Load Alleviation for Large Aeroplanes by Active Mode Control of the Coplanar Motion of the Horizontal Tailplane

A standard FE-analysis of large aeroplanes reveals one or several 2-4 Hz modes of the horizontal tailplane (HTP), termed coplanar modes. They describe a coplanar or a fore / aft motion of the HTP. Due to their low eigenfrequencies, these modes can be easily excited by lateral gust, in particular by continuous turbulence on the fin. As the aerodyamic damping of these modes is small, strong resonance phenomena occur, yielding high loads at the HTP root. Via a mode control system, consisting of a dynamic feedback of the x-acceleration at the HTP-tip to the rudder, active damping and thereby a loads reduction of more than 20 % is demonstrated. The system is termed HTP-contol(ler).