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HelicopterEngines Plugs Mufflers Fuel › 2-Cycle Pipe Tuning
11-10-2017 05:15 AM  37 days agoPost 1
EEngineer

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TX

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https://www.helifreak.com/showthread.php?t=794530&page=2
Post #34

While posting a nice diagram, this illustrates that the author left out a critical piece of info of how a 2-cycle tuned pipe actually works...

What is left out from this picture.....is the baffle within this picture of a tuned pipe that is used on 2-cycle competition pattern aircraft.

This baffle...while not shown(which is the key of how pipes are tuned....rather than where the pipe diameter starts to become narrow)...is an aluminum ring with a center hole...spot welded to the inside of the tuned pipe....BEFORE the pipe diameter narrows.

The purpose of this baffle is to "reflect" the acoustic shock wave caused by the engine's exhaust emission....which travels down the pipe...and is reflected back towards the 2-cycle engine's exhaust port..."tuned" to arrive EXACTLY as the engine's piston closes its port.

Since one cannot usually adjust the position of the baffle within the pipe(although it can be done...JR......), the length of the pipe must be adjusted...from the engine's exhaust port to achieve proper timing.

The timing is dependent upon the RPM that one desires from the engine....which determines the length....of not the pipe...but the distance of this exhaust baffle from the engine's exhaust port.

There is NO guessing involved...as the author of the post suggests.

It's simply a matter of using a tachometer to measure the RPM increase to determine the proper distance....plain and simple.

One can also further increase performance by "porting" the engine's exhaust header so that the opening of the engine's exhaust port and the header are "matched".....so that any exhaust reflections at this area are minimized.

These are the facts when using a fixed pitch prop....

It's been done and documented for decades on C/L speed....FF...and pattern aircraft.

With a collective pitch heli, things become more difficult.....because the 2-cycle's RPM changes given the blade pitch.

So, the manufacturers make a combination header/pipe which works for the "average" pitch...whatever that would be....

To make it precisely tuned for all blade pitches, would require the pipe baffle to move....within the pipe....to account for the engine's RPM change as the main blade pitch changes......which would be very complicated to implement.

Perhaps a "slider" arrangement could be made....using "feedback" from the engine's RPM via an RPM sensor....to locate said baffle in such a position where the engine's exhaust is "tuned" regardless of blade pitch.

FWIW

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11-10-2017 07:46 AM  37 days agoPost 2
InvertedDude

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USA

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EEngineer

Dang!

On serious note: Where do you find the time to do this stuff!

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11-10-2017 02:16 PM  37 days agoPost 3
GyroFreak

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Orlando Florida ...28N 81W

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exhaust port..."tuned" to arrive EXACTLY as the engine's piston closes its port.
I have heard this but I wonder what that timing really does. I know it's supposed to increase engine performance, but what does reflecting the shock wave do, in detail ?

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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11-10-2017 02:39 PM  37 days agoPost 4
JuanRodriguez

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The Villages, Florida

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GyroFreak
I know it's supposed to increase engine performance, but what does reflecting the shock wave do, in detail ?
It simply adds an "extra" amount of exhaust gas which contains unburned fuel back into the combustion chamber where it mixes with the incoming fuel..... thus, "boosting" the normal intake of fuel..... more fuel = more power...

Been there, done that and old enough to know better.....

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11-10-2017 03:32 PM  37 days agoPost 5
Pistol Pete

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Seffner, FL

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EEngineer
While posting a nice diagram, this illustrates that the author left out a critical piece of info of how a 2-cycle tuned pipe actually works..
* Did you let the "author" know?

Baffles are optional and dependent on what you're after.

Baffled: Best for low end torque and quieter at the sacrifice of top end HP (restricted air flow)

Unbaffled: Best for top end performance and louder (less restricted airflow)

I've seen tunable pipes activated (motocross) by a servo to throtle (linear) but have my doubts it was optimized to actual RPM.

