The 11'' header on my ZDZ-80 RV-J has about 6 inches of flexible. I have been to the machine shop 2 times to repair with tig weld but the header breaks after a few minutes of running at different locations, always between 2 joins of the flexible header.

I am thinking about permanently tig welding all the flexible parts/joins together of the header.

Do you see another solution? I need a small curve in the header to connect with the canister in the fuse. Is there a kind of metal sleeve that we could pass over the flex tube?

Daniel

Scoub, how is the engine mounted? It looks like it can swing too much, or you are in a spot of resonant frequency.

You might try to tightly wind the corrugations with the white pipe fitting teflon tape. This will dampen out vibrations, and limit the free travel, so you may just stay clear of failures.

Hi Pé!
The engine is mounted at 8 oclock and i have already wrapped all the flex part with teflon tape to eliminate leaks.

I think think the resoant frequency is between 2000-3500 RPM with 26x10 prop because the vibrations stop after and under these rpms.

Daniel

Dang Scoub, there's always more problems than solutions! That's a fact of life for us.
The resonant frequency is right in the lower section of minimum throttle pull, so you will have a hard time eliminating it.
How about some extra pipe bend support, loosely and flexibly applied of course. Make it a not tight fitting bracket, but very loose, even with a slight amount of play? Silicone tube should work well here to stop the destructive oscillations.
This is the best I can think of at the moment, having seen your picture.

Would JB weld all over the flexible part work on my header? I can live with vibrations, if i can stop breaking my header..

I doubt it will. though don't take my word for it: there is always the unexpected.
Important is, to break up the relationship between the engine vibratory system, and the silencer vibratory system, This is much too complicated to handle without computer simulation for us mortal souls, though some claim they can do it, like horse whisperers.
What I intend to say is, that any system that upsets your current resonances might do the trick. Maybe soft mount the engine? that would lower a frequency part for sure, so it would play up at idle only.
Increasing resonant frequencies in general (making components stiffer) is surely not the solution, because then all should be above 150 hz, which is the max 9000 engine rpm. (this works for my tow plane, which has a heavy fuse to act as seismic mass).
Your planes are light, so the plane itself will resonate at a higher frequency. That is double trouble when you want to lower all resonances.
maybe we can pick someone elses brain about this?? I hope.

I am going to see another skilled welder this afternoon. He can do a solid header without flex for my plane.

My next project will definatly use a short header like BMB or JMB canister..

Seems like your engine is soft mounted and your canister is hard mounted.

Try soft mounting your canister.

This is the solution used in the car industry.

Scoub has his engine hard mounted. Mufflers should always be softmounted though, to allow for expansion and protect the thinwalled designs.

We replaced all the flex header today by a new stainless steel header thicker and stronger but same lenght of old one. We tig welded to the existing elbow. My canister is install into an homemade plywood bracket like MTW canister system.

This should solve all issues. Changing of propeler may help to change resonnant freqency too. I begin to thrust ZDZ with their propeller recommandation. I am turning 6700 RPM hot on the 26x10 after only one gallon, 26x12 or 27x10 is the next step.

Daniel

No more flex header for me[>:][>:]

Hey Scoub,

I've only done one canister setup, so I am far from an expert. When I ordered my 3W80 from CA, I talked to Bobby in great length about the canister set up. He said the mount on the canister is critical. If it's too firm the header will break. I made up a support from plywood/tubing, but just wasn't satisfied with it. Seemed a bit too rigid for me, so I used the mount that CA offers. I had to take it out of the plastic ring and add an extra piece of tubing to it, but so far after 80 flights, no problems.............

Your ss header looks great. I had lots of trouble trying to bend my header to fit........

I have similar set up with my canister, like your pic.
After talking with the welder, we conclude to not install the clamp on the teflon coupler. This would give a little play (1/4'') between the header and canister inside the teflon coupler for header expension.

Looks good.
On a gas engine, the teflon coupler will float anyway on the very hot header, with or without the clamps.
The end of the muffler must be restrained, so it cannot move backward.

My canister mount must be snug enough to keep it from sliding back. I don't have any kind of restraint on the rear of the canister, I'm using the spring type clamps on the teflon coupler on the header and the canister, and it hasn't moved in 85 flights.............

here is what Pé means
All my canisters installation moved backward without that.

That's it, though I would prefer something springy like a silicone O-ring or something to avoid any rattle and muffler dings.
That muffler rear is right in the exhaust gas blast, so the rear wall gets very hot.

FWIW- on very short headers-I use rigid setup and a thick centering silicone on the aft end of the muffler
On ANY tuned setup --whre there is more than 6" of header -- I weld in flex about 4" of it and NEVER put a bend in the flex. If you operate it with a bend it will fail. the tuned can/muffler must be fully, independently mounted in a compliant fixture of some kind

The modied header broke for the thirf time after only 2 flight

The KS SS elbow is so thin, i think it's not recommended for a single 80 CC engine.

you have something moving --engine?
I have used these for years!

I used red lock tite for the muffler screws and i can easy remove them without propane torch after one or 2 flight. What does it mean dude??

Ok Scoub, Now you got me spooked.[X(] My aluminum header broke on my 3W80Xi yesterday. I had 85 flights on it. Some other guys broke on like flight 10 or so. I actually thought I was in the clear.......I had the KS parts here, so I brazed( ?) them up with a propane torch and the rod that AI sent me. I'm going to fly it tomorrow. Hope I have better luck than you. The reason I didn't use the KS first was I couldn't keep it in the cowl. [>:] Working on these headers/canister set-ups is starting to test my patience.........

Your aluminium header seems thicker than my KS (1 mm). It may explain why it last 80 flights. The new 80 engines are stronger but we must upgrade the header too.

I am talking with some IMAC fliers here to find another solution.

The aluminum is thicker, but the SS is much harder.

I know what my solution will be if this header breaks. A side dump muffler! [&o]