THE AEROELASTIC BEHAVIOUR OF A FORWARD-SWEPT WING CONFIGURATION WITH FOCUS ON ENGINE GYROSCOPICS AND T-TAIL FLUTTER

摘要

Since more and more modern civil aircraft for reasons of fuel efficiency and environmental aspects are equipped with UHBR-engines, the need to tackle specific engine related dynamic problems has occured. The request for UHBR-engines with high bypass ratio numbers and with their intrinsic advantages of economic fuel consumption and lower acoustic emission asks for enhanced prediction capabilities. Beside the energetic benefits such engines add to the aircraft design their rotating large diameter fans can influence the dynamic behaviour of the complete elastic aircraft fuselage in a very unfavourable manner. Especially in the scenario when large rotating engine masses are to be combined with elastic suspension structures the possible occurance of structural vibration problems can be avoided by taking the gyroscopic effects into account. As another important engine related question the modelling and the impact of the engine thrust is highlighted by integration of the follower force induced terms into the dynamical simulation model. A further approach towards lower fuel consumption is the drag reduction of the airplane. This can be realized by keeping the flow field around the wing surfaces laminar as much as possible. With the ALLEGRA-S configuration a short and medium range aircraft has been designed with the aim of drag reduction by keeping the wing flow laminar as long as possible. Together with laminar aerodynamic wing airfoil sections the forward sweep of the wings has a favourable influence on the laminar character of the wing flow. The forward swept wings as well as the T-tail empennage and the backward position of the engine nacelles on both sides of the fuselage also have a formative influence on the flutter behaviour and thus the stability margings of the design. The flutter behaviour of several baseline mass configurations has been examined. Important questions with regard to the enhancement of the flutter model and the impact on structural dynamics and aeroelasticity are treated in this work. For example by introducing additional d.o.f. coupling into the aeroelastic model the component correction terms have influenced particular flutter eigenmodes and caused (minor) deviations in flutter frequencies and velocities.