Date: Tue, 9 May 2000 02:47:00 -0400
From: Marshall Michaelian <73663.457@compuserve.com>
Subject: More on Engines
Sender: Marshall Michaelian <73663.457@compuserve.com>
To: "INTERNET:lancair.list@olsusa.com" <lancair.list@olsusa.com>
Message-ID: <200005090250_MC2-A44E-619E@compuserve.com>
Mime-Version: 1.0

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Okay Fred, I'll bite the bait.  You write:

<<  I flew leaned to peak in cruise at maximum
cruise typically at 11-12,000 feet with EGT's around 1450F, and head
temperatures of 400F.  At 800 hours I had to overhaul three cylinders
due to burned exhaust valves>

Much data on this subject has recently been developed by George Braly at
GAMI in Ada, Ok.  To summarize, up until recently (with GAMI's) no one
could properly fly at peak or lean of peak, because we were using poor
single point temp probes and when we flew at peak some cyl were already
lean of peak and others were still on the rich side.  If we leaned even
more, then things started shaking because of the greater discrepency
between those cylinders LOP and those ROP.  Consequently we could only fly
ROP, otherwise temperatures would be too high and you'd end of burning
valves, as you did.  Today with accurate (+/- 1 deg) 6 point engine
monitors and with GAMI injectors we can experience LOP operation in which
the EGT are 75 to 100 deg LOP and the CHT are cooler than when operating
100F ROP.  This means that valves see the same  lower temperatures as
operating ROP (100deg ROP or 100deg LOP = same temp), and more importantly,
cylinder heads operate at much lower temperatures.  Needless to say, fuel
flow is also significantly reduced.  The only negative when  operating  at
those levels LOP is the speed goes to hell.  So, in a turbocharged plane,
you increase the MP up to the level required to get back to the same
airspeed as when operating 100deg ROP.  Now for the magic.  When you do
this, you'll find fuel flow of course increases as you increase MP, but for
the same airspeed, the fuel flow at 100deg LOP is still less than the fuel
flow 100deg ROP at the same airspeed.  Experienced GAMI drivers use wide
open throttle (WOT), LOP, as standard operating procedure (SOP),  and use
the red knob to determine how fast they want to fly, within the constraints
of 1600deg max EGT on any exhaust probe, and 380 to 400 deg max on any CHT.
 And therein lies the problem for Cont/Lyc engines in LIV's at high
altitude.  It is difficult to fly at 25,000 ft 75% power even running
100deg LOP (with the cooler CHT's) and still remain under the 380 to 400
deg max CHT.  If we could do that, then the aircooled engines would live to
their TBO.  But that will not happen with or without balanced injectors. 
Liquid cooling comes at a price, but the upside potential (speed and long
engine life) is there.  

Ok, now I've got to get back to work installing the radiator in the
underbelly nacelle so that someday soon I can enjoy the benefits of liquid
cooling.

Marshall Michaelian (SQL, 80% LIV-P, Eagle 540V8)

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