Shedding Weight: Connectivity in Military-Aerospace Applications

Weight is among the most critical factors behind component choice when it comes to aerospace applications. Being among the bulkiest of components, connectors and cables need to embrace the latest scientific advances in order to reduce weight and enhance performance, fuel efficiency, and overall system reliability. This article outlines the recent advances enabling lighter connectors for aircraft, satellites, and drones.

For many systems, engineers try to balance SWaP-C (size, weight, power, cost) criteria to deliver the functionality, performance, and robustness demanded by a project, but within constraints placed upon it. However, in aerospace, few considerations outweigh the second of these SWaP-C criteria and every gram must be justified.

The importance of weight can be seen clearly if we look at a tactical drone as used by the military. These are required to fly at high speeds and high altitudes for distances of up to 160 km. These distances increase as we move toward high altitude, long endurance (HALE) surveillance drones, which go far further and are required to be as undetectable as possible, and therefore, need to be fast and extremely manoeuvrable. Excess weight therefore must be eliminated. Indeed, the only constraints deemed more important are functional — can it survive the cold temperatures, high-vibration, and low-atmospheric-pressure conditions without failing.

A similar need for low weight can also be seen when we look at equipment destined for operation in space (Figure 1). Yes, the electronic components selected need to withstand the temperature, pressure, and radiation of this harsh environment; and yes, the system will operate in a weightless environment; but with the launch costs being in the region of $66,000 per kilogram, weight is still a major factor behind every single choice.

Being among the largest and bulkiest electronic components in a system, connectors tend to come under particular scrutiny in such applications.

Traditional Connectors - the Micro-D

Before we delve into the latest technology, it’s important to look at some history. The miniaturization of electronics led initially from the D connector to the Micro-D. This had the same distinctive shape and staggered contact arrangement, but in a smaller form factor and with a higher contact density. Versus the original D connector, the Micro-D found less widespread use, but did establish itself as the de-facto choice where high performance was paramount (Figure 2).

Today, Micro-D can be found in a variety of high-end equipment, including missiles and aircraft. Indeed, the Micro-D connector even has its own military specification, MIL-DTL-83515.

However, the electronic connector industry has continued to evolve and ensure systems can continue to get smaller and lighter.

Material Advances

Materials science research has enabled many of the key advances behind today’s smaller, lighter electronic connectors. In particular, it has enabled the shift from traditional metals (for example steel) to lighter, higher-performing alloys and plastics.

An example of this can be seen in Harwin’s Gecko range of dual-row connectors. These use a 30 percent glass filled thermoplastic, which not only reduces weight versus a traditional Micro-D connector but also gives an exceptional mechanical strength as well as a resistance to thermal and chemical degradation.

The material also enables a higher number of mating cycles, for example Gecko’s Screw-Lok variant delivers a working life of 1,000 mating cycles, which is approximately double that of a comparable Micro-D connector. The switch to thermoplastics and the manufacturing techniques used, also enable a greater range of contact counts, enabling less pin redundancy which is, in and of itself, a source of unnecessary weight.

The electrical contacts within connectors are equally important, and advanced materials such as copper alloys and beryllium copper are now commonly used in aerospace applications as a result of their excellent electrical conductivity and mechanical properties.

Additionally, gold plating can also be applied to contact surfaces to prevent oxidation and to ensure long-term electrical performance, even when exposed to the high-vibration, high-altitude conditions faced by UAVs.

Finally, when we look at connector housings, aluminium alloys have become a de-facto choice. These materials have exceptionally high strength-to-weight ratio as well as corrosion resistance. This gives not just the mechanical protection for the connector’s delicate electrical contacts, but also adds very little additional weight to the overall system.

Connector Layouts

Arguably, the next most important weight savings have come from the connector’s layout with designers implementing layouts that feature lighter and smaller interconnects with smaller pin pitches and enhanced electrical conductivity. This reduces weight while also maintaining the reliability requirements demanded by such operational environments.

The reduction of weight in general also tends to lead to more space-constrained systems and here, a fine pitch is often preferred. A fine pitch also leads to smaller connectors which are, by definition, lighter. Furthermore, by combining signal and power in a single connector, designers can eliminate a number of connectors from the system entirely.

The effect of these advances on size and weight can be seen when we look at some of the most recent high-performance, micro-miniature signal connectors. These offer pitches as small as mm and are up to 75 percent lighter than more conventional Micro-D counterparts.

We can see this if we overlay the traditional Micro-D connector with a modern equivalent, for example a 26-pole Gecko connector with a 1.25 mm pitch onto a 25-way Micro-D equivalent (as per Figure 3a). Measuring 18.80×5.00 mm (94 mm²), the 26-pole thermoplastic connector has a footprint that is just over 60 percent smaller than the Micro-D equivalent.

And even if we use a Screw-Lok variant, which provides a secure retention in harsh conditions, we see a similar size and weight reduction. In this case with a footprint that is almost 44 percent smaller (see Figure 3b).

Beyond the Housing

Careful consideration of the thickness of materials, the design of contacts, and the overall structure of the connectors ensures optimized designs in which connectors are engineered to eliminate excess material wherever possible while still meeting stringent requirements for reliability, vibration resistance, and durability. However, these advances in materials can also be applied beyond the connector housing itself and examples of this include smaller gauge wires and contacts developed to be robust enough despite the reduction in weight.

Additional examples include the use of innovative and high-reliability contact systems such as the four-finger system employed in the Gecko family. These allow for secure connections with smaller, lighter components, while technologies that combine the fine-pitch signal connectors with 10 A power contacts bring weight benefits to mission-critical applications that demand interconnects for both signal and power.

Flexible Printed Circuits

In aerospace and high-density applications where weight, flexibility, and space are critical factors, flexible printed circuits (FPCs) offer several advantages over traditional cable assemblies.

Flex circuit assemblies are made from a combination of rigid PCBs and a flexible section where metal tracks are encased in protective insulation. This results in tracks that are extremely thin and, as their thin metal tracks use far less material, are significantly lighter than traditional cables.

Being more flexible than typical cable cores, FPCs accommodate dynamic bending over millions of cycles, which makes them ideal for applications that require repeated motion. And unlike cable assemblies, which require more vertical space and allowance for bend radius, FPCs offer more compact integration to reduce the height and space needed for connections.

Like the connectors themselves, FPCs can be manufactured from materials that are suited to extreme environmental conditions, be they high temperatures or exposure to chemicals, and are less prone to electromagnetic interference than cable bundles.

Conclusion

Electronic components make up a significant proportion of today’s military and aerospace equipment, with this affecting acceleration and manoeuvrability. In such situations, every gram must be justified. Being among the bulky components, connectors and cables fall under particular scrutiny.

The industry’s embrace of material science research to implement alloys and thermoplastics has enabled significant weight reductions to be made. However, this needs to be combined with advances in layout as well as cabling to ensure these weight reductions continue.

This article was written by John Brunt, Product Manager, Harwin (New Albany, IN). For more information, visit here  .

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