With as many as six examples of its Dhruv twin-engined military/civil light helicopter ready to perform in the Changi skies over the next few days, Hindustan Aeronautics (HAL) is nicely placed to soak up any spare demonstration slots.

The two-crew, 12-passenger Dhruv - which arrived on board an Antonov An-124 freighter - won civil certification from Indian authority DGCA last October, and HAL is aiming for European Aviation Safety Agency (EASA) approval later this year. The Indian manufacturer reports 300 contracts with domestic civil and military operators and is exploring export sales.

Potential buyers would be advised to compare this week's experience with what will be on offer when HAL shows off a pair of Dhruvs at the FIDAE show in Chile next month - those aircraft will be fitted with a pre-production vibration-control system from US helicopter systems specialist Lord Corporation.

Last month Lord was awarded a contract for series production of 20 shipsets of its Active Vibration Control System (AVCS) for installation in Dhruv, also known as the Advanced Light Helicopter (ALH).

First

The first aircraft with production-standard AVCS is expected to fly in the third quarter of this year.

"We look forward to partnering with HAL on other technologies in the future," says Jim Potter, Lord's international technical director for aerospace products. "In the meantime, we're developing further Dhruv applications that will substantially reduce HAL's costs while enhancing service life, improving reliability and reducing direct operating costs. Flight testing and certification are planned for the second half of this year."

The US company's involvement in the programme began with contracts to supply elastomeric bearings for the main and tail rotors, bearings for the pylon isolation system and instrument-panel isolators. Then in mid-2002 Lord was asked to help minimise fuselage vibration, using its proven AVCS technology.

A contract for diagnostic ground and flight testing was awarded in September 2002, and the AVCS capability was demonstrated in November 2002. Subsequent flight tests of a prototype system in two aircraft - one with a skid undercarriage, the other with wheeled gear - revealed impressive vibration reductions, the company says. While the initial objective was to cut vibration in the cockpit, the tests showed that the system yielded improvements throughout the aircraft in all flight conditions.

AVCS is based on the use of active "frahms" (actuators) to reduce fuselage vibration arising from the mechanical and aerodynamic effects of the main rotor.

Sensors

Responding to data from fuselage-mounted sensors, the system controller commands the frahms to act as needed to cancel vibrations. Benefits include a more comfortable, less fatiguing ride for passengers and crew and improvements to the serviceability and operating lives of onboard systems.

Two, three or four frahms can be used simultaneously, depending on mission and conditions.

BRENDAN GALLAGHER

Source: Flight Daily News