Stiffness Scaling for Solid-Cloth Parachutes

The parameters affecting the inflation of solid-cloth, flat circular parachute canopies were investigated. A primary dimensionless parameter in addition to mass ratio, Froude number, and permeability is a stiffness index. Comparison of sub- and full-scale C9 parachutes, along with small-scale wind- and water-tunnel models has revealed that a relative stiffness index is able to correlate the filling and opening times of various sized canopies. The filling and opening times can be expressed as the relative stiffness index raised to power -0.064 , with a proportionality factor of 1.3 for the filling time. The proportionality factor that correlates opening times is 0.86 fo r mass ratios in the range of 0.1- 0.2, and it approaches 1.3 as mass ratio becomes very large. The index has utility in correlating peak forces as well.