An Integrated Analysis Model for Assessment of Critical Load Conditions for the Vertical Tail Plane

This paper presents a modelling scheme suitable for loads analysis of manoeuvres and gusts of a flexible controlled aircraft. 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 maneoeuvre conditions as well as discrete lateral gusts. The resulting design loads are heavily influenced by the flight control system and the associated parameters for yaw damping functions or travel limiter. This poses an interesting problem regarding trade-offs between handling qualities and the structural loads acting on the VTP. This paper investigates the influence of lateral flight control laws on the loads of the different gust and manoeuvre load conditions for certification as specified by the authorities. Sparked by previous incidents, a new load condition was recently introduced: the rudder reversal condition. This new condition features three full reversals of the rudder pedal input instead of just one step input and a mere return to neutral. The loads resulting from the new load condition are considered to be ultimate and not limit loads. The new load condition is assessed and compared to loads envelopes according to the old certification specifications. The introduction of the new rudder control reversal load condition was mainly motivated by wake vortex encounters during which the pilots made excessive or inappropriate use of the rudder. The conjecture is that the loads are primarily caused by pilot action and not the external windfield. Since the present modelling scheme is also capable of simulating position and attitude dependent windfields such as wake vortex encounters, the resulting loads are compared to the new rudder control reversal condition as well