Aerodynamic Flow-off of Type II and Type IV Aircraft Ground Anti-icing Fluids

The certification process for aircraft ground anti-icing fluids involves flat plate wind tunnel aerodynamic flow-off tests. This test method was developed in 1990 from flight and wind tunnel tests results on full scale and model airfoils, and flat plates; the resulting lift losses were then correlated to the Boundary Layer Displacement Thickness (BLDT) on a flat plate. This correlation was made for Type II fluids existing at the time. Since the introduction of Type IV fluids in 1994, with significantly longer anti-icing endurance times, the same test procedure was applied. However, Type IV fluids are generally more viscous than Type II fluids of the same concentration. At the FAA's request, a study was undertaken to see if aerodynamic certification testing should be different for Type IV fluids as opposed to Type II. After a comparison of existing certification BLDT data which showed no significant differences between Type II and Type IV fluids, aerodynamic tests were performed on five commercial fluids, two typical Type II and three typical Type IV fluids. Tests with different initial thickness showed that the thickness had little effect on BLDT and fluid elimination data, with the exception of one fluid, near the temperature at which it is acceptable. Examination of energy data showed that more energy was required by the wind tunnel to move the Type II fluids as opposed the Type IV fluids. When these fluids were tested using an identical fixed fan speed profile at 0, -10 and -25°C, little difference was seen in the BLDTs as compared to those generated by a certification profile adjusted to obtain the same acceleration. These preliminary tests suggest that the aerodynamic certification method developed for Type II fluids is adequate for assessing Type IV fluids.