From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: IO-550 operation 
To: lml
Date: Thu, 05 Jun 2003 23:32:32 -0400
Message-ID: <web-2404596@logan.com>
In-Reply-To: <52548863F8A5D411B530005004759A933920A8@QBERT>
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Posted for George Braly <gwbraly@gami.com>:

David, 
   
Let me comment on a couple of things in your message.
   
First, putting the mixture full rich at the top of descent at FL 200  - - is
really not all that great an idea.   If there is anything on this earth that
has been responsible for premature cylinder damage from rapid thermal
changes, it would be that practice.
   
Second, it is, in my view, much better to simply push up the mixture and the
prop when the engine and aircraft are in the low power condition in the
pattern or on short final.  Easy to train for.   Easy to do.  
   
If you properly train to do go-arounds in the proper sequence - -   red
knob, blue knob, black knob - - - which should be reflex-automatic - - this
should be adequate double check.
   
People who are properly trained to do proper go-around power ups that want
to land with the prop at 2300 and the mixture at cruise settings can do so
safely.  The engine will produce more than enough power to meet the FAA
climb gradient requirements in this condition - - even if the pilot forgets
to push up the prop and the mixture.
   
If you have the airplane set up at 2500 RPM and 50F LOP, and you pull the
throttle to 15" MP - - the engine will not die  while airborne.   It MAY die
on the ground after the airspeed has decayed below about 50 knots.
Otherwise, if you shove up the MP to 39" - - the engine will run fine and
produce lots of power - - even if you forget the mixture and the prop.
   
As to operating the engine at 2700 RPM - -  well.... we actually do
certification testing and write engine certification test plans.   You are
mistaken  in assuming that the engine was operated at 2700RPM  for 1700
hours as part of the certification test plan.  It was not.  The basic
certification requirement only requires a 150 hour engine run - - and not
all of that is at full power/full RPM.   There is often further testing
done, but it seldom exceeds a further 150 or 200 hours and that is not all
at 2700 either.
   
Now, having said that,  2700 is not a bad deal.  It is always  a bit less
efficient than 2500 or 2400 RPM, and at very high altitude, the higher RPM
probably reduces the prop efficiency enough so that it is self defeating to
operate at 2700 verses 2500 or 2400 RPM.   One is better off to push up the
MP 2" and keep the RPM at 2500 than the other way around - - at least,
assuming one is operating with reasonable CHTs and LOP.  
   
Regards,  George