Originally Posted by
tdracer
Yea, I saw that - basically the Boeing 7J7 proposal from 45 years ago (but with the engines moved from the tail to the wing so that the passengers can enjoy that ear splitting sound from the counter-rotating unducted fan).
I give it about the same probability of actually turning into reality as well (as in slim and none). Until someone - somehow - comes up with a solution to the noise generated by counter-rotating unducted fans, they are going to be a non-starter.
The noise generated by the trailing fan slicing through the vortices from the leading fan create a noise that would put an early pure-jet 707 to shame - and being unducted there is no way to attenuate that noise.
Time has passed.
1. Noise Level is expected on par with LEAP now
2. Only one rotating fan, the second is variable stator
3. the above enables a simpler and single gearbox, fan speed can be reduced and noise will meet near future limitations.
4. efficiency step up by 20% compared to best in class engines today for single aisle market
I personally see noise level in 3. still as a dead end
if no more improvement can be made thereafter.