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Avionics mass storage without prototypes

Courtesy of VT Miltope, Inc.

For a major Boeing avionics upgrade to the Air Force's C-130 aircraft, VT Miltope developed a digital mass storage system to collect high-speed digital map and ground terrain data. The system consists of a chassis-mounted processor, high speed interface and sealed, removable hard disk drive. Design requirements specified 10.1 psia air pressure and steady-state operation at 55C with short-intervals up to 71C. For operator safety, equipment surfaces could not exceed 11C above ambient air temperature.

The disk drive, which dissipates 16 W maximum, is cooled by a 102 CFM muffin fan that draws air from the front of the chassis. Initially, the design was based on a standard drive cartridge, but Coolit analysis indicated that the unit would overheat. To boost heat transfer, VT Miltope engineers added cooling fins. While the fins helped, they did not solve the problem. Using Coolit's flow visualization capabilities, engineering discovered that much of the air was bypassing the fins. To increase cooling efficiency, an air duct was added to force the air through the fins.

The power supplies, processor module , server electronics, Fibre Channel, and gigabit Ethernet chips were mounted via a thermal pad to a custom aluminum heat spreader plate that sinks heat to the chassis' aluminum right sidewall. Because of difficulties in identifying actual power dissipation for the chips, Coolit analysis was performed assuming maximum power dissipation, a worst-case scenario. Even under these conditions, Coolit predicted component temperatures would be below the maximum temperature specifications, giving VT Miltope the confidence to proceed without prototype testing. Released product testing validated this confidence.

Coolit model of a digital mass storage system for the Air Force's C-130.

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