Thomas Klimmek

Maneuver Loads Calculation with Enhanced Aerodynamics for a UCAV Configuration

The authors present the development of a software for loads and aeroelastic analysis with aerodynamic enhancements. The background for this effort is the investigation of an unmanned combat air vehicle. The DLR-F19 is a flying wing configuration with a geometry based on previous research conducted in the scope of the “Mephisto” project and its predecessors “FaUSST” and “UCAV2010”. While there is a considerable amount of knowledge for conventional configurations, unconventional configurations lack of experience and data for comparison is rarely available. In a previous work a structural model was created with DLRs parametric ModGen/Nastran design process. Using that approach, the conceptual design becomes more sophisticated as the structure is sized with typical design load cases. It allows for the investigation of physical effects of maneuver, gust and ground loads or flutter at an early stage of the design process. In this paper, the focus is on static maneuver loads. The analysis is conducted with a commercial software and an in-house software. In contrast to the use of commercial software, the development of the so-called Loads Kernel has the benefit of having full control of the whole procedure of a static maneuver loads calculation. In addition, it allows the implementation of new features. One example is the selective use of aerodynamic forces obtained from CFD. This promises better and more physical results than from fast aerodynamic methods such as the Doublet Lattice Method. In this paper, the Doublet Lattice Method delivers a baseline and is enhanced with results from CFD. It is shown that the aerodynamic characteristics of the DLR-F19 are rather complex and require detailed investigations. The impact on structural loads is significant and an aerodynamic enhancement is absolutely necessary for sophisticated and reliable loads analysis.

Aero-Structural Optimization of the NASA Common Research Model

A combined aerodynamic and structural, gradient-based optimization has been performed on the NASA/Boeing Common Research Model civil transport aircraft configuration. The computation of aerodynamic performance parameters includes a Reynolds-averaged Navier-Stokes CFD solver, coupling to a linear static structural analysis using the finite element method to take into account aero-elastic effects. Aerodynamic performance gradients are computed using the adjoint approach. Within each optimization iteration, the wings structure is sized via a gradient-based algorithm and an updated structure model is forwarded for the performance analysis. In this pilot study wing profile shape is optimized in order to study engine installation effects. This setting was able to improve the aerodynamic performance by 4%.

Stability and Control Investigations in Early Stages of Aircraft Design

This paper provides an overview of current activities of DLR (German Aerospace Center) with respect to stability and control investigations in the context of early stages of aircraft design. For this purpose, DLR follows an interdisciplinary and multi-level design approach. Using an integration framework in combination with a central data exchange format, largely automated process chains are set up that combine calculation and simulation capabilities of the multitude of disciplines required in early aircraft design. Rather than using empirical relations and assumptions based on experience, the underlying methods applied by the tools are mainly based on physical model representations. The major aim of this design approach is to generate all relevant data needed for stability and control investigations, including aerodynamic damping derivatives and to assemble them within a flight dynamics model. Not only does this approach allow for an early consideration of stability and control characteristics, but it also respects interdisciplinary effects and enables automated design changes. This paper describes the infrastructure used for setting up the described process. It presents disciplinary tools used to calculate engine performance maps, calculate aerodynamic performance maps and structural properties, generate flight dynamics models with associated control laws and to assess aircraft handling qualities. Furthermore, this paper provides application examples of early stability and control considerations, using integrated interdisciplinary process chains. This comprises a handling qualities assessment under uncertainty considerations and vertical tailplane sizing for a blended wing body. In addition, engine and split flap sizing processes for an unmanned combat aerial vehicle are shown. The interdisciplinary design approach presented here, serves to find a well justified early configuration and reduces the risk of later design changes.

Flight Loads Analysis and Measurements of External Stores on an Atmospheric Research Aircraft

The research aircraft DLR HALO (High Altitude and Long Range Research Aircraft) is able to carry external stores which are attached a t wing hardpoints. The external stores are designed to house several measurement instruments for atmospheric research. However, each modification on the aircraft has to be investigated with numerical analyses and / or experimental data to ensure the structural integrity of airframe and stores. The DLR project iLOADS aims at the development of an internal DLR loads process and being able also to support certification capabilities for the DLR aircraft fleet. To assist the DLR HALO operations, a simulation model of the aircraft was set up and loads analyses have been carried out in the Institute of Aeroelasticity at DLR Göttingen. For the experimental part, flight tests with DLR HALO with 14 flying hours in total have been performed. In the flight tests strain data of wing external stores, acceleration data of installed sensors and turbulence data were collected. First analyses have been carried out and the findings can be utilized in the further development of the DLR loads process.

Loads and Structural Optimization Process for Composite Long Range Transport Aircraft Configuration

Background: The consideration of composite design in an early design phase has become more and more necessary in aircraft design. In the scope of multidisciplinary optimisation, a composite aeroelastic reference model is often desired to investigate multidisciplinary effects on a near-industrial application. Objective: The aim is to generate a benchmark aeroelastic model by developing a robust design process for composite configurations. Method: This is done by using a continuous gradient based optimisation with lamination parameters as design variables followed by a discrete stacking sequence retrieval combined with a comprehensive load analysis routine comprising manoeuvre, gust, landing loads and a manoeuvre loads alleviation system. Simulation Models: The process utilises a GFEM/Dynamic, a DLM and a condensed FEM model based on the reference XRF1 configuration. Results: Results presented show the optimised wing-box design, comparing the effect of a manoeuvre load alleviation system, the effect of including blending constraints in the optimisation, and the change of the structrual design when moving to a stacking sequence design.