For a while now I’m thinking about where to position the muffler for the engine, because despite the roomy interior of the Fokker, there’s not much space left with this 85cc engine in it. The original ROTO mufflers for this engine look like this (and obviously I’d need two of them):

http://www.rotomotor.cz/rotomotor/eshop/3-1-Exhausts/0/5/79-Muffler-ROTO-for-35FS-85FS-85FSI-170FS

In terms of diameter (32 mm) they’re not that big, but it still is 23 cm long, which is quite substantial. And a combined muffler would be easier to build in.

After a short search I bumped into this muffler from Valach, which is also designed for a 85cc engine (a boxer, but that doesn’t make any difference). Both being four stroke engines of the exact same capacity, I’d say it would do:

https://toni-clark-shop.com/Silencer-for-Valach-VM-85B2-FS

This one is 6 cm in diameter but only 14 cm long. Which makes it a little more compact.

I was hoping that it would fit next to the engine, because that is exactly where the scale exhaust should be! It goes out on the right side, pointing downwards. But lengthwise it doesn’t fit, and in a vertical position I still think it won’t work:

Because I also need room for the cylinder exhausts, and I need to be able to cool the engine and muffler sufficiently, and this way, the rear cylinder and muffler are not going to help a lot with that.

And I also need some space for baffling towards the second cylinder. I really need to do that on this side as well, because the carburetor is on the other side of the engine, consuming quite some space over there as well:

And then I noticed this unused space behind F3, just below the tank floor and in front of the servo tray:

If I would mount it onto F3 with brackets, I can use 30 cm long connectors from the cylinder exhausts to here. The inlet for the muffler would point straight towards the front of the airplane, and the exhaust would point backwards in an angle, exiting the fuselage between the landing gear struts:

The downside of this, is that the gasses won’t come out of the scale exhaust location this way, which really is a pity. But I believe cooling everything, both the engine and the muffler, would be way easier, resulting in a better performing setup that is easier to build in and to maintain. Without formers, the engine and muffler layout would be like this:

This way, I can even create a cooling opening solely for the muffler, taking air from the underside of the fuselage (because it is positioned lower than the engine).

As I said, the scale exhaust would be a dummy one in this case, and the fumes would exist the fuselage on the bottom. From a distance, you won’t notice, and you’d have the advantage of the exhaust fumes not going over the wings, but from a scale perspective it is not such a great concession. But even if I would get a custom exhaust to fit the scale location, I would have trouble cooling and baffling everything efficiently.

So for now I think this will be my solution..