With electrical power being a key driver of advanced air mobility, it is understandable that prospects for success seem to hinge so much on motor and battery technology. But the technical challenges in bringing electric aircraft to market to support commercially viable operations are bigger and more complex than just these elements.
As pioneers of so-called "more electric aircraft" have already found with airliners and other fixed-wing aircraft since the 1990s, increased reliance on electricity is raising the technology bar in several ways. The higher power levels required mean that increased voltages have to be safely and effectively controlled, and the resulting higher temperatures necessitate improved thermal management. Weight and space limitations are also key factors.
The bar is even higher for new all-electric aircraft, and especially so for those needing high power output for the vertical takeoff phase of flight. This has generated a need for all supporting components and systems to be optimized—just like motors and batteries—in terms of size, weight, and power to ensure that all the aircraft’s electrical interconnections are fit for purpose.
In recent years, specialists such as Carlisle Interconnect Technologies (CarlisleIT) and TE Connectivity have stepped up their investments in line-replaceable units, such as cables, contactors, power interconnects, and relays. These and other companies are already working closely with electric aircraft pioneers, and also with regulators and organizations like SAE and ASD that are setting technical standards.
“The current standards don’t go up to the new voltages,” explained CarlisleIT product manager Tom Turner. “In North America, most of the aerospace cable standards say that these cables have only been used in applications up to 115 volts or 28 DC, and while some European standards go up higher, aerospace designs and experience are barely half what the new eVTOL aircraft want. So we have to have a way to certify to those levels.”
SAE is beginning the process of developing standards that can be used to qualify cables for these applications, and testing by CarlisleIT and other companies has established that current insulation technology is safe up to around 1,000 volts, though more insulation needs to be added to current designs. Beyond that level, new insulation materials would be required and the companies developing electric aircraft also will have to prove that the hardware will last in service.
Beyond 1,000 volts, the laws of physics make the situation more challenging, and more specifically Paschen’s Law, which calculates at what point dangerous arcing could happen through a phenomenon called a partial discharge. “Designs that have been used for decades at lower voltages will see corona-like discharges inside the insulation, Turner explained to FutureFlight. “[With these discharges] we get increased heat, which causes degradation and erosion of the insulation [for cables, wires, connectors, and even motors]. With enough insulation degradation, we would get faults that can cause shutdowns and increased maintenance costs.”
CarlisleIT, which has been innovating power connectivity technology for commercial aerospace applications for many years, also focuses on making cables and wires easier to install and maintain. The Florida-based company’s engineers work closely with their counterparts at aircraft and powerplant manufacturers to introduce improvements such as cables that are able to bend more tightly.
Given the tight physical constraints for the architecture of new eVTOL aircraft, the need to combine high performance and reliability with lower weight and scale is a key differentiator for interconnect technology. To withstand the high level of vibration that VTOL aircraft can be subject to, connectors need to be rigid and cables have to be chafe-resistant.
Aircraft require a wide variety of cables, wires, and protective braids for applications and locations such as engine compartments, fire-detection circuits, and flight-critical systems. In some instances, these need to be compatible with use in fire zones or meet so-called SWAMP (severe weather and moisture-prone) requirements.
Among the more recent additions to CarlisleIT’s product portfolio are its lightweight UtiFlex cable assemblies, which use the company’s Aracon fiber shield material. This has an outer layer with a metal coating for good electrical conductivity. The company also provides high-performance 10 Gps Ethernet cables and connectors.
The past decade has seen an enormous transformation in the use and management of electrical power for the latest airliners, such as Boeing’s 787 and the Airbus A350, according to Russell Graves, aerospace business development manager with TE Connectivity. The Switzerland-based group, which also provides power-switching solutions, has worked to support tier-one suppliers involved in programs such as Pratt & Whitney’s latest geared turbofan engines.
More recently, TE partnered with UK-based eVTOL aircraft developer Vertical Aerospace, which is working to complete certification of its five-seat VA-1X model in 2024. “It’s a very collaborative relationship,” Graves told FutureFlight. “They give us good feedback on how our equipment is working on their aircraft; they identify issues and we propose solutions.”
Electromagnetic interference is one of the issues on which the TE team has focused. The company also has experience in the hardware needed to carry data from sensors, including those that will be required to support autonomous flight.
Like Carlisle, TE sees significant potential in the emerging advanced air mobility sector. “The sweet spot for this part of the industry is probably a decade away and it will likely come down to around 12 to 20 companies [producing aircraft],” Graves concluded.