Lord/Sikorsky Hub-Mounted Vibration Suppressor (HMVS)

Triton

Donald McKelvy
Senior Member
Joined
14 August 2009
Messages
9,707
Reaction score
2,021
Website
deeptowild.blogspot.com
"Rotorcraft Vibration Can Be Almost Eliminated"
Smoother ride promised for helicopter occupants and components
Jun 11, 2014 Graham Warwick | Aviation Week & Space Technology

Source:
http://aviationweek.com/defense/rotorcraft-vibration-can-be-almost-eliminated

A version of this article appears in the June 9 edition of Aviation Week & Space Technology.

Vibration has been an enemy of rotorcraft designers since before Igor Sikorsky began building helicopters. Not only is it debilitating to passengers and crews, vibration is also detrimental to avionics and components, reducing reliability and life.

The unsteady aerodynamics of rotor blades in forward flight produce vibratory loads that enter the hub, travel down the mast to the gearbox and from there into the airframe. Traditionally, vibration has been reduced using absorbers placed in key locations—initially passive and tuned to a single rotor rpm, but more recently active and able to adjust to variable speeds.

Crrdit: Sikorsky Aircraft
Now Sikorsky plans to demonstrate that vibration can virtually be eliminated in a helicopter by using a combination of rotor and gearbox suppressors to create a “choke point” that blocks unsteady loads from entering the airframe.

The “zero-vibe” demonstration late this year will follow flight tests of a hub-mounted vibration suppressor (HMVS), completed in March, that achieved a substantial reduction in main-rotor vibration. Anti-vibration actuators will be added to the main gearbox to create the choke point and achieve a global reduction in airframe vibration, says Bill Welsh, Sikorsky dynamics technical fellow.

Current helicopter active vibration control systems can reduce forces in specific areas of the fuselage, such as the cockpit, but can increase the problem in other parts of the airframe. Sikorsky’s goal is to “eliminate all vibration from the main rotor, through the main gearbox to the airframe,” he says. “We want to stop the gearbox moving so we create a choke point that stops vibration entering the airframe.”

Developed by Lord and Sikorsky, under the Army Aviation Applied Technology Directorate’s (AATD) Active Rotor Component Demonstration program, the HMVS was flight-tested on a UH-60A Black Hawk. The HMVS comprises four brushless electric ring motors, each with an eccentric tungsten mass, in a housing atop the main rotor hub. One pair turns in the same direction as the rotor and the other pair in the opposite direction, but at four times the speed of the rotor.

In the hover, no vibration suppression is required, so each pair of eccentric masses is 180 deg. apart. As the helicopter moves into forward flight, and the blades start to produce vibratory loads in the plane of the rotor, the masses are moved closer together to produce an unbalanced load.

“We arrange the phase of the unbalanced load to counter what the rotor is producing,” says Welsh. “If the rotor is producing a 1,000-lb. load at 140 kt., then the device produces 1,000 lb. to counter. We need masses spinning in both directions to get complete suppression of rotor in-plane loads.”

Flight test results were “as expected . . . we put the device on a UH-60A and got significantly lower vibration than the current bifilar [vibration absorber],” Welsh explains. Mounted atop the hub, the bifilar (left in photo) comprises dynamic masses on the ends of four arms that are tuned to absorb rotor vibrations. The HMVS (right) is 50 lb. lighter than the Black Hawk bifilar, and electrical power is supplied via the slip ring already used to power the rotor anti-icing system.

Through the 1980s, higher harmonic control (HHC) of blade pitch was pursued as a way to reduce rotor vibration, but it was limited to certain frequencies. More recently, there has been research into individual blade control, with actuators on the rotor; but both involve placing increased demand on the flight-critical rotor control system. “HHC never promised to nullify every load. This does, and we are not wearing out the main rotor servos,” notes Welsh.

The zero-vibe flight tests will be performed under an AATD program known as the Combat Tempered Platform Demonstration, which aims to increase the durability and survivability of Army helicopters. In addition to the HMVS, Sikorsky will install four Lord active vibration-control (AVC) spinning-mass actuators at the four corners of the main gearbox. “This will give us a total of six knobs to turn to stop the motion of the gearbox. The key is positioning them very near the choke point, which first-generation AVC didn’t do,” Welsh explains.

To reduce risk, the first generation of AVC systems “put the active suppressors where the old absorbers used to be . . . and allowed vibration to leak through.” Forces entering the fuselage are sensed by 14 accelerometers distributed around the airframe. “They feed information into a control computer that tells the system how much force to put out in what places to minimize vibration,” Welsh says.

While the goal of zero-vibe is to achieve “very low” global 4/rev vibration levels, “there is a little bit of higher harmonic vibration—8/rev, 12/rev—but low enough that the crew will not notice,” he adds. “It is close enough to zero to be good enough.”
 

Attachments

  • AW_06_09_2014_1931L.jpg
    AW_06_09_2014_1931L.jpg
    29 KB · Views: 171
"Sikorsky, Lord Test HMVS Vibration Reduction Technology"

May 22, 2014

Source:
http://www.aviationtoday.com/regions/usa/Sikorsky-Lord-Test-HMVS-Vibration-Reduction-Technology_82251.html#.U5pH3yjLOew

Lord Corporation and Sikorsky Aircraft have finished testing the hub mounted vibration sensor (HMVS)[sic] on a UH-70A Black Hawk. The flight test took place at Fort Eustis, Va., in partnership with the U.S. Army’s Aviation Applied Technology Directorate.

During the American Helicopter Society International’s Forum 70 this week in Montreal, Lane Miller, vice president of global technology at Lord, noted that the company is “driven by innovation. We define innovation as converting technology into value – value for Lord, value for Sikorsky and value for Sikorsky’s customers. Failing that, the technology is not truly innovative.”

The March 2014 flight test took place as an element of the Active Rotor Component Demonstration (ARCD) program. According to Sikorsky, the trials included progression from a hover to 150 knots, autorotations and 60-degree angle-of-bank turns. HMVS cancels the largest vibratory loads near the source of the vibration, the main rotor hub, and keeps the loads from propagating into the airframe.

Chris Van Buiten, vice president of technology and innovation research and engineering for Sikorsky, put a timetable on the HMVS development: “We expect to be demonstrating near-jet-smooth operation of the Black Hawk to the U.S. Army before the end of this year.”

Lord HMVS. Photo courtesy of Sikorsky Aircraft
 

Attachments

  • Lord_HMVS.jpg
    Lord_HMVS.jpg
    56.4 KB · Views: 171
Is this system or a variant of it incorporated in the S-97 Raider?
 

Similar threads

Back
Top Bottom