Wing Planform Optimization of a Transport Aircraft

Abstract

The present work deals with multi-disciplinary design and optimization (MDO) of a transport aircraft wing. The aircraft must fulfil a given mission requirements under restrictions imposed by different aeronautical disciplines. The mathematical model of the MDO framework includes the calculation of aircraft drag polar (based on geometrical characteristics), engine trust, aircraft structural weight, volume available for fuel tank (which is stored only in the wings), stability derivatives, and performance for some flight phases. MATLAB was used then to implement build the related computational routines. Some design tasks for a twinjet aircraft, carrying eight passengers and a crew of three, were carried out for some specified maximum ranges and the results are analyzed here. 22nd Applied Aerodynamics Conference and Exhibit 16-19 August 2004, Providence, Rhode Island AIAA 2004-5191 Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 2 Introduction Each new generation of commercial airliner must present lower operational cost coupled with some degree of improvement in passenger comfort, to become a best seller among airlines. Future aircraft must also be carefully designed to achieve reductions in design cycle, maintenance, and manufacturing costs. The combination of efficient aerodynamic shapes with judicious use of new materials, structures, and systems is the way to design high-performance aircraft with low weight, and substantially reduced costs. In addition, today aircraft must be quiet and nonpolluting. However, despite of the utilization of numerical tools such as CAD systems and Computational Fluid Dynamics (CFD) in aircraft design, it is still a formidable task to integrate efficiently all of them and existing corporate expertise into the whole aircraft design process. Aircraft design is performed by a hierarchical sequence of steps. It begins with ideas, missions and concepts, takes successively developing shapes until the configuration can be frozen, continues with the practical considerations about hardware, certification issues, finally resulting in a set of drawings, manufacturing instructions and airworthiness documentation. This evolutionary process usually is split into conceptual, preliminary, detail design phases followed by manufacturing, flight tests and production. As this process evolves, design freedom decays rapidly while knowledge about the object of design is increasing. As the design process goes forward designers gain knowledge but lose freedom to act on that knowledge. It was demonstrated mathematically in that this natural evolution may lead to suboptimal designs. Recent transonic airliner designs have generally converged upon a common cantilever lowwing configuration. It is unlikely that further large strides in performance are possible without a significant departure from the present design paradigm. One such alternative configuration is the strut-braced wing, which uses a strut for wing bending load alleviation, allowing increased aspect ratio and reduced wing thickness to increase the lift to drag ratio. The thinner wing has less transonic wave drag, permitting lower wing sweep angles for increased areas of natural laminar flow and further structural weight savings. Such departure from conventional design and corporate knowledge poses cultural barriers in aircraft development, which can be lifted by the adequate utilization of MDO. Multi-disciplinary design and optimization (MDO) address the previously mentioned critical issues from earlier phases of aircraft design. Besides simply designing optimal configurations, MDO allows for the fulfillment of requirements, which are constrained by factors such as costs, material properties, wing thickness, and cabin height. The trend towards MDO was triggered by both high-performance low-cost computing systems and new efficient analysis and design