I was told (but I cannot substantiate this) that the most susceptible systems to GR were three-bladed rotors and that the ultimate 'risk' was a three-bladed rotor with wheeled undercarriage. As I understand, it can occur on 4 or more bladed rotors also.
Makes sense. Centre of mass moves more significantly in case of one blade not where it should be in 3-bladed MR. No need for rocket scientist (or Shawn Coyle)
