Tuesday, December 1, 2009
Product Focus: Databus
Highly reliable for flight-critical functions, 1553 military databus technology is getting a new look for civil aircraft applications
With digital flight control systems on aircraft like the under-development Airbus A350XWB becoming more prevalent, commercial manufacturers are beginning to follow the path laid by the military in using 1553 databus technology, adopting it for actuation of flight-control surfaces.
"1553 has been around for 30 years in the military, but use outside the military has been few and far between," said Mike Hegerty, principal marketing engineer for Data Device Corp. (DDC), acknowledging that a number of regional jets employ the technology. "Today, however, flight control systems are moving away from analog feedback loops to digital flight control, which is reliable, deterministic and can operate in lightning conditions even in composite aircraft."
Roy Nardin, data bus product line manager with National Hybrid, Inc. (NHI), Ronkonkoma, N.Y., said his company’s plastic ball grid array 1553 terminal is being designed into the rudder control system of the A350.
"It’s really the way to go," said Nardin. "What was 1553 originally designed for, what is it used for? It’s used for critical applications. Of course, it was first used in the military for weapons and for surface control — something that had to be highly reliable could not get corrupted by noise or any kind of interference on the bus.... Moving into the area of commercial aircraft seems to me a natural thing to do. And for safety, as commercial aircraft become more and more fly-by-wire, where everything is automatically controlled, it’s a natural. Anything that’s flight critical, I would expect to see 1553."
The biggest hurdle manufacturers of 1553 chips and circuit boards have had to deal with in getting their systems onboard commercial aircraft has been certification, specifically meeting DO-254, Design Assurance Guidance for Airborne Electronic Hardware, and DO-178, Software Considerations in Airborne Systems and Equipment Certification, both published by RTCA.
The fact, though, that the hardware has decades of service under its belt on the military side gave Airbus, for example, confidence that standards could be met.
"Chips with millions of flight hours talk to the reliability of these components," said Chris Stabile, DDC marketing communications manager. The use of proven 1553 technology made the certification process go faster, he added, something of particular importance to Airbus, which was trying to shave time off the two-year head start Boeing had with its 787 Dreamliner.
"How many Ethernet chips, for example, have flown at -50 degrees and in lightning conditions?" he asked rhetorically.
DDC, Bohemia, N.Y., considered going the route of ARINC 429, which is designed to limit electromagnetic interference but provides less protection against lightning, according to Hegerty.
In addition, technology based on the ARINC 429 standard adds weight. "The problem is that there are a lot of distributed elements (on a commercial aircraft) that need to communicate, and 429 is not a multi-drop bus, so a separate cable is needed for each element," he said. "1553 is a multi-drop bus, so it reduces weight."
When the U.S. Air Force abandoned its efforts last year to develop aircraft databus technology that operated at 200 Mbps, it was thought that the Ottawa, Ontario-based company developing that technology would drop the effort. That’s not been the case for Edgewater Computer Systems, which continues to refine what it calls Extended 1553 (E1553), though at more down-to-Earth transmission speeds.
"Speaking only for Extended 1553, there are a couple important developments that have occurred," said Edgewater Vice President of Marketing Greg Fielding.
"Extended 1553 has been proven in a number of disparate platforms on a variety of dissimilar 1553 data buses to provide high throughput, deterministic capacity operating concurrently and in parallel with the legacy 1553 signaling. Extended 1553 has been proven to operate on the existing 1553 data bus without any changes to the 1553 data bus network and without changes or impact to the existing 1553 signaling solution."
The U.S. Department of Defense’s increased emphasis on intelligence, surveillance and reconnaissance (ISR) systems, for example, is driving the need for increased network capacity, and Fielding says E1553 provides an affordable solution for the rapid deployment of ISR systems that require higher bandwidth.
The need for greater bandwidth solutions is being met by advancements in higher performance data link solutions such as Enhanced Throughput from ViaSat and Flexible Access Secure Transfer (FAST) from BAE Systems. Both are approaches to increase the throughput of the Link 16 network by roughly one order of magnitude.
ViaSat’s Enhanced Throughput increases coded data throughput of the Link 16 waveform from a current maximum of 115.2 kbps to more than 800 kbps in Multifunctional Information Distribution System (MIDS) Low Volume Terminals. It is a stepping stone to the MIDS Joint Tactical Radio Systems (JTRS) now under development, which has been demonstrated to increase throughput of MIDS by a factor of four in flight testing on F/A-18E/F aircraft.
The BAE FAST waveform provides low-latency messaging, MANET (mobile ad hoc networking) and IP (Internet Protocol) connectivity. The addition of FAST to MIDS terminals provides Global Information Grid-enabling connectivity.
The throughput of these higher performance data link waveforms in some instances, though can exceed the capacity of legacy 1553 data bus interface solutions. Fielding said E1553 can help in this regard.
"Extended 1553 has been identified as a viable approach to affordably and rapidly support the consumption of this additional capacity within the platform," he said. "This approach will not only provide the additional capacity for the enhanced Link 16 waveforms, but will provide substantially more available capacity to support many other high-throughput applications such as multiple channels of streaming video.
"Funding within the DoD has been allocated to Link 16 enhancements, a portion of which is expected to support the tailoring of a low-risk, Extended 1553 form-factor solution consumable for integration by the MIDS data link vendors into the MIDS terminals," Fielding said.
