Re: Refrigerator monitor ideas?

["Robert L Bass" <no-sales-spam@bassburglaralarms>]

> How do they detect wing icing on airplanes?

There's an audible warning device in the cockpit of almost every airplane called a "stall warning."  Of course, by the time that one
goes off the icing problem is pretty bad.  :^)

> I remember reading about one design that
> used an inflatable rubber wing surface that
> flexed and allowed the ice crack off but I
> don't recall how they determine wing icing
> depth...

There are two methods I'm aware of.  Some use engine heat to warm the leading edge of the wing.  Others use pneumatic boots to break
it off.  There are three main types of sensors to detect wing ice -- magnetostrictive, electromagnetic, and ultrasonic.

Magnetostrictive sensors use a vibrating coil.  As ice accumulates the frequency of the vibration decreases, signaling the pilot and
(in some systems) automatically inflating the deicing boots.

The space shuttle uses an electromagnetic device called a resonant microstrip patch antenna.  There's an article on it at
http://www.findarticles.com/p/articles/mi_qa3957/is_199905/ai_n8851736

> I do seem to recall that Palm 90 crashed
> here a while back because the pilots
> didn't know how badly iced they were at
> the moment of takeoff...

Wing ice is a major problem.  It can build up very fast when conditions are right for it.

> I believe someone used diluted deicer
> that actually froze up on the wing surfaces.

That is not what happened.  It was a 737.  The pilot made several mistakes.  First, he used reverse thrusters to try to push back
because the airplane's wheels were bogged in heavy snow at the ramp.  Then he tried using the hot exhaust of the airliner ahead of
him to melt ice on his own wings.  Instead of removing the ice, it allowed the water to refreeze on the trailing edges of his wings.
The deice boots on a 737 don't help with ice on the trailing edges but that would not have mattered anyway.  The pilot didn't even
use his deicing system on or before takeoff.  The first officer repeatedly told the pilot they were in trouble (or words to that
effect) but he refused to listen.

Using reverse thrusters inappropriately may have been a contributing factor.  The engines sucked in a lot of storm debris (ice,
snow, etc.) at the gate.  That reduced the available power.  Low power combined with ice-laiden wings caused a stall on take-off.
BTW, for those who don't already know it, when an airplane is said to have "stalled" it does not mean the engine stopped.  It means
that the wing has stopped generating sufficient lift to maintain flight.

Someone I know claims to have snap-rolled a brand new 737 at low altitude after having borrowed same from Boeing.  :^)

--

Regards,
Robert L Bass

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