Bell Tests Electric Tailrotors


Bell Helicopters unveiled a 429 modified with four electrically driven tail rotors that it says has proven the concept over almost a year of testing. The Electrically Distributed Anti-Torque (EDAT) system has been flying since last May from the company’s Mirabel, Quebec, facilities and it works just fine. “This is the first time anyone in the world ever done this, so the first step was just to make sure that it actually works—and yes it does work,” Eric Sinusas, Bell’s light aircraft program director, told Vertical Magazine. Each rotor has its own motor powered by a generator on the Pratt&Whitney PW207 engines and their thrust is modulated depending on the demands created by the torque created by the main rotor.

While it adds a new system to the helicopter, EDAT also eliminates the maintenance-heavy shaft and gearbox assembly that drives the tail rotor of regular helicopters, while adding redundancy. Three out of four fans is enough to control the helicopter. The fans are controlled by the fly-by-wire system and can spin in both directions, making the precise application of anti-torque force possible. That, says Bell, cuts noise and makes the aircraft more efficient.


  1. I’d be interested in knowing if the NOTAR idea could be employed on this machine and — if so — what the weight advantages or penalties would be compared to this EDAT idea. What is the weight advantage of EDAT over the mechanical system it would potentially replace. Finally, have any reliability analyses been done to determine the relative advantage of EDAT? If it simplifies the tail rotor function but isn’t 110% reliable, what’s the point?

    Actually, this may well be the first application of an electrically driven system that makes sense to me based upon the limited description here.

    • That is true, as we know nothing about its failsafe mode, are they driven by a totally different bus and generators, that produce power as long as the rotor turns, which should be the safe way of doing things, or is it just an add-on to the main bus, thus fails as soon as the normal bus goes belly up?!

      NOTAR is an interesting McDonnell-Douglas patent and I doubt very much that they would let Bell use the system or vice versa.

      Having worked around helicopters as a heliguard on platforms and rigs I know very well that tail rotors are a deathtrap, that just too many have walked into, or been hit by during crashes, not to mention the driveshafts and gearboxes that at times sheer off, or overheat, and prove an extra hazard during an emergency landing.

  2. Equivalent level of safety?
    If the vehicle already is full-on fly-by-wire (no mechanicsl connections), then ELS may be a given. If not, then the failure-mode-analysis game is on: likelihood versus consequences; same as it ever was. Interesting, for sure. And apropos in a world of quadcopters.

  3. Presumably, the battery is tasked with providing enough backup power for an autorotation landing. I’m not all that rotorwing savvy, but I would think the final flare would require virtually 100% anti-torque for at least a few seconds.

    • John, as I understand autorotation, that happens when the engine is producing no power to the rotor, thus no torque to correct for. But I’m not all that rotorwing savvy either. Either way, there should still be plenty of battery power available in event of an engine failure.

  4. Mac H. – True about torque during auto. (Auto rotation is usually the Emergency Procedure for loss of Tail Rotor thrust). But the Tail Rotor IS the main yaw control and would assist in choosing where to best land in a power off auto rotation. I hope by now, aviation has learned that LiFe batteries are safe enough (and lightweight) to be used as alternate electric power in the case of engine failure or alternator/generator failure.

    Just observing the meteorological conditions, I’m wondering about Bell’s considerations for Tail Rotor icing. I DO like the thought of the requirement for only 3 of 4 rotors needed for full functionality.