Dave,. .A small spring could serve as a soft bumper to help reduce the effects of mast bumping. Several aircraft have this, including V-22 (which has a zero offset gimboled rotor head). .. .This whole subject underscores the neat idea behind the articulated rotor. Its strong head moment is a product of the centripital force, which creates high head moment with no weight penalty of a spring (although the increased moment requires stronger masts, transmissions and airframe structure).. .Nick