Abstract: In view of the serious nonlinear response problem of strain bridge for load measurement of aircraft folding wing structure in the load calibration ground test, based on the structural force transmission characteristics and structural load meas-urement mechanism in the folding region, Bending moment with respect to the folding boundary plane is taken as the state variable, and the bending moment due to the gravity of the folding section is taken as the boundary load, a piece-wise multivariate linear model is established, and the method of determining flight measurement load by piecewise model is presented，which is verified in flight test of folding wing load measurement of a certain type of aircraft. The results show that the load obtained by the piecewise model is closer to the actual load, which can significantly reduce the influ-ence of the nonlinear response of the strain bridge on the load measurement in the folding region, and improve the accu-racy 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 of the piecewise model respectively; at the maximum negative load factor of the symmetric push-down maneuver, the shear and bending mo-ment obtained by the upward load model are 14.87% and 12.83% larger than that of the piecewise model respectively. The research provides a theoretical basis and engineering method for solving the nonlinear response problem of strain bridge for load measurement of wing structure.

Key words: folding wing, structural load, flight measurement, strain bridge, nonlinear response, piecewise model, load calibra-tion