Mast moment measurement in hingeless rotors
I want clarification with reference to the mast moment measurement in 4-bladed hingeless rotor (Example like in BO 105, EC135, BK 117 and ALH from India). The measurement of mast moment was done on rotating mast with reference to main rotor blade through strain gauge/slip rings. There were strain gauges put on the four lift rods connected to fuselage attachment point from MGB. When we compared the mast moment measurement from rotating mast and through lift rods (by taking difference between rear and front lift rod and multiplying by arm distance w.r.t rotor centre), the moments were different.Kindly specify the reliable and sensitive method to measure the mast moment either by using rotating mast (rotating coordinates) or by lift rods (stationary coordinates).