Application of MDO to Large Subsonic Transport Aircraft

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(c)2000 American Institute of Aeronautics & Astronautics or published with permission of author(s) and/or author(s)’ sponsoring organization. The present study however, suggested modifying the wing load distributiort’the wing sweep and the root chord simultaneously. This new planform design is shown in Fig. 8. The kink region was not very noticeable in the planform view any more and the wing sweep is increased a few degrees. The wing thickness ratio was not changed much. If we analyzed these design changes with our preliminary code we would get a performance gain of not less than 10,000 kg for every scenario. Verification of the design performance At this point the new preliminary design was finished. It was however hard to predict whether the large performance improvements were real. For that purpose a detailed design needed to be made. So we needed a detailed aerodynamic design based on the same specifications (multi- points) as the original reference design and analyzed with the same codes as the reference design. We used the Pointer-Aeropt code (as described in ref. 8.) to design the detailed aerodynamic shape of the wing using 130 shape variables and 3 critical operating conditions. The start configuration for the detailed aerodynamic 12000 -- Total Mass versus AR (reference) Mass 8000 -- 6000 -- current value (kg) 4000 -- 2000 - - 0 -- 5.00 6.00 7.00 8.00 9.00 AR Fig. 4 1-D scan of the aspect ratio before and after the optimization. design loop used scaled A340 type airfoil sections. The drag of that wing was 30% higher than the reference configuration. After 2 cycles (1 month) the design had converged to a shape that produced a drag that was 5% lower than the drag predicted for .the reference configuration with the same (Navier Stokes) code. This configuration is shown in Fig 9. Since we now also had the detailed section shapes we could repeat the application of the structural design and weight estimation tool FAME with more accuracy. The overall performance gain was slightly higher than the 10 tons predicted. The improvement came equally from the drag and the weight. The reason for this can be found in the detailed design. Fig. 8 shows the location of the thickness maxima on the reference and the new wing. The reference wing puts the thickness maxima on an almost straight line. The optimal detailed wing sweeps the location of the inboard maximum thickness a lot more as compared to the outboard wing. We suspect that this (and the overall sweep increase) enables the higher inboard wing load without drag penalty. O- Total Mass versus AR loWimized1 7 American Institute for Aeronautics and Astronautics
(c)2000 American Institute of Aeronautics & Astronautics or published with permission of author(s) and/or author(s)’ sponsoring organization. 16000 14000 -- “ae ro” \ solution l l l 0 2000 4000 6000 8000 10000 12000 14000 16000 Savings in Structural Mass (kg) Fig.5 Performance improvement over reference of wings optimized under various scenarios 20 Ok I -20 - -40 -60 Fig.6 Range of value of optimal design variables for all scenarios. 8 American Institute for Aeronautics and Astronautics
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Application of MDO to Large Subsonic Transport Aircraft

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