I was reading the instuctions for tuning a pipe on the Macs Products website. http://www.macspro.com/tuning.asp

It talks about shortening the header in 1/4 inch increments until you reach peak RPM, which is determined when you start to see a drop off in RPM. What I would like to know is, if your application will require require a length of silicon tubing between the header and pipe, How does this affect the overall tuning? In my case I plan on a Supertiger G90 in a CG Ultimate with the pipe inside the Fus.

Thanks for your thoughts and experiance.

Well, if you use the Macs method of cutting the pipe and running the engine until you experience an RPM drop then you have already taken in account the small space between the pipes when you use a silicone connector. I usually leave about a 1/4" space between the header and pipe so that they don't rub and create nasty black goo.

Of greater importance is the pipe parts not touching, and causing radio
interference. The parts rubbing is not causing the black goo. The goo is
from the castor burning in the pipe, and turning black. (thanks Chuck )

That "pipe rubbing" bit is another Internet Old Wives Tale.

Dave.

Let me add some additional information I left out originaly. If for example, I needed to add say 3 inches of flexible tubing with some curves in it to get from the header to the pipe. Does this 3 inches need to be accounted for when adjusting the length of the header? It seems as it if should be because total length is what tunes the system.

Flyboy Dave, have you ever polished aluminum? When you rub on aluminum it produces black residue, and lots of it. Give it a try, you'll be amazed. You can start with the pipe on your .61RF

Yes, you need to include the length of your extension. True pipe length is determined by measuring from the exhaust port to the halfway point of the converging cone of the pipe. Or the first baffle of a muffled pattern pipe such as the type available for the big Webra pattern engines.

Thanks Guys for the input

Yes, ChuckN....I am aware that polishing aluminum will produce black, but contrare....
a loose, or rubbing pipe won't produce all that black goo....flight after flight. It simply
isn't possible....think about it.

Dave.

Actually, I am thinking about it. [sm=wink.gif]
I'm thinking about the tuned pipe header setup I machined for an MVVS 40 GRRT a few years back that coupled metal-to-metal (ala motocross and kart racing pipes). And I'm thinking about all the tuned pipes I ran normal fashion with a silicone coupler. The only pipe setup that ever produced black goo was the GRRT and it all came out at the joint. And I'm thinking about the engines I've seen where their mufflers came loose in flight and all the black goo that oozed from the fretting surfaces between muffler and crankcase. And I'm thinking about the full scale airplanes that I work on for a living and all the black goo that comes from sheetmetal fretting together. (Ever notice the black streaks that trail back on a jetliner's flaps?) And I'm thinking about my O.S. 45 FSR that spun it's rod bushing at the big end and my friend's ST GS-45 that broke it's wrist pin, both engines spewing black goo out the exhaust at the time of failure. I've even seen wounded engines spew black goo when running 100% synthetic oil.

Ok, ChuckN....

....sounds fair. Where does all the black goo come from when nothing is rubbing?
I have three planes that spew....all have tuned pipes. Now I'm starting to think it
comes from the extra castor I sometimes put in my engines. I took an engine
down last week that was spewing. I thought perhaps it was spinning a bearing.
It was mint inside....two years running wide open at 14K. The bearings were perfect.
The whole inside of the motor looked like I dipped it in clean castor. I was gonna
replace the bearings just for drill, but put them back in. The black is burnt castor.

Back to the pipe joint thing....yes, if you put some oil on two pieces of aluminum
and rub them together....it will turn black. In the same vein, if you push a piece of
iron into a grinding wheel....it will make sparks. However, when you stop pushing
the iron....it quits making sparks. Likewise it is not possible for a tuned pipe joint
inside the rubber coupler to rub together forever, and make a ton of black goo....

....week in, and month out. Flight after flight, after flight after flight. What is to keep
pushing the two pieces of the pipe together, when in fact....they are being pushed
apart by air pressure.

Therefore I contend....it is not possible for the joint in a tuned pipe to spew the
goo indefinately.

Dave.

Heh heh.....You go Dave.

I must confess however...that one time I did a slow fly-by and sure enough...standing on the wing
was a small, begoggled gremlin...busily forcing the pipe into the header. Surely, if that were allowed
to continue, he'd have been feeding the pipe stinger into the exhaust port before long and that would
have been an end to the whole works. A quick outside snap roll took care of him. <G>

Seriously though...you really ought to leave a 1/4" or so between the header and the pipe. No reason
under the sun for anything to rub, IF the pipe is installed correctly. If it were rubbing..the radio interference
created would likely put a swift end to any "black oil" concerns one had.

