From: jlw@world.std.com (James L Walker)
Subject: Re: Tuned Pipe Questions
Organization: The World Public Access UNIX, Brookline, MA
Date: Wed, 19 Aug 1992 17:03:29 GMT

In article <1992Aug18.195206.17141@news.eng.convex.com> mccrorey@convex.com (Martin McCrorey) writes:
>I am about to use a tuned pipe for the first time.  This will be a
>Super Hots with a rear exhaust OS 46 ABC.  Before I start on the
>fuselage, I would like to establish the header length as closely as
>possible.  I have built a bench for running in and tuning the engine,
>but I have never bench run an engine or set up a tuned pipe before, so
>I would like any advice I can get.  In particular, I have the following
>questions:
>
>    1. Should it be broken in without the pipe, and if so, with what?
>       (There is no muffler with this engine, so I can't use that,
>       and I am going to run it in my garage, so I won't be running
>       it with an open header, either).
>
There was an article in RCM this month on the construction of the q'icksilv'r
in which the guy recommends running the SF in with the muffler.  No reason
given.  It could be so that you don't have to mess with the pipe to keep
the engine running at the same time as you are running it in.

>    2. How do I break in the engine on the bench?  I have been advised
>       not to "four stroke" an ABC, apparently because they run too
>       tight when that cool, so I am planning to vary the speed a lot
>       while keeping it a just lean enough to hit every time.  
>
I keep hearing this lately.  I've always run my ABC engines in on one tank
slobberingly rich.  It seems to me that if you are trying to loosen up the
sleeve and piston, that running them too tight is just the ticket.  After
the slobbering rich tank, I run another tank and alternate between 5 and 
15 clicks of the optimal needle setting every few minutes.  This is the 
standard method at my field.

>    3. What is a good header length to start with?  I am more 
>       interested in a strong climb than top speed.  I looked at
>       another similar pipe, and the manufacturer recommended
>       9.25" from glow plug to the fattest part of the pipe.
>
This construction article in RCM also says that MAC sells a pre-tuned
pipe with header, etc for the SF version of this engine.  Perhaps they
also sell one for the RF?  See your SIG catologue.

>    4. I plan to start with a 10x6 prop, although I will probably try
>       a variety of slightly heftier props when the plane is flying and
>       the engine is run in.  Is this a good starting point for this
>       engine?  I am also curious to know what kind of RPM to expect
>       from this engine with varous props (and how it will compare
>       with the side exhaust 46 with muffler).
>
Again, from the article:

	10x6 Master Airscrew
	Muffler 12,900-13,100
	Muffled Tuned Pipe 14,900-15,200
	Tuned Pipe about 200 rpm faster than muffled tuned pipe

I run my Enya .45 CX with a 10x7.  As I understand it this slows the engine
down and reduces prop noise.  At my field we are pretty paranoid about 
sound, so I would always raise the pitch before the length of the prop.

>    5. Is a 10% nitro, castor/synthetic mix fuel OK for break-in?
>
It has been said here before that once you go up in your nitro content, your
engine loosens up for the higher running temperature.  When you then reduce
the nitro content your performance will be worse than when you started at
that content.  Check the oil content of your fuel.  It should be about 20%
especially when running the engine in.  Most of the fuel I buy is 18% oil
and I add 1/3 cup of synthetic oil per gallon to make up the balance.

>    6. Can a put a tank pressure fitting on the side of the pipe
>       and have it work OK, or do I really need a pump?
>
I've seen several tuned pipes work with tank pressure.  The pressure line
is a little long though.

>Thanks,
>Martin