A Hybrid Trim Strategy for Coaxial Compound Helicopter

TL;DR

This paper develops and compares trim strategies for coaxial compound helicopters, demonstrating that a hybrid control approach significantly reduces power consumption at various speeds while maintaining acceptable control loads.

Contribution

It introduces a novel hybrid trim strategy for CCHs, optimizing control allocation and power efficiency over a range of speeds.

Findings

Hybrid trim reduces power by up to 13% at 100m/s.

Significant power efficiency improvements at medium and high speeds.

Control variables remain within reasonable ranges.

Abstract

Interest in the coaxial compound helicopter (CCH) has been increasing in the civil aviation and engineering community for its high-speed and high-maneuverability features, and is likely to continue to do so for the foreseeable future. Since the control in CCH is totally different from the conventional helicopter, the redundant control strategy design is one of the biggest challenges. In this study, the CCH model based on XH-59A is built to investigate the impact of the propeller and the elevator on the flight performance. Four trim strategies with different objectives are proposed and then compared to find the optimal control allocation. A heuristic descent search method is applied to search the optimal velocity at which the propeller and the elevator are engaged. A significant improvement of power required at medium and high speed with acceptable rotor airloads increment was found by using the Hybrid Trim strategy in the speed range of 0-100m/s, with regard to a pre-configured pitch angle schedule. The corresponding control variables obtained locate in a reasonable control range, with a maximum power reduced of 13% at 100m/s, which showcases the potential of the Hybrid Trim strategy.