'Race

Yo, 'Race....you have the Gremlins too, huh ? A clove of garlic stashed under
the pilots seat usually keeps them little buggers at bay....heh heh heh .

There is a 1/4 to 3/8 gap between my header and pipe as well. You've seen
the OS demise thread....Chuck Auger let the cat out of the bag, and confirmed
my suspicions about the burnt castor. There have been a couple threads about
black goo in the past, and the final answer has been loose mufflers, aluminum
rubbing and such....and I too took the answer at face value. However after
thinking about it, and my own extreme black goo spewences (is that a word)
the rubbing aluminum theory is just not possible, just that simple.

Next flying session I am going to do the unthinkable and run a tank of 20/20
PowerMaster YS blend through two spewers, and see what happens. So please
forgive me in advance for my evil deeds. I put a YS .91 FZ in a WM Mustang, and
am shooting for the 'Buck and a half Club"

Once again, I'm going to use the clever Fidel disguise for this endevour, so don't
tell anyone. I'll let ya' know what happens.

Dave.

looks more like a william robison diguise to me


dave

Dave...

Since this is an internet forum, it is imperative that one DEFINE "black oil"....

It's 2004...and things need to be made VERY clear. <G>

The black oil one gets from aluminum rubbing is considerably "blacker" than that
produced by castor carbonizing in the pipe. The latter looks more like BOSCO chocolate
syrup spewed on the airframe.

I'll warn you though, that it does not taste nearly so good as BOSCO. After licking the plane clean
on one sunny afternoon, I did indeed spend the rest of a perfect afternoon perched inside the club
porta-john....wishing I'd just cleaned the oil off with paper towels like everyone else does. A VERY
up front and personal demonstration of the lubricating qualities of castor....in humans!

This of course leads me to the paper issue, and what paper is "BEST" for such situations?

Heaven forbid...I don't want any scuffing or peeling going on in MY nether regions...

Out of the porta-john and back to models...

Perhaps loose metal fittings are common on others planes, but they're rooted out of mine
LONG before the plane goes to the field.

I'm going to try the garlic trick Dave, but I've heard that some types of garlic can make the
engine run lean in the midrange, and in extreme situations...cause the liner to peel?

<GGGG>

'Race

Fair enough I've personally never had a pipe rub the header, but I keep them spaced apart just in case.

Guys, got a question for yaz...I was at the local R/C car hobby shop awhile back, and we got to talking about pipes. Guy I was talking to said there was another guy who blew up a few engines in rapid succession. They couldn't figure out why at first, but I was told they finally figured (he said) that the reason was because the pipe was rubbing the header, and the resulting black metallic crap was going back into the cyl. and doing damage(!) Do you think the (is it) reflected wave or pulse could push gunk into the cyl./ piston enuf to damage things? Car pipes are the same, only different, right like 1/4 wave, or whatever the tech. term is?

I think you would blow lots of plugs before you toasted an engine. It doesn't take much metal swirling around in there to blow the plug.

And out of all my pipe running days, I have to agree with Dave that if you butt a pipe up to the header enough for it to rub, it'll rub enough off to make a gap right quick and quit rubbing. I always put a length of aluminum tubing inside the silicone coupler to keep from having a long piece of unsupported silicone tubing...the silicone burns out quicker and also pulses if left open to the exhaust.

I've pulled those pieces of aluminum tubing out to make a cut and you could see where it had rubbed the pipe/header. I had lots of hours on lots of engines, if the rubbing was causing my engines to blow, or my radio to glitch, I'd have known it.

Just my observations. I did recently have a spat of glitches on a piped engine powered plane, but that header was run up inside the pipe...I don't know if that's what caused the glitches, but when it goes back up it'll be (almost) butted up, not slid into.

Another thing...There are pipes that connect directly to the engine with just a silicone O Ring sealing the exhaust. There is no way to keep the pipe from rubbing metal-to-metal on the engine. If this caused radio glitches, looks like these engines would be unusable in RC planes.

That's kinda what I figured Chuck, about blowing the plug first, not the engine. Who knows though, maybe it caused the plug to blow, then the element fell down into the cyl. and wiped the piston/ sleeve? Whatever, could be the guy just didn't know how to adjust an engine. And about the glitch thing, it doesn't seem to me that non-ferrous metals cause glitching. Steel parts yes, but in my experiences anyway, alum. or brass, etc. contacting ea. other doesn't make any real ammount of "noise" (does it? maybe a radio guy would know better) Back in the "old days" (I'm talking mid '70's when I started) we were extra careful to avoid any metal to metal contacts, but these modern radios are much less sensitive to that.