At my club in France we will shortly be fitting a silencer to a Lycoming O320 engined Rallye. The system is manufactured by Chabord, who previously made exhaust systems for F1 cars, and it is claimed that there is no performance degradation.
Whether there is much sound reduction is debatable, though!
I recently attended a fly-in where several aircraft were equipped with silencers. When they overflew at low power settings, the silenced aircraft were noticeably quieter. At full power, however, there was little discernable difference.
This is something that has been seized upon by the National Association of Nimbys in France (a miserable group whose real title is C.A.N.A.L. If you read French, and want to be made angry, click
here. ) They did some tests in Toulouse with a number of light aircraft equipped with different silencers, and found the silencers weren't all that great, especially in the take-off / climb phase. This "comforted" them in their view that draconian limits on private flying are required (no training at weekends or bank holidays, no flying near schools or shopping centres (because of the dangers of us crashing on them...) etc. etc.).
This bunch of killjoys have big European plans, if they are able to get their act together. Obviously it's not good enough to take action against a local airfield that bugs them - they need to make sure that action is taken against ALL airfields, everywhere in Europe so that people who aren't able to complain for themselves are given the peace and quiet they deserve!
What we need is quieter engines, not add-ons to the ones that have been in use for the last few decades. Does anyone know if the new diesel engines are quieter?