Flight Testing of an In-Flight Tuning System on a CH-53G Helicopter

In-Flight Tuning (IFT) can be realized by a set of so-called Smart Pitch Rods (SPR™) which replace the conventional fixed-length pitch links. Electrically driven and digitally controlled by a corresponding "IFT commander", the length of each pitch link can individually be changed during the flight. Thereby, the RT&B process can considerably be simplified and the blade pitch settings can continuously be optimized depending on the actual flight condition. ZFL was contracted to develop, fabricate and flight test such IFT system on a CH-53G testbed of the German Armed Forces. This paper gives a brief overview of the system architecture, the chosen safety concept and the aircraft integration. Then, the major qualification and certification steps from component to system level are summarized. The main part discusses the results from the first 20+ flight hours of dedicated IFT flight testing. This covers flights with open loop and closed loop control, partly with the main rotor intentionally "detuned" as well as test cases with simulated sudden changes of the blade properties. Finally, some results from maneuver flights with the IFT system kept active are presented. All flights have shown the flawless and safe operation of the system. The tests have proven the capability not only to streamline the initial RT&B procedure but also to optimize the vibratory condition of the rotorcraft across the complete flight envelope and for different operating conditions through the continuous and automatic re-adjustment of the pitch settings.