In 1996, DARcorporation was hired by Omega and AEL to determine the optimal location of the fuel hose port on the 707 fuselage. To find this location, water tunnel testing was performed where red dye was inserted into test points on the model and the turbulence could be visualized by the red streamlines. The least turbulent streamline was then selected as the location of the fuel hose port. You can find a link to this Mighty Planes episode here: Mighty Planes: Season 2: Episode 1.