Function crossflow_eta 

pub fn crossflow_eta(fineness: f64, crossflow_mach: f64) -> f64

η for a body of fineness fineness at crossflow Mach number crossflow_mach: Fig. 6’s value scaled by Fig. 4’s for the body’s length, the scaling fading as Fig. 6 rises toward 1 (see the module’s Combining the two ηs).