While helicopters have many practical purposes in the modern world – casualty evacuation, troop relocation and fire-fighting to name but three – they are also associated with noise, vibration and cost. With that in mind, NASA scientists have come up with a new type of helicopter blade technology that, from an environmental perspective, could mean that helicopters of the future are more energy-efficient that the current generation, as well as suffering less from vibration and noise.
Energy Savings from Piezoelectric Actuators
The NASA blades incorporate devices called piezoelectric actuators – objects that include a material able to reconfigure itself when electricity is applied to it. Within the context of a rotor blade, such material acts to reshape the whole structure, meaning that the helicopter’s whole way of flying is improved.
Physical trials of a rotor blade that featured piezoelectric actuators took place in 2008, through a collaborative effort involving NASA, along with the US Army, Boeing and DARPA (the Defence Advanced Research Projects Agency). It was discovered from tests that, when in place, the system would generate less in the way of shake, more in the way of energy savings and an improvement in the degree of controlled precision that could be exerted over rotor movement. Noise reduction, while not then apparent, is thought likely to be a benefit that will emerge in due course.
While the 2008 trials took place in a wind tunnel, the next stage is to actually fit the blade to a helicopter and see how it performs in the air, although the timing of this event has not yet been scheduled.
“Right now, we are trying to understand and appreciate everything that we have accomplished in the full-scale wind tunnel”, NASA Flight Vehicle Research and Technology Division Project Leader, William Warmbrodt, explained.
Helicopter vibration occurs as a result of the blades’ interaction with the air. On a standard, multi-bladed unit, the motion of the most-forward facing blade through the air creates a wake, which the rear-facing blade passes through, making such vibration occur.
MIT professor Steven Hall – who is involved in the new rotor blade project – commented on how it was able to make a difference to this, stating: “Having blade actuation allows you to put a periodic motion into the blade flaps with the right amplitude, phase, and frequency to cancel out that vibration.”
He continued: “People have been talking about using smart materials in aircraft for a long time, but what [has] really been lacking is the right kind of actuator to make it practical.”
The actuator is positioned in close proximity to the part of the blade on which the strongest aeronautic forces are exerted, the tip, along with a flap located on the blade’s trailing edge. This flap moves in response to electric current sent to the actuator – a movement that can aid lift or velocity, and that has no restrictions on when it can be deployed.
The whole system can easily be retro-fitted to current helicopter designs, negating the need for substantial alterations to be made in order to incorporate it.
“Smart materials hold a tremendous promise for revolutionizing how we design, build, and operate our helicopter aircraft”, Warmbrodt commented.