Correlation for control force coefficient of parafoil airdrop system

• Determining the dimensionless numbers affecting the control force factor. • Revealing the influence law of each dimensionless number. • Presenting new general correlations for the control force factor of the parafoil airdrop system. The maximum control force is a key factor in the selection of a servo motor for a parafoil airdrop system. However, the reliable and rapid prediction of the maximum control force remains challenging. In this paper, the control force coefficient is predicted using the fluid-structure interaction method. The results show that the errors between the test and calculation results do not exceed 8%. On this basis, the influence analysis for the control force coefficient (dimensionless maximum control force) is studied. Combined with the dimensional analysis, it can be determined that the mass ratio, control stroke, Strouhal number, and glide ratio are the dimensionless numbers that affect the control force coefficient. The effects of mass ratio and glide ratio are small. The control force coefficient is positively correlated with the control stroke and negatively correlated with the Strouhal number. As the Strouhal number approaches zero, the control force coefficient approaches a constant value. A database of control force coefficients, including data from airdrop tests and the results of calculations, is established. Based on these results, a correlation for the control force coefficient is presented by means of the Levenberg-Marquardt method, with 80% of the data having an error of less than 20%. The correlation can efficiently predict the maximum control force and provide a theoretical basis for designing precision airdrop systems.