Optimizing avionics for harsh environment

Courtesy of VT Miltope, Inc.

VT Miltope's Mass Memory Server 2 (MMS-2), which resides in the aircraft's hot, cramped avionics bay, is a lightweight, networked, solid-state storage platform that is part of the helicopter's Avionics Management System. It serves as a digital map server and collects aircraft data including usage, maintenance, vibration monitoring, and engine, rotor, and balance information in order to monitor aircraft health.

Cooling the MMS-2, while protecting its interior electronics from sand, dust, rain, humidity, and salt fog, required a separate, "dirty" conduit for air flow and heat exchange. Two rear fans pull air into the chassis from the lower front panel. The air then runs through a short, wide duct below the circuit boards before exhausting through the rear. A baseboard with its processor module and power supply board is cooled using custom aluminum heat spreaders, which pull heat from the processor chipset and memory. Attached to heat spreaders are finned heat sinks that project downward into the cooling air flow of the internal duct.

Harsh environment placed very tight limits on modeling accuracy. Coolit modeling ensured a reliable cooling system design across an operating temperature range of -40C to +71C. After a few tweaks to the design of the ducting and placement of fans to achieve lowest chip temperatures, Coolit predicted that all major components would remain within their manufacturer's specifications with a healthy thermal margin. This modeling outcome later was verified by thermocouple measurements on pre-production hardware.

 

 

Ambient T = 60C

Predicted

Measured

Difference

CPU die

71.8

70.6

-1.2

PCH die

72.0

71.8

-0.2

T1 transformer

75.6

74.4

-1.2

 

 

Ambient T = 71C

Predicted

Measured

Difference

CPU die

82.8

79.2

-3.6

PCH die

83.0

83.4

0.4

T1 transformer

86.1

85.8

-0.3

MMS-2 functions as map server and monitors helicopter health. It is designed to stay cool in the helicopter's hot and cramped avionics bay.
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