Aerospace & Defense Technology - April 2023 - 16

Electrification
2000
EDF
1500
1520N, 1.9g/W
1474N, 2.3g/W
1000
1213N, 2.7g/W
Un-ducted
Propellors
500
16%
RDP
Z01 - 001 - 4 blades - 2000.0rpm
Z01 - 001 - 15 blades - 2000.0rpm
Z01 - 001 - 6 blades - 2000.0rpm
Z01 - 001 - 10 blades - 2000.0rpm
Z01 - 001 - 4 blades - 5000.0rpm
Z01 - 001 - 6 blades - 5000.0rpm
Z01 - 001 - 10 blades - 5000.0rpm
Z01 - 001 - 15 blades - 5000.0rpm
Z01 - 005 - 10 blades - 2000.0rpm
Z01 - 005 - 12 blades - 2000.0rpm
Z01 - 005 - 15 blades - 2000.0rpm
I01 -001 - 6 blades - 2000.0rpm
101 - 001 - 10 blades - 2000.0rpm
I01 - 001 - 14 blades - 2000.0rpm
I01 - 001 - 6 blades - 5000.0rpm
I01 - 001 - 10 blades - 5000.0rpm
I01 - 001 - 14 blades - 5000.0rpm
12 3
4
efficiency [g/w]
240N, 4.6g/W
230N, 5.6g/W
190N, 6.7g/W
56 7
A graph comparing thrust vs efficiency (power loading) for different blade architectures. (Image:
RogersEV)
7.50
A graph comparing trust vs efficiency (power loading) for different blade architectures.
6.03
Conventional Approach
HaloDrive System
Radial Rim-Motor
Conventional Rotor
HaloDrive Rotor
4.55
>12% Motor gain.
>7% Aerodynamic gain.
>6% Ducted blade gain.
>5% - 8% Cooling loss mitigated.
The motor, having been distributed
around much larger radius, exploits the
benefits of efficient operation and passive
cooling. Being intrinsically a much
larger diameter system it produces
much more torque. Rim-distribution of
the motor also dramatically increases
surface area to volume ratio and in turn
heat radiation.
This new architecture offers opportunity
to explore ultra-efficient high
solidity ratio blades, running at lower
RPM with a significantly reduced
acoustic signature and physical profile.
Whilst heat and particle ingress tolerance
will allow the system to operate
in harsher environments the reduced
complexity of having fewer moving
parts will cut inspection, maintenance
and certification requirements. These
operational and performance benefits
make the HaloDrive completely scalable
and able to address a broad spectrum
of aerospace market verticals.
3.08
1.60
50.0090.00
Thrust [kgf]
130.00
170.00
A graph comparing estimated performance efficiency gains with HaloDrive compared to conventional
approaches to electric aircraft propulsion system designs. (Image: RogersEV)
significant gap before early successes are
scaled and eventually made available to
the demanding requirements of aerospace.
Innovation in the powertrain is
needed to bridge this shortfall and better
leverage existing energy storage
capability. To achieve this effectively we
need to reach efficiencies of 70 to 90
percent by reimagining the classical
electrical solution from the ground up.
Benefits of RDF vs an EDF?
RDFs have several key differences to
their cousins electric ducted fans (EDF),
in the case of the HaloDrive system in
16
development by Rogers these are the
conjoining of the blades to the rim
(forming a complete rotor) and the
migration of the electro-mechanical
motor elements to the rim. The benefits
of these changes span multiple domains
and offer interesting concinnity across
sub-systems.
Aerodynamically we see approximately
a 7 percent gain in thrust from
the perfect ducting, where no leakage of
air between blade and rim can occur, we
would see this increase as we tolerate
larger gaps needed to reduce structural
mass and account for tip-erosion.
mobilityengineeringtech.com
Why Has No One Tried Rim-Driven
Electric Aircraft Propulsion?
Well there are some pretty unique
challenges when it comes to implementing
this architecture of system.
One key challenge is the bearing and
air-gap challenge. For any motor, it's
air gap - the distance between its stator
and rotor - typically kept between
0.5-1 mm, is performance critical. This
fine tolerance does not allow a central
bearing system at large diameter as
such a design would leave too much
rotor material exposed for deformation.
However, due to the velocity at
the rim and therefore relative " track
speed " bearings at this diameter would
also be unviable despite being able to
prevent deformation.
The HaloDrive system overcomes this
though the use of a core-less circumferential
flux motor (CFM) architecture,
technically a Lorenz machine the circular
magnets sit around the periphery of
the rim and run in a ring of toroidally
wound coils. This arrangement captures
undirected magnetic flux from
almost the whole circumference of the
magnet and so can tolerate much larger
airgaps in the order of >2.5 mm.
This approach also solves another
issue, frequency losses. At high frequenAerospace
& Defense Technology, April 2023
thrust [N]
Efficiency [g/W]

http://www.mobilityengineeringtech.com

Aerospace & Defense Technology - April 2023

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