Hey Gang!

Recently bought a Rossi .61, front intake-rear exhaust. Along with the engine came a round, long, telescoping pipe. It is at least a foot long and the exit pipe can slide out 8-10 inches or so. What is the procedure to adjust this? I want it to be, you
guessed it, "on pipe"! Ross

Slide it in or out to get the most rpm.

Enjoy,

Jim

I have had a rossi 53 with telescopic pipe. just put on the prop you are going to use and fire it up. full trottle and slide the pipe back and forth, use a tachometer to find the spot where the pipe peaks and gives the most rpm.then secure it with zipties on the silicone coupler. use a heavy leather glove on your hand it gets hot! may have to adjust the high end needle a little to, along with the pipe. this assuming it have been broken in first of course.

When it jumps on the pipe, it will go lean.

Enjoy,

Jim

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Agreed, but not while the engine is running.

You can pull the engine into resonances that cannot be repeated from a dead engine start if you "trombone" the engine up or down with it running.

Asmund,


This information is correct, but also very partial.

It is important to verify that the engine can repeatedly recover to that maximum, measured RPM, after running at part throttle.

Finding the so-called 'peak' is done while also tweaking the needle; not only extending and retracting the pipe.
Often, setting the pipe this way result in having to pinch the fuel line momentarily, for the engine to get back on-the-pipe.
It cannot reach the base-line RPM of the system at its richer setting (to provide enough fuel for on-the-pipe operation).

This obviously cannot be done in flight, so a slightly greater tuned length is needed, for the engine to get on-the-pipe, on its own, with the main needle at a safe, not-too-lean setting.
A greater pipe length is needed, to be tuned for the lower RPM, the engine is capable of reaching on its own.

So you would want set the pipe to a length that would provide a slightly lower-than-peak RPM.

Too short a pipe can burn up your engine, if it only gets on-the-pipe when flight speed unloads the prop, resulting in too lean a mixture.

A greater pipe length is needed, to be tuned for the lower RPM, the engine is capable of reaching on its own. -quote

So once I get this thing peaked out at its highest RPM, the pipe needs to be lengthened some more to keep it from going
lean in the air, right? Now, one more question, do I keep it at full length during break-in to keep it from leaning too much at that time? Or should I try to adjust it for max RPM fairly soon, and not run it too rich, since it's an ABC engine?
Thanks for your help! Ross

Ross,


This would be the end result.
If an engine is leaned to peak, while it is off-the-pipe; when it gets on-the-pipe, its fuel needs skyrocket and the leaner mixture results in earlier ignition and faster burn, which results in pre-detonation, which is the essence of a lean-run...

In an R/C plane, the pipe must actually be set so the engine would be on-the-pipe, when on the ground.
The pipe must be just long enough so the engine will get on-the-pipe, on its own, as the throttle is advanced in static conditions.

The higher flight RPM will still be within the tuned RPM range of the pipe, so you will lose only a couple of hundred RPM.


In other classes, like C/L F2D, speed records are broken by engines with pipes set to go on-boost only in during high speed flight...

You can actually hear the engine run erratically rich... until it comes on-song - 35-39,000 RPM song...


Do the break-in with a 1" smaller diameter prop and you don't really need the engine to get on-the-pipe.

The smaller prop will allow it to spin at the same RPM rich.


Don't even think of adjusting the pipe length, with an engine that has not yet been broken-in.


A great break-in technique that will bring the engine to top condition, is illustrated in [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this thread[/link].

Hi!
Ofcourse you should adjust the pipe when the engine is running!
It's much easier to find the rpm peak that way!
You do it from behind the engine ofcourse....

Regards!
Jan K
Sweden

You got my attention. I should set up sliding tubes with my mousse can!

Ernie