SMART SNUBBER/DAMPER FOR FIVE FOLD INCREASE IN DAMPING OF BEARINGLESS MAIN ROTOR BLADES

Snubber/damper damping performance is severely limited by component size and load constraints yielding insufficient RLM damping. Solutions using existing technology lead to excessive snubber damper size and weight to accommodate all operating conditions. Also, current snubber/damper designs are not sufficiently reliable and have limited life. High damping is required for stabilizing ground and air-resonance (rotating frequency of interest typically 0.3-0.7P). However, simply increasing the damping of snubber/dampers designs will also increases the 1P lead-lag associated loads and reduce related component lives One solution to the above problem would be to design a ¡smart¡" snubber-damper that takes advantage of the superimposed 1P motions by producing damping forces that oppose ƒçlag motions but produce zero or low force when the net damper loads are not favorable for suppressing ƒçlag motions. This is not possible using conventional passive dampers because passive elements like relief valves, orifices, produce forces that oppose the net velocity even if the resulting force excites the regressive lag mode! The new active concept arises from the recognition that the net damper force, i.e. from the combined ƒçlag and 1P motions, often produces forces that can be advantageously used to suppress ƒçlag response, thus converting a chronic difficulty in damper technology, unwanted 1P motions, into a benefit. The proposed concept relies upon two actions: 1) Minimizing the net damper force when it is in the same direction as the ƒçlag velocity. This avoids adding energy to the ƒçlag mode. This would be done by selectively opening a controlled valve to equalize the pressure in the damper chambers thus not allowing pressures to build. 2) Maximizing the net damper force when it opposes the ƒçlag velocity. This would extract energy from the ƒçlag mode. This would be done by selectively closing a controlled valve to maximize the damper load.