Advances in Aircraft EWIS

Continuing electrical advancements help keep planes flying and systems functioning

Aircraft cables, connectors, interconnects, wires and harnesses are considered to be aircrafts’ central nervous system because they interface with a variety of applications on board. Forming an electrical wiring interconnect system (EWIS), they are the lifelines of modern aircraft, enabling the transmission of power, signals and data that keep planes soaring and systems functioning flawlessly. Continuing advancements in these components are contributing to the increasing reliability and performance of aircraft systems.

Cables
Cables are an essential component in electronic systems. If a cable goes down, an entire system can fail. Technological advancements are trying to prevent that from happening. The performance requirements for modern aircraft cabling continue to increase at a pace that is driving the need for advanced materials, design and performance evaluation. With a focus in the defense sector on air dominance, there is a need for high-performance RF/microwave cables operating to 40GHz and beyond.

“Microwave cables operating in this band of the electromagnetic spectrum are typically smaller in diameter making durability during and after installation a significant requirement,” says Tamera A. Yost, Ph.D., Chief Technologist at W. L. Gore & Associates, Inc., Elkton, Maryland. “This is compounded by the integration of more computing power within the Electronic Warfare subsystems by designing multiple functions with one LRU and thus reducing the number of LRUs. Small, rugged, routable high-frequency cables using advanced low-loss dielectric materials that are inherently designed to withstand the installation and lifetime of the aircraft can reduce development and build time and provide connectivity over the life of the aircraft.”

Michael Traskos, President, EWIS DER, Lectromec, Chantilly, Virginia, explains that a recent development in cables/wires has been the heavy investment and focus on addressing the need of high voltage applications. “While meeting the needs of high voltage may seem to be simple (e.g., add insulation), the aerospace segment is weight sensitive and seeks solutions that optimize performance and weight. Other areas that have seen benefits have been the metalized fibers for shielding applications. While this is not a new development, the implementation has increased in the last couple of years taking advantage of the work and research performed a decade ago.”

As avionic systems move to digital infrastructures, low-latency, high-speed interconnects provide the backbone of the avionic architecture. Whether choosing an optical or copper interconnect, the error-free, real-time availability of information being transported, processed and made available to the assets within the mission is required to ensure coordination among all. Within digital interconnect systems, error-free operation is the key to having the information when it is needed to make a critical decision.

“When choosing a digital interconnect, specific attention needs to be placed on not just meeting the specification but having sufficient margin in performance to allow for system performance degradation to temperature fluctuations, vibration and other environmental factors,” Yost says.

Connectors and Interconnects
RF and microwave connectors are precision manufactured components. Digital interconnects are now operating in the GHz range and Yost believes connectors for high-speed differential signals will require similar design expertise and manufacturing tolerances to provide impedance controlled transitions from the cable through the connector. “Without impedance-controlled transitions, the interconnect will suffer from reflections that can lead to sub-optimal link performance.”

Advancements in high performance digital interconnects start with a well-balanced differential pair cable that Yost says is terminated to an impedance-controlled connector that operates cleanly beyond 5 GHz. “Similar to techniques used for RF and microwave cable termination, skill is required to prepare the cable properly to enable a robust termination to the connector with minimal excursions from the specified impedance.”

Elizabethtown, Pennsylvania-based TE Connectivity’s MULTIGIG HD connector was recently selected by the VITA Standards Organization (VSO) as the Next-Generation VPX plug-in module connector and will Matt McAlonis, Director of Advanced Systems & Architecture and Engineering Fellow for Aerospace, Defense and Marine at TE Connectivity says it will become a defense industry standard. “The redesigned MULTIGIG HD connector builds on the previous variants of TE’s MULTIGIG HD product family, while bringing significant technical advances including doubled pin count, 112 Gb/s data rates, increased current capacity and support for rugged environments.”

Wires and Harnesses
As is the case with aircraft cables, electronically controlled and powered, high dielectric strength materials for insulation systems enable higher voltage (>600V) power distribution systems to operate at elevated temperature and altitude. These insulation systems require void-free materials with low permittivity to enable partial-discharge free operation well beyond the system voltage to provide a necessary safety margin to account for the drop in partial discharge performance when operating at 50,000 feet and elevated temperatures beyond 200 degrees C.

“Routing and installation of these large-gauge power feeder cables can become a challenge as insulation wall thickness is increased and the force-to-bend and amount of spring-back when bent creates significant stresses on the cable connection and the ability to route the cable,” Yost says. “The use of high strand count center conductors can minimize these forces and combined with high dielectric strength materials the wall thickness can be reduced to provide an overall flexible, high voltage power cable that can be easily installed.”

For both large and small power wires and cables, abrasion resistance of the insulation system is important when choosing a solution for modernizing and retrofitting existing aircraft. “Not having the freedom to choose the routing puts additional burden on the installer to be able to have a solution that not only fits within the existing airframe but is able to be pulled through without fear of damaging the insulation,” Yost says.

