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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.
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Ambient T = 60C
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Predicted
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Measured
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Difference
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CPU die
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71.8
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70.6
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-1.2
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PCH die
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72.0
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71.8
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-0.2
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T1 transformer
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75.6
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74.4
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-1.2
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Ambient T = 71C
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Predicted
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Measured
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Difference
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CPU die
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82.8
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79.2
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-3.6
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PCH die
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83.0
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83.4
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0.4
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T1 transformer
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86.1
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85.8
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-0.3
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