Sender: "Marvin Kaye" <marv@lancaironline.net>
To: lml@lancaironline.net
Date: Fri, 25 Feb 2005 21:56:55 -0500
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From: Adam Molny <Adam@ValidationPartners.com>
Subject: Re: FADEC Rough idle explanation
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Just kidding:
I find it amusing that some our our listers have taken up the Donald
Rumsfeld school of self-question and answer:
Do I want a system with good BSFC? You bet I do!
Should it have fail-safe capabilities? Wouldn't fly without it!
Where can I get one? Why I just happen to know of a company...

But seriously:
I am 100% in agreement that accurate spark timing under all operating
conditions is critical to efficient and reliable engine operation. It
sounds like the GAMI system implements all of today's engine wisdom, and
adds bells and whistles that will provide real benefit to pilots. 
However good spark is only half the solution. Fuel metering is the other
half of the equation.

The TCM fuel injection has some serious drawbacks. These engines are
notoriously hard to start, and lots of bandwidth has been expended
discussing various hot and cold starting techniques. Invariably, these
techniques involve lots and lots of priming, followed by lots and lots
of cranking. The previous owner of my engine had to replace the starter
adapter and boost pump within the first 100 hours for just this reason.
We all know the negative consequences of over-priming: excess fuel
washes oil off the cylinder walls, accelerating ring wear and diluting
the oil in the sump. Too much fuel can cause hydraulic lock bad enough
to bend conrods and cause other internal engine damage. 

But over-priming is so commonplace that TCM has required us to install a
drainage system specifically to handle this problem. Am I the only one
who finds it crazy to install sniffle valves in our 21st century
airplanes? SNIFFLE VALVES! We have somehow been conditioned to accept
that it is normal for our engines to dump raw fuel on the ramp during
startup!

I want good ram air for my engine, but apparently it can't be too good.
As Rob Logan found out, if manifold pressure is too high fuel blows back
out the fuel injector screens and onto the engine. This forces us to add
yet more plumbing to equalize pressure. 

Although there are techniques for leaning, no human can possibly get it
right every single time, or constantly adjust the mixture during every
phase of flight. Both TCM and GAMI offer position-tuned fuel injectors,
but no mechanical system can ever match a computer-controlled
closed-loop system that individually adjusts the mixture to every
cylinder on every power stroke.

To be fair, the FADEC only operates in the closed-loop feedback mode
when operating below 75% power. Above that, the system switches to best
power and uses a pre-determined fuel flow map that is based on MAP, air
temperature, throttle postion, and RPM.  For normally-aspirated engines,
75% power can be maintained up to about 8000ft.

As you can see, I am driven as much by what new systems can do as by
what's wrong with today's engines. The only real solution is a system
that manages both fuel and spark. The only system out there is FADEC. If
anyone knows of another EFI system, I am all ears.

Sincerely,
Adam Molny
Legacy #151