planned to be built in the vicinity of airport runways
This study focuses on the potential impact on safety of small helicopters and ultralight rotorcraft, such as autogyros or coaxial helicopters, flying within strong wind turbine vorticities
R The most critical conditions are experienced when the vortex lies within the rotor disk and r r is oriented in longitudinal direction
Summary
Vortex-rotor interactions and their impact on the flight mechanics of helicopters were first studied in the 1980s when heliports were planned to be built in the vicinity of airport runways. The vortex orientation normal to the disk is placed at the hub center in longitudinal direction and at different lateral positions all across the rotor disk For any of these configurations the shaft angle remains unchanged and a retrim of the rotor is performed to compute the control perturbations needed to retrim, which can be divided by the available control margin. The lowest impact can be expected for the Bo105 main rotor blade, because of its high tip speed and its large radius These relations are useful for judgement of the pilot control magnitudes required to mitigate the vortex impact on trim.
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