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To: lml
Date: Wed, 31 Jan 2007 18:54:16 -0500
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Subject: Re: [LML] Re: Altitude Switch -- how's a guy to know?
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From: "John Schroeder" <jschroeder@perigee.net>
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Bob -

The Continental IO-550 has a very clear set of instructions on the maintenance and operation of the engine fuel system;  that begins with its first responsibility: the engine driven fuel pump and goes on down the line, so to speak. The service bulletin on the system makes it clear what one has to do on installation of the engine, and at periodic intervals after that. It is not overly complex and mostly involves an iterative process of adjusting the fuel pressures of the system using two direct reading, calibrated gauges. We had a mechanic set our IO-550 up according to the specs and have had absolutely no problems with idle, rough running or any thing else. It runs great.

But as Joe Bartels (TSIO) and Drew Dickinson (IO) have said, when you have very hot fuel in the tanks and it goes to the higher altitudes where it cools, one can get some vaporization. Drew had a scary one at about 10,000 after taking off from Las Vegas. The cure was a quick response by turning on the boost pump to low, as I recall.

Lancair has finally moved to a standard of 1/2" feed lines to the engine driven pump. I understand that this will be adequate for the IO's and TSIO's. The excess fuel/vapor return line to the fuel tanks, via the fuel selector comes off of the engine driven pump and remains at 1/4". It really is a well engineered and reliable fuel system for at least the ES's, and I would suspect for any Lancair flying an IO or TSIO 550.

The discussion about the altitude switch has focused on a way not to forget to turn it on and then off at about 10K'. If one forgets to turn it on and some vaporization causes a problem, turn it on to low or even high if necessary. If you forget to turn it off going down, the engine will run a little richer. I personally doubt that on a properly tuned fuel pressure system, you will notice it. Any comments or experiences otherwise would be welcome.

There is one final, and fine, point to consider about turning it on to low for takeoff. Charlie Kohler and the gurus at the Advanced Pilot Seminar recommend a higher fuel flow (higher fuel pressure on the top) to ensure lower T/O temps and internal cylinder pressures are ensured. "Gobby Rich" as George Braley characterizes it. One can always lean it a little with the mixture, but you cannot make it any richer if the engine needs it. So the boost to low on T/O would tend to raise the flow a bit and that is on the good side.

Hope this helps understanding the system. If you are interested in more depth, I can send the SB-97-3C as a.pdf file.

Best,

John


On Wed, 31 Jan 2007 16:27:30 -0500, Marvin Kaye <marv@lancaironline.net> wrote:

>  As an example of engine fuel injection problems, I submit
>   that if changes in the fuel pressure delivered to the injector
>   servo cause the engine to run unacceptably rich or lean,
>   then the injector servo is not doing its job. I don't have
>   a Continental IO-550, and I am not familiar with its operation
>   other than what I've read here. What I have read here makes me
>   think that the fuel injection is overly sensitive to fuel
>   pressure variation.