The Loads Analysis and Aeroelastic Design Department is concerned with questions that arise in the context of aircraft design with regard to aeroelastic properties or aeroelastic requirements. In addition, the Department deals with the subject of aircraft loads ‘in general’ (for example, for design tasks) and in-depth consideration of dynamic loads (among others, those due to gusts).
The design of an aircraft must ensure that the aeroelastic requirements are met; these include the adequate control effectiveness of control surfaces and avoidance of flutter and divergence speeds in the required flight envelope. Depending on the design phase (conceptual, preliminary or detailed design) variations are possible in the following areas:
A structural model is used to model the stiffness and structural dynamical properties for aeroelastic analysis and optimisation. For static aeroelastic problems (for example, effectiveness of control surfaces, divergence speed), the stiffness properties must be modelled. An appropriate mass model is also required for flutter analysis. This includes, among others, the structural and non-structural masses for various fuelling and loading conditions. In addition, realistic attachment stiffness must be provided for the control surfaces in the structural model.
To produce appropriate structural models for the aircraft as a whole, or for assemblies such as the wings, the Department is involved in the development of methods for creating structural models that are suitable for aeroelastic analysis. For this, methods are developed in which a parametric geometry representation of the aircraft and the load-bearing structures is gradually created.
The structural model generated from the geometric model is dimensioned for selected loading conditions. The dimensioning process utilises structural optimisation methods, whereby restrictions from the field of aeroelastics are considered (effectiveness of the control surface, flutter speed, divergence speed). Special optimisation methods have been developed for the dimensioning of fibre reinforced composite materials. The aerodynamic modelling, which is necessary for aeroelastic optimisation as well as the optimisation model (design variables, restrictions), is also constructed with the aid of the parametric geometry model.
In addition, procedures have been developed for the selection of the loads that are to be dimensioned for the design, in order to determine the load conditions. Certification specifications (for example, CS25) are also taken into account. In addition to manoeuvring loads, increased dynamic loads (for example, due to gusts) and landing impact loads are also considered.
In order to enable a large number of high precision load analyses within a short time, the Department develops approaches in which rapid calculation methods on the basis of DLM are combined with the results of a few selected CFD simulations. This allows load analyses under realistic assumptions, including in the limiting region of the flight envelope.