AEFA/Boeing Vertol Demonstration of the Effectivity of the YUH-61 A in Simulated Moderate Icing Conditions

The YUH-61A helicopter was tested by the U.S. Army Aviation Engineering Flight Activity (AEFA) and the Boeing Vertol Company under simulated icing conditions at Fort Wainwright, Alaska, using the Helicopter Icing Spray System (HISS). The test conditions included 0.75 gram per cubic meter (g/m3) liquid-water content (LWC) at –5°C, 0.5 g/m3 at –10°C, and 0.25 g/m3 at –15°C. At 0.5 g/m3 and – 10°C the aircraft flew in the simulated icing cloud for 29 minutes, at which time the water supply in the HISS was depleted and ice accretion on a visual probe was more than 2 inches. Testing was completed after a total of 3 hours and 21 minutes flying time in simulated icing conditions. The deicing and anti-icing systems performed satisfactorily under all conditions and there was no uncontrolled ice accretion on the heated portions of rotating lifting surfaces. All transparencies except for the lower nose bubble and unheated center windshield remained clear of ice. There was no perceptible change in aircraft handling qualities or vibration levels with the deicing system functioning in simulated moderate icing conditions. AEFA and Boeing Vertol concluded that the aircraft in the configuration tested was ready for testing in natural icing conditions. The aircraft tested was a basic YUH-61A prototype with a deicing kit installed. The kit consists of a control unit, outside-air-temperature sensor, ice detector, cockpit panel, and electrical cables and hardware. The rotor-blade deicing system, similar to that in Boeing Vertol's CH-46 and CH-113 helicopters with spanwise electrical blankets under the erosion caps, is described in detail including operating logic of the Lucas Aerospace controllers. The anti-icing system includes windshields built by Sierracin and engine-transmission fairings built by Goodyear. The results of icing flights with the deicing system active and inactive are discussed with details including changes in aircraft power required, vibration, and aircraft ice accretion. Nonrotating aircraft-mounted cameras were used to photograph the rotor blades at fixed azimuths which, in film playback, gave the illusion of one blade fixed in space. Camera-system design and photographic results are described.