TM 1-1520-238-10 2-59 Section  VIII.    ROTORS 2.41   ROTOR SYSTEM. The rotor system consists of a single, four-bladed, fully ar- ticulated main rotor and a four-bladed tail rotor assembly with two teetering rotor hubs. 2.41.1   Main Rotor. The main rotor has four blades. The head  is  a  fully  articulated  system  that  allows  the  four blades  to  flap,  feather,  lead,  or  lag  independent  of  one another. The head consists of a hub assembly, pitch hous- ings, rotor dampers, and lead-lag links. Attached to the ro- tor head are four easily removable blades. The main rotor is controlled by the cyclic and collective sticks through a swashplate mounted about the static mast. a.   Hub Assembly. The main rotor hub is a steel and aluminum assembly that supports the main rotor blades; it is  driven  by  the  main  rotor  drive  shaft.  The  hub  rotates about a static mast, which supports it. This arrangement allows  the  static  mast,  rather  than  the  main  rotor  drive shaft, to assume all flight loads. The hub is splined to the main rotor drive shaft by means of a drive plate adapter that is bolted to the hub. The hub is secured to the static mast by a large locknut secured by multiple bolts. The hub houses  two  sets  of  tapered  roller  bearings  that  are grease-lubricated  and  sealed.  These  bearings  transfer hub loads to the static mast. Mechanical droop stops limit blade droop. When blade droop occurs, a striker plate on the pitch housing contacts a roller. The roller presses a plunger against a droop stop ring on the lower portion of the hub. b.   Pitch Housing. The pitch housing permits blade pitch  changes  in  response  to  flight  control  movements transmitted  through  the  swashplate.  This  is  made  pos- sible within the four pitch housings by V-shaped stainless steel strap assemblies that are able to twist and flap to permit blade feathering and flapping. Cyclic and collective stick inputs are transmitted to the pitch housing horns by pitch links attached to the swashplate. Feather bearings are installed inboard on the pitch housing to allow vertical and horizontal loads to be transferred from the pitch hous- ing to the hub. Centrifugal loads are transmitted by each strap assembly to the hub. c.   Lead-Lag Links. The lead-lag link for each blade is connected to the outboard end of each pitch housing and is secured in place by a pin and two bearings that al- low the link to move horizontally. The pin goes through the V-portion of each strap within the pitch housing. d.   Damper  Assemblies. Two  damper  assemblies control the lead-lag movement of each main rotor blade. Each damper attaches outboard to a link lug and inboard to a trunnion at the pitch housing. The damper contains elastomeric elements that distort to allow the blade to lead or lag. e.   Main Rotor Blades. Each main  rotor blade is a constant-chord asymmetrical airfoil. The  outboard tip is swept aft 20° and tapers to a thinner symmetrical section. The blade has a 21-inch chord. Tip weights are installed within  the  blade.  Chord-wise,  the  leading-edge  and  for- ward half of the blade is a four-cell structural box of stain- less steel and fiberglass with a stainless steel spar. The aft half of the blade has fiberglass skin with a nomex hon- eycomb core and a bendable trailing edge strip to aid in blade tracking. Each blade secured to its lead-lag link by two blade attachment pins. These pins can be removed without the use of tools and they pass vertically through the  lead-lag  link  and  blade  root  fittings  which  are  both made of titanium. Five sets of stainless steel doublers are located on the upper and lower surfaces of the blade at the blade root. The blades may be folded by removing the appropriate  blade  attachment  pin  (one  for  each  blade) and  any  two  adjacent  pitch  link  bolts  and  pivoting  the blade to the rear position using a hand-held blade support device. 2.41.2   Tail Rotor. The tail rotor is of semirigid, teetering design. Two pairs of blades, each pair fastened to its own delta hinged hub, provide antitorque action and directional control. A titanium fork houses two elastomeric teetering bearings  and  drives  the  rotating  swashplate  through  an attached  scissors  assembly.  The  tail  rotor  assembly  is splined to, and driven by, the tail rotor gearbox drive shaft which passes through a static mast. Blade pitch changes when  directional  control  inputs  cause  the  non-rotating swashplate to act upon the rotating swashplate. One pitch link  for  each  blade,  attached  to  the  rotating  swashplate and pitch horn, causes blade movement about two pitch- change bearings in the blade root. Centrifugal forces are carried by stainless steel strap assemblies that attach out- board to the blade root and inboard at the hub center. An elastomeric bearing assembly positions the hub and strap pack in the tail rotor fork. Each blade has one stainless steel spar and two aluminum spars. Doublers and rivets attach the blade to the blade root. Brackets on the root fit- ting hold chord-wise balance weights. Spanwise balance weights are installed at the tip of each blade in an alumi- num tip cap.