ACTIVE CONTROL TO AUGMENT ROTOR LEAD-LAG DAMPING

Hingeless and bearingless rotor designs are today well accepted for mo dern helicopters. Continued development, however, revealed some defici encies in the area of aeromechanical stability and vibration. In gener al there is a good basic understanding of how to avoid these instabili ties. But since it becomes more and more desirable to focus Q rotor de sign on aerodynamic features and flight performance, these R aeromecha nical instabilities gain new importance due to the difficulties R to p rovide the required damping. Since all rotor concepts suffer from the lack of sufficient natural lead-lag or inplane damping most designs in use show artificial lead-lag v, dampers to overcome aeromechanical in stabilities. Additionally, active control offers the possibility for a n artificial stabilisation of aeromechanical instabilities. Meanwhile, many research activities focus on active control to augment rotor lea d-lag damping and many authors demonstrate the potential inherent in t his approach. The paper shortly repeats the problem of aeromechanical instabilities of hingeless rotor-systems. A simple rotor blade model w ith flap, lag and pitch DOFs is used to derive the coupled set of diff erential equations. The emphasis of this paper is to demonstrate the p otential of active control and to gain physical understanding. Lead-la g damping augmentation of an isolated rotor blade with lead-lag rate a nd attitude feedback even in forward flight is shown. However, some pr oblems that may limit the success of an active control approach are di scussed.