Aerodynamic, Laser Scanning and Photogrammetric Measurements of Cold Soaked Fuel Frost

Abstract

After an aircraft landing during a stopover Cold Soaked Fuel Frost is often formed on the wing even at temperatures above 0 o C. It is of interest to measure the frost geometry and corresponding aerodynamic effect on lift coefficient. To investigate these effects a HL-CRM wing model, representing the wing of a modern jet aircraft, was built including a wing tank cooling system. Real frost was generated on the wing in a wind tunnel test section and the frost thickness was measured with an Elcometer gauge. Frost surface geometry was measured with laser scanning and photogrammetry. The measurements were made with titanium dioxide painting to enhance surface reflectivity and without painting. The accuracy of laser scanning and photogrammetry were compared in these four cases. The aerodynamic effect of the frost was studied in a simulated aircraft take-off sequence, in which the speed was accelerated to a typical rotation speed and the wing model was then rotated to an angle of attack used at initial climb. Time histories of the lift coefficient were measured with a force balance. Time histories of the upper surface boundary layer displacement thickness were measured with a boundary layer rake. The measurements showed that depending on the ambient temperature the frost may evaporate/melt during the take-off sequence. Highest lift losses occurred after the rotation. The lift losses correlated with average frost thickness and the increase of the boundary layer displacement thickness.