Constant STEEP_BOATTAIL_RAD 

pub const STEEP_BOATTAIL_RAD: f64 = _; // 0.17453292519943295f64

A boattail steeper than this, in radians, warns past SUPERSONIC_DRAG_MACH: 10°, the steepest that issue #72 measured inside its spread (−6.3% to +17.4% at 10° and below). It measured 15° at +13.5% to +50.8% and 16° at +26.4% to +54.1%; between 10° and 15° is unmeasured, so the warning takes it in rather than leave a high drag unwarned.