Scientists working on smart material for ALH
Scientists at the Indian Institute of Science and public sector aircraft maker Hindustan Aeronautics Limited (HAL) are working on a way to reduce vibrations in the advanced light helicopter (ALH) using smart materials.
The project, funded by HAL, aims to build an “active trailing edge flap” and a “controller” that will make the flap, mounted on the aircraft’s rotor blades, respond in such a way to the aircraft’s vibrations that they will be reduced.
Reducing vibrations, apart from making the flight more comfortable for passengers, puts less strain on the aircraft’s structures, making them durable.
HAL’s Rotary Wing Research and Development Centre is collaborating with IISc’s department of aerospace on the Rs 6 crore effort.
IISc’s scientists said there are five different parts of the project. “Some of them are at the fabrication and prototype stage, at both the institute and HAL, following which there will be wind tunnel and other tests. Others need more work. An initial prototype, to demonstrate the concept, will be ready in two years. After that, to actually build an ALH-ready system that can get certification will take till 2010.”
The controller is a box, with hardware and software in it, taking inputs from all over the helicopter on its natural vibrations. It will then send out instructions to actuators, little motors, that will drive the flap.
“We use piezoelectric materials (substances that change structure in response to an electric current) to build the actuators. Mounted on the rotor blades, the flap will try to imperceptibly twist the blades in such a way as to oppose the deflection caused by the natural vibration of the helicopter and so reduce it, even as the aircraft is in full flight,” the scientists explained. The technique is called independent blade control.
In theory, these materials, either “surface mounted” or “embedded” in the rotor blades, can twist the blades by up to two degrees, reducing vibrations by up to 60 per cent. There are hurdles, of course. Helicopters are subject to unsteady aerodynamics as they use their rotors for both lift and thrust (moving forward).
They also work in environments of high (electronic and/or electrical) noise. The software programmes in the controller must then be robust enough to handle measurements made in such environments.
Further, much work was needed on the operational capability of the smart materials themselves - on their fatigue tolerance, for instance. Finally, repeated flight tests will be required to show that the system was both effective and safe.
Similar work is going on in other parts of the world and some scientists are trying variations of the independent blade control.
For instance, a research team in Canada published a paper in the Journal of Intelligent Material Systems and Structures last year, on a “smart spring” they are building, for “active vibration control of helicopter blades”.
They found, the researchers C Yong et al say, the piezoelectric actuator based control had its limitations and the smart spring was a way to do better.
Work at the IISc-HAL combine too may evolve as such projects often do. Success will mean not only a superior aircraft, more attractive to overseas buyers, but also 100 per cent indigenous know-how in this area — far more important in the long run.
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