I'm about to bolt a TH .75 engine to a new airframe. I have a Macs header and tuned pipe for the engine. The airframe is not designed to go fast. I'm building a sport plane and I hope to have good slow speed aerobatics and even some mild 3D capability.

The main goal is to increase the size/diameter of the prop - go up 1 or 2 prop sizes - and maintain good mid range throttle

I've only had one tuned pipe on a glow engine and it was for a speed plane. The prop was small diameter with a lot of pitch. I tuned it by cutting the header off in 1/4" increments until it peaked out. Simple enough. Plane was fast. I was happy.

I have read about people tuning a pipe for mid range throttle but I am confused on how to do this. Isn't a tuned pipe designed for all out RPM? How would you tune it for mid-range performance? If you could tune it for mid-range performance - how on earth would you know that you were in the sweet spot? Seams to me you'd need to have 2 headers and be willing to cut both of them up.

Here's my issue:
The TH .75 engine usually turns a 13-6 prop very nicely at my altitude. I'm usually taching these engines around 10,000RPM with the 13-6 Pro Zinger wood prop and 5% fuel. I want to try and turn a 14-6 or maybe even a 15-6 with this engine on a tuned pipe. But I don't know how to accomplish the tuning process.

Here is what my brain is thinking:
Buy a 13-6 prop
Buy a 14-6 prop
Buy a 15-6 prop

Run the engine with an open header and tach each prop.

Assume (we all know where that usually leads [sm=lol.gif]) the engine will gain 10% - 15% power with the pipe. Pick the prop thats turning about 8500- 9000RPM. Install that prop and the pipe. Tune for max RPM. Fly it. That sounds reasonable, but is the pipe going to be a dog if the engine isn't at full throttle? I don't necessarily want all out RPM and speed. I want thrust from a big prop disc and I want nice throttle transition in the mid-range.

How do I get the engine to spin a 14-6 or a 15-6 prop and have nice mid range performance? Am I totally screwed up and should just set the pipe aside? Or can I accomplish the performance goals with the pipe?

Only thing I know for sure - is I'm really confused and don't want to start cutting up $40 headers until I know what the heck I'm doing.

I'd really appreciate any help from some of you guys that have practical knowledge of tuned pipes and tuning experience. I can read theory until I'm blue in the face. That gets me nothing. I need help from you guys that actually know how to do it - not somebody who is guessing - I can guess on my own.

Go with the Macs Aero tuned or quiet pipe. Stay away from the marine pipe.

The aero type pipe is not so "peaky" and has a broader tuning range.

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Here is some info.
http://www.osengines.com/faq/faq-q652.html
Jeff

You might want to look into a "throttle pipe" from justengines or westonuk.

A throttle pipe will give an increase in performance over a standard muffler, dramatic noise reduction, linear throttleability, (non-peaky) as required in 3D and funfly.
Email: [email protected]

You can buy one "Throttle Pipe 60 / 75 tapped" for the exhaust spacing used on the Tower .75, attach it to your engine and go fly.

WestonUK also make them.

You can also make one from one of the aluminum "beer/softdrink" bottles as I can't find anyone here in the states that make them commercially....

You wouldn't need to cut your header as the "beer bottle" just slides front to back like a trombone slide to tune. Try-it-n-Fly-it...kind of thing.

http://www.westonuk.co.uk/westonuk2_193.htm

I hope this helps.

More info.
http://rcboat.com/pipe.htm

Tuned pipes are pretty terrible for the type of throttling you need for 3D. I would however recommend the Macs one piece muffler.
They throttle nice and linear without the on/off power-band that tuned pipes have.

Guys,

I am sorry for not being more specific in my first post. I do have the aero tuned pipe from Macs.

I'm not interested in pipe theory. I've already read every single link you guys provided here.

I'm not interested in spending more money to buy some other pipe or muffler or exhaust divertor.

I ALREADY have the header and the pipe. Already spent the money about 2yrs ago on this combo - just never installed it and tuned it because my interests changed and I sold the plane (pattern ship).

Skip forward 2yrs. New airframe. I'm planning to fly it relatively slow. I still have an almost new TH .75 engine and I have a brand spankin' new Macs header and AERO tuned pipe.


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I'll try and simplify my question:

Can I make this combination of pipe and header work to spin a 14-6 prop on an engine that normally would spin a 13-6 prop? Can I have any mid range throttle control or will it be rich and gurgly when it's not "on the pipe" ?

