Thiemo Kier

Comparison of Unsteady Aerodynamic Modelling Methodologies with Respect to Flight Loads Analysis

This paper addresses the development of aircraft models for flight loads analysis in the pre-design stage. The underlying model structure consists of the nonlinear equations of motion of a free flying, flexible aircraft, as well as a model, which calculates the distributed aerodynamics over the entire airframe. Different possibilities in modelling the unsteady arodynamic interactions for pre-design purposes are explored and the effects on the loads are compared in order to assess the tradeoffs between accuracy and speed.

Integrated Flexible Dynamic Maneuver Loads Models based on Aerodynamic Influence Coefficients of a 3D Panel Method

The integration of loads analysis models using so called aerodynamic influence coeffcients (AICs) is described. These AICs relate a change of normal velocity at panel control points to a change in panel pressure distribution, allowing to consider aeroelastic effects in a straight forward manner. The aerodynamic method employed for aeroelastic applications is typically the Vortex or Doublet Lattice Method, discretizing mean lifting surfaces. In this paper, the AICs are obtained by a 3D panel method, which significantly increases the geometric fidelity and accounts for previously unmodeled ight mechanical effects. These effects are verified by comparison with the Vortex Lattice Method and CFD results. Further, an interpolation scheme is required, since the AICs of 3D panel methods depend nonlinearly on the underlying flight state. The setup of a reduced order aerodynamic model for AICs (AIC-ROM), based on proper orthogonal decomposition is presented and results are assessed.

Longitudinal Manoeuvre Load Control of a Flexible Large-Scale Aircraft

Abstract This paper discusses the design and validation of an integrated long range flexible aircraft load controller, at a single flight/mass configuration. The contributions of the paper are in twofold: (i) first, a very recent frequency-limited model approximation technique is used to reduce the dimension of the large-scale aeroservoelastic aircraft model over a finite frequency support while guaranteeing optimal mismatch error, secondly, (ii) a structured controller is designed using an ℋ ∞ -objective and coupled with an output saturation strategy to achieve flight performance and load clearance, i.e. wing root bending moment saturation. The entire procedure - approximation and control - is finally assessed on the high fidelity large-scale aircraft model, illustrating the effectiveness of the procedure on a high fidelity model, used in the industrial context in the load control validation process.

Geometry Based Quick Aircraft Modeling Method for Upset Recovery Applications

A complete tool chain is developed for generating extended and enhanced flight models for low speed flights for applications of upset recovery research. Starting from geometry based automatic generation of the baseline model, additional algorithms are introduced to supplement the model for simulation of aircraft dynamics near stall and post-stall regions using decambering corrections, dynamic stall calculation and spin dynamics modelings. Together with additional functions for 3D lift corrections, drag estimations and weight distributions, significant enhancement has been made to the model generation capability of the vortex lattice method program. The generated Fokker 100 aircraft model is validated with direct comparisons to wind-tunnel measurements, manufacturer’s reports, academic publications as well as the flight data recordings of different accidents involving aircraft upsets.

Aeroservoelastic Modeling and Analysis of a Highly Flexible Flutter Demonstrator

In this paper, the aeroservoelastic modeling of a highly fexible futter demonstrator is presented. A finite element model of the demonstrator is generated and condensed to a reduced number of degrees of freedom to represent the structural dynamics. The unsteady aerodynamics are captured by the doublet lattice method based on potential theory. By interconnection of structural dynamics and unsteady aerodynamics an aeroelastic model is derived, which provides a basis for the design of a futter suppression controller. In order to enable an efficient futter suppression a clear separation of the occurring futter mech-anisms in speed and frequency is desired. To achieve this, the positions of the actuators controlling the faps are varied within the scope of the aircraft design process. Due to their large mass contribution, the placement of the actuators has a crucial impact on the overall futter characteristics and optimal actuator positions are determined by means of a mass sensitivity study.

Flight Dynamics Modeling of a Body Freedom Flutter Vehicle for Multidisciplinary Analyses

Integrated flight dynamic models play an essential role in all aircraft design phases. Examples are flight loads analysis for sizing of the structure, design of control laws, as well as design and analysis of missions. For these purposes, DLR has developed a robust, quick and unified process for generating, pre-processing and automatically integrating aircraft models. The process is called DLR Aircraft Model Integration Process (DAMIP) and is able to draw from a variety of different (best available) data sources. The DAMIP proce- dure is based on an unified environment, allowing aircraft modeling projects to be set-up in an easy and comfortable fashion. After this, the individual steps can be performed automatically, making it very suitable for the use in multidisciplinary design analysis and optimization loops. This paper outlines and demonstrates the DAMIP process as applied to the Body Freedom Flutter (BFF) vehicle that is currently studied and in-use at the De- partment of Aerospace Engineering at the University of Minnesota. In order to validate the integrated models the modal basis of the BFF vehicle is corrected by data obtained from ground vibration test (GVT). Linear state-space models are then generated to feed linear parameter-varying (LPV) system approaches and perform a flutter analysis by inspecting stability of the system matrices. The results are compared to those of the P-K Method analysis performed by Lockheed Martin Aeronautics. To demonstrate the flexibility of DAMIP, nonlinear models were generated in the equation-based, object-oriented Model- ica language and exported as S-functions to be used in the Matlab/Simulink simulation environment.