Feathers McGraw
In scale model test the silencers produced quite promising results. However on the aircraft itself they proved to be worse than useless, the only real difference they made was that they resulted in a reduction of thrust. (But because the fly over altitudes would consequently be far lower, they did a good job in INCREASING the noise nuiscance).
As far as your point about the prototype engines; they were way down on thrust anyway, (even without the 'help' of the silencers), produced more black smoke than a 1930's coal fired power station, and would not have enabled Trans-Atlantic revenue load crossings. (And what with the noise and the smoke, I guess our environmental friends down there would REALLY have had something to complain about
).
Dude
