Mass distribution method and apparatus

A helicopter having a longitudinal axis, a lateral axis and a vertical axis, a helicopter centre of mass and a maximum gross mass of less than 5000 kg, the helicopter comprising;

• a fuselage elongate along the longitudinal axis, the fuselage comprising an aerodynamically shaped shell defining a front, a rear, a top and a bottom of the fuselage and a passenger cabin therein having two forward-facing front seating positions for the pilot and a co-pilot or a passenger, and forward-facing rear seating positions for at least 2 passengers, optionally 3 passengers;
• a primary fuel cell mounted substantially behind the passenger cabin;
• a tail boom assembly extending from a tail boom bulkhead at the rear of the fuselage and including a tail rotor;
• a main rotor assembly comprising a hub, at least two main rotor blades mounted by a rotor mast to the top of the fuselage to permit the main rotor blades to rotate with respect to the fuselage;
• the front seating position for the pilot having a centre of mass at a first location substantially in front of the rotor hub location, and the primary fuel cell having a centre of mass at a second location substantially behind the rotor hub location;
• a landing gear arrangement;
• a power plant mounted substantially above and behind the passenger cabin, wherein the primary fuel cell is arranged to provide fuel to the power plant;
• and
• a secondary fuel cell having a centre of mass at a nose location in front of the rotor hub location by at least 1500 mm.