The weight is over!

Not unlike our own attempts to lose weight through dieting, airframe design integrators too are increasingly looking to reduce the weight of their interconnect components, while at the same time coping with the increasing functionality and complexity of power density and high speed digital communications demanded by today's aircraft OEMs.
Typically, the kinds of performance demands placed on interconnect suppliers by airframers will involve satisfying the usual suspects of weight, miniaturisation, robustness and functionality.

According to ITT Interconnect Solutions' director of engineering, advanced technology, Peter Hyzin, there is an overlap in performance demands between commercial and military airframers; the primary one being weight reduction.

“The emphasis on weight reduction is more prevalent in military aircraft,” he begins. “For example, take the common connector type, MIL-DTL-38999. There are more than 1,000 of these connectors of various sizes and configurations being used in the Lockheed Martin F-35 Lightning II. Selecting a lower weight material for the connector housing could generate savings of up to 50lbs. This may not sound like much, but when an aircraft is over the weight budget, every pound counts.”

He goes on to suggest that the airframers of today do not typically challenge the connector manufacturers with performance demands; they are more interested in standardisation and reduction of the number of different types of connectors that are being used on their aircraft. This approach is more about reducing procurement and inventory cost and about assembly process optimisation for the few select products.

“There are however areas in the aircraft, especially commercial aircraft, like the cabin, where new in-flight entertainment systems are being developed so there is a need for new interconnect solutions,” Hyzin continues. “This is where miniaturisation, robustness and flexibility play a vital role in selection and design of connectors in applications like seat-to-seat, or in-seat implementation of ethernet onboard aircraft, which has also generated interconnect performance demands.”

As with many connector manufacturers, ITT needed to overcome the technological barriers relating to the use of carbon fibre composites in its housings, such as interference problems, dissimilar materials leading to mating issues, different thermal expansion rates leading to distortion and cracking, and particularly in withstanding lightning strikes.

“Fortunately, advances in carbon filled composite materials enable the production of composite connectors that, in most cases, can meet the same performance requirements as their aluminium counterparts,” Hyzin notes. “However, they do have some limitations relating to a resistance to indirect lightning strike currents. The lower resistance to these currents has not been, and may never be overcome; we are dealing with insulating materials, not conductors, even though the composite materials are plated with conductive finishes. To allow use of composite materials and to benefit from weight reduction, lightning strike performance requirements for composite connectors have been reduced; an acceptable trade-off. For example, the peak current requirement has been reduced from 10,000A to 6,000A with 3,000A for the smallest size connector.

“Another critical aspect of carbon filled composite materials lies with secondary processing. Because these connectors must have conductive surfaces for shielding effectiveness and shell to shell conductivity, a robust process for applying metallic coatings is necessary. Loose metallic particles in the connector are detrimental to its performance. However, the risk of the conductive plating blistering and peeling off is always there.”

In terms of weight savings, it's the material construction of the connector housing where carbon fibre offers the biggest advantages to airframers, making it suitable for UAV applications.

“The composite MIL-DTL-38999 is a direct replacement for the metallic version and meets most of the requirements of its metallic counterpart,” he notes. “Therefore, it can be used in the same applications such as UAVs, military aircraft and commercial aircraft. The only limitation, as described before, is a lower resistance to indirect lightning strike currents.”

Regarding ITT's materials technology developments in the future, Hyzin points to the complementary use of carbon filled composite materials in connector housings. “It's a technology called moulded interconnect devices (MID) that in the past, has not realised its promises,” he continues. “However, with recent advances in MID materials and processing, this technology may find new applications in the near future and may prove to be cost-effective.

“Another consideration is expanding the use of stainless steel or titanium materials by utilising a unique metalworking process called MIM (Metal Injection Moulding) to produce low cost, complex parts. It is not a recently developed technology, but it could be a viable alternative to other methods of fabrication.”

With a long history of creativity and innovation, ITT lays claim to being the original inventor of what are probably some of the most popular and widely used connectors in the world: the D-Sub connector, the commercial three pin audio XLR connector and the DL product - claimed to be the first zero insertion force connector.

“Many of our products have been and are still being used in every imaginable application,” Hyzin concludes. “From the first Douglas DC-1 aircraft when the connectors were referred to as ‘cannon plugs', to the International Space Station, and from the oil fields to the battlefields, ITT Interconnect Solutions' products provide the reliability required in all of these applications.”

www.ittcannon.com