Modeling Flapping Dynamics for Tiltrotor Flight Dynamics Applications
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Abstract
Tiltrotor aircraft combine the vertical takeoff and landing capabilities of helicopters with the speed and range of fixed-wing airplanes. Modeling their transitional flight dynamics, particularly the role of rotor flapping, remains a challenge. This paper develops an analytical framework that incorporates first-order rotor flapping and nacelle tilt dynamics into tiltrotor simulations. Using small-angle assumptions and blade element theory, the model captures the coupling between rotor flapping and body angular rates across different nacelle tilt angles. Results indicate that the influence of flapping dynamics is more noticeable in configurations closer to helicopter mode, particularly within 30 degrees of nacelle tilt from this regime. In these conditions, the rotor blades experience higher effective angles of attack, amplifying rotor-induced moments. As the nacelle tilts toward airplane mode, the incoming airflow approaches more from above the rotor plane, reducing the blades’ effective angle of attack and, consequently, their contribution to flapping dynamics. The study also highlights that nacelle tilt rates introduce gyroscopic precession and transient moments, which are more pronounced during fast transitions or asymmetric maneuvers. While heavier tiltrotors like the XV-15 show limited sensitivity to flapping dynamics in airplane mode, trends in lower-speed and rotor-dominated conditions emphasize the need for accurate modeling of flapping effects. This is especially relevant for lightweight tiltrotors and urban air mobility vehicles, where reduced inertia amplifies rotor-induced responses. These findings suggest that including flapping and nacelle tilt dynamics in flight dynamics models can improve predictions of handling qualities, particularly during transitions between flight modes.
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File under embargo until 01-03-2027