Use the header with a aluminum beer bottle mouse can muffler. The pipe wont do what you want no matter what; the engine will run bad enough that a stock muffler would be better.

So your mind is already made up. Why ask?

Tuned pipes put you into higher RPMS on smaller props. Just the opposite of what you want for 3D. Larger lower pitched props.

You will make it worse than the stock muffler like TFF said.

No, my mind is not made up. I'm not clear on exactly how to tune or if the manner in which I'd like to tune is even possible.

I told you in my first post that I had already purchased the header and pipe. Then I went on to indicate that I wasn't sure if the pipe could be tuned to the parameters I was seeking. So I started asking questions.

Don't know how you made the ridiculous leap of logic that I already had my mind made up because I asked some questions.

Being as you already have the parts, try it in the manner you described. Typically the pipe would not need to be cut. You may need to lengthen it a little?

It will help a little. The greatest effective gain of the pipe would be at higher rpms though.

Well, I've got a giant box full of empty aluminum mousse cans too........ and I have the header. I've got about 50 different mousse cans. Some as tiny as 1.5" diameter x 3" tall. Some are significantly larger 2" x 8" or even 3" x 10". I save every aluminum mousse can, hairspray or perfume can my wife brings into the house.

I've been doing google searches and also searches on RCU for the last couple hours (based on advice from TFF - my mine is NOT made up yet Thumbskull) and trying to determine the correct volume of a mousse can.

I'm sure there is a calculation of formula to tell what size can for a given engine displacement. I got my calipers out and measured the stock TH .75 muffler. It's about 16 cubic inches ..... equal to 21x the volume of the engine.

Then I looked at the Bud Light aluminum beer bottles and calc'd one of those at 62 cubic inches. I see guys using those for 100cc engines. A 100cc engine is about 6 cubic inches - so the Bud Light can is only 10x the volume of the engine. But some guys use a can for each cylinder. So each 50cc cylinder gets a Bud Light can - a ratio of roughly 20:1. And then some guys are using a Y header and running both cylinders into a single can. Back to the 10:1 ratio.

This is why I'm even more confused than when I started. [sm=lol.gif]

How does higher rpm relate to the greatest effective gain of the pipe?
Attached is what we did with a tuned pipe to bring the peak power from 17k to 10.5k rpm look at that huge gain in power at that 10.5k rpm point, from 1.4 hp to about 1.72 hp. It is almost back up to the same power it had at the 17k rpm point. This was for an 10cc FAI F3A Pattern engine.

Being as you have the header and the cans, why not try some 20:1 variations and see what you get?

Thank you Konrad.

I also disagree that peak RPM is the "holy grail" of a tuned pipe. It's been shown that you can over speed the engine and loose power on a given pipe. The piston closes the exhaust port before the rebounding sound wave can push the escaping fuel charge back into the combustion chamber.

We all know that RPM's is power. But too many RPM's on a given pipe volume can actually hurt performance.

I'm calling Macs tomorrow and ask him about his theory in designing the aero tuned pipe. Was it designed for all out RPM? Or was it designed for a more mild boost across a flatter curve?

I'm gonna do that. I'll start fabricating mousse cans this week after work. I'm going to start with 10x the engine displacement and try every combination I can come up with.

I need some 3/4" aluminum tubing. Most of the cans I have are 3/4" opening at the mouth.

To be fair to others, what I show is not done with inexpensive pipes. The Hanno pipe is wonder of design second only to the pipe sold with the Webra Race Red Head for pulling the HP into the lower rpm bands.

Experimentation that is the name of the game in this hobby. Otherwise you are just a check book modeler.

All the best,
Konrad

The Aero Tuned pipe has no sharp peak like a boat racing pipe.

The 10cc ones I've been around had a broad range and made a very nice OS engine.

I thought OS made OS engines. Are you saying Mac's makes OS engines? []

Good grief....

You know one comedian to another, that was my attempt at humor. I won't quit my day job!

All the best,
Konrad

I fail to see the connection here or what gave you that idea?

Is this a Hanno pipe? Or is it a pipe that os commisioned from Hanno?? <hr /><span class="ultrasmall">kochi
</span>

The Hanno pipe would be a good candidate for the TH 75

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I have had luck spinning a larger prop with less pitch, tons of pull, less all out speed. Such as and 11X4 on a fox 40 in a spad saturday night special. If I knew anything about hovering back then, it would have done it with ease.