From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] Flying Our Lancairs - Using the Prop as a Speedbrake
To: lml
Date: Mon, 25 Nov 2002 14:32:12 -0500
Message-ID: <web-1886758@logan.com>
In-Reply-To: <001e01c294b8$76b4aa00$1805000a@shannon>
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Posted for "Shannon Knoepflein" <kycshann@kyol.net>:

I'll have to disagree.  The first reason is totally hogwash IMHO.  Sure,
if the spark plugs were out and you were developing no compression, it
COULD be an issue.  However, even with no fuel in the cylinders to
increase the ICP (internal cylinder pressure), the ICP is still probably
around 140-160psi, or maybe even higher.  If we were to believe that,
does this mean that everytime we start our engines, or do a compression
check, that we are doing damage to our engines by only have 160psi ICP?
That's ridiculous.  Also, it should be noted that rarely does a person
pull the mixture to idle cutoff during one of these slowing/decent
exericises, so the engine is still producing power, probably to the tune
of ICP's in the 3-400 range.  I can't see how this would ever have a
detrimental effect on rings.
   
Here is a prime example:  Take the typical sky dive jump plane versus
the typical C172 cruiser flown my joe pilot.  The jump plane climbs at
full power to 10-15k just as fast as possible, then chops power and rpm
to get back to the ground ASAP.  The jump plane wpends 70% of its life
at full power and full rich at low IAS, and 30% of its time at low
power, damaging its rings I presume if we believe that.  The C172
cruiser is flown gingerly by joe pilot and he always runs it 25-100ROP
like the manufacturer says, spends 15% of it life at full power (climb),
10% at low power (landing), and 75% at high speed cruise running
25-100ROP.  If we are to believe what is said about reducing RPM to come
down, explain why the jump plane makes TBO, and the cruiser needs a top
overhaul at 700 hours.
   
My hope would be that people would take the effort they use to propagate
these old wives tales and use that energy to truly understand how their
engine works and how to run it.  I honestly feel this one can be chocked
up and hogwash.  If anyone disagrees and has any logic to it, I'd love
to hear it, as I feel I'm always learning...
   
---
Shannon Knoepflein   <--->   kycshann@kyol.net

>  Piston ring flutter - the design of the compression ring/piston