S-70, as I wrote, Delta 3 had it correct in that the main reasons were:
- Aircraft balance with an aft CG design. A secondary, related benefit is a shorter aircraft, although one might ask which comes first.
- The aircraft hover performance benefit.
Tail rotor tip clearance to ground was not a factor in any of the SA canted tail designs. The design approach to that question in the first such machine, the UH-60, was to select a tail wheel over a tricycle configuration, and we would have done that, canted tail or not. In the CH-53E and S-92, both tail rotors were sufficiently high to allow a tricycle and in the Comanche, the tail fan was ducted.
Nor was the selection of a canted tail decision on the four models influenced by tail thrust requirements, the primary one being a sideward flight capability of 35 kts for the first three* and I'm unclear on the spec for Comanche, but it was at least in the 80 kt range.
*The FAA only requires 17 kts as I recall but SA and most military req'ts call out 35.
Thanks,
John Dixson