Silencing a Rotax 912
Posted: Sun Nov 15, 2015 3:49 pm
Dear Microlighters
I just thought to share a few pictures of an exhaust mod I made to my Rotax 912. My Hawk has a pusher engine and no noise insulation to speak of, so the noise level during flight was brutal, overwhelming my headphones and making radio transmissions difficult and intercom talks near impossible. Due to weight considerations and the fact that the exhaust protrudes into free air above the aerie, I didn`t want to add a second silencer. Instead I opened the old silencer and added 1.6 and 2mm perforated stainless steel walls and a single, inclined baffle to each side of the silencer. The space between the two walls is filled with glassfibre padding taken from an old automotive exhaust. The old tailpipe was removed and the holes closed up, instead the gases now exit directly from holes drilled into the centre section.
The result is not amazing, but certainly effective enough. The engine sounds deeper and the propeller is now audible, while before it was completely overpowered by the engine noise. The noise cancelling headphones are now able to do just that. Weight was increased by 1.0kg over the standard exhaust. I can't say much about the effects on back-pressure, but can only guess that it hasn't increased much over the standard system. The removal of the old outlet should compensate for the added baffles.
Blue skies
Arthur
(I had to resort to stick welding, so the welds are really not what they should be.)
I just thought to share a few pictures of an exhaust mod I made to my Rotax 912. My Hawk has a pusher engine and no noise insulation to speak of, so the noise level during flight was brutal, overwhelming my headphones and making radio transmissions difficult and intercom talks near impossible. Due to weight considerations and the fact that the exhaust protrudes into free air above the aerie, I didn`t want to add a second silencer. Instead I opened the old silencer and added 1.6 and 2mm perforated stainless steel walls and a single, inclined baffle to each side of the silencer. The space between the two walls is filled with glassfibre padding taken from an old automotive exhaust. The old tailpipe was removed and the holes closed up, instead the gases now exit directly from holes drilled into the centre section.
The result is not amazing, but certainly effective enough. The engine sounds deeper and the propeller is now audible, while before it was completely overpowered by the engine noise. The noise cancelling headphones are now able to do just that. Weight was increased by 1.0kg over the standard exhaust. I can't say much about the effects on back-pressure, but can only guess that it hasn't increased much over the standard system. The removal of the old outlet should compensate for the added baffles.
Blue skies
Arthur
(I had to resort to stick welding, so the welds are really not what they should be.)
- Perforated double skin added to original exhaust
- AExh1.jpg (34.94 KiB) Viewed 4160 times
- Inclined baffle
- AExh3.jpg (39.82 KiB) Viewed 4160 times
- Pod completed and void stuffed with glass fibre
- AExh4.jpg (38.49 KiB) Viewed 4160 times
Ja but then the noise starts in the cockpit 