American Institute of Aeronautics and Astronautics 1 Aerodynamic and Aeroacoustic Three-Dimensional Design for a “Silent” Aircraft J.I. Hileman, * Z.S. Spakovszky, † M. Drela ‡ Gas Turbine Laboratory, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139 and M.A. Sargeant § Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK This paper presents a three-dimensional airframe design methodology for low noise emission and high fuel efficiency, based on a blended-wing-body type aircraft. The design methodology uses a combination of high and low fidelity tools to assess the performance and acoustics of the aircraft. The goal set by the Silent ** Aircraft Initiative is a viable, commercial aircraft design with noise levels imperceptible outside the airport perimeter in a well-populated urban environment. To be viable, the aircraft requires a fuel burn comparable to modern conventional aircraft. The detailed airframe design incorporates leading edge camber of the centerbody to provide pitch trim without penalties in induced drag, wave drag, and trim drag. A low noise approach is achieved with reduced approach velocity and increased distance between the airframe and the observer. This slow and steep approach profile is enabled through a combination of thrust vectoring, quiet drag generation, and leading edge high-lift devices. The blended-wing-body type airframe design presented in this paper is both quiet with an OASPL of approximately 65 dBA and highly efficient with a cruise ML/D of 18.5. The paper concludes with ideas to further reduce noise to meet the aggressive SAI goal with minimal cruise performance penalty. Nomenclature b = span c = chord C D = drag coefficient C f = skin friction coefficient C L = lift coefficient C m = moment coefficient D p = pressure drag D f = friction drag D R = u m & , ram drag d/l = ratio of diameter-to-length for equivalent body of revolution L/D = lift-to-drag ratio m & = mass flow through the engines * Post-Doctoral Associate, hileman@mit.edu, AIAA Member. † Associate Professor, AIAA Member. ‡ Professor, AIAA Member. § Ph.D. Student, AIAA Member. ** “Silent” in the context of this research does not refer to the absence of acoustic sources; instead, it is meant to reflect the step change in noise reduction. 44th AIAA Aerospace Sciences Meeting and Exhibit 9 - 12 January 2006, Reno, Nevada AIAA 2006-241 Copyright © 2006 by The Cambridge-MIT Institute. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.