I would like to share our tail rotor issues at high altitude. The tail rotor is 4 bladed bearingless designed at ISA, SL. But when helicopter is doing spot on turn to right(of course our main rotor rotates in clockwise when seen from top) at approximately 20,000ft we ran out of pedal requirement i.e there was not enough thrust to maintain that spot on turn right(60deg/sec). During rigging pedal travel was -10 to 24 deg. While performing above flight condition tail rotor thrust was almost constant beyond 22 deg to 24 deg. We thought that tail rotor is stalling beyond 22 deg and there wasn't enough thrust to maintain that flight condition.
How we can check theoretically/empirically that tail rotor is stalling at high altitudes so that we can put flight limitations in flight manual.