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Submitted By:   Erich_Weaver@URSCorp.com
Email List:   Kolb-List,Ultralight-List
Name:   

Erich Weaver

Date:   

Jan 31 2004

Subject:   Brace for Titan Exhaust System on Rotax 912
Description:   

Some time ago I had a pipe break on the Rotax 912 exhaust system made by Titan aircraft. As everything was secured, nothing flew off into the prop, but it still alarmed me at the time, because I didnt know exactly what had happened until after I was able to land. As a result, I fashioned a support brace which held the muffler to the gear box. This seemed to work fairly well for about 75-100 hours of flight time, but I did notice a lot of wear at the joint between the exhaust pipes and the muffler, and it finally got so bad I pulled everthing off to send back to Titan. When I pulled it off, I found a few cracks at the front end of the expansion chamber that clearly were on their way to complete failure. Titan ended up replacing everything at half price, which I was grateful for, although thats still pretty pricey.

In looking at the damaged pipes and exhaust, I concluded that the damage was probably due to excessive tension in the attachment springs that mate the exhaust pipes and the muffler, as well as the rigid connection between the muffler and gear box that my support brace made, together with the ever-present engine vibration. I had put in the rigid connection brace thinking that was best at the time, but it may have been tightened down so that it exerted a tweaking force on the exhaust system that together with the vibration, eventually caused the cracking.

Titan adjusted the position of the spring retaining hooks on my new exhaust system to reduce the amount of spring tension and hopefully cure the excessive wear problems at the muffler-exhaust pipe junction. When I received the new muffler, I then modified my brace to correct the other problems. First, I added compression springs under the brace so that it was no longer a completely rigid system. Secondly, I made sure that when tightened down, the brace holds the muffler in its natural position and does not exert a tweaking force in any direction.

The following photos show the modified muffler support brace. From the bottom up, the brace consists of the following:

  • A piece of steel angle that is bolted to the gear box using existing bolt holes;

  • A muffler support piece made of aluminum stock that is cut with a flat bottom side and a semi-circular top side to conform to the bottom of muffler;

  • A U-bolt that goes around the top of the muffler, through the aluminum suppport and steel angle;

  • Compression springs that fit over the legs of the u-bolts and seat against the aluminum support piece on the top, and the steel angle on the bottom; and

  • Two drilled nuts and associated cotter pins that tighten up against the bottom of the steel angle to secure everything.

    To make everthing slightly slicker and neater, the compression springs are only partially exposed. Most of their length is hidden up inside the holes in the aluminum support piece, which are overdrilled for about half their length. See the photos to see what I mean - only a little bit of the springs is visible. The gap the springs provide between the steel angel and the aluminum support piece defines the maximum amount of travel that can be accomodated to absorb vibration and bumps.

    I had originally used a piece of thick aluminum angle instead of steel angle for the attachment to the gear box, but that soon cracked right along the length of the corner. The steel angle has worked great, although its probably overkill. If I was to do it over again, I would try aluminum angle once more, this time using extruded aluminum angle, which I have since learned is much stronger at the corners.

    I now have about 25 hours with the modifed brace and exhaust system, and it appears to be working well. For what its worth, the fellow at Titan thought the concept sounded fine and indicated there were quite a few peoople who had added some kind of additional support brace to their exhaust system. While many have apparently had no problems with the Titan exhaust without any brace, I know there are at least a few others out there that have shared my original problem. Perhaps this will help a few now or in the future.

  •  
        photo_-1.jpg View of muffler brace from rear left; note the extremely tight fit for the nut on the left side of the u-bolt, between the steel angle and the gear box.
        photo_-2.jpg View of muffler brace from top-front-left; the springs at the muffler-exhaust pipe junction are secured with high-temp ATV and aircraft cable that is bound together at the ends with Kearnies (electrical wire splicers) and finished off with shrink wrap.





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