In 1988, the Boeing Co. experienced first-hand the dynamics of a natural vs. forced air-cooled, solid-state system. Following the unscheduled replacement of roughly 4,000 flight data computers due to a high incidence of failure, Boeing determined that the cooling system, which relied on forced air, needed to be replaced by a passive cooling system, which circulated air by natural convection.1 By relying on forced-air cooling, the old system had introduced far more components with no improvement in overall system reliability. Aircraft cooling systems were steadily increasing in size and complexity, with early systems weighing just 30 lb. Later model cooling systems (from the 1980s) had reached nearly 600 lb and required more electricity to run. Boeing called this “new” passive cooling system “buoyancy-induced convection.”

With much attention to detail, Boeing successfully discovered the many design changes that are required when using passive cooling. Environmental changes such as component placement and mounting all circuit boards vertically often are overlooked. By placing the hottest components at the bottom of a vertical circuit board, they have the first contact with cooler air. By paying attention to detail and creating efficient natural convection designs, Boeing successfully redesigned a critical flight control system to run cooler for longer periods of time with no fans.

Designers are no longer limited in placing avionics computers only where access to mechanically cooled or forced air exists. Boeing saw the advantages of natural convection cooling and realized its application to the next generation of “integrated avionics approach.”

Reference

1. Norwall, Bruce D. “Boeing Studies Passive Cooling For Next-Generation Avionics”. Aviation Week & Space Technology, January 4, 1988.

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