Muffler Mounting

Muffler mounting is one of those things that is likely to be put off to the last minute, mostly because the builder things it will be an easy job, best put off until all the difficult stuff is solved. Not so!Muffler mounting is critical and not at all easy.

The simplest and most basic approach is side-mounting. On the prototype Gyrobee this was achieved using a flat plate of mild-steel sheet stock, extending from the engine mounts (engine side) upward at an angle tp near the top of the muffler. Slots in the plate (with a small groove to clear the ridge in the case) allowed the muffler to be attached to the plate with large stainless hose clamps. This system was simple and cheap, but the plates would develop cracks after 2-3 seasons, requiring replacement. Failure was never catastrophic, so you simply had to look at the plate during preflight - something you should do anyway. Attachment of the muffler to the exhaust manifold was via the standard Rotax springs, which were themselves a source of aggrevation. High-temperature silicon seal and safety wire were both required to make sure spring pieces did not feed into the prop in the event of a broken spring. We never lost one, in part because we treated the springs very carefully, but such incidents are not uncommon.

The first thing we did in looking at a new mounting system was to ditch the troublesome springs. California Power Systems has a "Exhaust Ball Joint Conversion Kit" (#30385, $44.95). We first ran into this approach when flying trikes and decided to us the hardware on the new gyro.

For the actual mounting system, we chose a clever system from California Power Systems (#12204, $99.95). The mount can be used with the 377, 447, and 503 Rotax air-cooled engines. Two pieces of steel angle stock function as cantilevered beams, attached via the front and rear sets of head bolts. The mufflers hangs at the free ends of the "beams" using stainless clamp hardware (very high quality) and vibration isolation mounts. The whole thing will go together very nicely, with two cautionary notes:

• The instructions provide drilling templates for the cover and the steel angle stock. Do not rely on these templates - make your own from your engine!

• You will have to drill two 10mm/3/8" holes in each piece of steel angle stock. Use a drill press, plenty of oil, and take your time. The result will be a very clean set of holes!

UNDER CONSTRUCTION