# Durability of Superamphiphobic Polyester Fabrics in Simulated Aerodynamic Icing Conditions
## 3 Results and Discussion
### Flat Plate Configuration
#### 3.2.1 Superhydrophobic Fabrics  
The water wetting properties of superhydrophobic fabrics exposed to a water droplet cloud at airspeeds of 90-115 m/s, at freezing and non-freezing temperatures, and on a flat plate at two constant angles of attack are plotted in Figure 6a,b. Figure 6a represents fabrics tested in a warm cloud at 12.5 \({}^{\circ}\)C. Warm droplets had a negligible effect on the fabric's wetting properties. The water contact angle in Figure 6a exceeded 160\({}^{\circ}\) for both angles of attack across all speeds presented. The same holds for the roll-off angle, although the standard deviation increased with increasing airspeed. Their water contact angle above 150\({}^{\circ}\) and water roll-off-angle below 15\({}^{\circ}\) means the coated fabric retained its superhydrophobic properties. Figure 6b represents fabrics tested in a supercooled droplet cloud at \(-\)5 \({}^{\circ}\)C. The contact angle in Figure 6b shows stagnant behavior for the 45\({}^{\circ}\) angle of attack, but that of the 20\({}^{\circ}\) angle of attack increased with increasing airspeed after 100 m/s. The roll-off angle was constant for the 45\({}^{\circ}\) angle of attack, but was steadily decreasing for the 20\({}^{\circ}\) angle of attack, along with the standard deviation.  
The maximum speed tested in the flat plate configuration did not fully remove the top part of the coating as in the airfoil configuration. Figure 5a shows that the suction side portion of the fabric saw a greater reduction in the water contact angle than the pressure side did. The stall behavior of a rectangular block is the opposite of an airfoil. An airfoil approaches stall (flow separation) as the AoA increases, whereas the rectangular block sees flow separation starting from 0\({}^{\circ}\) (Figure 2b)  
Figure 6: Wetting properties of fabrics exposed to cloud conditions for 10 min at increasing speeds while on a flat plate at an angle of attack of 20\({}^{\circ}\) (horizontal dash) and 45\({}^{\circ}\) (cross). (**a**) Water droplets on a superhydrophobic fabric after exposure at +12.5 \({}^{\circ}\)C. (**b**) Water droplets on a superhydrophobic fabric after exposure at \(-\)5 \({}^{\circ}\)C. (**c**) Oil droplets on a superamphiphobic fabric after exposure at +12.5 \({}^{\circ}\)C. (**d**) Oil droplets on a superamphiphobic fabric after exposure at \(-\)5 \({}^{\circ}\)C.  
and transitions to a fully connected boundary layer between 10\({}^{\circ}\) and 20\({}^{\circ}\) (Figure A2d,f) [26]. In the flat plate test, the fabric was placed on the pressure side. Since flow separation on an inclined rectangular block (occurrs at angles of attack lower than 10\({}^{\circ}\), the suction side would not be exposed to high flow velocities or droplet impacts. To ensure that the fabrics would be exposed to high speed airflow and droplet impacts, it was placed only on the pressure side. Superhydrophobic fabrics saw the most damage at lower speeds and shallower angles of attack while in icing conditions. Figure 6b revealed that increasing airspeed in icing conditions did not proportionately affect the wetting properties of the superhydrophobic fabrics.