Well the engine is 1 1/2 times more powerful, why would it be quieter ?
About 20 jears of development past the F-100, and they can't make the bloody thing (F-135) a bit less noisy???
You can absolutely make jet engines quieter today than 20 years ago.
It just takes mass and volume away from payload for sound suppression systems. That's OK, right?
On the assumption that this is not OK for a combat aircraft, the issue is that, fundamentally, low bypass turbofans generate more noise per Newton of thrust than quieter high bypass turbofans and less noise than pure turbojets.
Some of the efficiency losses in all gas turbines is lost in noise. Pure turbojets are aerodynamically inefficient and are faaaar noiser than any turbofan, while low bypass turbofans are more noisy than high bypass turbofans (a byproduct of the higher fuel efficiency of the high bypass fans). You need a low bypass fan because the frontal area and fan tip speed of the high bypass fans limit maximum speed. So, for supersonic aircraft with moderate efficiency you are stuck with a low bypass fan, in which case you are stuck with a certain level of noise.
The new GE variable cycle engine that increases fan ratio at lower speeds will probably be quieter for a given low speed thrust as it is more efficient and loses less energy to noise at the slightly higher bypass ratio. Won't be a lot, but it should be quieter.
Of course, that's on straight military or dry power. As soon as you kick in the afterburners, the efficiency goes into the toilet and a huge amount of energy gets wasted as noise, so don't expect a reduction in take-off noise even on the variable cycle engines.
Here endeth the lesson.
Paul
