Avionics News October 57-10 - 50

TEMPERATURE TORTURE
Continued from page 49

Observed issues
Pull out the instruction manual or spec sheet of
that new tablet or smartphone common with pilots
today. Down in the specifications: a list showing the
temperature range within which the device manufacturer
knows the device works.
Different components may each come with their own
temperature limits, but it's the sum of the parts that
dictate the known temperature range within which the
device has been shown - through testing - to function
normally.
Today's advanced avionics systems suffer less from
extreme cold - and only slightly more from insufficient
cooling in hot conditions. Heat, it seems, is a problem
for digital electronics in consumer, industrial and
commercial products. But compared to a few decades
ago, temperature extremes must truly be extreme before
today's avionics systems begin to balk from the effect of
environmental extremes in both directions.
To prove the temperature tolerance of modern
avionics, manufacturers engage in testing across an
extreme range of conditions. That means exposing
system hardware to temperatures down in the range of
-30 Fahrenheit to -40 - where the Fahrenheit and Celsius
scales merge. Minus 40 on one scale is also -40 on the
other.
Avionics makers today subject their systems to
temperatures in the 150-degree range, according to
several manufacturers. It's truly a change from decades
past. At least for aircraft electronics systems.
Cold causes few problems for modern digital
electronics compared to the electronics used 30 years
ago and more, according to input from several avionics
makers. Heat, however, is an enemy of electronics in
general - and more so for the fine connections embedded
in the tiny digital circuitry inside chips.
For example, the MEMS used in solid-state gyro
systems - AHRS and ADAHRS - have a temperature
sensitivity that can be offset with proper calibration,
a step common to the production of modern attitudesensing systems. Extreme temperatures can also cause
failure of the fine wire connections within some MEMS.
And letting some electronics sit in a heat-soaking
environment can cause issues, as well. Excessive
temperatures are simply an anathema to electronics.
Just ask an electronic flight bag user about leaving
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AVIONICS NEWS

OCTOBER

2020

their tablet computer on the glareshield or seat for the
sun to heat it to the point that it shuts itself down.
Ask any iPad, iPhone or Android tablet user about
their experiences using their devices in the cockpit.
Chances are you'll hear a few experiences that occurred
from the pilot leaving the device up on the glareshield,
sandwiched between two unhealthy heat sources: the
sunlight streaming through the windshield and the
electronics in the panel, just below the glareshield.
These tablets are prone to overheating in such
conditions since their mere operation generates heat
within their tightly packed shells and fan cooling is not
usually a feature. Moving these devices, popular for
running electronic flight bag software, into the shade
and, even better, into the flow of cool air typically brings
them back to life.
Several avionics companies noted that heat can cause
display screens to seemingly fade and lose the rich colors
as the mercury rises above 120 degrees Fahrenheit.
Keeping cool
Channeling cool air around installed avionics long
ago became a standard solution for many aircraft -
particularly avionics-heaving aircraft predominantly
used in business-turbine aircraft. The cooling became a
significant issue when avionics makers started fielding
new integrated avionics systems using CRTs for displays
of everything from flight data to engine status and
multifunction displays.
CRTs require space, a lot of electrical power and
plenty of cooling to keep them operating within their safe
temperature range. Cooling sources varied, with scoops
in some aircraft, cooling fans in others, but both installed
to circulate cooling air through the avionics installed in
the panel. After all, it's typically hotter behind the panel,
where all the electronics work.
But not all instrument panels provide a path for the
free flow of air to cool avionics, especially with many
smaller light-sport aircraft and experimental, amateurbuilt aircraft. With digital panels the dominant standard
today, keeping these panels cool can be as much of a
challenge as it can be for turbine aircraft.
To assure their products enjoy a sufficient flow of
cooling air, many avionics and accessories makers
integrate cooling fans into their products - assuring that
the product gets air flow, albeit what often may be air as
hot as ambient cabin temperatures.
The issue of excess heat can even exist during cold
weather. Maybe it's because the aircraft sits on a sunlit

Avionics News October 57-10

Table of Contents for the Digital Edition of Avionics News October 57-10