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Larry keeps trying to fly.

Hey Larry,

You're doing a good job...keep it up.



After this flight I increased the peddle throw so the tail rotor would go neutral pitch (even a bit negative) since it looks like I need more "right". It's not only me learning autos but my machine too. (BTW: If I had the factory build the kit I wouldn't be doing all this adjusting!:-) The instructions are great - if you follow them!

The repaired muffler started cracking again so I put the old Rotax one back on and noticed the fuel flow again decreased about 10 to 15%. Maybe it's tuned a little different (better?) and so I need less throttle to hover? It seems like a good thing but I'm not an engine engineer x-spurt. If you are - please chime-in. Leon said the muffler is not tuned and is used only to muffle the sound. I don't think the temps went up but I'll fix the factory muffler and make sure.

Thanks for your comments, they really help!
mybest, larry,


You continue to do a real good job with your stick time.

I'm facinated with the smooth sound of the Rotax muffler/engine. It has a lower tone, and sounds like the engine is happy. I know the diameter of the Rotax ball joints are larger than the MZ202. Did you weld a Rotax joint on the MZ exhaust manifold or a MZ joint on the muffler. Do you have any close up photos of the installation? Really interested in seeing it up close.

Keep on keeping on!


Great job! When you planning on go out over that water? Wink

I have to say as well, from all the videos I've watched on the 2 strokes, that Rotax muffler makes the engine sound great.

Well done.

I don't know about the MZ muffler, but a Rotax muffler is definitely tuned. Sounds like the Rotax muffler is close enough to your RPM and displacement to get you some extra umph. You may have stumbled across something no one knew.

If the MZ muffler is not tuned, I surprised it puts out the HP claimed. I know for fact, if some one takes the muffler off a Rotax it will not perform as advertised. A friend and I proved that with a Hi-Max and a 447.

If your temps are in the green and your not having problems with cracking, I would probably keep the Rotax exhaust on it.

Tuning an exhaust is a complex thing. I got into the math one time, and there is definitely some science to it.

James L
Is there a difference in a helicopter exhaust/engine and a motorcycle exhaust/engine other than the obvious? I have experimented with a number of 2 into 1, dual pipes with baffles, straight pipes, etc and the ones that were always by far the best performers were the tuned 2 into 1 pipes such as the Hooker Header or a Supertrapp and then that tuned pipe is dialed in to the engine/carb with a dyno and you can expect to gain at minimum of 10 HP and 5 foot pounds of torque or vise versa depending on the cam chosen and what you were looking for in power numbers as well as a sweet running and sounding set up. However I have never seen a tuned pipe dialed in with the engine just because it's "tuned". Close, but there was always a carb adjustment or a differnt needle needed or jetting that had to be done to optimize the results.

Does this work the same way with a heli muffler and is there a dyno to tune the engine and muffler to allow them to perform to their optimum levels?
Well, by the construction of a Rotax muffler, there was a lot of engineering which went into it.

There is a tube (calculated length) which is inside the muffler, which is a certain distance from the inlet. The separation distance, and the length of the chamber (inside, and outside) give the engine a wider power band than it would have with a simple tuned chamber.

At the lower part of the band, the engine uses the inner chamber, at the high side of the band the engine uses the outside chamber.

Rotax really did their homework for the engine to perform well, without a huge amount of carb tuning. Also remember that an aircraft and a motorcycle are different when it comes to required power. An aircraft is demanding maximum power most of the time, where a motorcycle is not.

Also, you can't tune a 2 cycle carb the same as a motorcycle. The needles must be set for EGT to be in the correct areas, so the engine is performing at it's maximum already. One thing that is not available on a motorcycle. If they had EGT and CHT gauges, you could tune with just those alone. Trust on the fact that if these show in the correct range, the engine is not going to be any more efficient with a different tuning.

James L

I'm sorry for helping hijack your thread. Please keep posting of your progress with the videos.

Also, if you would, start a thread about the Rotax muffler. I think it may prove to be an interesting conversation.

James L
I've always wanted to leap over wide rivers. Yesterday was my first island hop. I checked out a landing area over on the island a week or two ago and finally felt ready to give it a try.

Hey, that was great Larry. Gives you a little more room to practice in.
Small suggestion though, and this is from experience, whenever possible always make your pedal turns with the tail in the area with the least obsticles. It was hard to tell how close you were to the brush on the bank of the island but on the river side there were no obsiticles. Keep it up your doing great!! Smile

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