Rotax 912 (100 Hp) Muffler Cracks

[mnewbery]

...photo time I think. Metal springs won't dampen anything. The underside of your car uses rubber bushes to isolate the exhaust from the chassis. Something like this would be a damper.

 

Motorcycles go fine with rigid exhaust mounts. Some have quite a bit of stack length and a very wide operating range.

 

 

[skippydiesel]

When I used to ride motorcycles the exhaust systems were all fairly well mounted/supported. As with the Rotax 912 set up, the muffler(s) were the largest/heaviest part of the system and in both cases well mounted.

 

The glaring difference between my exhaust & that of a motorcycle is that;

 

· motorcycle exhausts have the muffler at the end of the exhaust system (little or no tail pipe)

 

· should a motor cycles exhaust system fail you get a bit more sexy sound.

 

· should my aircraft system fail I risk an in flight fire and or CO2 poisoning

 

My set up has a relatively long, unsupported tail pipe, hard joined (welded to muffler) that will resonate/vibrate.

 

The concern is that this resonation/vibration will cause premature failure of the tail pipe to muffler join and/or the end wall of the muffler (this is how the last system failed, after 16 years & 720+ hrs).

 

Resonation/vibration can cause rapid (a few minutes/hrs) failure where circumstances conspire to magnify the effect.

 

As I have no way of testing/predicting the performance of my assembly I seek to minimise the resonation/vibration thereby hoping to reduce the chance of premature failure.

 

 

[facthunter]

I think you are correct in anticipating a problem. Your engine is rubber mounted and free to move and all of the exhaust system has to move with it. A long tailpipe aggravates the problem. How to support it and what sort of harmonics may occur. Another option is a flexible connection that works effectively( Similar to big trucks) and mount the tailpipe to the fuselage by rubber and supports. In Europe where silencers are required to cut the noise substantially they have extended exhaust lengths and must have to resort to this method. Once you get to a cooler area you may be able to use aluminium for the components, and save weight. Nev

 

 

[skippydiesel]

[facthunter]

That's not very far. You could probably just run a small tubular stay from the rear LH exhaust Pipe to damp the vibrations and keep an eye on it. Nev

 

 

[skippydiesel]

Thanks Nev - the photo is a little deceiving as the pipe bends away fro the photographer toward the centre line of the aircraft.

 

I take it you don't think a spring from each exhaust (or list from the LH) would do it?

 

 

[facthunter]

No . Something without a lot of give. I don't even think I would triangulate it from the other side, if you keep to the top of the last bend. (highest point, and closest). Nev

 

 

[skippydiesel]

Nev ; No concerns regarding possible differences in expansion/contraction between very hot tail pipe and relatively cool bracket ? (this was why I was thinking along the lines of a spring (or two)