~~Enjoying the hobby one flight at a time~~

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11-10-2017 04:46 PM  37 days agoPost 6
EEngineer

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TX

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No, Pete, I didn't let him know.

When that author hears a contrary opinion, he is of the sort that puts the contrarian on "ignore".....which demonstrates that he is not interested in other than what he thinks.

And with regards to RC pattern tuned pipes, they all have baffles....

I didn't realize you flew pattern in competition.

Very cool. Perhaps I competed against you!

Did you fly Masters or F3A perhaps?

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11-10-2017 04:57 PM  37 days agoPost 7
EEngineer

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TX

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On serious note: Where do you find the time to do this stuff!
Many years ago, I lived and breathed pattern competition....and was very successful to a certain degree....

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11-10-2017 07:28 PM  37 days agoPost 8
wjvail

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Meridian, Mississippi

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http://www.amrca.com/tech/tuners.pdf

Traditional tuned pipes wouldn't have any internal baffling.

Read from page 51 forward. It is an accurate if not incomplete explanation of expansion chambers. It will tell you how to design a pipe to meet your needs and offer a theoretical starting point for length. The difficulty is in determining the speed the sonic waves moves through the chamber. There is considerable valuable reading in the Two Stoke Tuner's Handbook. I'm sorry but there is no soundbite, twitter 100 character answers to two-stroke resonate pipes.

I say that it is incomplete because it doesn't cover "alternate" convergent cones - namely baffles. Nor does it cover 1/4 wave pipes or other resonate tuned systems.

The traditional double cone pipes will offer the best power. Others systems offer benefits such as reduced overall length, quieter operation, or broader power band, although typically at reduced performance.

Pattern pipes (and helicopter pipes) typically put a premium on quite operation, very broad power band, manageable weight/length, and overall engine tuneablity to include smooth running. A loud "On-Off" pipe would extract the maximum power from the engine but would be unacceptable to the average pattern flier.

Bill

"Well, Nothing bad can happen now."

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11-10-2017 11:06 PM  37 days agoPost 9
EEngineer

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TX

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As I mentioned, in pattern, the pipes have internal baffles.

This is because, in pattern, noise requirements have to be met.

In addition to reflecting the acoustic shock wave to create the tuned pipe effect, the baffle also serves to "muffle" the exhaust to the extent needed to meet the noise standards that the exhaust is tested to.

At the AMA Nats, as well as at local contests.

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11-10-2017 11:13 PM  37 days agoPost 10
EEngineer

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TX

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Good article, I think....

Will save the article for later reading.

I really didn't need to design my own pipe....as the Hatori #601 worked great and I had other pipes(forget the manufacturer's name) that were made of CF and were much lighter.

All I really cared about was that there was a definite increase in RPM, using the prop of choice, when the pipe length was properly adjusted....and a further increase in RPM when the exhaust header was ported to match the engine's exhaust port....using a tachometer.

And that the noise spec could be met.

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11-10-2017 11:30 PM  37 days agoPost 11
wjvail

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Meridian, Mississippi

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Good article, I think....

Will save the article for later reading.
It's a book. 150+ pages. Arcane I know. It will take considerable time to read and digest. As I said, it doesn't fit well in a texting world.

"Well, Nothing bad can happen now."

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11-11-2017 02:46 AM  36 days agoPost 12
icanfly

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ontario

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anyone tell you what the two stroke "tuning" business is all about yet? It's really quite simple if you imagine as the exhaust flame exits the port it contracts causing a high pressure wave in the ex pipe more accurately a wave of percussive dense air than that coming in the combustion chamber. Tuning the pipe volume and shaping the pressure ring formed in a round pipe from the exhaust combustion wave, you want to slow the intake combustion chamber air from getting out too soon. What your ultimate wish is is to shut the exhaust port BEFORE it takes the intake charge with it thereby leaving as much fuel in the combustion chamber as the motor was designed to optimize. The returning exhaust shock wave will effectively push back the intake charge before much leaks past before the exhaust ports are closed.

but what do I know, nothing.

