When we published our scoop about Bell’s new electrically distributed anti-torque (EDAT) system on Feb. 19, we were expecting a high level of interest, but the actual reaction was off the charts. The story quickly shot to the top of our list of most-viewed stories of all time, and it provoked a corresponding amount of discussion on our website and social media channels.
We noticed some recurring topics in these online conversations, so we asked Bell’s program director of light aircraft, Eric Sinusas, to address our readers’ most frequently asked questions. Our follow-up interview (edited for length and clarity) appears below.
To recap: EDAT is a replacement for conventional helicopter tail rotors, comprising four small fans each driven by a separate electric motor. The fans have fixed-pitch blades and change rpm constantly. The company has been flight testing EDAT on a Bell 429 helicopter in Mirabel, Quebec, since May 2019, but only revealed the program in February. If you missed our initial report, you can find it here.
Vertical: Does the EDAT system incorporate additional battery/generator capacity above the baseline aircraft?
Eric Sinusas: Yes, we added two generators specifically to power the EDAT motors, but no additional battery capacity. The generators are driven off of what was formerly the tail rotor output shaft from the main rotor gearbox.
Vertical: What happens to the system in the event of a dual engine failure?
Sinusas: When you lose both engines, the main rotor gearbox is still rotating. So because the generators are mounted off of the main rotor gearbox and not the engines, even if you lost both engines, the fact that the main rotor would be spinning in an autorotation means it would still be driving the generators.
Vertical: How much equivalent power does EDAT draw compared to a standard tail rotor?
Sinusas: We’re not getting into specifics at this point, but I can say that the power consumption and overall performance is similar to a conventional aircraft. For this, it was such a huge step to just see what the flying characteristics were of an EDAT system with a constantly changing rpm that our primary focus was on demonstrating the technology. And now that we’ve proven that the technology works and the pilot feedback is positive, the next step is getting into the optimization of the system, and answering some of those questions about energy management, and seeing where we can continue to upgrade the design.
Vertical: How well does the tail rotor shroud handle crosswinds?
Sinusas: We’re still continuing to expand the flight envelope, but we have done a series of different flights in different winds. We’ve also done right sideward flight where the helicopter is flying sideways and towards the right, and then flying sideways towards the left. We’ve done the full forward and backwards flight maneuvers. So far the handling qualities have been good and the pilot feedback has been good, saying that it handles similar to a conventional tail rotor.
The shroud design and what we put on this aircraft was what we could get to demonstrate the fundamental technology as quickly as possible, but we still have a lot of optimization to be done on the ducting as well as the rest of the system.
Vertical: How does the pilot manage the system? For example, to keep it turned on while resting on slippery surfaces, or turn it off when ground personnel are working around the aircraft?
Sinusas: The way it’s working currently is the pilot’s pedals provide a signal that goes through an algorithm and ultimately determines the speed of the motors or the fans. So the pilot is constantly managing his heading. Even when he’s on the ground, if he were on the ground on a slippery surface, he would need to manage his heading, and put in the amount of pedal that he needs to keep the aircraft where he wants it.
The pilot can individually turn on and off each motor — he’s got a switch for that. But if he is on a regular, high-friction landing surface, then he simply won’t demand any rotation with his pedals. So even without turning them off, just by where his pedals are, he can have them such that they’re not rotating or slowly rotating.
In the future, because of the fly-by-wire system, we can certainly upgrade the software and the algorithms to provide more autonomy and ultimately get to the point where the pilot could take his feet completely off the pedals and have the EDAT control itself to maintain heading.
Vertical: How much anti-torque authority does the system provide with one or more fans inoperative?
Sinusas: When you lose a number of fans, you lose some of your thrust capability but not all of it. The maximum thrust design point is in right sideward flight, or the equivalent of hovering with a significant side wind hitting the aircraft broadside. But if you’re not in that condition — if you’re in a hover with no wind, let’s say, or if you’re in forward flight — you don’t need as much thrust. So you actually could have all the authority you need without all four fans.
We would say certainly if you all of a sudden lost even one of your fans, we’re going to consider that an emergency landing procedure and the pilot’s going to know that he had a failure. Our point is that because it’s only a partial failure, not a complete failure of the tail rotor, he still has some authority to help him get down safely.