Optimized European Supersonic Transport

The basis for the comparison was the already (fairly) optimal 1995 European Supersonic Trans­port Design. The goal of the optimization was to improve the cruise lift-to-drag ratio of the design by at least 5 % without penalizing the structural weight significantly and keeping the basic layout in terms of minimum dimensions. The engine nacelle was configured for cruise and not modified. The span was kept constant. The canard was considered to be not lifting at supersonic flight and was taken into account by a small drag increment.

The design variables were:

1. Angle of attack a, and twist angles expressed as a Taylor polynominal a (iCiy+cjy^+cj^+Cjy4). The root incidence was kept constant.

2. Wing location (x) at 33 52 <k, 86 of the semi-span and the tip.

3. Wing chonl(y) at 33 9b, 52 9t 86 of the semi-span and the tip. The root chord was kept constant.

4. Wing shape functions Y( (Cg4c/ у-fc^y*+cj у4)

5. 19 Fuselage cross-sections as a function of x.

The following constraints were used:

1. Cruise lift coefficient C{ <0.125.

2. Cruise pitching moment C *0 around reference point.

3. Same neutral point location as the reference configuration.

4. Cruise floor angle < 4.5°

5 23 Minimum dimensions for cockpit and the landing gear bay. and also a cabin external di­ameter of 4.0 m ,

6. For landing: 5 ° Bank, 12 ° pitch sufficient clearance for wing and nacelle with a gear not higher than 5.5 m..

7. Acceptable wing-body fairing by constraining root incidence, camber and thickness distribu­tion.

8. At least the ESCT-basclinc local wing stiffness

9. 6 Minimum spar depths for the wing to assure landing gear storage, fuel volume

The coniiguiation was optimized for two operating points at Mach 2.0. Since the wing span and area were not affected it was not expected that the subsonic efficiency of the configu­ration would be changed after optimal flap scheduling was implemented.

The time required to reach a fully converged design was about three hours on а НР935/ lOOMhz. The original design goal was almost met. but with significant changes to the geometry. A free optimization would have achieved a greater reduction

Figure 94 shows the optimized ESCT-6 as a coarse panel geometry. The optimizer swept the outboard panels more, but to keep the same stiffness as the reference ESCT. the thick­ness had to be increased. The optimizer also runs against the w ing tip clearance constraint using the maximum allowable gear height. A solution was found by using forward sweep near the lip. This allowed the wing to be banked and pitched without sinking the runway. As the eight wing section cuts show-, the wing shape gradually changes from a rounded leading edge at the root to a sharp supersonic leading edge near the tip The fuselage is significantly widened in the front. Although these changes were quite radical, the goal of 5Я drag reduction was barely achieved, and it remains to be seen whether this new geometry has any other problems associated with it. In the optimization и turned out that the outboard wing sweep was the principle driving force in reducing the w ing drag

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