The 1394 Trade Association (www.1394ta.org) says successful deployment of the IEEE 1394 networking standard in the U.S. military’s F-35 Joint Strike Fighter development program demonstrates the standard’s reliability and flexibility.
According to the trade association, Lockheed Martin Corp. (www.lockheedmartin.com) and its partner contractors selected the 1394b network standard after a trade study of other networking options, including USB, Fibre Channel, and military standard 1553.
The 1394b standard, says the association, is playing “a pivotal role” in the F-35 Lightning II program, providing guaranteed quality of service with predictable latencies in real-time control applications. Within the F-35 development program, more than seventy 1394 devices are delivering information about mission details, communication systems, weapon systems, engine controls, and flight controls.
The F-35 program evolved in response to the need to deploy fewer types of more cost-efficient tactical aircraft. Current plans call for production of 2,458 F-35 aircraft in three versions: conventional (CTOL), short take-off/vertical landing (STOVL), and carrier (CV).
A total of 14 Lightning IIs are now in various stages of assembly. The AA-1’s (CTOL) first flight was last December, and the first three STOVLs are scheduled to fly in 2008. According to Lockheed Martin, the 1394b-equipped AA-1 has completed 19 successful flight tests to date.
All systems go
1394b has been implemented in the plane’s Vehicle Systems Network due to its speed, bandwidth, and long distance capabilities, and because it enables operational software downloads to network components without the need to remove any component after installation.
Main F-35 flight control and subsystem processing are completed in a trio of the Vehicle Management Computers (VMCs), which act as the master for each bus. Triplex VMCs are cross-channeled and data-linked together. Most of the 1394b buses are looped to provide additional redundancy, so if one cable fails, there is an alternate path for communication.
1394b delivers the high bandwidth and predictable latencies that let the VMC house all flight control algorithms and all utilities in a highly centralized structure. While there are still some distributed processing functions handled by legacy buses, such as 1553, the 1394 Trade Association says 1394b is carrying the bulk of the processing load.
“The architecture also makes use of independent controllers for applications that require dedicated, high-bandwidth control loops,” says Lockheed Martin engineer Mike Wroble. The VMC incorporates Flight Control Systems (FCS) and Utilities and Subsystems (U&S) processing that has been performed separately on legacy aircraft, notes Wroble.
Components residing on the 1394b network serve: 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, and crash-survivable memory units; utilities and subsystems, such as weapons bay door drives, power system controllers, brake controllers, and 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; and flight test instrumentation, in the form of a high-speed data acquisition unit on each bus for capturing flight test data.
Designing for extremes
The F-35 design team reportedly maximized the distances served by the 1394b specification with physical enhancements, such as the active transformers, quad cabling, connectors, and termination method. These enhancements also serve to ensure optimal operation in the harsh temperature and vibration environments that characterize safety- and mission-critical applications for military and aerospace vehicles, as defined in SAE document AS5643/1. A second SAE document, AS5643, defines the deterministic, rate-based communication protocol overlaid on the existing IEEE-1394 standard capabilities (for details, visit www.sae.org).
Modifications made to 1394b for the F-35 have been fully documented and are available for other design teams who might want to use them in future programs.
According to the 1394 Trade Association, to meet the special test requirements for the F-35 design, test tool providers were able to use existing and commercially available technology to provide electrical signaling and protocol level tools.
For example, Quantum Parametrics’ (www.quantumparametrics.com) Signal Quality Tester provides transmit signal integrity and receiver sensitivity testing, and the FireSpy 1394 protocol analyzer from Dap Technology (www.dapdesign.com) 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 mission-critical program reflects the bandwidth, distance and quality-of service features enabled by the standard,” concludes James Snider, executive director of the 1394 Trade Association. “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.”
