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I think you would be surprised to find that data reflects the cylinder to cylinder F/A >ratio uniformity of the mechanical systems is every bit as good as the computer controlled >systems.
For how long?
These are mechanical systems that rely on a series of inter-dependent
adjustments to stay in calibration. TCM has a 38 page service bulletin
describing how to adjust the fuel system. You are expected to perform
this procedure at every annual or 100 hour inspection. The procedure
requires calibrated test gauges, multiple engine runs and
inter-dependent adjustment points. If you get everything adjusted
perfectly, how long will it be before things start to drift? How long do
injector nozzles stay in calibration? Balanced mixture distribution is
good, but it also has to be the right mixture. Which brings us back to
leaning technique. If you have all the time in the world, you can get it
right. By necessity, this is only possible in steady state cruising
flight. What about single-pilot IFR, with climbs descents, and power
changes? In contrast, the fuel adjustment procedure for the FADEC is a single
paragraph and a single adjustment (fuel pressure at idle rpm). You use a
laptop computer to read fuel pressure while sitting comfortably in the
cockpit. You don't have to tee dial type pressure gauges into the fuel
lines, purge the lines, and secure the gauges for safety. The pressures
sensors are already there to take the readings for you. In flight, the
fuel pressure sensors feed data to the computers. The computers then
factor in fuel pressure when calculating injector duration. There is no
performance degradation due to fuel pump aging or wear. Of course, if
the pump pressure gets too far out of whack the system will alert you. The truly significant advantage of the pulse modulated port fuel injection systems is that >the engine runs better during the critical long duration portion of the aircraft operating >cycle known as "taxi".
Regards, George
I think George's point here is that ground operations are an unimportant
phase of flight. The unstated implication is that these mechanical
systems only provided accurate metering during cruise flight conditions. How many of us have had to cancel flights because fouled plugs that
couldn't be cleared during runup? To avoid this, we lean for taxi, then
enrich for runup, then lean again while waiting to take the runway, then
enrichen again for takeoff. Have any of us ever had the engine sputter
and cough when adding power because we forgot to push the red knob back
in? The same potential for error is there following a level-off after a
long descent. FADEC users report that spark plugs are always the perfect tan color,
with no lead or carbon fouling. The only wear is gradual erosion of the
electrodes. I will be the first to admit that I am not a perfect pilot. I have made
just about every mistake in the book at one time or another, and will
probably make some of them again. Anything that can reduce my workload
is welcomed. Nobody turned up their nose when moving maps came along.
Why is there so much resistance to automated engine management?
-Adam Molny
Legacy #151
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