Last flight I dropped in at the local field and a mate commented in 'typical 2-stroke clatter'. I hadn't noticed it in the air as my headset is pretty good at passive noise cancellation, the little F23 runs quite smooth, so I didn't pay any attention to his comment.
But flying home I paid more attention, heard some clatter and felt some vibration that was not normal.
I found a sweet-ish spot in the engine rpm and landed back home after about 5 minutes.
On initial inspection one of the mount straps was clearly broken around the securing washer.
As I released the springs at the exhaust flange, the muffler fell off, hanging by the EGT probe cable.
Talk about lucky...or possibly foolhardy by not checking immeidatelymy mate made the comment.
Both mount straps completely failed, and evidence of hammering and cracking around the tube end that mates with the exhaust spigot.
I always give the exhaust/mufflers a good VI and shake during pre-flight- there was no noticeable looseness, but it must have been progressively failing over more than just today's 1 hour flight.
Off to an exhaust shop for repairs to the tube and mounts.
Will I do anything different in future? Listen to my mates, pay special attention to the exhaust system, perhaps safety cables/straps around the muffers?
Edit: And keep away from the <2000rpm shakes except for a short idle check pre-takeoff.
Stuart wrote to me in an email that after repairing the exhaust, his engine runs smoothly below 2000rpm. The exhaust damage was likely due to problems with starting a cold engine due to choke problems.
In emails with Fusioncopter, they said that in later models those tabs have been changed to a collar around the spigot, providing a full 360 degree face for the exhaust tube to locate against. No notches or cutouts- simpler, better!
Mine is an early model (s/n 14) - I am redoing my exhaust the same, so that problem should never recur.
Thanks for the help FC!
Further to this-
While the LH exhaust is away being repaired, I had a good look at the RH exhaust.
One mount starting to show a crack, and evidence of creep in the sliding joint over the exhaust flange spigot.
Same as in the pics above, but not as pronounced.
The issue is the joint is held under tension by the springs, and located by some tabs welded to the spigot which mate with cutouts on the muffler pipe.
The cutouts are folded out presenting an angled face to the tabs, rather than cut and having a flat face.
Under vibration and tension, the folded cutout slowly folds more and more.....
I will get both pipe ends replaced and make sure the cutout faces are flat.
And perhaps consider some securing screws, though not sure about that.
Any advice?