 The rotor blades (which turn in opposite directions) are built with a wooden spar and fiberglass trailing edge sections.Wood was chosen for its damage tolerance and fatigue resistance; and to take advantage of field experience and qualification data amassed from a similar spar on the HH-43 Huskie helicopter, built for the U.S. Air Force in the 1950s and 1960s.The pilot controls blade pitch with tubes running inside the mast and rotor blades to move servo flaps that pitch the blades, reducing required force and avoiding the added weight, cost and maintenance of hydraulic controls.