muffler location

by bill martin in General Tech Discussion 12 years ago

Saw an unusual situation with a 912uls installation today. Due to constraints in the engine compartment, the muffler had to be located with about 15" of space between the bottom of the engine and the top of the muffler. The owner has had no problems with the installation, but this is the question that came up. When engine torque tries to twist the engine, particularly at shutdown, the farther the muffler is from the engine, the more it tries to resist this movement. At what distance does this become a structural problem? Does Rotax have any recommendations as to the maximum allowable distance below the engine the muffler should be located?

Bill.

Re: muffler location

by John Otter » 12 years ago

John Otter

2 55 0

I presume it had better bracing than one in the standard location :woohoo:

John

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Re: muffler location

by bill martin » 12 years ago

bill martin

10 757 0

John,

"standard location" is exactly what we were wondering about. Does Rotax have any recommendations concerning location? I've seen them mounted under the engine both parallel and transversely and even once behind the engine. No apparent problems with any of them. This may be a non-issue altogether; we looked at assorted aircraft with Lycs and Continentals and some of them have have all sorts of twists, bends, and off center exhaust systems. On the other hand, they start, stop, and idle much more smoothly than a Rotax. My own muffler is about 9" below the engine and I've never had a problem. Have you seen any literature pertaining to proper mounting methods? I haven't been able to find anything.

Bill.

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Re: muffler location

by Ralph iRMT Sneer » 12 years ago

Ralph iRMT Sneer

0 38 0

In the Rotax installation manual section 11) Exhaust system page 39 it states that there is maximum allowable load limit on the attachment points and it cannot be exceeded.

There is no maximum or minimum distance or how long the exhaust system can be from the engine but you must keep in mind that there is a certain amount of back pressure that needs to be obtained at takeoff which can also change by the length of the exhaust system. Max 2.9 psi @ 3.93 in from exhaust flange connections.

Keeping the exhaust system closer to the engine is most desirable as long as you donâ€™t exceed your minimum bend radius on your exhaust pipe and you have proper heat shielding. Having the exhaust pipes at equal length will also keep your engine in tune

Probably one of the worst things you can do with your exhaust system is to route it over top of your engine! There are too many heat sensitive components on top of your engine I.E. Fuel lines /ignition modules.

DOC120323.pdf (You do not have access to download this file.)

DOC120323-001.pdf (You do not have access to download this file.)

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Re: muffler location

by bill martin » 12 years ago

bill martin

10 757 0

Thanks Lee,

I read all around force and bending limit specs and missed them entirely. As I suspected, it was a non issue. With the limits allowed, the light weight of the exhaust system, and it being about two feet from the attachment points, you couldn't beat that muffler off with a baseball bat.

Many thanks,

Bill.

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muffler location

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