Noise
Good news from Andre Goepfert in France
Hello Jerry & Reinhard,
A long time since we had a chat, hope that the high work load situation with
the new airline will improve and permit continuation of work on the Express.
At least, good news since a long time, last week I got the permit to build
the hangar on our local airport, so that I can move the Express with in a
few months.
Andre's comments about "aircraft Noise"
About your engine noise problem in the Express, I can give you the following
information.
- Studies performed in Europe (Rushmeyer and MT propellers) have shown
that the only satisfactory solution to reduce noise emissions on a piston
single is to reduce drastically the prop RPM. (around 1500RPM in cruise or
even less) As this is practically not possible on an old air cooled LYC or Continental engine, other solutions are available.
1) In cruise, reduce engine setting by 200 RPM compared to the AFM
tables.(or more on certain engines)
2) Install a 3 or better 4 bladed prop with modern design like MT or
Hoffman.Cruise performance is similar to a 2 bladed Hartzel.
3) Install an exhaust muffler (Gomolzig from Germany or Mecanair from
Switzerland )
In addition a floor noise isolation is needed in the cockpit as the long
outlet tubes run under the fuselage ( automotive or business aviation
material)
4) Firewall noise isolation blankets forward of the rudder pedals and side
of fuselage.
5) Electronic ignition. (the detonation is different)
6) Cabin door sealing must be perfect.
We installed recently such isolation blankets on a single with a 4 bladed
prop and the results were satisfactory. There is only ONE BIG NEGATIVE
ASPECT , effective material is very heavy.
This is all I can tell you for the time, if you are interested in technical
documentation about the exhaust mufflers, let me know, I can send it to you.
There is as well an electronic noise reduction system for the cabin, based
on the same principle as the Bose head sets, but it is expensive and
unreliable.
Best regards to all,
Andre Goepfert