Impact of Gust Loads and Manoeuvre Load Alleviation Techniques on the Design of a Highly Flexible Jet Transport

Kurzfassung

In the recent years, the structures of long range transport aircraft have become more and more flexible. At the same time, manoeuvre load alleviation techniques have become standard on those aircraft. Hence, the relevance of gust loads in the structural design of large aircraft - combined with their high flexibility - becomes of interest. To investigate this matter, a highly flexible long range jet transport, resembling an Airbus A350-900 or a Boeing 787-10 class aircraft, is taken as reference. Its simulation model components have been set up using an in-house model generator. In doing so, the main load carrying structure of the wing is optimised by the means of an comprehensive loads and optimisation tool chain built around MSC.NASTRAN. To obtain a highly flexible structure, a carbon fibre laminate optimisation is set up, using lamination parameters in combination with large strain allowables (up to 8000 $\mu$ in tension). Additionally, plate stiffening beam elements are sized by altering their height, limited by the application of crippling constraints. In order to guarantee the structural stability, intracell buckling constraints and linear global buckling analyses are incorporated into the optimisation as well. The result is a highly flexible wing structure, featuring a vertical displacement of up to 10 \% with respect to the semi-wingspan during cruise flight.\newline Since the pitch stability is a mandatory requirement for transient analyses like gust encounters in the frequency domain, the structural optimisation is carried out only incorporating static manoeuvre load cases. However, in order to fulfil certification specifications, loads resulting from the prescribed design gusts have to be investigated as well. In this case, this is achieved by superimposing linear trim calculations with results from dynamic gust simulations carried out in the frequency domain. Especially in combination with the application of manoeuvre load alleviation techniques, gust loads have proven to grow in significance. To evaluate the importance of gust loads for the optimisation of the presented aircraft, cut loads obtained manoeuvre calculations - carried out with and without alleviation technique - are compared to the results of gust load simulations.