Aerodynamic Design of Unmanned and Scaled Supersonic ...

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K. Yoshida and Y. Makino 1 INTRODUCTION After the development of the Concord, the U.S.A. and Europe investigated several advanced technologies for the challenge of realizing the development of the next generation SST. In general, the challenge can be undertaken within the framework of an international collaboration. We at Japan have to advance our technology level in order to join the collaboration and support the development. Japan Aerospace Exploration Agency (JAXA) is promoting the National EXperimental Supersonic Transport (NEXST) program. This program was initiated in 1997 and will last until 2005. It consists of fundamental research activity and flight test program. The main objectives of the fundamental research activity are to advance present technologies in Japan and to create some innovative technologies for the next generation SST in the future. Since Japan has high advanced capability in CFD technology, the principal goal is focused on developing a CFD-based optimum aerodynamic design technology. In the flight test program, we have designed and developed two kinds of unmanned and scaled experimental airplanes. The main objective of the first airplane is mainly to validate supersonic drag reduction technology by the flight test of a pure aerodynamic configuration without any propulsion system. The main objective of the second airplane is to validate the CFD-based optimum design technology by the flight test of a more complicated configuration with two engines and nacelles under the wing. The first airplane is called “NEXST-1” airplane and will be launched by a solid rocket booster (see Figure1). The aerodynamic design of the airplane was undertaken in the following two steps: i) applying the well-known clasical drag reduction concepts for reducing pressure drag, and ii) designing an original supersonic natural laminar flow (NLF) wing concept for reducing friction drag. The final aerodynamic design and production of the NEXST-1 airplane is already completed. The flight test plan is summarized in Figure 1. The aerodynamic forces, surface pressures and transition data will Woomera Separation Launch α-sweep at M=2 and low 18,000 m 15,000 m be measured at two α sweep tests. In its production, the severe roughness criterion of maximum height within 1 µ m was required for the successful transition measurement. The second airplane is called “NEXST-2” and is a jet-powered vehicle. In the aerodynamic design of the NEXST-2 airplane, first of all, the following basic design concepts were applied: an arrow planform with slightly higher aspect ratio than the NEXST-1 airplane, a modified warped wing with two embedded nacelles, an NLF wing at inboard, a supersonic leading edge at outboard. Secondly, an original non-axisymmetrical area-ruled body with an optimum nacelle configuration was designed using a CFD-based optimum design method developed in JAXA. This concept was utilized in reducing the interference drag between the airframe and two large nacelles. The basic aerodynamic design of the NEXST-2 airplane was 11,000 m α-sweep at M=2 and high Recovery Figure 1. Flight test plan of NEXST-1 airplane 2
K. Yoshida and Y. Makino completed in the middle of 2003. The aim of the flight test will be to ensure the practicality of applying the design method to real aircraft design. The flight test plan of the NEXST-2 airplane is summarized in Figure 2. Several technical data will be measured at supersonic and subsonic flight. The first flight test of the NEXST-1 airplane was conducted on the 14 th of July in 2002. Unfortunately the test was a failure, because of unexpected early separation of the booster due to an electric short on the firing system of separation bolts. The failure resulted in the M=0.8 at H=12 km NEXST-2 program being frozen until the success of the flight test of the NEXST-1 airplane. Since then, we have improved and redesigned the whole system. The next flight test is scheduled for the end of 2004. We really do our best to realize the successful fight test of the NEXST-1 airplane. Present paper describes details of the aerodynamic design of both experimental airplanes. 2 AERODYNAMIC DESIGN OF NEXST-1 AIRPLANE In general, we have the following standpoints in the aerodynamic design of the advanced SST: reducing supersonic drag, reducing sonic boom, improving subsonic aerodynamic performance, compromising aerodynamics and structures, and suppressing aerodynamic noise. However as the first step of developing these advanced technologies, we mainly focused on improving lift-to-drag ratio (L/D) at supersonic and subsonic speed in the flight test program, because improving L/D is the most key technology in all development of SST. Furthermore, reducing sonic boom and improving take-off/landing performance with high lift device are also important. Therefore, they are investigated as fundamental reserach activities. In the aerodynamic design of the NEXST-1 airplane, main target was placed on reducing supersonic drag only, because this configuration is clean – that is, it is an aerodynamically pure shape. Therefore, we can obtain the optimum effect of combining several drag reduction concepts. In the NEXST program, we developed advanced aerodynamic design technology according to the following philosophy: to design mathematically along the logical process without any empirical parameters and to incorporate some innovative technologies. To design the NEXST-1 airplane, first of all, we had to specify some typical requirements on an expected real SST aircraft such as fuselage length, volume, tail shape and position. We selected the following dimensions, referring the study [1] of JADC (Japan Aircraft Development Corporation) and other foreign papers: M=2 (cruise Mach number), C L =0.1 (cruise lift coefficient), H=15km (flight altitude), S=9000 ft 2 (wing area), L=300 ft (fuselage length), V=30000 ft 3 (fuselage volume for 300Pax) and scaled tail configurations of the Concorde. Then, we selected a scale ratio of 11% of the real SST aircraft dimensions above. However, tail cone length of the scaled fuselage was slightly extended to keep the fire-on take-off M=1.7 at H=15 km Test region separation data-link landing engine cut-off X-38 scaled model Figure 2. Flight test plan of NEXST-2 airplane 3
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