Sikorsky develops new counter-vibration system
Sikorsky (Booth Nos. 2737-2743) has completed rig testing of an active counter-vibration system that could make a helicopter ride “jet smooth,” thanks to hub-mounted actuators that counter loads at their source, the company claims. The hub-mounted vibration suppression system (HMVS) is expected to yield improvements in comfort, weight and durability, and, the company said, it could be in service in 2015.
The HMVS was one of the key subsystems on the X2 compound demonstrator, enabling it to reach its vibration goal last year. At 250 knots, the vibration level was said to be similar to that of the Black Hawk military transport at its 140-knot cruise speed. Sikorsky plans to certify the HMVS for production helicopters.
Lord Corp., Cary, N.C. has teamed with Sikorsky and the U.S. Army’s Aviation Applied Technology Directorate on the HMVS. The equipment manufacturer describes the dual-frequency system as “motorized imbalanced rotors that rotate at the blade-pass frequency to create centrifugal forces.” According to the company, the magnitude and orientation of the centrifugal forces can cancel lateral hub vibration through phasing of the two rotors. The force generator, controller, sensors and power electronics are contained in a single unit, and vibratory loads come from blade movement asymmetry and blade-vortex interaction.
Bill Welsh, chief of Sikorsky’s dynamics and internal acoustics group, told AIN that the HMVS is adaptive. “It learns how the helicopter reacts to dynamic load inputs and applies a sample load from each actuator and analyzes echoes. The algorithm determines what command to apply so that the HMVS load suppresses loads coming from the main rotor,” he explained.
Current passive systems use springs and loads, he said. The springs are tuned to the worst vibration frequency in the helicopter. There usually are five devices per helicopter located in various places: for example, the rotor head, cabin, nose and cockpit.
The new system suppresses vibration throughout the fuselage. Typically, helicopter vibrations are in the 0.1- to 0.15-g range, Welsh said, adding that the HMVS will cut this down to “0.03 g or below–virtually undetectable vibration.”
The company also hopes the HMVS will yield a weight savings. Current passive systems comprise about 0.2 percent of the aircraft’s empty weight, and the HMVS will cut this to 0.1 percent, according to Welsh. In terms of durability improvement, he said, “It is debatable but one can expect the system to enable a 10-percent reduction in parts removal.”
The HMVS will be slightly more expensive than current systems, Welsh said, which “is because of its electronic content.” However, upfront cost should be offset by savings from weight and durability improvements.
The flying testbed for the HMVS will be an H-60 Black Hawk, scheduled to fly late this year or early in 2012. The main remaining job is designing the actual connection to the aircraft, Welsh said, adding the company is planning 10 to 15 flight test hours.
A major certification challenge will be demonstrating a degraded mode where the helicopter remains safe with one actuator failed. One could expect to see the HMVS in service “in about five years,” Welsh had commented back in November, adding that Sikorsky plans to integrate an HMVS into all its helicopters.