Connectors Fly High on Commercial Aircraft
Thousands of new commercial aircraft are currently in production. They will contain lightweight, powerful, high-speed electronics systems that will enable connectivity on a level the skies have never seen.
Commercial aircraft come in many shapes and sizes, from small executive jets to large, long-haul, wide-body planes that carry hundreds of passengers. Electronics are taking a leading role in all aspects of commercial aircraft design as their use increases in areas such as power management, navigation, and control. At the 2019 Paris Air Show, forecasters announced that world demand to replace aging commercial aircraft will rise steadily, accounting for 10,550 new planes over the next 20 years in the up-to-150-seat category alone. Demand for narrow-body, 150- to 210-seat aircraft will almost double to 20,500 planes.
In more exciting, unusual examples, commercial planes recently showed what they can do, besides ferry passengers on prescribed routes. Over 50 scientists and eclipse enthusiasts on a special LATAM Airlines Group flight watched the total solar eclipse from the skies on July 19, 2019. Departing from Easter Island in a Boeing 787-9 Dreamliner, they chased the Earth‘s shadow over South America. LATAM is the only airline authorized to fly over this part of the Pacific Ocean.
In a Qatar Executive Gulfstream G650ER, a pilot and an astronaut completed the fastest-ever polar circumnavigation on July 11, 2019, smashing the Guinness World Record in 46 hours, 40 minutes. Pilot Hamish Harding, chairman of Action Aviation; Colonel Terry Virts, former commander of the International Space Station; and their crew of six achieved this feat in partnership with Qatar Executive. Owned by Qatar Airways, this company is the world’s largest operator of the Gulfstream G650ER, the fastest ultra-long-range business jet.
To continue to achieve milestones like these, as well as everyday commercial air travel, the industry will require continued innovation in connectivity. Adding 30,000 more aircraft in 20 years will represent a huge variety of connectors in different places all over the plane. The location and application determine the electrical, mechanical, and environmental requirements to be met by the connector of choice, said Travis Warmouth, Radiall’s program development engineer.
Those requirements can include dielectric withstanding voltage, operating temperature, mating cycles, insulation resistance, and resistance to electromagnetic interference, vibration/shock, flammability, and smoke/toxicity. Connector size and shape, which are generally less important, carry more weight when space is restricted, said Warmouth. “Rectangular-shaped connectors can provide higher contact density, since multiple connectors can be stacked. This can be a great advantage when space is limited and input/output count is high.”
The requirements that are usually most important for onboard electronics connectors are ability to handle shock, vibration, general durability, and temperature cycling, said David Koenig, vice president of AirBorn’s space strategic business unit. Adding to that list, AirBorn’s Robert Kleinschmidt, senior vice president of its air and defense strategic business unit, cited reliability and fail-safe connections. “In the airframe, where there’s more room, connector size is less important,” he said. “But in areas like the cockpit avionics section, small and micro connectors are necessary.” There, connection and cabling density are also very important size considerations.
Connection Speed Keeps Going Up
The increased need for speed and bandwidth is driving much new interconnect design, especially in cabling and box-to-box connectors, said Koenig. “The typical data rate we’re seeing now is 10 gigabits per second per lane.” The company’s new verSI (versatile signal integrity) open-pin field interconnect is designed for high-speed, high-density, high-signal-integrity, and high-reliability serial bus applications. With up to 500 contacts, this high-pin-count connector can handle 28Gb/s board-to-board. It’s used on the engine controller of CFM International’s LEAP engine for GE Aviation.
Higher data rates, and the distances data must travel especially in the airframe, are also key, said Kleinschmidt. “Recently, a customer was getting interference with high-speed data rates in some cable assemblies inside a helicopter. About three or four meters of cable assemblies were bunched together, causing flicker on the avionics displays.” This problem, and AirBorn’s solution, show the need to design for signal integrity across the entire cable assembly as well as the connector. Data rates, EMI shielding, and rugged and reliable connectors must all be considered.
The need for high-speed data links, whether copper or fiber optics, is definitely increasing, said Warmouth. “Not all customers want to transmit data at 10Gb/s via fiber; therefore, connectors are being developed that can accommodate such high speeds but still not make termination too cumbersome.”
For example, Radiall’s QuickFusio insert design meets Cat 6A requirements and offers excellent digital, high-frequency performance. This series also has inserts to accommodate Luxcis ARINC 801 termini for fiber data links.
Demand for Fiber Optics Continues to Grow
Demand is rising for higher-density fiber optic solutions, resulting in ruggedizing solutions originally intended for other markets, such as Radiall’s MTitan Series, said Warmouth. Comprising C-MTitan contact options for “inside the box” applications and Q-MTitan contact options for electrical wiring integration system applications, the products let 12 fiber optic cables pass through a single size 8 quadrax contact cavity. Radiall’s Q-MTitan design was chosen as the base design for the recently released ARINC 846 aerospace industry standard for interconnect assembly solutions based on the mechanical transfer (MT) ferrule. Combining Radiall’s D-Lightsys active optics with MTitan gives customers a complete fiber optic end-to-end solution.
Commercial aircraft use lots of fiber optic interconnects, traditionally point-to-point physical contacts where two termini produce optical coupling, said Koenig. In a newer type, expanded beam light travels between termini. A third kind, active optical cable (AOC), is used in data centers. In AirBorn’s rugged AOC (RAOC) for commercial aircraft, based on its space-rated AOC (SAOC), electrical-to-optical transmission occurs within the cable’s backshell, since shock and vibration can harm traditional optical interconnects, he said.
Demand for fiber optics is growing especially quickly because copper interconnects are limited by length, weight, and cable routing inflexibility in tight spaces, said Kleinschmidt. Although fiber provides better distances and data rates, it also introduces other issues, such as reliability, since fiber optic connectors are often exposed to dust, dirt, and fingerprints. “While the expanded beam design helps address some of that, we think there’s an opportunity in the middle with RAOC,” he said. “It has the benefits of fiber — weight and space savings plus flexibility — coupled with the traditional benefits of copper connectors: no field maintenance needed, and boards don’t need to be designed for transceivers.”
On the Horizon
An upcoming trend in commercial aircraft electronics is autonomous systems, which will make reliability and durability even more crucial, said Koenig. “In autonomous systems, we’ll see triple redundancy — already in place on the military side — versus the double redundancy we have now in commercial aircraft.”
Also trending are connectors that accommodate quick mating and unmating, said Warmouth. “Aircraft production is at an all-time high and every second counts on the build line,” he said. Quick installation is another key focus, especially connectors that don’t require mounting hardware. This saves installer time and prevents foreign object damage. Radiall’s Quick Multipin (QM) and QuickFusio connector series were designed with time savings in mind.
Commercial aircraft connectors need to be versatile for the different applications they serve, said Warmouth. Connectors that can accommodate a wide range of contact options may include insert options for signal, power, RF, and fiber optic termini, as well as hybrid inserts that can include all of these options. “This is key, as frequency and data transmission needs continue to increase on commercial aircraft,” he said.
Ann R. Thryft has been writing about manufacturing- and electronics-related technologies for 30 years, covering interconnect, single-board computers, robotics, machine vision, embedded devices, manufacturing materials and processes, and all kinds of datacom and telecom. She’s written for EE Times, Design News, COTS Journal, RTC Magazine, EDN, Test & Measurement World, and Nikkei Electronics Asia.
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