Originally Posted by
etudiant
Would not the duct constrain the bypass ratio pretty severely?
Why would counter rotation help in this case? It adds considerable complication, so there needs to be a large benefit to justify it.
I'm guessing all the same benefits of contra-rotating props but with the advantages of a duct. Reduced fan diameter, increased propulsive efficiency (need a caviat for that one). Noise reduction? The Tu-95 Bear is apparently, hellishly noisy!
With of course ALL of the disadvantages too. Complexity, weight, maintenance, development costs.