additional information on turbo issues

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From: George Braly
Subject: IAT

New Induction Air Temp probe in the Cirrus Perspective

The Cirrus Perspective has something new under the cowl. It is a direct
reading measurement of the induction air temperature immediately
upstream of the throttle plate.

This air temperature, commonly referred to as the "Induction Air
Temperature" (or IAT) is often confused with either OAT or less often
with compressor discharge temperatures (CDT). The CDT is the temperature
of the air coming out of the turbocharger's compressor section - -
measured before the air has gone through the intercooler. But the CDT is
not measured in the Cirrus. Really no need to do that.

But even if you pay close attention to the Garmin engine display, you
will never find any displayed indication of the IAT.

So what is it for?

The short answer is that the IAT provides the data that works the magic
to drive the LOP target fuel flow indicator in the Garmin engine display.

As any of you who may have happened to spend a weekend with the APS
engine management class know, manifold pressure and RPM control the mass
air flow through the engine.

That is well and good - - but to get it really "right" you need to also
know the temperature of the air flowing in the induction system at the
point where the MP is measured.

But if you know the rate of mass air flow through the throttle and you
know the fuel flow - - then it is just a few short steps away to get the
GARMIN to calculate and display a "target" air/fuel mixture ratio.

This is the magic that has enabled the ultra simple "set it and forget
it" mixture magic in the Cirrus Perspective.

Curtis Sanford wrote:
"But if you know the rate of mass air flow through the throttle and you
know the fuel flow - - then it is just a few short steps away to get the
GARMIN to calculate and display a "target" air/fuel mixture ratio."

And only a servo away from losing the mixture knob completely?

Trip Taylor wrote:
With about 50 hours of Perspective time, I am in awe of how this plane
is incrementally better in so many ways from the '07 model. The little
magic triangle and the better reaction of the digital gauges are a good
example of this. Thanks for the hard work.

George Braly wrote:
"... a servo away" from losing the mixture control completely.

Well... that and a half million dollar DO-178 software certification
effort!!! And a lot of redundant hardware.

That's all.

Marc Wiese