Living in Ethernet Times
October 13, 2014 | BY: Stephen WillisDownload PDF
The task of flight test instrumentation (FTI) hardware today isn't simply to give flight test engineers the data they need. Rather, the challenge is to deliver access to the ever-increasing amounts of test data that customers want, which these days typically far exceeds the amount of data needed to meet certification and to prove flight models.
FTI equipment is used by flight test engineers to collect data from a platform during its flight test campaign, and usually consists of sensors, an airborne data acquisition system (collecting data from sensors, avionics interfaces, audio/video sources), monitoring equipment, network switches, consoles and data recorders. This specialized FTI equipment must be rugged enough to operate reliably under flight conditions in harsh environments such as high vibration, shock and temperature gradients. While using equipment designed for industrial data acquisition can save on initial purchase costs, such equipment can fail to produce reliable and complete data when subjected to flight test conditions. This bad or incomplete data results in repeating flights, delays in the program, and inefficiencies in the development and analysis teams. Any flight testing time lost due to equipment failure can be extremely expensive and can easily exceed the initial cost of purpose-designed equipment over the lifetime of the program.
Today, the job of meeting the increasing demand for greater amounts of FTI data, while ensuring that FTI system SWaP-C is kept to an absolute minimum, is benefiting from a number of recent trends in data acquisition unit (DAU) and data acquisition system (DAS) design. These trends include higher levels of integration, the growth of Ethernet-based networks, modularization and the use of FTI metadata open standards.
DAUS AND ETHERNET NETWORKS
Today's FTI systems are moving away from traditional PCM-based architectures and increasingly embracing Ethernet networks. These networks use rugged Ethernet switches specifically designed for the unique requirements of aerospace networks. Deterministic, reliable and fast due to their hardwired switching design, FTI Ethernet switches are built with a sturdy compact form able to survive the extreme conditions of the aerospace environment. Every parameter can be synchronized using the IEEE 1588 Precision Time Protocol, ensuring coherency across even a massive system.
The use of rugged airborne Ethernet switches supports the development of distributed node architectures for FTI. This approach means that smaller DAUs can be located closer to the sensors on the aircraft. This increases the accuracy of the acquired data while potentially freeing up valuable space. With a single Ethernet cable being used to connect all the remote DAUs, the amount of wiring, and its associated weight is greatly reduced. This results in a simpler installation process and, typically, as much as a 30% reduction in overall wiring. Ethernet also supports higher data acquisition and recording rates and helps to lower costs and ensure long system lifetime by easing integration with COTS equipment.
The Ethernet network architecture approach also directly supports users' desire for greater amounts of FTI data and parameters, because the Ethernet backbone significantly eases the expansion of the test system, making it possible to simply add the additional desired DAUs when required. To add more parameters only requires the addition of another DAU chassis to the network. This approach can be used to support FTI systems ranging from a single small chassis to relatively massive systems, as more DAU nodes can be easily integrated into the existing networked system.
The trend toward higher levels of integration also helps provide access to more FTI data, because as modules used within the DAU chassis increase in channel density, they are able to support greater amounts of data input without adding additional overall weight to the platform.
ADDING CAMERAS WHILE REDUCING WEIGHT
Another trend that both provides greater amounts of FTI data while reducing SWaP-C overhead is the move from older video camera technologies toward modern HD digital video. Althought this move brings with it greater amounts of video data that must be supported and moved around the FTI system, older cameras are typically much heavier than modern cameras, and because the former were not usually digital and network-ready, two separate systems and data networks were required.
Today, we are increasingly seeing designs that combine the video sensor and the DAU into one unit, which reduces overall weight and simplifies the process of piping the resulting video data around the aircraft. For example, Curtiss-Wright and Kappa Optronics recently announced plans to jointly develop a new family of highly rugged FTI airborne video cameras. These new HD cameras will feature built-in video compression and dual-channel Ethernet streaming. They are designed to seamlessly integrate with DAUs to reduce SWaP-C by eliminating the need for separate compression cards or video processing units.