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11-11-2017 04:15 AM  36 days agoPost 13
EEngineer

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TX

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anyone tell you what the two stroke "tuning" business is all about yet?
I guess you will attempt to do so.
the exhaust flame exits the port it contracts
No, it doesn't! And there is no flame either.
you want to slow the intake combustion chamber air from getting out too soon.
Total BS!
shut the exhaust port BEFORE it takes the intake charge with it thereby leaving as much fuel in the combustion chamber as the motor was designed to optimize.
Already done by the design of a 2-cycle's intake/exhaust timing....by the crank hollow/sleeve openings...
The returning exhaust shock wave will effectively push back the intake charge before much leaks past before the exhaust ports are closed.
You're emphasizing the obvious....captain....

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11-11-2017 05:09 AM  36 days agoPost 14
Gearhead

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Vt

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Edited

EE,
it's funny you post this,, cause,, this summer I paid a welder $40 to weld me up a Manifold Adapter (see my photo), so I can mount a 50 size Heli Muffler (Century pt #CN3038A) to an OS 61FX Plane engine,, while this 50 size Heli Pipe on a 61 size Plane Engine did not create a peak RPM as high as a Cone to Cone Pipe would, it was, very-very impressive that it did create an "instant acceleration" from Idle to a peak RPM of 13,800,, with the correct prop it would be a great combO..

the plane is a GP Shoe String, the prop is an APC 11X8..

sorry for the edit, I had the RPM wrong,,

OS 61 FX on 20 Nitro,,
with a SlimLine Pitts Muffler was.. 11,800,,,
with that Century Heli 50 size Muffler.. 13,800

Jim
Buzz Buzz Buzz

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11-11-2017 01:27 PM  36 days agoPost 15
icanfly

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ontario

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And there is no flame either.
odd, how about top fuel dragsters?

odd, what's behind an explosion in terms of pressure fronts?
Already done by the design of a 2-cycle's intake/exhaust timing....by the crank hollow/sleeve openings...
odd, aren't both ports open at the same time so the intake charge helps push the exhausted charge out hte proper port?

odd, you said I stated the obvious yet there was no reference to this specific activity of the two stroke cycle mentioned anywhere so even a monkey could see it for the first time? or was it mentioned and my mind is monkeying with me? lol.

what do I know anyway.

btw, baffles are for sound, tuning is for BACK PRESSURE.

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11-11-2017 04:19 PM  36 days agoPost 16
EEngineer

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TX

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how about top fuel dragsters?
The discussion was about 2-cycle engines.....dragsters use 4-cycle engines...try to keep up and not twist the post...

You need to learn more about 2-cycle engines.

Once you do so, perhaps you can then re-invent tuned pipes and then claim it was your idea all along that people used.....like heli blades, vortexes, and such.....

Until then.....well....

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11-11-2017 07:07 PM  36 days agoPost 17
icanfly

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ontario

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I know nothing

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11-11-2017 07:26 PM  36 days agoPost 18
JuanRodriguez

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The Villages, Florida

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icanfly
I know nothing
You are the next Einstein!

Been there, done that and old enough to know better.....

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11-12-2017 01:08 AM  36 days agoPost 19
ICUR1-2

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Ottawa, Ontario

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Admitting you know nothing leads to wisdom for some, most just remain the same.

Too bad tuning a pipe wasn't as easy as just changing the size of the pipe exhaust..

spending time, paying attention

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11-12-2017 02:06 AM  35 days agoPost 20
spaceman spiff

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Tucson

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I have played with a couple tuned pipes on planks. Mostly littel combat planes where you are limited to a small sized engine. The LHS (rip) provided these great little mouse can pipes. They were adjustable length so you could set them to your engine and prop. Very noticable improvement. If the throtle was set to anything near full, it would lock in and pull like a futhermucker. I still use one on an old Cougar fun fly plane, makes it light and more than powerfull enough. Love em.

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HelicopterEngines Plugs Mufflers Fuel › 2-Cycle Pipe Tuning
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