Drawing: Cobra Drawing: Cobra

Yoke (flexure plate)

Drawing: Yoke (flexure plate)

  1. Purpose — by flexing, it provides the door hinge effect and is preconed (2½ to 3 degrees).
  2. Attachment — bolted to trunnion with elastomeric bearing caps which restrain flapping of rotor through steel sleeves and rubber cores.


Drawing: Trunnion

  1. Purpose — provides flapping axis of main rotor
  2. Attachment — mated in top spline of the mast and secure on the top by a main rotor retaining nut and locking device. Security on the bottom is provided by split cones.

Blade grips

Drawing: Blade grip

  1. Purpose — provides the rotating portion of the blades feathering axis.
  2. Attachment — mounts on the extension by two feather bearings (tungsten carbide steel) which provide for mounting of the pitch horn on the rear side. Also provides for mounting of drag brace on the rear side and provides the outboard attaching point for the tension-torsion (TT) straps.

Main Rotor

  1. Type — B540 and K747
  2. Purpose — aerodynamic surface to produce usable lift forces and thrust.
  3. Description  B540 — The B540 is an all metal blade with a 27 inch chord. The blade weighs 227 pounds and is 226.5 inches in length with a symmetrical airfoil.
  4. Description  K747 — The K747 is a fiberglass blade with a 30 inch chord tapering to a 10 inch chord at the tip. The blade weighs 237 pounds and is 224 inches in length with an asymmetrical airfoil. This blade has a longer life span, improved performance and reduced noise level which results in increased survivability.

Drag brace

Drawing: Drag brace

  1. Purpose — To prevent the blade from leading and lagging and provide a means of sweeping the blade for cordwise balance.
  2. Attachment — Mounted on the inner trailing edge of the main rotor blade and the rear portion of the blade grip.
Main rotor mast


  1. Description — one piece tubular steel.

  2. Purpose — drive shaft extends rotational loads from the transmission to the rotor and any components mounted to the splined areas: i.e., swash plate, collective hub and sleeve.

  3. Length of mast is 77 inches

  4. Diameter of mast is 4.33 inches

Drawing: Main rotor mast


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Updated: 12 January 2008
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Born on 01 January 1999