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Rensselaer research to focus on increasing helicopter speed

Researchers from the Center for Flow Physics and Control (CeFPaC) and the Center for Mobility with Vertical Lift (MOVE), both located at Rensselaer Polytechnic Institute, are partnering to address how controlling air flow can help usher in the next generation of high-speed helicopters.

With the support of grants from the Army Research Office and the Israeli Ministry of Defense, researchers from the two Rensselaer centres plan to develop and test methods of making helicopters fly faster and more efficiently by controlling the flow and separation of air over their blades.

“The question is: How do you fly at very high speeds while trying to mitigate the effects of reverse flow?” said Farhan Gandhi, the director of MOVE.

Rensselaer explains that when a helicopter goes into forward flight, the advancing side of the blade — that’s moving into the wind — sees much higher velocities than the retreating side. As that phenomenon increases, regions of reverse flow start to develop, generating negative lift and drag.

It takes a lot of power and energy to overcome those conditions, continues Rensselaer, reducing the distance a helicopter can travel before it runs out of fuel, or reducing payload in order to make room for extra fuel. The program goal is also designed to focus on how faster helicopter speeds, for example, can help save lives through medevac applications.

Through this partnership, Gandhi and his team will build on their research and design a blade that is shaped in such a way that it can mitigate reverse flow. Michael Amitay, the director of CeFPaC, and his team will then test those designs with model blades inside a state-of-the-art wind tunnel.

“We need to understand how — in these conditions — the lift is generated, how you can reduce the drag, and how you can quantify that,” said Amitay. “All of that we can study, and test, here.”

Amitay and his team have already started testing, and he said they have found that by changing the shape of the blade, they can reduce drag by 50 per cent.

The research teams, however, want to take their testing further, noting how flow conditions during hover and forward motion are different, so changing blade shape to improve one mode will have a negative effect on the other. To this end, Gandhi’s team will also develop an actuation system that will allow for a change in configuration of the blades during operation.

“You have to manage to do well in both states, and this is where shape change or geometry adaptation starts to come in,” Gandhi said.

Rensselaer explains that Amitay hopes this research changes the way future high-speed helicopter blades are designed. In addition to protecting military personnel from enemy fire and improving their rescue efforts, he said there are clear civilian applications as well. “In situations where time matters, like when medical crews are helping burn victims or people in car accidents,” Amitay said, “if you can fly faster without compromising on performance, that’s what we think is the solution.”