ADDRESSING THE TOP 10 CONNECTIVITY
CHALLENGES IN DEVELOPING
ELECTRIC AIRCRAFT
by: Matthew McAlonis, Technical Fellow and global leaderof Engineering for the Aerospace Defense & Marine

AEROSPACE, DEFENSE & MARINE / Addressing the Top 10 Connectivity Challenges in Developing Electric AircraftAddressing the Top 10 Connectivity
Challenges in Developing Electric Aircraft

Electric Vertical Takeoff and Landing (eVTOL)
aircraft designers are addressing voltage and power
challenges in batteries, pods, and fast-charging
stations with advanced connectivity solutions
Just as electric vehicles are revolutionizing the automotive industry, electric aircraft promise toboost the sustainability and convenience of air travel. Designers of urban-air/advanced-air mobility(UAM/AAM) “air taxis” and electric-powered vertical-takeoff-and-landing (eVTOL) vehicles facenumerous challenges when connecting High Voltage (HV) and High Power (HP) systems. ElectricalWiring Interconnection Systems (EWIS) engineers and eVTOL aircraft designers are findinga wide range of solutions are now available to address these 10 connectivity challenges:

1. Significantly HigherVoltages (kV) andPower (MW)
Applying high voltage cables and powersystems is nothing new for electricalengineers acquainted with Ohms law(P=IxV).
But
applying
appropriatetechnologies for hybrid and electric
aircraft presents novel situations. By using
a “follow-the-wire” design approach,
EWIS engineers can help ensure that all
the links—connectors, wiring, jackets/
insulation, converters, contactors, power
sharing networks, and more—can handle
the voltage and environmental conditions
unique to electric aircraft.
Higher voltages are found in the following
situations:• Electrical systems for conventional
aircraft
employ115VAC/400Hzand270VDC with “high-voltage” (HV) power
requirements typically limited to 230VAC.
In eVTOL aircraft, the thrust required overrotor area for lift during vertical takeoffand hovering, referred to as disc loading,can necessitate fan speeds from 2,300
to 20,000 RPM delivered by brushless
800VDC motors.
•HV
alternating
current(AC)is encountered in generators, power
converters, and controllers employed in
fast-charging stations. Other electricaldifferences include non-linear powersharing networks and multi-directionalcharge paths.
Of course, designing for higher voltage
typically translates into using productswith thicker dielectric materials and areconsequently heavier, stiffer, and take up
more space. Advanced power wiring mustallow flexibility for routing and dynamic
bending of pods and wings, with optimized
wiring weight, cable cross sections,and consider ribbon-type (flat) cable
geometries. Respective HV connector
solutions must enable current carrying
capability often up to 1,000 Amps in nontraditional connector geometries. Theseand other connectivity solutions must
address the challenging power density,power frequency, and size, weight, andpower (SWaP) requirements for electricaircraft.

2. Mitigation of Partial
Discharge/Corona EffectManaging HV at altitude is more
complicated than on the ground. That’s
because HV can ionize surrounding air
particles more quickly with catastrophic
effects, due to lower air densities at altitude
as the less constrained particles canachieve higher velocities sooner. Released
energy generates a corona discharge
resulting in power losses through voids,cavities, and electrical treeing in insulation.
Electrical discharges can occur across avoltage gap between two points/surfaces,
because the high electrical field cannot becontained by the material(s) in the area.
The discharge can also initiate electricalarcing, potentially igniting a fire. Selecting
dielectric materials and constructions
suited to HV conditions--such as coronaresistant polytetrafluoroethylene (PTFE)-can minimize discharge risks due toinsulation breakdown. Elimination of
air bubbles/pockets (porosity) can beachieved by employing over-molding andinsert molding around connector contacts.

3. Increased Reliability
for Harsher Environment,
Frequent Maintenanceand Inspection, Shock,and VibrationeVTOL vehicles fly shorter distances thancommercial aircraft and are anticipatedto make numerous takeoffs and landings
per day. Consequently, they require
high reliability in interconnects that canwithstand vibration and shock from more
frequent landings and takeoffs. Reliability
is essential because eVTOL flightpaths may typically occur over densely
populated urban environments. To help
ensure performance, electronic/electrical

AEROSPACE, DEFENSE & MARINE / Addressing the Top 10 Connectivity Challenges in Developing Electric Aircraft2Addressing the Top 10 Connectivity
Challenges in Developing Electric Aircraftcompartments need to be easily inspected.
Strain relief on connectors, molded cable
assemblies, and secure tiedowns can help
avoid chafed components and material
fatigue. High reliability connectivity
products include high performance,
fatigue and stress relaxation resilient
connector materials and redundancy inconnector contact systems.

Unmanned Power connector (UMP)
offers up to 80Amps per contact
and mix power flexibility.

4. Premium on
Weight Reduction
Unlike conventional aircraft that become
lighter by burning fuel, eVTOL aircraft
weight does not diminish over distanceand discharged batteries are quite literally“dead weight”. That’s why EWIS designers
need to carefully calculate and compare
the weight of connectivity components fora given amperage and wiring architecture.
Components used in industrial energy
storage and management are typically notweight optimized. Advanced, lightweightmaterials (plastics and composites)and 3D printing can create “right sized”
components for tight spaces and weight
optimization.