One of the keys to acceptance for E1553, according to Fielding, is integration of the technology into a commonly accepted form factor.
Based on customer feedback and international military interests, Edgewater has designed E1553 into a single-width PCI Mezzanine Card (PMC) form factor. This solution will be targeted at a variety of line-replaceable units, including the integration into a mission computer and an advanced targeting pod (ATP) over the next 12 months. Again, the cost benefits of an Extended 1553 solution that enables the incremental upgrade of avionics to support increased bandwidth without having to add networks or rewire platforms remains an important and key consideration in the selection of Extended 1553.
The avionics databus technology that Edgewater has developed with E1553 allows wideband data to be carried over existing aircraft 1553 wiring and bus components without interruption or interference with other systems by maintaining the deterministic command-response nature of the legacy system. It is interoperable with Mil-Std-1553B terminals and cable assemblies, and results in the establishment of a separate network on the existing 1553 wiring infrastructure.
"When compared with legacy 1553, which is now over three decades old, Extended 1553 provides roughly two orders of magnitude of additional capacity and brings airborne data bus technology into the 21st century," said Fielding. "As important as capacity is, it is equally important to ensure the deterministic nature of the data throughput. Extended 1553 is designed to support a very low bit error rate to reduce the occurrences of retries, which, by their nature, are sporadic and lead to non-deterministic behaviors.
"This is one of the reasons that commercial networking solutions are less desirable for military applications," Fielding said.
"Commercial networking solutions are designed to support maximum throughput at the expense of errors that drive retries. These errors are typically due to unexpected changes in the conditions on the data bus due to interference from jammers, for example, a common occurrence in military platforms such as fighter jets and attack helicopters.
Extended 1553 has been designed from the outset to maintain very low error rates even in the presence of dynamic and degraded network conditions."
While it may have been unrealistic to expect that the technology could have resulted in a 200-fold increase in throughput at this moment in time, the basic architecture that creates a separate network continues to have merit in the eyes of Edgewater.
"There are a number of challenges associated with high bandwidth databus networking," said Fielding, "but fundamentally they all distill down to cost and time — the cost and time to integrate and certify a network that provides the necessary capacity, the cost and time to upgrade and certify the avionics and electronics to interface to the network, the cost and time to recertify the platform for weight and balance, the cost and time to rewrite and recertify the software that drives mission and flight-critical applications and ensures guaranteed determinism in the network.
"Extended 1553, by its nature as a network interface card solution, provides a separate, parallel high-speed network on the existing data bus which dramatically reduces both the cost and the time to integrate high-bandwidth data bus networking capability by eliminating the need to add cabling for new data networks, or to rewire the platform, or to upgrade all of the avionics residing on the new data bus, or by forcing changes to the existing 1553 data bus software solution," Fielding said.
"Further, an environment such as that found in a fighter jet or an attack helicopter requires that the data bus network is robust and immune to electromagnetic interference and, itself, does not generate or radiate electromagnetic interference into the surrounding avionics suite. Extended 1553 has passed the necessary EMC compliance testing to ensure it falls within the necessary parameters for deployment in military platforms."
Over the next 12 to 18 months, Edgewater expects to see E1553 being part of a number of integration activities for mission computers, data links, ATPs and other avionics and electronics in both fixed-wing and rotary-wing platforms.
Without naming names, Fielding said some of these integration activities will be for demonstration, some for System Development and Demonstration phases and others for rapid deployment into the battlefield.
"We will continue to reduce the form factor, drive down the power, and increase the density and number of interfaces per square unit of area as we expand the family of products based on Extended 1553 technology," he said.
Avionics Magazine’s Product Focus is a monthly feature that examines some of the latest trends in different market segments of the avionics industry. It does not represent a comprehensive survey of all companies and products in these markets.
Actel Corp. www.actel.com
Aero Express www.aeroexpress.com
AIM GmbH and AIM-USA www.aim-online.com
Alta Data Technologies www.altadt.com
Avionica, Inc. www.avionica.com
Ballard Technology www.ballardtech.com
Beta Transformer Technology Corp. www.bttc-beta.com
Curtiss-Wright Controls www.cwcontrols.com
DAC International, Inc. www.dacint.com
Data Bus Products www.databusproducts.com
Data Device Corp. www.ddc-web.com
Edgewater Computer Systems www.edgewater.ca
Excalibur Systems www.mil-1553.com
GE Fanuc Intelligent Platforms www.gefanucembedded.com
Holt Integrated Circuits www.holtic.com
Hytronics Corp. www.hytronicscorp.com
MAX Technologies www.maxt.com
National Hybrid Inc. www.nationalhybrid.com
North Atlantic Industries www.naii.com
North Hills Signal Processing www.northhills-sp.com
Phoenix Logistics www.phxlogistics.com
Raycom Electronics Inc. www.raycomelectronics.com
RTX Systems, Inc. www.rtxsystems.com
Sanmina-SCI Technology www.sanmina-sci.com
Sital Technology www.sitaltech.com
Tech S.A.T GmbH www.techsat.com
Teledyne Controls www.teledynecontrols.com
Tepro of Florida www.Tepro-Vamistor.com
Ultra Electronics BCF www.bcfdesigns.co.uk
Western Avionics Ltd. www.western-av.com
YED USA www.yed.com
Databus Manufacturers, Providers Report New Products, Ongoing Innovation