Bell's Electrically-Powered Tail Rotor Tech Breaks Cover And It Could Be A Game-Changer
Bell
has been quietly flight testing a modified Model 429 helicopter with
a new all-electric tail rotor configuration in Canada for months. This
Electrically Distributed Anti-Torque system, or EDAT, offers improved
efficiency and reliability, as well as a reduced acoustic signature and lower
maintenance costs compared to traditional tail rotors.
The
Fort Worth, Texas-headquartered helicopter maker brought its EDAT work to the
public's attention when it posted a video montage of the experimental Model 429
on its social media
channels on Feb. 20, 2020. However, the video's caption says
that this particular helicopter made its first flight on May 23, 2019. The
flight testing has been taking place at Bell's facility in Mirabel, Quebec.
"In
a nutshell, we removed all of the conventional mechanical anti-torque
components – which is gearboxes, driveshafts, and tail rotor hub and blades –
and replaced it with four electric motors and fans,” Eric Sinusas, Bell's Light
Aircraft Program director, said in an interview with Vertical magazine.
"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."
A
standard Bell Model 429 has
an exposed four-bladed tail rotor. All helicopters with a single main rotor
require some sort of tail rotor or some other anti-torque system to counteract
the force from the large main rotor on top spinning in just one direction.
The
EDAT-equipped helicopter replaces the Model 429's standard tail rotor with four
individual four-bladed electrically-powered fans. Each one has its own separate
electric motor, provided by French company Safran. They are all built into the
tail assembly, similar to helicopters with Fenestron tail rotors. In
this configuration, they function as ducted fans.
This modified helicopter's two Pratt
& Whitney Canada PW207 turboshaft engines are linked to generators to
provide the requisite power for the EDAT system. In a regular Model 429, the
engines are linked mechanically, via driveshaft in the tail boom, to the tail
rotor.
Without that mechanical drive, EDAT
relies entirely on a computerized fly-by-wire system to connect the controls in
the cockpit to the tail rotors. What this means is that the helicopter can be
more efficient than others with traditional tail rotors.
Traditional tail rotors use variable
pitch blades to alternate the amount of force they put out and in what
direction it is flowing. EDAT's four rotors have fixed-pitch blades that can
spin either forward or backward. Bell says that this means its
electrically-powered and controlled system can more precisely and dynamically
change how much anti-torque force it's putting out.
“They
are fixed-pitch blades and they’re changing rpm [rotations per minute] constantly,"
Bell's Sinusas told Vertical. "A single large fan or two medium fans are going to experience
rotational inertia, so it is going to be less responsive," he explained
to Aviation Week.
Having four fans instead of one single
rotor also offers valuable redundancy, which in turn makes the helicopter safer
to fly. Bell says that the EDAT system can provide sufficient anti-torque force
even if three of the four electric fans fail.
BELL
The modified Bell 429 helicopter
with the EDAT system.
Bell says that the variable speed of
the fans and their ability to operate at low RPMs whenever possible also
reduces the helicopter's acoustic signature, though they haven't yet given
specific figures. The information the company has collected so far “shows that
it is significantly quieter than a conventional 429,” Sinusas said to Aviation Week.
Lastly, eliminating the conventional
mechanically-powered tail rotor would also help lower maintenance costs, by
getting rid of the associated potential points of failure in the drivetrain and
the tail rotor gearbox. This means maintenance crews wouldn't have to perform
regular inspections of those components or spend time replacing them. Operators
wouldn't have to keep those spare parts on hand anymore, either.
Helicopter
companies around the world have been working on electric tail rotors and other
anti-torque systems for some time now, but Bell's is the first to achieve
flight, according to Aviation
Week. It's not clear how long the company
has been working on this particular project, but it submitted at least one patent application regarding
relevant technologies in 2017, approval of which is still pending. The
accompanying documents include line drawings that show a variety of notional
multi-motor configurations, including variations with ducted fans, as well as
exposed rotors. A modified Bell Model 407,
rather than a 429, is depicted as the representative helicopter.
The effort is primarily self-funded.
However, Bell did receive grants from authorities in Ottawa in 2018, according
to Aviation
Week.
The advantages the EDAT system offers
could be valuable for civilian, commercial, and military helicopter operators
alike. Everyone likes greater efficiency, added safety, and lower operating
costs.
The
noise helicopters produce often provokes complaints from people living below
high traffic routes and means that individuals can hear them coming from
relatively far away. A reduced acoustic signature could mean fewer noise
complaints for commercial and military operators, as well as help military
helicopters better avoid detection during combat operations. Finding ways to
reduce tail and main rotor noise has been a major issue in
the development of stealthy
helicopters. Bell says that
customers' requests for ways to reduce noise, in general, including for
occupants, was a major driver in developing EDAT.
The
storied helicopter manufacturer states that the EDAT system, as it stands now,
is still very much experimental and that it is already working to improve it.
The company also views it as a pathway toward future helicopters and other
rotorcraft with hybrid or all-electric propulsion. For example, it could help
inform work on the Bell FCX-001 experimental
helicopter concept, which the company first unveiled in 2017, also includes
"electric distribution and motors to drive the anti-torque system."
However, the FCX-001 has a very different configuration for the EDAT-equipped
Model 429, with the thrust-vectoring anti-torque system contained entirely
within the tail boom that similar, broadly, to Huges Helicopters' No Tail Rotor (NOTAR)
configuration.
"We have already had several
optimizations and changes, just based on feedback from pilots, and it is much
quicker to do than with a mechanical system," Sinusas told Aviation Week. "We do see it as a stepping stone to the fully electric
aircraft... We feel like it should make the certification paths for these
technologies easier."
Whether EDAT actually sees widespread
use or if it serves simply as a developmental milestone, it is hard to imagine
how this concept doesn't have the potential to change rotary-wing aviation as
we know it.
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