Fourier Domain Rotor Track and Balance

Abstract:
Rotor Track and Balance (RTB) and the related shaft balance function are common helicopter maintenance practices. A smooth helicopter reduces high-cycle fatigue in components, improving operational readiness. For the flight crew, a smoother ride enhances safety and reduces fatigue. RTB algorithms attempt to provide blade adjustments to hub weights, pitch control rod links, or blade tabs to reduce vibration at aircraft sensors. Prior studies have described the mathematical formulations underlying RTB optimization with little attention given to implementation. This paper presents a Fourier-domain approach to RTB using the linear least-squares method for both vibration minimization and blade-track split reduction. The methodology is demonstrated across a range of operationally relevant scenarios, including rotors with varying blade counts, non-orthogonal blade spacing such as in the Bell 429 tail rotor, and unequal adjustment on the Bell 407 tail rotor system. Considerations such as adjustment directionality, input shaft balance coupling, and maintainer-centric implementation constraints are addressed. Rule-based expert systems leveraging engineer-curated knowledge are introduced for this narrow-domain application, with a brief discussion of their relationship to large language models (LLMs).

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