Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Thu, 22 Aug 2002 10:38:11 -0400
Message-ID: <redirect-1702487@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: FADEC
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<<I have never yet failed to get one started
promptly - - hot or cold, so long as somebody had not left the master switch
on and run down the battery.

So what is the big deal that justifies 10 lbs of wire and multiple 50 pin
connectors just to attempt to automate something that is done ONCE on each
flight - - on the ground in a low workload environment ?

Again... is it really worth the failure modes that are interjected into the
system?

You obviously have a lot of experience in this area - - and understand the
issues - - so help me understand this?>>

George, your questions are the crux of the matter - how much of an advantage
would electronic engine management have and is it worth the total cost?  If
you just want to max out the performance the combination of a mechanical
fuel system and an adaptive ignition timing system (like the PRISM) pretty
much does it.  But we are talking here about a "FADEC" fuel/spark system and
the best it can do is approach that efficiency.

I can't really answer the original question as it would be different for
each operator.  And, yes, the biggest advantages are while the aircraft is
on the ground.  Both the Continental and Precision mechanical systems use,
as you know, a distributor with a shut-off valve going to the injectors,
allowing the fuel in the injector lines to boil off during a hot soak.  The
reason an electronic system (it has nothing to do with electronics, but has
to do with the resulting fuel system configuration) SHOULD have better hot
start characteristics is that the fuel stays pressurized right up to the
injector after shutdown, preventing vaporization.  I say SHOULD because it
is certainly not guaranteed - some automotive systems operate up to 90 psi
and some have cooling fans that run after shutdown to keep the injectors
cool.  There are flight schools that complain that if they keep shutting the
engines off they have trouble starting them and if they keep them idling
(the instructor waits in the plane for the next student) they can still have
problems and the plugs tend to foul.  A good electronic system SHOULD be
able to allow the engine to idle indefinitely and start up every time.  They
also complain that the students have lots of trouble managing the fuel
system.  Another complaint is that teaching the proper engine management
technique takes away from flight training ("why should you have to know the
intricacies of running an engine to fly a plane?").  I was taught "keep it
rich all the time - we'll show you how to use that knob later."  Any flight
safety issue would up the stakes dramatically, but is this a flight safety
issue?  Not really, although some people have been known to run the battery
down and then try to hand-prop it with very bad results.  Also, there have
been fires caused by poor starting procedures.  The flight safety issue that
I can think of comes mostly from the Continental systems and the difficult
to understand use of the boost pump - I do remember reported accidents
caused by using the wrong speed setting of the boost pump.  In-flight vapor
lock issues have, I think, mostly to do with how the fuel gets to the
engine, not how the fuel system operates.

Your other question was reliability and failure modes.  No, I haven't read
the FADEC manual, but I'll bet it would make for interesting reading.  The
10 pounds of wire and all those connectors?  I've been involved in this
technology for as many years as George has been flying and I am totally
perplexed as to how it could possibly take that many wires and connectors to
do such a simple job.  That is probably the main reason I won't buy an
Aerosance system - it is almost as though every time they had a question
with one system they just added another system on top of the first.  Just
way, way too much STUFF.  But, there ARE better ways to do it.  On this type
of project (or any project for that matter) my motto is "relentlessly add
more and more simplicity until there is nothing left."

To go to the opposite extreme you can operate without any electronics
(sorry, George) and it isn't all that bad.  Use a Precision Airmotive
(Bendix RSA) system insulated fuel lines and two independent mags on a
turbonormalized engine with George's balanced injectors.  If you run at
essentially a normal cruise condition at any altitude (constant manifold
pressure, regardless of altitude) the fuel system will remain at nearly a
constant air/fuel ratio and the optimum spark will be nearly correct at the
fixed setting.  Sure, you won't be able to take full (I just misspelled
"full" as "fool" - is that a Freudian slip or what?) advantage of LOP
operation, but you won't be very far off.  You could fly your whole career
like that and be pretty much satisfied as long as being 90% optimized is
okay.  Try to operate a naturally aspirated engine above 10,000 feet and I
think the PRISM system will give you a large advantage.

So in the end the question is whether the improvements are worth it to you.
Assuming all that complexity improves safety and doesn't compromise it.

Gary Casey