Meridian Curve

Geometry of the hull

Meunseir elliptical

separation of boundary layers in positive pressure gradients

"Goodyear" modified elliptical

${\displaystyle r(x)=r_{max}(a-b{\frac {2x}{L}})[1-({\frac {2x}{L}}-c)^{2}]^{\frac {1}{2}}}$

NACA/Göttingen

${\displaystyle r(x)=a_{0}{\sqrt {x}}+a_{1}x+a_{2}x^{2}+a_{3}x^{3}}$

${\displaystyle r(x)=d_{0}+d_{1}(1-x)+d_{2}(1-x)^{2}+d_{3}(1-x)^{3}}$

Optimal Fineness Ratios

Neutral Buoyancy Aerodynamics

Navier-Stokes equations - low speed aerodynamics - typically neglect the buoyancy of the vehicle...

${\displaystyle L=(vol)\delta g}$

where

${\displaystyle \delta =\rho _{air}-\rho _{helium}}$

${\displaystyle D=q_{0}C_{D_{0}}(vol)^{\frac {2}{3}}}$

${\displaystyle (L/D)={\frac {(vol)\delta g}{q_{0}C_{D_{0}}(vol)^{\frac {2}{3}}}}}$

${\displaystyle C_{D_{0}}=0.19Re_{vol}^{-0.15}}$

${\displaystyle C_{D_{0}}=0.24Re_{vol}^{-0.15}}$

where

${\displaystyle Re_{vol}={\frac {V(vol)^{\frac {1}{3}}}{\nu }}}$

Aerodynamics of Static Heaviness or Buoyant Conditions

${\displaystyle L=(vol)\delta g+q_{0}C_{L}(vol)^{\frac {2}{3}}}$

${\displaystyle D=q_{0}(C_{D_{0}}+KC_{L}^{2})(vol)^{\frac {2}{3}}}$

${\displaystyle (L/D)={\frac {(vol)\lambda g+q_{0}C_{L}(vol)^{\frac {2}{3}}}{q_{0}(C_{D_{0}}+KC_{L}^{2})(vol)^{\frac {2}{3}}}}}$

${\displaystyle K=1.4-0.035\alpha }$

${\displaystyle C_{L_{\alpha }}=0.021}$

References