Abstract: Large flexible aircraft tend to produce great bending deformation under aerodynamic force, so that it is difficult to obtain their load analysis and optimization solutions by means of the linear theory. In order to consider both the structure and aerodynamic nonlinearity, the structure is denoted by joined geometrical nonli-near Euler beams, while the aerodynamic model employs a spanwise compressible horseshoe vortex lattice, and the deflecting multiple control surfaces are coordinated to optimize the flight loads. Numerical results show that with the increase of aircraft deformation the linear analysis results will produce errors up to 20%. Through coordinating and deflecting the four groups of control surfaces located on the wing and the elevator, the wing root bending moment load is alleviated by 13.6%. It is concluded that structure bending effect leads to lift loss, which explains why linear theory analysis produces significant errors, and that coordinating and deflecting multiple control surfaces can alleviate structure loads effectively.

Key words: aeroelasticity, nonlinear analysis, flight load, multiple control surface, geometrical nonlinearity