Bell Electric anti-torque system
Bell has revealed a ground-breaking new electric anti-torque system in development for its commercial helicopter line; one that promises enhancements to safety and operating costs, as well as a reduction in noise compared with helicopters fitted
with a conventional tail rotor.
The electrically distributed anti-torque (EDAT) system is composed of four small fans within a tail rotor shroud in an offset two-by-two pattern. Each of the rotors contains four blades and they are powered by four separate motors, with the electrical energy provided through generators driven by the turbine engines.
“In a nutshell, we removed all of the conventional mechanical anti-torque components, which are gearboxes, driveshafts and tail rotor hub and blades and replaced them with four electric motors and fans, with fixed-pitch blades, whilst they are changing rpm constantly” said Eric Sinusas, programme director of light aircraft at Bell. Sinusas explained to Aviation Week: “This is the first time anyone in the world has ever done this, so the first step was just to make sure that it actually worked. We are still going to be optimising the system, but the product feedback in its current configuration has been very positive. They are fixed-pitch blades and they are changing rpm (rotations per minute) constantly. A single large fan or two medium fans will experience rotational inertia.
The system has been installed on a Bell 429 demonstrator aircraft at Bell’s facility in Mirabel, Quebec, and began flight testing on 23 May 2019. Since then, the programme has completed about 25 flight hours, with the aircraft gradually expanding its flight envelope. Bell is not ready to share any performance figures, but Sinusas said the feedback from the customers that have seen the system in action has been positive. The system’s anti-torque fans are controlled through pedals, as with yaw control in a traditional helicopter, but the link between the pedals and the motors is entirely electric “fly-by-wire.” All mechanical linkages and the control tubes of a conventional system have been removed. Other than the tail rotor and the control mechanisms, the demonstrator aircraft is unchanged to accommodate the system, using a conventional main rotor, engine and airframe.
Sinusas said the driving force behind the EDAT system’s development was customer feedback. He said: “We were looking at what are our customers were demanding from the aircraft. Whilst safety is paramount, this system certainly meets those requirements and it has some interesting features that conventional rotors don’t have with redundancy and when the aircraft is on the ground, the electric fans are not rotating at all.”
Sinusas continued: “The redundancy is extensive, with the aircraft capable of still producing a level of anti-torque thrust even if three of the four fans become inoperable. What it provides, unlike any other conventional helicopter out there today, is the ability to give the pilot some torque authority to get down safely.”
The next driver was reduced operating costs and whilst presently Bell is not sharing any figures, Sinusas said that by removing conventional components such as lubricated gearboxes and greased bearings, whilst moving to a more simplified electrical system, should help keep those costs down. Thirdly, the design promises a reduction in noise levels.
The visual impact of the system is a blend of the familiar and the strange. It is not as radical an anti-torque rethink as the tail boom fan-driven system proposed in Bell’s FCX-1 concept helicopter two years ago, or even MD’s NOTAR, which does away with the need for any type of tail rotor, but the sight of four smaller tail rotors instead of one may takes a little getting used to. The shrouding around the rotors certainly looks heftier than the simple vertical fin of a traditional tail rotor. Bell says the footprint is similar to that of shrouded tail rotors produced by other manufacturers. To date the focus of the programme has been proof of concept rather than optimising its performance, whilst the team is not working to a timeline for commercialisation. Both retrofit to existing products and incorporation into clean-sheet designs ‘would be an option’ for the product when it does come to market and the technology is scalable to larger and smaller aircraft.