Carsten M. Liersch

Conceptual Design and Aerodynamic Analyses of a Generic UCAV Configuration

Applying DLR’s conceptual aircraft design system to military flying wing configurations, the design of a generic UCAV configuration is presented. For its outer shape, the SACCON geometry specified by NATO STO/AVT-161 Task Group was taken. For mission analysis and structural sizing, aerodynamic data from fast and robust conceptual design methods (i.e. potential flow theory) were used. In order to assess the validity of these simple methods for such configurations, a comparison with results from RANS aerodynamics and wind tunnel measurements was performed. The results of this design task were included into the stability and control investigations performed within the AVT-201 task group.

Aerodynamics and Conceptual Design Studies on an Unmanned Combat Aerial Vehicle Configuration

The ability to accurately predict both static and dynamic stability characteristics of air vehicles using computational fluid dynamics methods could revolutionize the air vehicle design process, especially for military air vehicles. A validated computational fluid dynamics capability would significantly reduce the number of ground tests required to verify vehicle concepts and, in general, could eliminate costly vehicle “repair” campaigns required to fix performance anomalies that are not adequately predicted before full-scale vehicle development. This paper outlines the extended integrated experimental and numerical approach to assess the stability and control prediction method capabilities, as well as the design and estimation of the control device effectiveness, for highly swept low observable unmanned combat aerial vehicle configurations. The aim of the AVT-201 Task Group is to provide an assessment of the computational fluid dynamics capabilities using model-scale experiments and transfer this knowled...

On the Design of a Strut-Braced Wing Configuration in a Collaborative Design Environment

Due to its drag saving potential through application of high aspect ratio wings, the strut-braced wing configuration is considered a promising candidate as a next generation single-aisle aircraft. This potential is reflected in the results of the renowned Sugar and Albatross projects of Boeing and ONERA. In the course of DLRs project future enhanced aircraft configurations (FrEACs), a strut-braced wing configuration is examined with focus on the interaction of aerodynamics, loads, structures and aeroelastics. The present study outlines the applied design process for the strut-braced wing configuration in DLRs collaborative design environment and highlights lessons learnt from an organizational and technical point of view. It proves that the level of confidence in the design process is largely increased by effectively combining both the explicit and implicit knowledge of the heterogeneous specialists involved. The explicit knowledge is incorporated through automated execution of the specialists tools in structured simulation workflows. Implicit knowledge of the specialists is required to interpret results both in the respective disciplinary context as well as on overall aircraft design level. Applying the collaborative design process enables statements on the possible gain of strut-braced wing over conventional tube and wing configurations. The paper describes the applied collaborative design procedure, shows results concerning the physical aspects of the strut-braced wing configuration and concludes by providing lessons learnt and an outlook into the application of collaborative design.

Evaluating the energy balance of high altitude platforms at early design stages

High altitude platforms, also known as pseudo-satellites, are envisioned as unmanned aircraft flying at altitudes above 15 km to provide observation, remote sensing or communication services. A challenging yet recurring requirement for such aicraft is to be able to perform long-endurance missions over multiple days or even weeks. A sophisticated onboard energy management system including solar panels and batteries is needed to achieve this. The energy balance of such an aircraft depends on many factors which should be considered in the design process. In this work, we propose a systematic approach to evaluate the energy balance of high altitude platform designs for specific mission scenarios. This approach can be employed at very early design stages and incrementally extended to follow the design process. We demonstrate the methodology with an exemplary parameter study for a generic fixed-wing aircraft. In particular, the impact and correlations of the mission latitude, wind conditions, flight trajectory optimization, sizing of the platform and solar panel coverage of the main wing was evaluated. A key result is that battery mass can be reduced significantly, especially for missions at high latitudes, by optimizing the holding pattern that is flown throughout the mission or by increasing the solar panel coverage. Generally, the results indicate that the method allows to evaluate mission-specific effects on the energy balance of high altitude platforms.

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.