That’s amazing.
I would have expected rapid cowling damage in such a case. The TB20 has quite a lot of room around the engine but the exhaust pipework is around 5-10cm from the lower cowling.
It also risks CO ingress into the ventilation system. The exhaust only has to burn through one of the pipes coming back from the muffler jacket.
As I keep saying, these systems should be made in Inconel and then they would last as long as the aircraft. But for some reason exhaust makers don’t like doing it. There is nothing actually difficult about it but one hears all kinds of crap like the Russian invasion of Ukraine causing Inconel price increases to $50/kg (which is utterly immaterial looking at how much new exhaust pipes cost – about 100x that figure). I think a more likely reason is that exhaust makers buy in pre-bent sections from outside, and these don’t exist in Inconel, perhaps…
We had a hole develop in our exhaust (discovered during preflight inspection – since we have a cowling that opens, I saw discolouration of the lower cowling that wasn’t there before, so I stuck my hand in to feel around the exhaust and found a hole where there hadn’t been one before). The cowling is metal, but the heat had caused the paint on the inside to erode and I could feel a slight bubbling of the paint on the outside of the cowling.
I think I heard the bit of exhaust departing, although I didn’t realise it at the time – I heard a slight change in engine note after the glider I was towing released, but I had been easing the throttle out at the time so I didn’t think much of it till I found the hole the next time we went to fly.
In my case, the hole was facing the oil pan, so did not show up as a discoloration of the cowling. There was some soot on the oil pan, but it was difficult to see, and the hole was not visible from the outside view with the cowling open for a normal pre flight inspection. I have adjusted my pre flight inspection to feel the inside of the exhaust manifold.