Harnesses—a collection of bundled electrical wires that protect and route electrical wiring throughout an aircraft—are vital to aircraft operations and success. There is continuing movement toward custom harnesses, which require an initial investment, but offer significantly reduce maintenance costs over an aircraft’s lifespan. Generic wiring cannot keep up with modern bandwidth, power and weight requirements. A well-built custom harness minimizes failures, preventing costly repairs and unscheduled maintenance downtime. They can also improve power efficiency, protecting avionics and sensitive electronics from premature failure.

Developments continue to be discovered for harness protection. New materials for fire protection and arc damage protection help OEMs reduce separation in critical areas easing installation challenges.

Lighter Weight
McAlonis says innovators are developing advanced materials and miniaturized electronics to help reduce weight. This will improve fuel efficiency, increase payload capacity and enhance performance. “The demand for electric flight is increasing the need for high-speed battery charging and weight reduction. Special cables, contactors and switches are being designed to handle the high voltages, amperages and temperatures encountered during fast charging. For battery weight reduction, engineers are balancing weight and power to deliver peak power for takeoffs and landings without adding excessive weight to the airframe.”

Traskos explains that while some of the economics of flight/space-applications has changed, the push for lighter weight components has always been part of aerospace. “The use of metalized fibers has increased significantly in the last couple of years, primarily with regard to shielding applications.
The current carrying capacity is still not comparable to copper. They present challenges for lightning-strike prone areas of aircraft, but there are plenty of aerospace applications where the weight-savings benefits can be realized.”

Next-Gen Fiber Optics and Nano Miniature Connectors
Fiber optics and miniature connectors can enable higher data throughput. Fiber optic cables can provide more bandwidth than may ever be needed in a single aircraft and provide a tremendous weight benefit.

TE Connectivity has launched several new developments leveraging fiber optics including fiber optic flex cabling and a transceiver, MULTIGIG TRX, and has connectors for VNX+ in development for launch in late 2025. “Our Optical Flex solution effectively offers complex harnessing with thousands of possible connections and routing capabilities, with drastically reduced space envelope and weight that simply isn’t possible with copper, all at the speed and bandwidth of FO,” McAlonis says. “We have the FO connectors and transceivers for an immensely robust, high-bandwidth, high-volume throughput, lightweight signal connectivity system.”

Yost believes having the aerospace industry get comfortable with using fiber optic cables will take time and training. Additionally, “Having robust and durable jackets for fiber optic cables will enhance handling without damage and speed implementation of this technology. Miniature connectors increase the signal density which equates to more data per square area. High performance computing platforms that process tremendous amount of real-time data for AI algorithms require miniature connectors to provide the signal density required to minimize the overall system footprint and weight.”

Higher Voltage
Lectromec supports higher voltages. But Traskos explains that, “The aerospace sector does not have high-voltage component standards developed at this point and given what has been learned about material degradation at high voltages/frequencies, there is a decent chance it will not for quite some time. The reason for standards is to have common parts and common parts require common needs. Right now, there are so many competing technologies, designs and power systems, each one requires customization and testing to verify the reliability for the application.”

A significant level of effort is going into the research, design and testing of wiring system components for high voltage applications. Wire/cables supporting high voltage applications now are assessed for partial discharge at ambient and reduced atmospheric pressures; something Traskos says was not done in the past. “This has then led to improvements in cable design, termination techniques and inspection/maintenance plans.”

Environmental Regulations Prompt Advancements
Regulation provides challenges but also opportunities for innovation. Yost contends environmental regulations have driven the move from fuel-based systems to all-electric or hybrid-electric aircraft and is the largest shift in aviation technology. “The need for electric propulsion has spearheaded the need for improved wire and cabling.”

RoHS is the EU’s Restriction of Hazardous Substances Directive, a regulation that limits the use of specific hazardous materials in electrical and electronic equipment (EEE) to protect human health and the environment. It restricts substances like lead, mercury and cadmium. The REACH Regulation is a comprehensive European Union (EU) law that aims to improve the protection of human health and the environment from the risks posed by chemicals.

Traskos says RoHS and REACH are creating problems in the supply chains and it can be in ways that take years to realize. The primary insulation types on aerospace wires/cables are various types of fluoropolymers, which Traskos says are close to being banned. “Not specifically being added to the banned lists, but from attrition from elimination of the supporting chemicals. The advances that are being made now are more related to trying to maintain the same level of performance with an ever-reduced set of tools to do it; almost like trying to keep ones footing in a river. At some point, there will be a material restriction that will require reduction of longstanding performance requirements. This may be something like cable markability, or it may turn out to be more impactful like fluid resistance or flammability.” 

By Mark Robins