Function wp_slope 

pub fn wp_slope(
    mach: f64,
    fore_radius_m: f64,
    aft_radius_m: f64,
    length_m: f64,
) -> Result<f64, AeroError>

A conical boattail’s normal-force slope increment at α → 0, per radian on the area π fore_radius_m², at Mach mach (at least 1): negative, from Fig. 5’s correlation (WP_SLOPE_PER_DEG).

Errors

AeroError::Domain for a Mach number below 1 or not finite, a length that isn’t finite and positive, an aft radius that isn’t below the fore radius (not a boattail) or is negative, or dimensions whose ratios overflow.