Verification of U-21 Cloud Parameter Measurement Equipment and Comparison of Natural and Artificial Ice Accretion Characteristics on Rotor Blade Airfoil Sections

摘要

The US Army Aviation Engineering Flight Activity icing research and qualification facilities include an instrumented JU-21A aircraft to measure icing cloud parameters, and a JCH-47C equipped with the Helicopter Icing Spray System (HISS) to provide an artificial icing capability. An inflight comparison of cloud measurements made between the JU-21A and the Univ. of Wyoming Super King Air atmospheric research aircraft in natural icing conditions showed reasonable agreement. A subsequent phase of this program investigated ice accretion characteristics on airfoil sections representing UH-1H and UH-60A helicopter rotor blades in 3 scale sizes in both natural icing conditions and the artificial cloud produced by HISS. Two airfoil sections of 18-in. span were mounted on a structural framework over the left wing of the JU-21A and progressive stages of ice accretion were documented with sequence photography. Airfoil icing immersions, which typically lasted 10-20 minutes each, were conducted at incidence angle of 0-9 deg. Ice profile tracings made from the photographs allowed comparison of ice accretions between natural and artificial cloud types, different temperatures, incidence angles, airfoil section types, and airfoil scale sizes. Analysis of the ice shape results indicated a lower than expected accretion rate for artificial icing conditions, and showed that artificial ice formations begin to assume streamlined profile characteristics similar to rime ice formations at temperatures 3-4 C warmer than for natural ice. Keywords: Droplet impingement; Helicopter blade section; Icing clouds; Icing similitude; Liquid water content; Particle measurement. (edc)