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1394 TRADE ASSOCIATION TECHNICAL BRIEF
IEEE-1394 is proving to be a Stalwart of Aviation Vehicle Management Systems
By Richard Mourn, Astek Corp.
IEEE 1394b (also known as beta) is completing its second successful deployment as an aircraft Vehicle Management System (VMS) network. It was first used in the F-35 Joint Strike Fighter, and now it is being used in a similar capacity in the X47B Unmanned Combat Air System Demonstration (UCAS-D).
Image courtesy of Northrop Grumman Corporation
Coupled with SAE defined AS5643, 1394b provides guaranteed quality of service with predictable latencies in real-time control applications. Because of the critical nature of the vehicle management system the X47B implements three redundant buses each with their own vehicle management computer delivering information about mission details, communication systems, weapon systems, engine controls, and flight controls. Northrop Grumman Corporation and the US Navy along with their many partner contractors selected the 1394b network standard based on the success of the F-35 program.
The X-47B employs stealth technology and has a wingspan of just over 62 feet and a length of 38.2 feet. Capable of attitudes greater than 40,000 feet and a range greater 2,100 nautical miles this autonomously air refueled UAV can stay in theater for days while carrying weapon payloads of nearly 4,500 pounds. Powered by a Pratt & Whitney F100-PW-220U jet engine the X-47B achieve high subsonic speeds and is equipped with the latest in EO, IR, SAR, ISAR, GMTI, MMTI and ESM sensor technology.
Vehicle Management System Network
1394b was chosen as the Vehicle Management System (VMS) network based on its deterministic behavior, speed, bandwidth, fault tolerance and long distance capabilities, and also because 1394b enables operational software to be remotely downloaded to network modules without removing them.
Image courtesy of SAE AS5643
Main X47B flight control and subsystem processing are completed in a triplex network of the Vehicle Management Computers (VMCs), which act as the master for each 1394b bus. The three VMCs are cross-channeled and data-linked together to provide redundancy. In addition to the triplexed VMCs, the X47B takes advantage of 1394b’s loop topology feature to provide additional redundancy protecting against single port or cable failures. If a single port/cable fails the 1394b bus will automatically reconfigure using the alternate path for communication.
1394b delivers the high bandwidth, and when coupled with AS5643’s fixed frame rate synchronization, provides the predictable latencies that allow the VMC to house all flight control algorithms and all utilities in a highly centralized structure in manner which interfaces easily to legacy buses such as 1553. The architecture also makes use of independent controllers for applications that require dedicated, high-bandwidth control loops, according to Northrop Grumman engineer Matthew Pugh.
The VMC incorporates Flight Control Systems and Utilities and Subsystems (U&S) processing that has been performed separately on legacy aircraft, according to Pugh. Components residing on the 1394b network serve the following systems:
- Vehicle Systems Processing, VMC and RIO (10 remote input/output units);
- Flight Control Systems with all flight control surfaces, including rudders, flaperons, horizontal tails, ailerons, air data probes, inertial electronics, inceptor control, crash-survivable memory units;
- Utilities and Subsystems such as weapons bay door drives, power system controllers, brake controllers, power thermal management system controllers;
- Propulsion Systems such as main engine FADEC (full authority digital engine controller), and prognostics health area managers;
- Mission Systems including standby flight display, display management computer, helmet display management computer, integrated core processor, lighting controller, communications/navigation/identification, and GPS;
- Flight Test Instrumentation, in the form of a high-speed data acquisition unit on each bus for capturing flight test data.
1394b Serves X47B's Distance Requirements
Commercial implementations of 1394b are typically limited to 4.5 meters between devices. However, the X47B utilizes AS5643/1 specified active transformers, quad cabling, connectors, and termination methods that operate robustly at distances up to 10 meters. These enhancements also ensure optimal operation in the harsh temperature and vibration environments that characterize safety- and mission-critical applications for military and aerospace vehicles.
Test Requirements Met by Commercially Available Tools
To meet the special test requirements for the X47B design, test tool providers were able to use existing and commercially available technology to provide electrical signaling and protocol level tools.
For example, Quantum Parametric's Signal Quality Tester provides transmit signal integrity and receiver sensitivity testing, and the FireSpy 1394 protocol analyzer from Dap Technology has been widely used in the program. Both test systems are used as part of system debug and sub-system qualification as well as module acceptance testing.
"The success of 1394b in this high-profile, mission-critical program led by Northrop Grumman reflects the bandwidth, distance and quality of service features enabled by the standard," said Richard Mourn, member of the 1394 Trade Association board of directors. "The guaranteed quality of service and predictable latencies provided by 1394 are ideal for these kinds of applications, as well as in the consumer, computer and industrial markets."
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