New general correlations for opening shock factor of ram-air parachute airdrop system

The attainability of the opening process directly determines the success of a ram-air parachute airdrop system. The opening shock is the most concerned parameter for designers. Focusing on the parachute opening process, the peak load is evaluated using the opening shock factor, which is obtained using the dynamic model and the Momentum Impulse theory. Comparisons with airdrop test results show that the two methods can accurately predict the peak load. In the similarity analysis of parachutes, the criteria for flexibility, elasticity, and air permeability are summarized, and the dimensionless numbers affecting the opening shock are identified as the mass ratio, the Froude number, and the Strouhal number. The frame design of the ram-air parachute airdrop system is completed, and a database of opening shock factors including airdrop test data and numerical results is established. New general correlations for the opening shock factor are presented for vertical and horizontal opening utilizing the Levenberg-Marquardt method for regression analysis, with R-2 of 0.9935 and 0.9880, and MAPE of 3.45% and 2.64%, respectively. The new correlations can quickly and accurately predict the opening shock for ram-air parachute airdrop systems.