Rotax 582 Expansion Chambers

[Earthboundmisft]

Anyone have any actual experience with dual expansion chambers on a 582?
Tinkeritis and a new expando design program has me thinking about hidden power potential.

 

[scottessex]

I think it will add more weight, give you more power above the rpm that we fly at.

 

[bryancobb]

Here's a little info for an application that may not be like yours but a lot can be learned about 582 exhaust tuning in general.

 

[Wiplash]

A 583 in a stock single piped Ski-Doo Formula gets around 90hp, the same engine piped around 110hp.

The problem with piping a 582 for gyros is the narrow power band. The Mini-500 could benefit from the power band because of the more consistant throttle setting. In a gyro or any other fixed wing aircraft, the wider the power band the better.

Don't forget the dependability factor. The engine will last longer at 65hp vs 90hp. .

 

[Earthboundmisft]

Thanks fellas.

 

[Earthboundmisft]

Has anyone rolled their own expando's?
I did, 27 years ago. RD 400. No computer.

 

[themonarch]

Be Carefull

Be Carefull

I suggest that you do not go to any non-Rotax exhaust expansion chamber for a Rotax aircraft engine application. This will open up a can of worms when it comes to calibrating the carbureators for the additional fuel that will be required for combustion chamber cooling. The first rule for a change to different expansion chambers is for a carbureator recalibration. Then you need to dyno test your new engine to find out it's power band. You have to be absolutely sure on how to re-calibrate, because now you will most likely have a more finnicky engine. What you need to decide is this: are quicker rpm's and a few horsepower worth the chance of an engine failure? Please be carefull.

 

[bryancobb]

Having access to a dyno IS most a plus and takes all the guesswork out of it.

Building a beautiful pipe that is not properly tuned FOR WHAT YOU ARE DOING is a waste of effort.

Always, always, always re-jet for proper mixture.

 

[Vance]

Some thought on two stroke pipes.

Some thought on two stroke pipes.

In my experience having a dynamometer does not take the guesswork out of it.

Years ago I was associated with Williams Pipes.

We tested every pipe that was available for the RD350.

We found that virtually every one made less power than the stock pipe.

It turns out people can feel a change during acceleration better than they can measure the acceleration.

The all narrowed the power band and came on with a rush.

People would dreamily say what “a rush it is when it comes on the pipe!”

We also went to a drag strip and found the same results, the stock pipe made the most power.

A different pipe does not always require different jetting and some pipes required a leaning of the main jet because of the pressure wave back through the carburetor. It seems that the venturi and main jet work both ways.

We often found a fog standing off from the carburetor and changing the air box often made more difference in the jetting than the pipe.

The pipe must work with port timing on a two stroke so the idea that someone without a dynamometer will find the perfect combination seems unlikely to me.

My friend Toney Williams studied two stroke exhausts for more than 30 years and there was always cut and try involved as he found the best combination of compression, crankcase volume, port timing, exhaust and jetting.

I burned up many hours playing on dynamometers and all I really learned is there are no answers, only more questions.

My advice is to find some way to measure the performance, try a pipe and see if you like it being careful that your seat of the pants feel is not influenced by the new thinness of your wallet.

Thank you, Vance

 

[bryancobb]

Vance,
This is an area where you probably are one of the most experienced people on here. Your work with going fast on motorcycles probably immersed you in trying to squeeze every drop of horsepower out of an engine possible.

I guess I worded what I said wrong. When I said "takes the guesswork out," what I was trying to get across is, with access to a dyno, the results of all the trial-and-error work can be SEEN graphically on the plots, and all experimenting can be done on the ground.

Yes there will be a lot of trial and error but it is done safely ON THE GROUND and it can be tested to see if it reaches your goals without risking your life. I think most if not all dynos have very high quality EGT, CHT, Coolant, Fuel Flow, and Air Flow sensors which are way better that what is in most 2-stroke powered aircraft.

Unlike motorcycle racing, in aviation, getting the last ounce of horsepower out is probably not the goal when someone discusses putting a pipe on.

The goal may be one or some of these:
* Make the engine have more reserve power for use at higher density altitudes
* Make a helicopter engine have more reserve power for better low rotor RPM recovery
* Move the torque curve to better suit a propeller or airspeed range of a particular aircraft
* Change RPM/Diameter/Tip speed of the propeller to meet your needs I.E. faster cruise, better climb, noise abatement, clearance of parts of the aircraft structure.

Deciding your goal(s) of installing a pipe first, and then dyno-tuning the pipe by trial-and-error to make sure your specific goals are met is the only real way to get any benefit from a pipe.
The o.p. was asking about "dual" pipes. I would suspect that the benefits of each cylinder having its own pipe would be erased by the added weight. A single pipe, fabricated from thin aluminum, or even carbon fiber would go farther toward reaching your goals.

If the published plats are true, in the PEP literature I attached, Dennis' plots of the results shows his goals were met. He was trying to get a little more reserve power for hovering and low RPM recovery, and takeoffs over obstacles. He said he wanted to shift the torque curve of the 582, to better suit the Mini-500. He said he wanted fewer jetting changes to be needed with weather and density altitude changes.

