A new study by Army researchers is looking at inserting carbon nanotubes into the structural design of helicopter rotor blades in hopes this approach eliminates a list of deficiencies highlighted particularly in Iraq and Afghanistan conflicts.

Dr. Bryan Glaz, Dr. Jaret Riddick, and Ed Habtour, research engineers within the U.S. Army Research Laboratory’s Vehicle Technology Directorate, are leading an effort to “… see if we can augment the inherent stability of the structure itself …” so that helicopters could be built better to “… eliminate some of these constraints on the performance and the design of the aircraft that have been in place since we’ve been building rotorcraft,” explained Glaz.

“Especially in conflicts like Afghanistan, it really highlighted the deficiencies of the DOD current fleet in terms of payload capacity, speeds in supporting the warfighter and a big thing for the Department of Defense was the maintenance and cost; they can’t be sitting in a maintenance bay because if they’re in a maintenance bay, they’re not out there supporting the warfighter,” he explained.

Rotor structural dynamics can be inherently unstable; their structural design and the aeromechanics of rotorcraft flight can limit forward flight and maneuver capabilities, and potentially lead to catastrophic structural failures in takeoff/landing conditions.

Glaz said as a general rule, there is a tradeoff 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 rotorcraft are a major source of maintenance, repair and logistics burden associated with the DOD 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.

“Our goal is to eliminate the trade-off. We would like to be able to design blades that transmit low loads yet still have good stability characteristics.”

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, which Glaz said “… gives more bang for the buck.”

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.

“We believe this improvement in damping can be exploited to so drastically improve stability without adding weight or mechanical complexity that rotorcraft designs never considered possible may become reality.”

ARL researchers turned to recent scientific publications that indicate that carbon nanotubes can effectively dissipate energy for small scale samples. They’re supersizing their efforts and venturing into unchartered 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 fiber reinforcement.

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

“If these new structures were part of the next-generation fleet, then DOD would have aircraft that are carrying payloads that they can’t think of right now, flying at speeds that they can’t think of right now and they would always essentially be ready to go with very low maintenance considerations.”