High-efficiency relays and contactors
are now available that can handle HVand high amperage within a compact
footprint. Advanced HV relays andcontactors offer voltage ratings up to
70 kV DC and current ratings up to
1,000 Amps within a useful size-to-power
ratio. Compact cables, terminations, andconnectors are also available for optimalsize, weight, and power rating.

6. Strict Flammability,Toxicity, and Smoke
Requirements
The air inside aircraft circulates within anenclosed space. That’s why all materials
are flammability, smoke, and toxicity
rated. Connectors, wiring jackets, andother insulating materials must not only
be self-extinguishable but also limit
emission of toxic smoke. Silicone may besuitable for high voltages but tends to bevery smokey when ignited. Halogenatedflame retardants act directly against thechemistry of a flame, but the smoke canbe toxic. Flame-retardant materials thatare either low-smoke zero halogen or lowsmoke free of halogen are ideal.

KILOVAC CAP120 high-voltage contactor

5. Resistance Against
Arc Tracking andHydraulic Fluid
With higher voltages come unusual causesof catastrophic failure. Dust, moisture,exhaust, and other pollutants can create
pathways for current to travel across amaterial. Electric discharges can thenoccur, which risk causing an explosionin flight--or on the ground when fast
charging aircrafts are in high moistureenvironments. An arc-tracking index canbe used to evaluate how readily a given
voltage travels across a material’s surface
if it’s clean or polluted. Wire is available
with dual-wall construction using radiation
cross-linked modified materials that
resists carbon arc tracking even whencontaminated with hydraulic and de-icing
fluids.

SHF260 highly flexible wire provides
oustanding chemicals and fluid resistance7. Altitude andPressure Effects
Voltage differences become more extreme
as altitude, temperature, and frequency
increase. The conditions under which agiven material supports partial discharge
inception voltage (PDIV) and partial
discharge extinction voltage (PDEV) canbe mapped in a Paschen curve. These
points can be used to determine thethickness of dielectric insulation required
at specific altitudes and distances between
conductive surfaces.

AEROSPACE, DEFENSE & MARINE / Addressing the Top 10 Connectivity Challenges in Developing Electric Aircraft3Addressing the Top 10 Connectivity
Challenges in Developing Electric Aircraft

Higher altitudes not only make the system
more vulnerable to partial discharge, italso promotes water seepage into gaps incomponents and eventual corrosion. Otherconditions—power switching, lightning
strikes—cause surges in power cablesystems that can cause cable voltage
to exceed PDIV momentarily, leading toinsulation erosion or catastrophic failure.
The usage of appropriate dielectricmaterials and design constructions thateliminate air gaps will result in designs
with minimal air pressure effects.

8. Handling OperatingTemperatures Ranges andThermal Management
Requirements
In battery charge cycles, a balance must be
struck between higher energy transfer andhigher temperatures. During high power
charging (HPC), individual components
are subjected to temperature extremes
at resistance points along the HV path.
Every microohm (υΩ) of resistance must
be minimized. Areas to reduce resistanceinclude cable terminations, contact
interfaces (crimps and contact types),and contact materials. Liquid-cooled
cables and laying cables in convectiveor conductive-cooling heat sinks are alsosolutions. Thermal sensing and thermal
modeling can be employed to design acooling “ecosystem” for charging systems
on the ground—and to detect hightemperatures during power surges on
landing and take-off.

9. New Cabling,
Management andCrimping Techniquesand certifications for today’s demanding
aerospace and eVTOL programs canaddress tomorrow’s innovative electricaircraft projects.

Sharp edges and non-smooth conductive
surfaces in HV connectors can produce
concentrated
voltage
gradients
contributingtocorona
discharge.
Electrically sealing crimp regions smoothout surfaces and the electrical geometries
to reduce the likelihood of voltage stress.
Any change in geometry requires analysis
to determine: Is that edge going tocontribute to a partial discharge or corona
effect? If so, then construction must be
modified to mitigate that risk. Just as HVutility power lines use circular corona rings
to prevent corona losses, rounded features
can be added to HV cables to control
electrical stress. Even a single loose strandof wire sticking out of a shielded cable cancause problems. All components must be
carefully designed, tested, and maintained
to help ensure performance.

10. Accommodating HighVolume Production
While not directly under a EWIS engineer’s
purview, designers must consider theability of a manufacturer to handle theproduction, delivery, and quality ofcomponents at scale. The eVTOL market
is projected to grow exponentially—andthe ability to supply quality components
in quantity is essential. All products should
be 100% tested and inspected to help
ensure performance and fitness for theapplication. Manufacturers who can handle
the tooling, supply chain, cost control,

About the author: Matthew McAlonis is Technical Fellow and global
leader of Engineering for the Aerospace Defense & Marine Business Unit
at TE Connectivity. He can be reached at mmcaloni@te.com.
For more information on TE’s product solutions for the urban-air/advancedair mobility (UAM/AAM) market, check out www.te.com/urban-air-mobility

AEROSPACE, DEFENSE & MARINE / Addressing the Top 10 Connectivity Challenges in Developing Electric Aircraft

4Addressing the Top 10 Connectivity
Challenges in Developing Electric Aircraft

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AEROSPACE, DEFENSE & MARINE / Addressing the Top 10 Connectivity Challenges in Developing Electric Aircraft