Recent advances in Eurocopter's passive and active vibration control

TLDR: In this article, a short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters, and the concepts and means to influence and control vibrations are outlined.

Abstract: This paper is about recent advances in Eurocopter’s research activities on passive and active vibration control systems. Emphasis is placed on the reduction of rotor-induced vibrations which is still one of the key challenges in helicopter dynamics. Both passive and active means for the reduction of vibrations are discussed. A short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters. The concepts and means to influence and control vibrations are outlined. The main focus of this paper is on recent advances on i) vibration control at the rotor, ii) vibration control at the transmission and iii) vibration control at the fuselage. In the section “vibration control at the rotor”, vibrations are attacked at their source – the rotor itself. Advanced passive and active rotor dynamic layouts are of interest. Here, a 5-bladed bearingless vs. 4bladed main rotor system on EC145 as well as an active flap rotor on the hingeless system of BK117 are discussed. For each system, key parameters of the design, data of the test configuration and test environment and in particular results on vibration reduction are presented. A substantial reduction of the exciting hub loads is achieved thus providing superior airframe vibration levels. In the section “vibration control at the transmission”, a new generation of pylon isolation system is presented. This passive system based on the SARIB principle combines advantages of efficiency, lightness, reliability and low cost design. This technology consists of a compact suspension and a flapping mass integrated in each gear box strut. It provides an important attenuation of the vibrations for all hub loads components and it was successfully tested in-flight. In the section “vibration control at the fuselage”, active anti-vibration control systems (AVCS) installed in the fuselage are presented. The systems rely on single-port active devices which are capable to generate inertia-based control forces which induce a secondary vibration field to compensate the vibration disturbance. Here, systems based on electromagnetic actuation technology for EC225 as well as Piezo-ceramic technology demonstrated on EC135 are presented.