From: bloom@inland.com
Newsgroups: rec.models.rc
Subject: Re: Tuned Pipe Questions
Date: 21 Aug 92 08:08:46 CST
Organization: Inland Steel Company; East Chicago, IN

In article <Bt8q1t.EpJ@world.std.com>, jlw@world.std.com (James L Walker) writes:
> 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:

A .46 engine is too small for a Super Hots!  You should be running a 
.60".  

>>    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).

Don't break it in inside your garage!!! You can poison yourself from the 
carbon monoxide.  Any bench running should be done totally outside.  For 
bench running, I'd just put the head pipe on and leave the expansion chamber/
muffler off.  


> 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.  

This is correct!!!  Run it in a rich 2 cycle, not a slobbering 4 cycle.

>>
> 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.

Running an ABC engine slobbering rich means the piston to cylinder clearance 
is too tight and it can gall and scratch the piston and or peel the sleeve 
chrome plating (nickel plating on the OS).  In addition, you are yanking 
the piston up and down under a lot more stress, which can break the connecting 
rod.

 
>>    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.

Start with the stock length header and stick with a propeller size to do all 
your testing.  Cut the header off 1/4 inch at a time until your rpm is 
maximized on the ground.  Use a tachometer.


 
>>    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

Once again, if this is really a .60 size Super Hots, then you have the wrong 
prop and engine.  No way is a .46 (pipe or not) going to pull a Super Hots 
thru the air at the kind of theoretical speed a 10x6 will generate. For the 
.40 size Hots, this combo is just fine.


> 
> 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.

Break the engine in on the same nitro content you plan to use later.  During 
break in you are trying to mimic the heat and thermal expansion that the 
piston and sleeve will see in service.  
> 
>>    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
> 
> 
Newsgroups: rec.models.rc