Question for the aircraft maint experts

[widgeon13]

I know this is really off topic but I have a lot of respect for the depth of knowledge here and also know that there are some aircraft enthusiast/maint people here so I would appreciate some recommendations.

I have a recurring problem with the exhaust pipe tabs on my Maule aircraft. They (tabs) keep breaking at the weld on the pipe, probably because the stainless pipe is too thin to hold up under the stress and the connection is too rigid. I'm hoping I can get some constructive feedback on how to solve this problem. The pipes have to be able to move some but need to be secured at the lower point.

This is what the broken tab looks like:


This is an old pipe and clamp that I have from previous break, it has been welded/ repaired.


The lower end of the pipe just needs some support, it's not a structural issue and the top end of the pipe is pinned at the exhaust connection and secured with a clamp but is designed to allow for some movement.

I'm open to any suggestions or dialogue and can add additional pics if helpful. Unfortunately, the hangar is not the most comfortable place these days with temps going below 32 deg.

[A930Rocket]

Looks like part of a muffler hanger strap. Auto parts places carry them, but maybe an aircraft parts place has better quality ones?

[widgeon13]

I'll be checking auto parts, probably no better quality at aircraft shops but the price will certainly be higher. I can't remember what the 2"OD stainless pipe cost the last time I got one but I do remember it almost knocked me out of my chair. Of course they charged me for the bends, that's what drives up the price.
Thanks for the recommendation.

[James Brown]

As a A&P, I can't recommend anything but the manufactured parts for your certified aircraft. This is a common problem on Maules. There are several STC's that fix this problem. But, there not cheap and if you do the work, the napa option would be ok. (don't tell anyone)!

[widgeon13]

Originally Posted by James Brown

As a A&P, I can't recommend anything but the manufactured parts for your certified aircraft. This is a common problem on Maules. There are several STC's that fix this problem. But, there not cheap and if you do the work, the napa option would be ok. (don't tell anyone)!

I know what you mean. Thanks, I've already forgotten what you told me.

[Jeff Higgins]

Tim Hancock is your man. If he doesn't see this thread, pm him.

[MT930]

It can be TIG welded avoid any sharp angles rounded or chamfered parts are less prone to cracking. The I.D of the tubing should be back gassed with argon to prevent stainless granulation or (sugaring). With the design is just a matter of time before it cracks again. I would look in to the STC to see how they addressed it.

[widgeon13]

I'm going to be calling Maule on Friday. Not sure they have addressed it but I'll find
out.

[944Larry]

Remember when you go to changing things that an IA does an annual inspection on your a/c every year. Is he a guy you use a lot and would cut you some slack if he spotted some "non-approved" work if he thought it was safe? Any modification would require a PMA, STC, or a field approval to be approved. I'd just TIG weld the thing whenever it broke and look at it as one of the annoyances of being an aircraft owner, kinda' like some of our Porsche problems!

[widgeon13]

All excellent points.

That may very well be what I end up doing.

[944Larry]

Still, a really cool airplane though!!!

[Tim Hancock]

A few more pics would be nice to help get a feel for the location. If it were mine, I might think about simply tig welding on a new tab, but maybe make it a tad thicker and wider (coped out to provide a wider amount of contact with the tube). You might also think about welding on a wall doubler first out of something a tad thicker than the .035 wall tubing to create a "pad" to weld the bracket to. You can buy a small piece of 321 sheet to make the bracket or you might "cheat" and use some 304 stainless (I have scraps laying around so I would use 321).

That pipe looks pretty solid it will tig weld just fine with stainless rod.... once the pipes get much older and corroded, they can get to a point that weld repairs become less suitable. Weld repairs to non heat treated aircraft parts are not uncommon, so long as you use sound aircraft welding techniques.

I would refrain from using auto muffler straps or changing the basic design..... The feds don't go for that kind of stuff (often for good reason).

I just made some pipes for my cafe racer using some surplus 321 tubing I picked up at Oshkosh. I love the stuff, but it is stupid expensive (+$20 per foot last time I priced some new 321 from an aircraft supplier). In thin walled light weight exhaust systems, it holds up better than 304 in extreme temp use with corrosive exhaust gases and can be used in the "as welded" condition.

[widgeon13]

Tim,
Thanks for the input. The second pic of pipe (my pics) above has had a larger piece welded on to the old pipe to create a pad. Perhaps I'll remove the current pipe and take both to the welder and have him duplicate the angle while placing the old tab on to the pipe with the pad.

Here are two more pics.

This is the right side. Looking up into the cowling.


Can someone tell if they are using 304 or 321 to make these pipes? I'll be talking to Maule Friday so will ask them what they use.

It is a great plane and other than this and some peeling paints, it's been very reliable so guess I shouldn't complain. Weather isn't conducive to flying now so have time to get the job done.

Appreciate all the input from everyone.

[James Brown]

321 gets a nice light brown color on it when heated. just looking at the pictures it looks like there is some tention on the muffler pipe at rest, I would bend that stress out of that muffler pipe prior to fixing it. no need to "help" it to crack again. does that make sence? Also, a L bracket attached to the rubber mount and fixed with a hose clamp around the pipe might offer some insurance. ala Cessna heater box.

[URY914]

A little JB Weld should take care of that.

[Normy]

Boy oh boy man....all I can say is that you should follow the FAR's-

Exhaust leaks on light aircraft are VERY dangerous! Carbon monoxide is always an issue, since the engine is in front and the exhaust pipes usually end in front of the cabin, unlike an automobile. But the real problem has to do with fires. Every year you hear about light aircraft having smoke in the cockpit and often times it is because part of the exhaust system came apart and super-heated exhaust gas starts the rubber on the hoses or wires under the cowling on fire. If your Porsche catches fire while you are driving, you just stomp the brakes, pull over, and get out with your fire extinguisher and try to put it out. That takes a few seconds. It doesn't take a few seconds to land your Maule- it takes minutes, and in that time some very un-good things can happen.

I can't emphasize this enough- repair the exhaust pipe the way it is supposed to be done. If that means constantly re-welding that joint, then so be it. That or sell the plane and buy something else.

Aviation isn't inherently dangerous- it is just very unforgiving of any carelessness or neglect....

N

[Joeaksa]

Am really surprised that your crankcase vent tube in the last picture is not scarfed on the end. As well please make sure that you have a hole drilled in the tube to provide some venting in case the end of the pipe ices over.

Tims suggestions are spot on. The mount is breaking from vibration at a certain freq and thats what you need to fix but doing so by using the maintenance manual or AC 43.13 limits you. Still having it break and flop around is not going to help either so...

[dar636]

I would email Tim Boughner at Tim's Aircraft Repair:

Tim Boughner
Tim's Aircraft Repair
Vaughan Ranch Airfield
tim@timsair.com

Close to Seattle. He knows Maules very well and has a repeatable field approved repair for this Maule installation that you can present to your local FSDO for approval on your aircraft. The Maule design is poor to say the least. Good luck.

Seattle A&P, IA, DAR.

Matt

[widgeon13]

Matt, Thanks, I'm familiar with his name, appreciate the recommendation.