Thanks Bud.
After posting this topic yesterday I was emailed by Donald Cameron who flies
from
Oban on the Scottish West Coast. He has experienced at least one similar crack
at the same location on the tube from #3 cylinder. He also sent pictures of
cracks on top of his muffler box, which fortunately I haven't yet suffered.
Since installation of the CKT exhaust system 4 years ago, my aircraft has done
230 hours airborne and also about 50 hours running on the ground, before the
fracture occurred. Not too bad, I think.
If I remember correctly, Kevin Dilks (a UK Rotax engine rebuilder who used to
work
in the factory in Austria) advised that the 912S engines have a "sweet spot"
around 4700 rpm, so in the cruise I generally set my Airmaster propeller control
to Manual and reduce engine speed below 5000 rpm, which subjectively makes
everything feel considerably less harsh.
Whether other Rotax 912S powered aircraft are achieving more than 200 flight
hours
before cracks appear in their CKT muffler systems would be interesting to
know.
Finally, yes Donald Cameron and I both had cracks originating near the spring
attachment.
Thanks again.
Jonathan
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