Another trend for providing increasing amounts of data without adding unwanted weight and space is the growing use of modular FTI systems. The modular approach lowers installation, setup and maintenance requirements and extends system lifetime. In contrast with costly one-off custom designs or DAU architectures that lack backward compatibility, true open standard interface-based DAU designs enable the reuse of existing systems and ease the addition of more system nodes as the need arises.
Even if the aircraft being tested has quite different requirements from the one for which the FTI system was originally designed, with the use of modular DAUs, adapting the existing system for use wth the new platform often simply involves swapping out a module or two, enabling the reuse of the majority of the existing system. This approach reduces complexity, saves space and weight and essentially future-proofs the customer's initial investment. Even if the legacy and current DAU designs are heterogeneous, Ethernet connectivity ensures compatibility across product generations.
Another approach for improving interoperability and increasing system flexiblity is through the use of open standards and protocols for file storage and for system synchronization, management and configuration. Open standards help reduce FTI equipment costs and simplify the task of gathering thousands of data parameters. For example, current FTI metadata standards such as XidML, TMATS, iHAL, and MDL provide a vendor-neutral hardware configuration approach for acquiring, processing and packaging data for transmission, storage and reproduction. Designed specifically to meet the needs of the aerospace industry, metadata standards such as XidML ease the storing and exchange of FTI data between hardware from multiple vendors. By freeing users from proprietary formats, it makes it possible, for example, to select a DAU from one vendor and have confidence that it will work well with a data recorder from another vendor. Today, while there are several competing metadata standards, which unfortunately hinder true interoperability, the trend is for the definition of a single standard that will be embraced across the industry in the not too distant future.
Another element of an FTI system that is important not to overlook is its software interface. As greater amounts of data are being acquired by greater numbers of sensors, the ability to physically cope with the increased system complexity can become a big concern. Furthermore, the prospect of learning a new custom-designed system setup and management software package can be a daunting task. One of the key goals of an FTI test engineer is to reduce the amount of time involved in conducting flight tests. Setting up complex systems and dealing with masses of complicated wiring can add significant time and expense to an FTI program. This problem is compounded when a fault occurs, as it inevitably will in a complex system. Locating the source of the problem then becomes the challenge. The use of an Ethernet-based network makes troubleshooting easier. Even better, FTI setup software that makes full use of an integrated network architecture can be easier to use and more powerful. A good setup software package will save its users significant time in entering, reviewing and validating setup information and ensuring that instrumentation is correctly configured. The result is that system validation and programming can be performed in minutes or even seconds. Specially designed software tools can reduce the time required for commissioning and calibration and simplify flight line inspections, pre-flight checks and system reconfiguration.
EXAMPLE OF AN ETHERNET-BASED MODULAR DAU
Curtiss-Wright's Acra KAM-500 provides an example of a flexible, modular DAU for FTI that makes full use of the benefits of Ethernet connectivity. The KAM-500's data can be optimally packetized for Ethernet transmission and recording but can also be converted to many other industry standard protocols. This facilitates the integration of hybrid systems such as PCM DAUs into an Ethernet system and allows Ethernet data to be converted to PCM for telemetering. Curtiss-Wright currently offers more than 100 types of modules for use in the KAM-500, providing system developers exceptional flexibility to meet the specific needs of a program. This modular system also helps developers control costs. Systems can be easily modified or updated as the Acra KAM-500 is only one module away from any application.
To facilitate setup and management of FTI hardware, Curtiss-Wright has developed the DAS Studio 3 software package. It saves a considerable amount of time by integrating the process of entering, reviewing and validating setup information, ensuring that instrumentation is correctly configured. It also provides an easy-to-understand interface that lessens the usual complexity involved in setting up a data acquisition system. Integrated tools save time by automating time-consuming tasks such as building optimized PCM frames and importing data from proprietary bus descriptions.
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