Aerodynamic optimization design for civil aircraft considering relaxed static stability

The study on the aerodynamic optimization design of the civil jet wing-body-tail configuration with different static stability is presented, which intends to efficiently reduce the aircraft's total drag considering trimming. It is obtained that considering static stability in drag-reduction design can have great potential of reducing the drag. The Free-Form Deform (FFD) technique is adopted to parameterize the wing shape for aerodynamic optimization design and rotate horizontal tail for trimming the pitching moment of the whole aircraft. The discrete adjoint technique based on Reynolds Averaged Navier-Stokes (RANS) equations is used to solve the gradients of targets with regard to design variables, and sequential quadratic programming is used to conduct the gradient-based optimization design. Based on the Common Research Model (CRM), optimizations considering trimming constraint with different c.g. positions are carried out to reduce aerodynamic drag, and feasibility of the optimization system is confirmed. The results of optimization cases show that when the c.g. position moves backward, the optimization configuration has smaller trim drag, obviously lower negative pressure peak of the leading edge in the outer wing, and weaker shock wave. The distribution of wing spanwise lift coefficient is improved to achieve the optimized design result.