To: Vfrpilotpb
The Sikorsky blades of that era were made in the following way. The primary load-carrying member is an aluminum spar. The spar is hollow and is extruded. In the extrusion process the interior surface of the spar is formed with several strips in the form of an omega. These omega strips as they were referred to provided a degree of stiffness preventing or limiting inplane or spanwise bending. The spar is hard anodized to protect it from erosion and corrosion.
The spar is placed in a jig that imparts a 7-degree negative twist, which helps to minimize the upward bending of the blade during flight. The inward end of the spar is drilled and a cuff is attached. This cuff is the connection with the rotor head. The trailing edge of the spar has a cut in the upper and lower surface that provides a mechanical connection for the individual pockets. The pockets are the rear portions of the airfoil and there are a number of them depending on the type of blade. The pockets are bonded onto the trailing edge of the spar and are also fitted into the cut thus providing a strong connection to the spar. To complete this process the spar and bonded pockets are placed in an autoclave which sets the bonded surfaces.
The blade is then statically balanced against a known weight. This is done on a knife-edge balance fixture. Weights are added to the outward end of the spar until the blade is in balance. These weights are capable of being moved forward and rearward to provide aerodynamic balance.
Once the blade is complete it is placed on a whirl stand and dynamically balanced against a master blade. The master blade has all of all the desired aerodynamic characteristics, which ensures the ability to change blades without extensive alterations as all of the blades of a given type are aerodynamically the same and are completely interchangeable.
I had to dredge my memory bank almost 48 years. The above description is basic as there is a lot more too it.
