The focus of the Preliminary Design and Assessment Group is on the assessment of technologies in the context of the complete aircraft. Most technologies promise benefits in one discipline, but cause drawbacks in other areas. For example adding a suction system for hybrid laminar flow to a wing might improve aerodynamic performance, but will result in additional mass due to the systems required. Therefore it is important to take the most important effects from all disciplines into account to drive technology development to the best overall solution.
The three main areas of work are:
High Speed Transport Aircraft
In the past, considerable work was put into the extension of the PrADO code to supersonic aircraft . This was accomplished by integrating a supersonic panel code (HISSS) into the framework. More recent activities have dealt with the design of high lift systems for supersonic transport aircraft (EPISTLE) and current work is dedicated to multi-disciplinary optimization using high level tools (CISAP project in the EREA group). In the subsonic range, an feasibility study on the design of a Sonic Cruiser has been performed .
Flying Wing Aircraft
A key area of research are flying wing configurations for transport aircraft. Studies have been undertaken for passenger carrying aircraft as well as military cargo aircraft . Currently most of the work concentrates on aerodynamic optimization as well as optimum trim and control using systems of multiple spanwise distributed flaps. The work includes the design of high-lift systems and a study of the behavior in ground effect. In the course of the European research program VELA, numerical work is dedicated to parametric aerodynamic design optimization for cruise conditions. On the other hand, experiments will be conducted in cooperation with ONERA to study interference effects of wind tunnel support systems on flying wings in low speed wind tunnels (ONERA S5, Toulouse) and to measure dynamic derivatives of two different flying wing configurations (DNW-NWB).
Three Surface Aircraft
The three surface aircraft concept promises a reduction of trim drag and improved performance. The results of the DLR project 3FF showed that the potential can be used if stability margins are reduced and if the loading of the canard is limited. During the course of the project the main disciplines aerodynamics, structures (in cooperation with the University of Braunschweig) and aeroelastics as well as flight mechanics were considered. The Preliminary Design Group provided integration and assessment of all results . The numerical results in aerodynamics and flight mechanics were validated experimentally by half model tests in the cryogenic wind tunnel KKK in Cologne.
Adaptive Wing Aircraft
Adaptive wing structures make it possible to adapt the shape according to the current operation condition. For example it is possible to smoothly adjust the camber of a wing or to produce a surface bump to control shock location and strength in transonic cruise. To assess the potential of adaptive technologies, a reference aircraft was analyzed compared with an aircraft having shock control bumps. The aerodynamic effects of such a bump were determined by two dimensional wind tunnel tests and the results were fed into the PrADO tool (see below). The results showed, that adding a well designed shock control system can have a beneficial effect on direct operating costs.
Environmental Friendly Aircraft
Future work is strongly directed towards solutions for environmental friendly aircraft. Here, aero-acoustics plays a very important role as it is one of the strongest drivers of the design . This not only affects the propulsion systems and their integration, but also the wing arrangement including the design of a low noise high lift system to reduce airframe noise. Additionally, the integration of the landing gear will be examined to minimize approach noise.
The Preliminary Design Group has a suite of tools of differing complexity available. Depending on the problem, the best suited tool is selected.
Tools include multidisciplinary tools like the preliminary aircraft design and optimization program PrADO (in cooperation with the University of Braunschweig) or optimization frameworks (e.g. Pointer/Pro), as well as single discipline based tools. Here, aerodynamic design and analysis codes are used, which stretch from potential flow methods (e.g. accurate higher order vortex lattice methods, the panel codes VSAero and HISSS) to more complex solvers for the Euler equations (the DLR codes Tau on unstructured and FLOWer on structured grids). Additionally, the latter codes can be used as Navier-Stokes solvers for high level optimization tasks, usually coupled with multi-discipline models.
Initially, a basic design is developed with the fast PrADO code. Then, optimization frameworks like Pointer/Pro or Epogy are used in conjunction with the Euler or Navier-Stokes solvers Tau or FLOWer and finite element codes (e.g. NASTRAN) to develop optimum solutions using higher level tools.
Furthermore, the group develops data specifications and software to link tools together. This work builds on a common aircraft description, which is suitable for preliminary design. This description can be used to build CAD or structural models automatically, which can then be used by various disciplines. Thus it is possible for the designer to easily select the best suited design or analysis tools without having to worry about data conversions and compatibility. The aim here is to provide a complete tool chain, based on a structured data set containing all relevant data to describe the aircraft configuration in a parametric way. All disciplines use the same basic description, enriched with discipline-specific data.
Der Schwerpunkt der Gruppe Vorentwurf und Bewertung liegt auf der Bewertung neuer Technologien am Gesamtflugzeug. Viele Techniken versprechen Vorteile in einer Einzeldisziplin, haben aber Nachteile in anderen Bereichen. Beispielsweise kann mit einem System zur künstlichen Laminarhaltung der aerodynamische Widerstand verringert werden, andererseits sind zusätzliche Systeme erforderlich, die Kosten verursachen und das Systemgewicht erhöhen. Es ist also erforderlich, die wichtigsten Effekte in allen Disziplinen am Gesamtflugzeug zu beurteilen, um die Entwicklung neuer Technologien in Richtung der besten Gesamtlösung zu treiben.
1996-2000 adaptive wing technology (ADIF)1997-2001 three surface transport aircraft (3FF)2001 analysis of a Sonic Cruiser concept
2003-2004 supersonic transport aircraft (CISAP)2002-2005 flying wing transport aircraft (The VELA-project)2003-2006 flying wing transport aircraft (LUFO III)2003-2005 cooperation on flying wing with ONERA2003-2006 environmental friendly aircraft (LUFO III)
 D. Strohmeyer, R.Seubert: «Improvement of a Preliminary Design and Optimization Program for the Evaluation of Future Aircraft Projects», AIAA-98-4828, 7th AIAA AIAA/USAF/NASA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, St. Louis, Sept. 15-18, 1998 (Download PDF).
 M. Hepperle: «The Sonic Cruiser - A Concept Analysis», International Symposium `Aviation Technologies of the XXIth Century: New Aircraft Concepts and Flight Simulation´, 7.-8. May 2002, International Aerospace Exhibition (ILA), Berlin (Download PDF).
 M. Hepperle, W. Heinze: «Future Global Range Transport Aircraft», RTO Symposium on `Novel Vehicle Concepts and Emerging Technologies´, Bruxelles, 7-10 April 2003 (Download PDF).
 D. Strohmeyer, R. Seubert, W. Heinze, C. Österheld, L. Fornasier: «Three Surface Aircraft - A Concept for Future Transport Aircraft», AIAA-00-0566, 38th AIAA Aerospace Sciences Meeting and Exhibition, Reno, 10-13 January 2000.
 M. Hepperle: «Environmental Friendly Transport Aircraft», STAB Symposium, 2002, Munich, to be published in `Notes on Numerical Fluid Mechanics´, 2003 (Download PDF).