Load Limiting Control for Component Life Extension

TL;DR

This paper introduces a Load Limiting Control scheme that enhances helicopter component life by effectively managing fatigue loads, especially harmonic loads, through a novel control approach that improves safety and component longevity.

Contribution

The paper proposes a new LLC scheme that considers harmonic loads and distinguishes maneuver aggressiveness, using a control margin and optimization for improved load management.

Findings

Effective load limiting during simulated flights

Pilot can track cues within 0.5 seconds after training

Improved component life extension demonstrated through simulations

Abstract

This paper presents the development of a novel life-extending control scheme for critical helicopter components subjected to significant fatigue loading. The primary objective is to synthesize a more efficient and less conservative life-extending control scheme than those currently available in the literature. The proposed Load Limiting Control (LLC) scheme is a viable solution that addresses several issues that current life-extending control schemes suffer from, such as the neglect of fatigue damage induced by the harmonic component of loads and the inability to distinguish between aggressive and non-aggressive maneuvers. The proposed LLC scheme treats desired harmonic load limits as limit boundaries and recasts the problem of load limiting as a vehicle limit by computing a Control Margin (CM) using a limit detection and avoidance module. The computed CM is used as a cue to the pilot. The limit detection and avoidance module comprises an optimization algorithm, a model predictive controller, and a computationally simple on-board dynamical model. Simulations were conducted to demonstrate the effectiveness of the LLC scheme in limiting harmonic pitch link loads during flight. One significant outcome is that, with sufficient training, the pilot can skillfully track the cue within 0.5 seconds of initiating the tracking task.