Construction of flight measurement model for folding wing structural load of aircraft

Strain bridge for load measurement of aircraft folding wing structure will have serious nonlinear response problem in the load calibration ground test. Based on the structural force transmission characteristics and structural load measurement mechanism in the folding region, a piece-wise multivariate linear model is established, with the bending moment with respect to the folding boundary plane being taken as the state variable and the bending moment due to the gravity of the folding section as the boundary load. The method for determining flight measurement load by the piecewise model is presented. The flight test of load measurement of folding wing of a certain type of aircraft is conducted for verification. The results show that the load obtained by the piecewise model is closer to the actual load, and can significantly reduce the influence of the nonlinear response of the strain bridge on load measurement in the folding region and improve the accuracy of the load measurement. At the maximum positive load factor of the symmetric pull-up maneuver, the shear and bending moment obtained by the downward load model are 8.48% and 11.13% smaller than that obtained by the piecewise model, respectively. At the maximum negative load factor of the symmetric push-down maneuver, the shear and bending moment obtained by the upward load model are 14.87% and 12.83% larger than that obtained by the piecewise model, respectively. The research provides a theoretical basis and practical method for solving the nonlinear response problem of strain bridge for load measurement of the wing structure.