Design Optimization of the Flap System of a Large Transport Aircraft

Takeoff performance is a major factor in the design of modern transport aircraft. Improving the high-lift behavior can have multiple benefits, including the ability to takeoff and land at an increased number of airports and a... [ view full abstract ]

Takeoff performance is a major factor in the design of modern transport aircraft. Improving the high-lift behavior can have multiple benefits, including the ability to takeoff and land at an increased number of airports and a possible increase in the maximum takeoff weight of a given aircraft. An optimization study was performed on the flap system of a large transport aircraft (shown in Fig. 1) to reduce the required takeoff distance. As part of the study, the number of flaps and the position, deflection angle, and the chord of each flap were modified, while satisfying geometric constraints such as maximum flap chord and ground clearance. The algorithm of the optimization process is shown in Fig. 2. A single level Python based SciPy optimization function was used in conjunction with an aerodynamic model, a weight model and a performance model to minimize the takeoff distance.

Results of this study are shown in Fig. 3. The optimum configuration is that of a single slotted inboard flap with a 72 inch chord deflected to 11 degrees and a single slotted outboard flap with a 45 inch chord deflected to 22 degrees. The gap distance for both sections was set to 3 inches.

Compared to an approach using CFD, the computational expense of the chosen optimization approach was relatively low and required less than two hours on a personal computer with an Intel® Core™ i7 processor capable of running at 2.9GHz. This is largely due to the aerodynamic analysis tool used in the optimization that is based on a higher order potential flow method. The method uses elements with distributed vorticity to model the lifting surfaces and their wakes. As a consequence of the wake being represented by a continuous vortex sheet, the method is computationally efficient and numerically robust, even when allowing for the rollup of the wake. This is specifically advantageous for this optimization task as zero user interaction is required during the iterative process. This optimization task can be easily extended to include a kinematics model to design the flap deployment hardware as well as an acoustics model to minimize aircraft noise.