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'Supersized' idea could massively improve helicopter performance

10 June 2013

US Army researchers are looking at inserting carbon nanotubes into macro-structures - helicopter rotor blades in this instance - to improve performance

An AH-64 Apache rises from behind a hill during a training exercise at Yakima Training Centre (photo: Captain Jesse Paulsboe)

The work is being undertaken by Dr Bryan Glaz, Dr Jaret Riddick, and Ed Habtour of the US Army Research Laboratory's Vehicle Technology Directorate in the hope that this approach will eliminate a list of deficiencies highlighted in the Iraq and Afghanistan conflicts.

Rotor structural dynamics can be inherently unstable; their structural design and the aeromechanics of rotor-craft flight can limit forward flight and manoeuvre capabilities, and potentially lead to catastrophic structural failures in take-off/landing conditions.

Glaz says that, as a general rule, there is a trade-off between rotor blades designed to transmit low vibrations to the aircraft and blades designed for stability. Blades with good stability characteristics tend to transmit high-vibratory loads to the aircraft, and the high-vibratory loads of rotor craft are a major source of maintenance, repair and logistics burden associated with the US Department of Defence's vertical lift fleet.

The reverse is also true – blade designs corresponding to low vibration tend to have structural dynamic stability issues that tend to limit the performance of the aircraft. This trade-off prevents the development of next-generation radical design concepts with substantially improved payload, speed, range, and cost.

Glaz and his team want to eliminate the trade-off. "We would like to be able to design blades that transmit low loads yet still have good stability characteristics," he says.

To do that, he and a team of structural, mechanical and aerospace engineers are embedding carbon nanotubes inside the composite matrix, resin material throughout the blade, and in specific locations like near the hub.

With the carbon nanotubes inside and inherent to that structure, researchers expect to enhance energy dissipation through friction at the nanotube-matrix interface, thus improving damping.

ARL researchers turned to recent scientific publications that indicate that carbon nanotubes can effectively dissipate energy for small scale samples. They're now 'supersizing' their efforts and venturing into uncharted research territory by investigating how much of the energy dissipation mechanism can be achieved when the carbon nanotubes are used to damp dynamic modes of actual structures as opposed to small laboratory samples.

If ARL's approach works out, it could lead to the design and fabrication of the next generation of rotor blades and fixed wings. These components would be similar to existing structures in the sense that the composite structures would still consist of a matrix with fibre reinforcement.

"In our case though, the matrix would be completely different since it would have carbon nanotubes inserted throughout," says Glaz. "The nanotube enhanced matrix would provide the damping (and thus the stability) while fibres would still be used for strength and stiffness of the structure."

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