Spinning Rotor Blade Tests in Icing Wind Tunnel

The Spinning Rotor Blade (SRB) is an apparatus developed at Anti-icing Material International Laboratory in collaboration with Bell Helicopter Textron to study ice physics, low energy de-icing systems and hydro- or ice-phobic coatings use for small helicopters. The SRB is a 1/18 subscale model of a small helicopter with 0.78 m diameter rotor of two blades rotated by a 10 hp engine to a tip speed of 130 m/s. The blades are 6066-T6 extruded aluminum with a NACA0012 airfoil of 69.64 mm chord and 0.315 m long. The icing tests were conducted in AMIL’s low speed closed loop Icing Wind Tunnel with a liquid water content of 0.84 g/m³, a median volumetric diameter of 26.7 ± 2.6 µm, an air speed of 15 ± 0.5 m/s and temperature of -15 ± 0.5°C. The power to rotate the SRB was 1 200 ± 120 W with a vibration of 2 ± 0.4 g; when the icing began, the power increased to 5 200 ± 1 400 W at a rate of 30 ± 4 W/s, suddenly, after 160 ±50 s, the power decreased, indicating that a piece of ice of 70 ± 15 mm length and about 4 g of weight was shed at the blade tip. The SRB is able to perform reproducible ice shedding tests with similar behavior to helicopters at low cost with repeatability below 30% and sensibility of ±5% for temperatures ranging from -5 to -20oC. The ice adhesive shear stress estimated from the SRB II at -15°C was 0.21 ± 0.06 MPa for aluminum. It decreased linearly when the temperature increased. Also, the adhesive shear stress obtained for icephobic Coating A was 0.10 MPa which is 2.1 less adhesive than aluminum, but its icephobicity is insufficient to be safely used on helicopters. Some empirical correlations for ice thickness, freezing fraction and adhesive shear stress were found with the SRB-II and also a criterion was proposed criterion to quantify the icephobicity of coating efficiency for helicopters, but without fundamental parametric scaling equations to helicopter, they are not helpful for helicopter.