The Hindu : Smart materials hold key to improved ALH performance

Online edition of India's National Newspaper
Sunday, Jan 04, 2004

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National

Smart materials hold key to improved ALH performance

By Harichandan A.A.

Bangalore Jan. 3. Vibration reduction is a big deal in helicopters. A public sector aerospace company, Hindustan Aeronautics Limited, has been working hard on that aspect of its star product, the Advanced Light Helicopter.

Now, academic research on smart materials at the Indian Institute of Science and applied research at HAL here and at other centres in the country may yield some results that may equip the ALH, already hailed as best-in-class, with an electronically controlled vibration reduction system, in five years.

Researchers at the IISc's Department of Aerospace are working on a "control algorithm" that when finished will look at the vibrations of the helicopter, and send suitable electronic signals to "twist" the rotor blades in such a way to reduce the vibration, even as the chopper was in full flight.

This is done by the use of smart materials of two types - Piezoelectric ceramics and Magnetostrictives, which as their names suggest are amenable to changes in their structures when subjected to an electric field or a magnetic field.

These materials which can be either "surface mounted" or "embedded" in the rotor blades will respond to commands from an onboard computer and twist the blades by up to two degrees, reducing vibrations by up to 60 per cent.

But before this happy flight, there are several hurdles to be cleared, researchers say. Helicopters are subject to "unsteady aerodynamic forces" as they use their rotors for providing both lift and thrust (moving forward). They also work in "environments of high (electronic and/ or electrical) noise."

The control algorithm then must be robust enough to handle measurements made in such environments.

Further, much work was needed on the "operational capability of the smart materials themselves — for example on their fatigue tolerance.

Finally, actual flight tests would have to be conducted repeatedly to generate enough data to validate the research work and make necessary corrections.

Now, American aerospace major, Boeing, was probably the only company to be running flight tests on a helicopter. However, no commercial helicopter was equipped with such a system, yet.

In the long run, research worldwide is more ambitious: To migrate helicopters to the safer, fly-by-wire system, being used on fixed wing aircraft, both commercial and fighter, for over two decades.

Now, a helicopter pilot still uses the stick and foot-pedal to control the rotors.

The use of rotors for both lift and thrust in helicopters has made them difficult candidates for fly-by-wire, experts feel. Cost was another factor.

But, in the long run the vibration reduction algorithm may also be integrated into an electronic control system, with an onboard computer.

Tie-up with Bell Helicopters?

Last month, a team of engineers from the U.S. helicopter maker, Bell Helicopters, visited HAL here. After getting the ALH DGCA certified for day flying, HAL was exploring the possibility of collaborating with the U.S. based company, in further improving the ALH, sources said.

The Chairman of HAL, N. R. Mohanty, led a team of senior officers of HAL, including Managing Director of the Bangalore complex, on a visit to the U.S., late last year. The possibility of an HAL-BELL collaboration was explored then. Among the technical problems that HAL was looking to solve, was one of vibrations, sources said.

Closer to home, HAL would soon sell one civilian version of the ALH to Jharkhand. "The Chief Minister of Jharkhand is very keen on having one," sources said. The hi-end military version of the ALH would cost about Rs. 30 crores.

HAL was going ahead with getting the ALH certified on more parameters. These include flight at 10,000 feet, for which the helicopter was successfully tested in Leh; night flying and lightning protection, for which the helicopter would soon be equipped at the Centre for Airborne Systems here. The ALH may make also an entry at the Singapore Air Show this year.

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