Flight test instrumentation (FTI) engineers today face a number of challenges when instrumenting aircraft including an increasing push to lower weight of equipment and wiring, gather more and more data and meet demanding time schedules. Additionally there is the need to operate equipment in a heterogeneous network, not only with equipment from the same vendor but also with equipment from third parties. But no compromises can be made on data quality of the reliability of the system. The success of a test flight relies on data being gathered reliably – not an easy task in harsh environments where brown-outs may occur. Predictable data acquisition with minimal loss of data during power dips is required – lost data can mean the need to repeat a flight.

A possible solution for reducing wiring would to move the data acquisition unit (DAU) chassis closer to the sensors. But there is typically less space closer to the sensor and the chassis will be subject to harsh environmental conditions, such as exposure to fluids, high vibration, and extreme temperatures. Another complication is the total number of measurements required for new flight test campaigns keeps increasing. This means more chassis and higher bandwidth networks to support the data throughput and results in more time required to design, test, install, program and perform pre-flight checks on the equipment. Integration of equipment from different vendors also presents a challenge that can impact schedules and reliability.

A solution that can satisfy the wiring, size/environmental, performance and connectivity hurdles without forcing the system integrator to resort to a costly and inflexible custom solution requires three innovations: 1) a small, lightweight modular COTS-based DAU chassis; 2) an Ethernet-based network; and 3) a selection of rugged data acquisition modules that can support hundreds of channels of data measurement that can operate optimally in constrained spaces while enduring harsh environments.

The Axon is a miniature modular chassis that fulfills these needs. It is a better alternative than using custom-designed, dedicated acquisition units as it eliminates the need to develop a unique box for every sensor location, each of which would typically require a different number and different types of measurements. The modular approach enables the same chassis to be modified, as needed, using a mix of different acquisition cards. This allows flexibility during a flight test program where data acquisition needs can change and can also have a significant long term impact as reusing equipment from one program to the next can save costs and reduce time in design, training and software configuration.

The Axon is a true Ethernet native device. It operates in a heterogeneous network, not only with standard chassis from the same vendor but also with equipment from third parties. To ensure this, the chassis is a full network node that supports open standards, including the soon to be published iNET standards. In order to connect multiple miniature nodes to the network, it has the built in capability to daisy chain other network nodes without needing a separate module. With these capabilities the remote miniature chassis solves many of the challenges FTI engineers are currently facing.

The Axon has an onboard processor to support in box compilation, in-service firmware upgrading and fast system check through the use of built-in web servers to report status. This facilitates faster programing, modifications and means pre-flight checks can be performed quickly. The Axon uses the open XidML metadata standard which allows simple integration with any other device as they can be described in the same language.

Engineering the for harsh environmentals is something Curtiss-Wright has a huge amount of experience in. The Axon builds on the decades of rugged design principals developed for the Acra KAM-500 and extends these with strategies for superior heat tolerance and fluid ingress. One example of an inhospitable location is the aircraft’s engine casing. Placing the chassis in a high temperature zone can cause electronic components to reach temperatures outside of their specification.

This can be a particular problem for miniature chassis where a large amount of electronics are co-located in a small box. One option is to add a large heat sink to the chassis to improve the cooling, but this is solution is directly counter to the goal of reducing the chassis size, and will likely reduce the number of potential locations in which the system can be installed. In order to get data acquisition as close as possible to the sensor, and into the smallest possible spaces, one option is to mount the acquisition card itself in a separate location from the chassis. The remote acquisition card would send acquired data back to the chassis via a serial cable from which it would also be powered. The acquisition card can be designed to fit into a space just marginally larger than its own dimensions. Multiple remote cards could be connected to single chassis, enabling a network of miniature acquisition to be placed most space constrained locations. Heat dissipation becomes easier as there is a much higher surface area available for each module and a lower density of heat producing electronics. 

The Axon is weather sealed by filling the gaps between modules with form in place gaskets. Form in place gaskets use elastomer to provide sealing between two surfaces. The elastomer is applied to one side of the acquisition module. When the modules are placed in the chassis side by side, the compression and the cohesion of the elastomeric material provided the seal. Even better, these gaskets are electrically conductive and provide an RFI shield. This solves one problem of solid chassis design – fluid ingress, without presenting the difficulties of disassembling ‘slice of bread’ architectures.


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