ive noticed on mine, as well as other helicopters some variations in turbine exhaust mounting, the exhaust does not clamp onto the turbine in some..
all are single wall pipes...
1) the turbine exhaust for my bell 230 clamps onto the turbines outlet pipe..
2) in trial fitting the exhaust for my turbine cobra fuse project, its bolted to the side frames but does NOT contact or clamp to the turbine outlet, sits 2-3mm behind it and is a substantially larger overall diameter than the turbine outlet, ide say 6-8mm all around
3) a friends 1/4 hughes, same thing, it doesnt, its mounted to the frame as well and is also spaced 2-3mm behind the pipe and is also oversized in relation to the turbine outlet
4) the NH90 im selling also had the exhaust clamped to the turbine outlet
1) is it to allow suction of cooler air into the exhaust tract?
2) is it clamped to prevent rotor wash from pushing exhaust back into the fuse ( highly unlikely) on vertical exit pipes?
3) we (my hughes friend included) are screwing something up and will burn up our helicopters?
and lets not get into turbine jets.. thats a whole other ball game.. you can fit your fingers between the turbine outlets and pipes..