Analysis of Automatic Control Function Effects on Vertical Tail Plane Critical Load Conditions

This paper presents a modelling scheme suitable for loads analysis of maneuvers and gusts of flexible aircraft with active control systems. In contrast to most ongoing research the component to be investigated is not the wing but the vertical tail plane (VTP). Critical load conditions for vertical tail plane include yawing maneuver conditions as well as discrete lateral gusts. A new rudder reversal load condition features a three full reversals of the rudder pedal input instead of just one step input and amere return to neutral. This condition, where resulting loads are considered ultimate, was mainly motivated by wake vortex encounters during which the pilots made excessive use of the rudder. The design loads resulting from all conditions are heavily influenced by the flight control system, the underlying control law design method, and associated control law parameters. This gives rise to interesting trade-offs between handling qualities and loads sizing the VTP structure. Therefore, in this paper the influence of different types of lateral control laws on the loads of the different gust and maneuver conditions for certification as specified by the authorities is analysed. The control laws considered vary from basic yaw damping with rudder travel limitation to full roll and yaw command augmentation systems. From a design methodology point of view, classical and (incremental) Nonlinear Dynamic Inversion-based methods are analysed.