All of my flying experience in the Mini-500 was pre-PEP pipe days so I have never flown with one. I look forward to having one on the ship I am building. There were a few very hot days in 1997 when I was hovering at full throttle and had to point my nose a little right of the wind and wait for a gust just to hop over a 4' fence and get into the pasture for a low performance takeoff. Then there were nice days where I was able to leave with a max-perf takeoff over the 40' telephone pole like in the video. A pipe would have been nice.

 

[bryancobb]

I fantasize about buying Barney Bahle's PEP pipe and creating a 10-12 pound lighter carbon-fiber/aluminum version that looks something like this...

 

[bryancobb]

Stock exhaust versus PEP.

 

[bryancobb]

Jetting changes with PEP as determined by the factory.

 

[mark treidel]

A previous hanger mate of mine put a R & D (I believe that was the Brand name) expansion exhaust on a MZ-202 (on a trike).
It has never worked right and created a 'flat spot' in the operating power band right where the aircraft ran for s/l flight. Either it kept 'burping' at 5200 rpm an wanted to die out or would surge when you gave it fuel and became 'jerky' with overpowering. He could never get that 'spot' ironed out no matter what he did. Rejetting, carb rebuilding & syncing, etc.
Nothing worked. In utter frustration, he finally sold the trike.
Although this was an MZ engine, it is not unlike the 582 in power relation.
Personally, I dont think the trade off is worth it. If it ain't broke....

 

[bryancobb]

Mark,

He's lucky he didn't get hurt. In the air is not the place to se if it works.

Something as simple as +1 or -1 degree of prop pitch can make the difference in whether you are able to climb or not.

 

[Vance]

We always had very specific goals.

We always had very specific goals.

Because the engine would be run close to maximum for several hours reliability was paramount.

Particularly with the flat trackers a broad power curve was important.

The Pep pipe looks good for several reasons.

A tapered head pipe has value in getting an expansion chamber exhaust to work.

The various tapers look appropriate.

I like the mount.

He has the stinger coming out of the middle of the pipe. This is not necessarily a feature but it indicates the designer knew something about two stroke pipes because it is counterintuitive.

If you are going to replicate the Pep pipe I would recommend that you copy it exactly particularly the tapered head pipe. Even small changes can make large changes in how it works.

In your fantasy carbon fiber pipe the stinger looks too short and there is no muffler. I suspect it would be loud making a very annoying sound.

An interesting thing about expansion chambers on a two stroke is that if you put the stinger entirely inside the pipe it will work just as well and be quieter. Just a little bit of an after muffler can reduce the sound a lot more. It doesn’t seem to matter where the stinger exits the chamber.

In my experience jetting recommendations are a starting point. Two strokes seem particularly sensitive to density altitude.

Another interesting thing about two strokes and altitude is that because the speed of sound changes with altitude a pipe designed for sea level air at Daytona will not work well at the 4,400 foot altitude of Bonneville. I know this from multiple personal experiences. One of the most successful two stroke racers at Bonneville was based in Denver.

It is not hard to get a dynamometer to lie and often the translation through the typewriter causes some further divergence from reality.

Regards, Vance

 

[mark treidel]

Vance,
You are sooo right about the altitude/D/A differencial. It is critical!
I believe I may have know the person you refer to.

Barney,
The prop was pitched to hold the engine to 6500 rpm's ..same as the 582.
It had plenty of power for a trike, even at this altitude but the 'flat spot' remained
an ever present & constant irritant. It flew nicely but the sound was 'tinny and hollow', especially at start up....sounded like it had washers chattering inside the muffler all the time.

Having never tried one personally, I cannot comment further although on my trike,
I had a standard 582 which flew flawlessly for over 500 hrs. before I sold it in 2008.
It flew circles around the MZ. all things being equal.

 

[bryancobb]

Fantasy

Fantasy

If you are going to replicate the Pep pipe I would recommend that you copy it exactly particularly the tapered head pipe. Even small changes can make large changes in how it works.

In your fantasy carbon fiber pipe the stinger looks too short and there is no muffler. I suspect it would be loud making a very annoying sound.

Vance, I WILL copy every detail and dimension of the PEP. Either in aluminum or carbon-fiber. The picture of the carbon pipe I posted was just as a reference for general appearance. I feel Dennis probably did his homework and did a lot of testing on the dyno. I would not go off in another direction other than weight reduction.

Dennis claimed that once you have the PEP installed and jetted for your elevation by his table, you would not need to seasonally change jets any more. Helicopters rarely climb much higher than 500-1000' AGL.

 

[bryancobb]

Here's some more of Fetters' 582 expansion chambers for his current UAV.

 

[PW_Plack]

...The Mini-500 could benefit from the power band because of the more consistant throttle setting...

Todd, when I listen to helicopters operate, it sounds as if the throttle opening varies widely, and it's the RPM that remains constant.

In this application, the engine would always be "on the pipe," even when at reduced power settings, because pipe tuning follows RPM. A flat spot at 70% RPM would be no big deal, because the only time you'd see that RPM was while first spinning up the blades or during cool-down.