1. A helicopter power train including a transmission for driving a multi-blade rotor for accommodating rotor tip-path plane flapping deflection comprising in combination:

(a) a resilient mounting including a plurality of independently operating mounts with travel limits for coupling the transmission to the fuselage of the helicopter, said mounting to accommodate from about 15% to 35% of said deflection,

(b) a flexible mast extending from said transmission to said rotor to accommodate from about 10% to 30% of said deflection,

(c) a yoke secured to said mast for connecting said blades to said mast, said yoke having a thin flexure section immediately outboard of said mast to accommodate from about 40% to 60% of said deflection, and

(d) each of said blades including means for providing beam bending to accommodate from 0% to about 10% of said deflection.

2. A helicopter power train as recited in claim 1 wherein said resilient mounting includes a load-bearing elastomeric member.

3. A helicopter power train as recited in claim 1 wherein said flexible mast comprises a tubular member extending from said transmission to support said yoke and drive said blades.

4. A helicopter power train including a transmission for driving a multi-blade rotor for accommodating rotor tip-path plane flapping deflection comprising in combination:

(a) a resilient mounting including a plurality of independently operating mounts with travel limits for coupling the transmission to the fuselage of the helicopter, said mounting to accommodate approximately 25% of said flapping deflection;

(b) a flexible mast extending from said transmission to said rotor to accommodate approximately 20% of said flapping deflection;

(c) a yoke secured to said mast for connecting said blades to said mast, said yoke having a thin flexure section immediately outboard of said mast to accommodate approximately 50% of said flapping deflection; and

(d) each of said blades including means for providing beam bending to accommodate approximately 5% of said flapping deflection.

5. A helicopter drive train including a transmission for driving a multi-blade rotor where rotor flapping tilts the blade tip-path plane to an angular deflection with regard to the helicopter fuselage, the combination comprising:

(a) a resilient mounting including a plurality of independently operating mounts with travel limits for coupling the transmission to the helicopter fuselage, said mounting statically accommodating a pre-established percentage range of the total said angular deflection,

(b) a mast extending from said transmission and having beamwise flexibility for statically accommodating a pre-established percentage range of the total said angular deflection;

(c) yoke structure secured to said mast for supporting said rotor blades and including a flexure segment immediately outboard of said mast for dynamically accommodating a part of said rotor flapping to accommodate a pre-established percentage range of the total said angular deflection, and

(d) each of said blades including means for dynamically accommodating a part of said rotor flapping to accommodate a pre-established percentage range of the total said angular deflection.