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Learn from my misfortune.

Regularly check the bracket that supports the muffler (after the expansion chamber and the C-curved pipe) for signs of cracking due to metal fatigue. Also check all parts of the exhaust system for cracking, loose manifold bolts, worn safety spring hook ends and loops, etc.

Have any of you heard of this kind of thing happening? (I know the PPG boys have muffler cracking problems...)

I've seen it on a microlite trike and our DragonFly. No surprises there. Lot's of vibration that's for sure...
Glad you are ok.

I have ordered a new (improved design) exhaust system. The cost of parts and parts fabrication (not to mention the running around) here in Auckland means that the new system from Sweden will be cheaper in the long run. Should be here in a couple of weeks. (I might post a video of the new system and safety wiring.)
I have installed the new Mosquito NRG exhaust system (manufactured by a different subcontractor and reportedly better and stronger).
I took this photo for Swedish Aerosport so that they can confirm that the exhaust system is angled correctly. Once they confirm that all the bits are correctly oriented (there were no instructions), I will add the supplied safety wire to the springs and bolts and crimp the two supplied ferrules. After that I will fire the engine up and see that she runs up (hope that there is no internal damage).
The only concern that I have is that the exhaust is a little close to the air intake filter. I liked the little 90-degree end pipe that spat the exhaust gases off to the side, but this new design is a straight pipe that points directly into the incoming air stream. Still, Sweden assures me that the pipe is the correct one, so the proof will be in the pudding.

(PS. In the background is my 2001 Yamaha R6 that I bought new in December of that year. It has Ohlins everything and has done almost 150,000 km. Everything other than suspension is stock. I love it.)
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Looks really good. Don't think you will have any issues with the exhaust near the intake. We added safety wire to our exhaust springs as well so that when they fail they will not fall into the prop.

I will safety-wire the group of 3 main connecting springs. I have the old (broken) exhaust to use as a guide. I will also apply a bead of Silicone sealer across the length of each spring to dampen spring coil harmonics. (A trike pilot suggested this trick to me.)
I will add the (supplied) safety wire to connect one of the expansion chamber's spring mounting loops to the header support bracket. I noticed that the header pipe support bracket is only welded to the header pipe on one side of the end of the bracket instead of both sides, as in the old pipe. This is cost-cutting. I will watch the weld in case it breaks.

Shall I safety-wire the muffler? That is a good question. This new design seems far more robust than the old one. There are now two brackets connecting the muffler to the expansion chamber, instead of one. Also, the brackets are much shorter and stronger-looking.

I would strongly recommend any pilot who has the old single-muffler-support exhaust system to safety-wire their muffler, or at the very least make pre-flight checks of their muffler bracket. If the single muffler bracket fails, all the weight of the muffler will go only the curved C-pipe, which will fail very quickly, leaving the entire muffler to fall back through the propeller, which is what happened to me. (I have attached a photo of my old exhaust showing the failed muffler bracket and the cracking of the area on the expansion chamber near the base of the bracket.) CHECK THESE AREAS as part of pre-flight checks.

I will monitor the new exhaust system and may add a safety wire between the exhaust header safety spring mounting loop and the forward mounting bracket on the muffler (although with the new design, this may be overkill). Regular exhaust system pre-flight checks may be sufficient.
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(The story continues...) Today I tested the engine and learned some stuff.

My goal was to confirm that the engine would idle and rev, to verify that there is no internal damage.

At first, the engine would not start. I checked for a spark by holding the plug against the cylinder fins, while my wife activated the starter motor. Sure enough. No spark.

I checked the kill-switch that is buried deep underneath the parachute. Sure enough, the kill switch red braided flat ribbon was adrift. This could be the problem! I had a look underneath the parachute and could see a "tuning fork" like arrangement where the two blades of the forks touch. I assume that this shorts out the circuit to the ignition. I inserted the red braided ribbon between the forks, then properly secured the Velcro sleeve that wraps around the braided ribbon and forks to hold them firmly together and to prevent the ribbon from accidentally slipping out of the side. (This Velcro had not be done up previously, which could explain how the ribbon came free in the first place.)

I checked my spark plug and this time there was a robust spark! Success!

The engine started easily and idled well. I briefly ran the engine up to about 5,000 rpm for several seconds. The engine ran as per normal, and returned to an idle. I conclude that there is no damage to the engine. (This will have to be verified at the beach.)

I felt the exhaust pulses coming out of the muffler at idle and they seem to be well directed away from the air intake, so Sweden's claim of no problems with exhaust gas getting sucked into the air intake seems to be true.

I removed the exhaust system. Next I will crimp on the two main safety wires. (Sweden supplied the wires and ferrules.) After that, I will be ready for a test flight.

In retrospect, I think I saved myself a whole lot of hassles by ordering a new (improved) system from Sweden.

Spend the money and make the problem go away!
YES- heat resistant rubber goo on the springs. Forgot that one! You can imagine the constant heating/cooling cycle on metal parts causing fatigue. Always try to keep from shocking the exhaust to much with quick cycling of engine speed when ever possible. Sounds like you have a handle on things...

Odakyu-sen wrote:
Tue Aug 22, 2017 4:45 am
The story has a happy ending. (The repairs are holding together.)

That forward-facing exhaust pipe may or may not affect engine performance, but I can't imagine the noise levels being okay for the pilot. If that pipe made a final U-turn, to point away from the pilot, it seems to me that the pilot would get a lot less noise from the engine. I can deal with almost everything about a powered HG, but so far, engine noise has been the deal-killer for me.

The electric powered HGs might be a good alternative, for me. I wish this was not a trike, though.
Maybe they used to be louder, but I just took delivery of a new unit with the exhaust pictured. Noise is absolutely not an issue. I ran mine up about 3/4 throttle on the ground while having a conversation with my instructor and we did not have to raise our voices.
red wrote:
Tue Aug 22, 2017 10:47 am
I can deal with almost everything about a powered HG, but so far, engine noise has been the deal-killer for me.
I was a little concerned about the new exhaust shooting straight forward (the old design had a stubby 90-degree pipe exiting from the muffler that shot the gases out to the side). I thought the new pipe had the exhaust outlet a little too close to the air intake, but this has not been a problem in terms of idling or maximum revs.

Two things to consider with exhaust noise: engine rpm and wind noise.
Once I get up, I cruise at 6,700 rpm (for level flight). At this engine speed, the cylinder head temperature is a nice 165 degrees C or so, there is little vibration, and the engine note can hardly be heard above the roar of the wind rushing past my helmet at around 42 km/h. Okay, at full power on takeoff, the engine is louder but I only run full power for about 3 minutes because the head soon gets up to around 205 degrees, which is not a good thing. Once I get up to around 600 feet I throttle back and start hunting for thermal assistance.
In reality, the exhaust is relatively quiet when cruising in level flight (where I spend 95% of my time when the engine is on).

Hang gliding for flying; FLPHG for exploring and sight-seeing. (The two compliment each other.)

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