gentelman

can someone kindly advise wht is the procedure / thumb rule for setting up os55 with a tuned pipe?

i did it once many years ago and allways had engine cut....
i know that you need to move the pipe fw/bwr untill u achive the correct rpm...?

still, i would like to get tsome basic procedure on how to do that correctly please.

my setup is a CF tuned pipe - dont know the exact size, and OS55 or my 46

kind regrads

gadi

Basically, you'll need to make sure the engine is fully broken in, then set it up on a stand or your plane or whatever.

Run it with no muffler, no header and get a tach reading at full throttle. (Put your earplugs in)
Then put your header on, and your pipe. Make sure there's only a very little gap in between the pipe and the header. Fire it up and run WOT. The RPM should be close to, or a little less than the reading you got with no muffler. Cut the header little by little...and each time fire it up and run WOT and note the tachometer. The RPMs should go up with each cut...until you've gone too far. Then you'll have less power, and an overheating problem...so be careful.

If you get to a point where your satisfied with the extra power, stay there. Otherwise, you may end up having to buy a new header and start all over.

You ought to use the same fuel you'll be using all the time too when you're doing the tests

Also to consider: You must richen the needle valve before each start and then lean the engine to peak RPM. USE A TACH! You cannot run the engine and "trombone" the pipe to find the proper length. You must start the engine, set the needle, and tach it. Then you can decide if you want to shorten the header. Shorten it in 1/4" amounts. When you have no RPM change, lengthen the pipe by 1/4" (you'll make the gap in the silicone tube a bit larger), and fly the system.

Listen very carefully to how it's running in the air to make sure you have the pipe and needle set correctly.

If the pipe is too long, the engine will trend rich. If it's too short, it will trend lean and could cause detonation, damage to the glow plug, or even burn a hole in the piston. Yes, we've seen the results of a too-short pipe coupled with detonation!

Here is an Java script that I like to use to give folks an idea of how the various variables effect pipe performance, selection and sizing.
http://www.mh-aerotools.de/airfoils/javapipe_en.htm

All the best,

Konrad

The old method was to put on a prop a pitch less than the in-flight prop. For example a .60 engine, 11x6 instead of a 11x7 prop. You then tune the engine and pipe to run on the ground OK with the 11x6 prop. The engine unloads in the air, so the 11x6 prop simulates the unloading in the air to some extent.
Then with the 11x7 prop on, you fly the plane and as Bax mentioned you have to listen closely to determine if it needs some more tweaking or not.
But that would get you close for the fine tuning then.
In the past it was popular to hook up a AUX channel on the RC system with a servo connected to the main needle, so you could tweak the needle a little in the air. You could get a 1/4 to 1/2 turn on the needle that way, But usually all you needed was one or two clicks on the needle, so the servo was quite adequate for this purpose then.
As mentioned a Tachometer is really important for this too.

gentlmen

first, thank you very much for the extraordinary answers..coulsnt being better

second, some Q? that i dont understand?

1. WOT- what do you mean by that?
2. "cut the header? - meaning to shorten the aluminum header after each try till i get the wanted RPM? kinna difficult to do at field...
3. GAP - you mean the gap btween the header and the oioe? the gap the silicon tube covers? this gap should be as small as possiable?
cant i leave the header as is, and just move the pipe forward and backwards to get the RPM's?


reagrds
gadi

Wide open throttle =WOT
Yes, cut the header instead of the pipe. Very easy to do with a pipe cutter, A hack saw also works well just be sure to clean any chips and burrs prior to assembly. It is often a lot cheeper to replace the header if you cut it too short. As you mentioned you have a carbon pipe this is very true, even more so. Also you want to start the divergent cone as soon as is practical.
With most after market pipe set ups you will want to maintain a gap (2 mm to 3 mm) so that the header and pipe don't rub causing particles that could foul, damage your piston and cylinder fit. You want to keep this gap small so as not to allow the coupler to expand like a balloon or be exposed to the exhaust heat and burn.

As Bax said you can't "trombone" the pipe. It doesn't work. There is too much stuff going on. A pipe is a very simple yet dynamic apparatus! For one thing you will need to adjust the mixture strength as the flow dynamics change. You really can't do this while tromboning the pipe.

It's not difficult to cut the header at all. It's 1/16th inch (if that) aluminum. Bring a fine toothed hacksaw, or even just a hacksaw blade.

Regarding the gap, what will happen is the silicone will blow if there's too much gap. It can handle a small amount of exposure, but if there's a lot the heat will eventually break it down

I have to ask what are you trying to do? A pipe can act a lot like a gear box moving the torque curve to where you want it. As you can see in the picture the pipe has brought the horse power from about 17.5K RPM down to about 11K RPM. Peak horse power is actually down, but one can now use a more efficient prop (larger).

On glow engine tuning it is wise to cut off a few pieces of different length, and please do not discard them. They can be inserted into the silicone tube coupler again to lengthen the header if so needed.
open space between coupler inserts should never be more than 1/4" (6mm)
In gas engines, a long teflon coupler can be used like a slide trombone, because the coupler has very little flexibility. In glow engines that use silicone couplers this is not possible. The silicone is too flexible to allow lengthening without inserting some piece of rigid tubing.
For best tuning, you do need the lengthening option as well, so you get best in flight results after trial and error.

gents

thank yoy for you wise answers ands expreince
will try to the best and if isee that it is going not well i allow my self to adress you again.


shalom from sunny Israel

gadi