Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Tue, 09 Mar 2004 13:26:42 -0500
Message-ID: <redirect-3070923@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: hot starts
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<<I am flying a Lancair with an IO-360...I would really like to hear from
anyone and everyone on how they go about a hot start.>>

<<fuel off at the selector valve>>

I fly behind an IO-360 as well, but with the Precision Airmotive system,
which I believe functions identically to the on in yours.  First I've found
it helps to define "hot start."  These engines cool down rapidly and even in
an hour the cold start technique might be more appropriate - that's where
I've found the "phase of the moon" comes it - to figure out when to use the
appropriate technique.

A number of things are useful to know:
1.  The fuel that vaporizes into the engine is primarily in the lines from
the distributor to the injectors.  That happens fairly quickly as there is
no valve in the injectors to stop a vapor bubble in the distributor from
pushing fuel into the injectors, especially if the distributor leaks.  I
think this leakage (the variation from one unit to another) is what makes
hot starts so individual.
2.  The amount of air drawn in during cranking is almost independent of
throttle position.  Having the throttle cracked a little has pretty much the
same effect as having it full open, so there is no real benefit in having
the throttle open all the way during a hot start.
3.  Incidentally, I've found a significant improvement with fire sleeves
around all the fuel lines, especially the line from the servo to the
distributor.  This mostly benefits idle quality after the start.
4.  Fuel flow (mixture in the rich position) is independent of engine
speed - it is set for a normal idle speed.  Therefore cranking with the
mixture rich will provide too much fuel and that's why all starts are
accomplished with the fuel shut off.
5.  Shutting the engine off by turning the fuel off at the selector doesn't
empty the system of fuel.  As soon as the fuel pressure goes to zero the
engine will quit running - the lines from the selector all the way up to the
distributor and out to the injectors will still be full of fuel.  The
mixture valve should be leak-free when in the off position as otherwise
Cessnas like mine would fill with fuel from gravity.  If the mixture valve
doesn't shut off completely it is time to get it replaced.
6.  It slightly helps to pull the throttle completely closed as the engine
shuts down, but it has nothing to do with the fuel system.  The engine will
shake in its mounts slightly less with the throttle closed as the
compression pressure is reduced.
7.  When cranking, you might as well keep cranking for several seconds as it
could take that much time to get the mixture from a too-rich condition to
one that will burn.  Cranking a few turns and then stopping doesn't help
anything.
8.  I've found that if it doubt as to whether the engine is still hot you
might as well give it a little prime - not much, but just a touch of fuel
flow indication.  That will flood the engine even more if it is already
rich, but the extra fuel will be cleaned out in a couple of extra crank
rotations anyway.  This is especially true with a hot engine on a cold day,
and even more if parked into the wind.  How hot the engine is doesn't
count - what counts is how hot the fuel distributor and injector lines get
AFTER the engine is shut off and with the engine into the wind they might
stay cold.  Under these conditions even a truly hot start may not have the
engine flooded and some prime will be necessary.

Hot starting usually requires a fair amount of cranking, but with reasonable
technique it should start without fuss.  I hear some people talking about
the added return line from the servo being a good thing, but I guess I'm not
convinced it is worth the added complexity.  It mostly cleans up engine
operation immediately after the hot start and that is mostly an
inconvenience.

Just my opinion(s)

Gary Casey