pub const SUBSONIC_BOATTAIL_RULE_RAD: f64 = 0.165_148_677_414_626_83;Expand description
The steepest boattail that Niskanen’s subsonic rule gives no drag, rad: where its length
ratio γ = l/(d₁ − d₂) is 3, so atan(1/6), 9.46° (Niskanen 2009 eq. 3.88,
hpr_aero::drag::boattail_factor). A steeper one takes a share of base drag below Mach 0.8,
which read from −40.8% to +41.7% on Cubbage’s measured 16° boattails and high on the Arcas
Robin’s 15° one (issue #73); between 9.46° and
15° is unmeasured, so the warning takes it in.