The measurement result of the force-measurement system (FMS) will be greatly impacted by the stiffness of the force balance when it is used in an impulse combustion wind tunnel. To study this issue, firstly, the FMS is simplified and its dynamic motion equation is given. Secondly, the stiffness matrixes and modal parameters of the FMS-A, FMS-B, and FMS-C with different stiffness are acquired by the virtual calibration and modal analysis. Thirdly, the transient simulations of FMS-A, FMS-B, and FMS-C are conducted to acquire their responses. The results show that the mean measurement accuracies before and after the inertia compensation are higher than 93.00% and 99.60%, respectively. The mean outputs of FMS-A, FMS-B, and FMS-C are close to each other when the same loads are applied on the test model. This proves that the stiffness of the force balance has little influence on the mean measurement accuracies of the FMS. In addition, the transient output histories are approximately consistent with the inputs. The transient measurement accuracies of FMS-A in drag, lift, and pitching moment are higher than 85.13%, 80.14%, and 68.40%, respectively. They are higher than 85.90%, 83.48%, and 69.90% as to FMS-B, respectively and they are higher than 85.91%, 89.05%, and 74.67% as to FMS-C, respectively. This shows that, on a certain range, the transient measurement accuracies are improved with the increase of the stiffness of the force balance.
