In-Flight Tuning: Flight Test Results and 2nd Generation System

Helicopter rotor systems feature adjustable elements, such as pitch links, balance weights and/or trim tabs that allow the vibration levels in the aircraft to be reduced. The required adjustments are normally determined using Rotor Track and Balance (RT&B) equipment on dedicated flights. However, these adjustments are a compromise intended to provide a solution for only the most common flight regimes and aircraft loading conditions. This work presents the development of an In-Flight Tuning (IFT) System, featuring Smart Pitch Rods (SPR™s) that enable continuous balance adjustments and optimization for any aircraft condition. Initial testing of a Flight Trial System on a CH-53G test bed showed that a noticeable effect on aircraft vibration could be achieved using the SPR™s in open-loop control and continuous vibration minimization was possible using a closed-loop control algorithm. Additionally, the flight trial showed that the IFT System could give improvements over the traditional RT&B compromise and also showed reductions in vibration to within aircraft limits after a blind blade exchange. A production IFT System is now in development, featuring redesigned components and an extended set of functions that are described in the final section.