Thrust pipe issue.
 

I was flying my L39 over the weekend and kept hearing this "tinging" noise. When I pulled it appart for storage, I noticed this crumpling near the end of the pipe on the outer heat shield. Never had it before with my previous plane or any other for that matter.
https://cimg4.ibsrv.net/gimg/www.rcu...e363e11bea.jpg
Crumpling at the end of the exhaust.
The inside of the pipe looks fine with no issues. Also, the airflow is pretty good around the pipe and the distance from the end of the turbine to the straight part of the pipe is 1". Does anyone have any idea what could have caused this? There are less than 10 flights on this bird.
Thanks,
Tone.

Im not going to say its a 100% the same as a recent issue but I would bet it is. I recently had this same issue with my pipe in a new jet, the problem is the pipe is most likely welded at both ends of the outer/inner walls. This is from the the inner wall expanding from heat and since the outer wall is not free floating at one end it stretches the outer pipe and when it cools it does this.
Who makes the pipe?

It came with the kit. I have to check when I get home tonight but I will have to check and see if the pipe was welded at both ends. I think I have had pipes made similarly in the past but this is the first time I have seen this particular issue.
Thanks,
Tone

Hi all. It does look like outer pipe is not sliding correctly. If it's welded on both end's or not I can't comment about but they need to move. Here is an example of good pipe. It finally gave away after 60 engine hours and 6 years of use. It still was not due weak pipe but loose mounting strap and engine misalignment instead. It did have plenty of broken welds and some hair cracks already.

Anyway this beeing well used one can see outer shell grinded grooves about 3mm in lenght. While taking picture it was 11C. In fight it is hundreds of degrees and it's visibly longer. This happened to have aluminium outer pipe but it makes little or no difference because of huge temp difference.

Check you pipes annually ;)

/Jyri

https://cimg6.ibsrv.net/gimg/www.rcu...c282909aae.jpg

That's a pretty good example. It was down pouring by the time I got home yesterday. I will try to check tonight and see if it is welded at both ends.
Tone

I recently bought a (NIB) BVM 1/6 F-16 and it had exactly this problem.

The outer pipe was welded at both ends and on the first ground run the outer pipe was pulled out from one end and wrinkled.

The pipe was utter crap. Not what you'd expect from BMV.

I got Joey (JET Pipes) to strip off the outer pipe and make it properly with a sliding fit at one end.


Paul

On my 5th start on a recently new plane the pipe did the same thing. At the time, when I heard it wrinkle, I first thought part of the turbine went down the pipe as the igniter failed on the next start. I also thought maybe the last former may have been too tight and when it expanded, it could not move. Also, I noticed when I put it together, that the outer pipe was a lot thinner than what I normally get. Mine is welded on the exhaust end too. I do not plan on using it.

https://cimg9.ibsrv.net/gimg/www.rcu...4f79d87522.jpg

instinctive judgement prevails of course
it sucks but those pipes have to be replaced.. do not be temped to fly with a wrinkled pipe,
.. if you have ever seen a collapsed pipe in the air, its something you wont forget as the model rear end consumes itself in fire going forward.

You guys were correct. The pipe is welded all the way around on both ends. Therefore, not allowing the pipe to expand and attract with the heat differential. Funny thin is that some of my other jets are the same way. However, those pipes are much smaller and use a smaller size turbine.
Thanks,
Tone

Seems all china pipes come this way,
smaller ones (45N ) get away with it but larger crumple...


Use box cutter and few blows with a hammer and you're done...

fixed mine and flew 30ish flights without a problem...

more pics:
https://www.rc-network.de/threads/jm...#post-12117864https://cimg6.ibsrv.net/gimg/www.rcu...530aad5e42.jpg

My dealer replaced the bad pipe for the T-1 with a Tamaz pipe. That pipe is for a 140-160N. The Tamaz pipe is not welded on both ends. In fact, the Tamaz pipe has fasteners on the inlet end that allow for movement, too. But since ... the last, T-1 that I ordered came with a pipe welded on both ends. Seems like they ought to figure this out and fix it. It is kind of stupid to design in such an issue. I assume it would be cheaper to NOT weld both ends! Here is a link to Tamaz's facebook site: https://m.facebook.com/profile.php?i...253578080&_rdr

My new Ranger also has a pipe welded on both ends. You can hear it uncrinkling every time it starts and crinkle when it shuts off.

Think I'll try cutting the welds on the old T-1's pipe and see what happens.

Voyager pipe mount
 

I'm just starting my Top Models Voyager build. So glad I happened on these posts and will check my pipe today! A question: there is one pipe unpainted ply former that snugly goes around the pipe. I assume it gets glued in the very back of the fuse and just gets painted black. what glue would i use on the pipe - or is it supposed to "float" to accommodate the expansion being talked about?
Many thanks! Len

Do not glue the pipe to the former.

Thanks, Len! Lots to learn.

For the first time build, it would be good to link up with a local Jet Guy and get that person involved. It will save you time, money & frustration, etc. In Florida there are plenty of jet guys that should and would be able to help. You just need to let them know you are asking for advice. Jets are something that you do not want to build and learn to fly in a vacuum. Good luck! But most important, have fun and don't compromise of safety.

Excellent advise, Len! Been in the modeling game for many years, and when I decided to jump into this big jet the first thing I did was to hook up with a couple of experts I met at Top Gun last year. (I've been a craftsmanship judge @ TG for 30 years). Manny Rodriguez of Aero Panda in Melboune and Henry Castellanos in Ft. Lauderdale, FL. They have both generously taken me under their wings and I am buying exactly what they recommend and will follow their guidance on the setup and get my ratings from Henry. The RCU forum has been a huge help!
Thanks again. Len