Report Blackhawk tail rotor in Aerodynamics, Mechanics, or other... Posted May 10 · Edited May 10 by iChris On 4/30/2021 at 6:54 PM, Disguise Delimit said: The problem was that the front of the blade, as it rotated, was going down with the main rotor downwash, and was losing efficiency - the back blade was in clearer air, but the loss from the front blade was substantial. That’s correct… Most U.S. manufacturers will turn the tail rotor clockwise when viewed from the helicopter's left side, taking advantage of the tip vortices coming off the main rotor. When the tail rotor turns in the same direction as the primary rotor vortices, it reduces the relative airspeed of the tail blades, and the available thrust is limited. When the tail rotor turns against the central rotor vortex, the performance increases because of the square-law connection between thrust and increased relative airspeed. Two notable helicopters turn their tail rotor in the so-called wrong direction. They are the MD500 and Robinson R22. However, they both share another less conventional concept, for their time, NACA 63-415 asymmetrical tail rotor blades. More common were symmetrical tail rotor blades like those on the Bell UH-1, AH-1, 204/205/206, 212, 412, and Hughes 269/TH-55. Frank Robinson left Bell Helicopter in 1959 and joined the Aircraft Division for Hughes Tool Company, assigned to the U.S. Army's OH-6 Light Observation Helicopter and other Hughes 500 projects. Frank had already established himself as an authority on tail rotor design. Frank found the NACA 63-415 asymmetrical tail rotor blades exhibited noteworthy improvement in performance over the symmetrical blades. Frank brought some of those design characteristics and gave birth to Robinson Helicopters (1973) and the R22. Frank reduced gearing in the tail rotor gearbox to save weight at the aft end of the tail boom. Consequently, due to the engine's reversed position (Front end facing aft), the driveshaft from the engine to tail rotor ended up turning the tail rotor in the wrong direction. Furthermore, asymmetrical tail rotor blades came with an inherent consequence, an undesirable twist or pitching moment. Frank countered the effect with a built-in coning angle designed into the tail rotor. The overall compromises ended up cutting weight, and light helicopters like the OH-6 and R22 still provide better than adequate tail rotor performance. MD Helicopters seem satisfied, sticking with the wrong-direction design on their current MD500E/F series. Incidentally, the R44 and R66 tail rotors turn the right way.