Rotor track and balance in GTV.(Helicopter ground test vehicle)
 

When we are doing track and balance in GTV (ground test vehicle) which means helicopter tied down on ground permanently the MGB lateral vibration was high at collective angle of 0%(collective range -2 to 16 deg) that is negative angle of attack, thrust will be downwards. Any standards specify on rotor track and balance at different collective in GTV or in your experience what should be the collective range for rotor track and balance in GTV. Is rotor track and balance can be done at negative thrust or only in positive thrust.