Just trying to add some activity to the forum.... My Nano is an earlier version with the slipping belt pre-rotate pump drive. I recently upgraded to the HD clutch option, and after some teething troubles setting it up have got it sorted and working well. Pre-rotate is much more positive with no slipping as the rotor load increases above about 160-170rrpm. I have posted a video of my flight yesterday on youtube- nothing spectacular, just a local round the patch- no dramas, just an enjoyable cruise. Link here- https://www.youtube.com/watch?v=KPgixOr-Rg8 I had earlier on struck some issues with the exhaust/muffler system due to engine vibration at startup and idle. I spent some time looking at the issue, and decided it would help to uncouple the inertial mass of the muffler from the engine to relieve any stress on the exhaust flange and joints. I added flexible joints into the exhaust tube between the engine and mufflers, and things look and feel a lot smoother at startup/idle. Pic below.

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.

NOTE: I submitted this report to Fusioncopter Poland. This is a Hirth manufacturing defect, NOT FC's fault. If you notice weeping of burnt oil at the exhaust port, best to check and if necessary weld around the joint on the outside. Aircraft: Fusioncopter JK-2 Nano Serial no: FCG014 Engine: Hirth F23 Serial no:MO-01000570 TIS: 15 hours History: At about 5 hours TIS some exhaust weeping was noted around the LH exhaust port. It was assumed to be leaking at the flange gasket, so the exhaust flange was retorqued. The weeping continued, but as it was slight I continued operation intending to replace the gasket at next major service. During the last flight I noticed a change in engine sound with a slight reduction in rpm. On landing the engine sound immediately changed to unmuffled. On inspection the LH exhaust pipe had disconnected at the exhaust port flange. Analysis: The exhaust spigot had pulled out of the flange. The flange/spigot is assembled with the spigot inserted full depth in the flange, swaged(?) and welded around the spigot end. On close examination it appears only 1/3 to 1/2 of the weld fused with the spigot end. The muffler security was inspected prior to every flight with no evidence of excessive movement wrt the engine. The conclusion is the problem was due to inadequate welding spigot to flange. Corrective action: The flange and spigot were cleaned and dressed and assembled with the spigot reinserted full depth. The spigot was welded to the flange on the outside around the circumference. Not as tidy as the internal weld, but more substantial. Ground run- no leaks. Good to go!