I have never heard or read an answer to this question that was satisfactory to me. The short answer to this question has been to provide lift to the tail. Two questions should come from this answer. 1 how much of whatever lift is provided is lost in an autorotation? Answer - all of it. 2. Why does this helo need lift in the tail when other single rotor helps don't.
There’s been much written on the canted tail on the H-60, as evidence in this post; however, you must analyze the tail section dynamics in its entirety (tail rotor, tail pylon, vertical stabilizer, horizontal stabilator, microprocessor controlled stabilator-incidence angle, etc.). Numerous technical papers and article from NASA and others, two listed below.
“Some basics first: The canted tail rotor is tilted so that some of the rotor thrust is directed upward, which means it contributes to the total lift of the aircraft. The cant angle is 20 degrees, so the tail rotor thrust in the vertical axis is over 30% of its total thrust, while the horizontal axis retains about 94% of the total thrust, a small cost to pay for that lift.
The two benefits for the H-60 and H-53E are that the lift from the tail rotor help the CG of the aircraft. The 53E third engine was added to the 53D and was placed aft of the transmission, so the tail rotor was used to retain aircraft balance. For the H-60, the aircraft was designed to fit inside a C-130, and so was made low and longer relative to its required payload and volume. The tail rotor helped the designers retain good longitudinal balance.
For the other aircraft with canted tails, the S-92, the AW-139 and the Bell 525, the lift from the tail rotor helps payload. For the S-92, the canted tail rotor is worth between one and two extra passengers."
”Nick Lappos, Technical Fellow Emeritus
You can also download Ray W. Prouty's article titled, Evolution of Sikorsky Tails, link below:
Center of Gravity & Evolution of Sikorsky Tails
Some try and make sense out of these designs. They often don’t make sense. From a designer’s quote below, it’s just the ‘least worst compromise’
“Many detailed decisions concerning the rotors and the stabilizing surfaces need to be made before the design is complete. The most sophisticated of the computer preliminary design programs contain logical procedures for making some, but not all of these.
Many have to be based on considerations that are impossible to computerize and depend on factors ranging from solid scientific fact to controversial aesthetic judgment.
In almost all cases, there are powerful arguments pulling the designer in opposite directions. Resolving these dilemmas so as to achieve the ‘least worst compromise’ is the designer's primary task.”
Edited by iChris, 18 August 2019 - 16:48.