TITANIUM SPAR MANUFACTURING DEVELOPMENT

Sikorsky Aircraft has recently introduced a family of titanium spar composite rotor blades into production. Developed over the past 7 years, the titanium spar rotor blade used on the U. S. Navy CH-53E, the U. S. Army UH-60A (UTTAS) and the commercial S-76 take advantage of the high strain allowable of titanium to permit aerodynamic optomization of the airfoil for both high speed cruise and hovering performance. The blades incorporate both high twist for improved hovering capability and an advanced SC 1095 airfoil for improved high speed forward flight. The titanium spar provides the fatigue capability for both. The CH-53E, UH-60A and S-76 rotor blades are all high performance blades. All consist essentially of a one piece titanium spar structure, fiberglass covering skins, Nomex honeycomb core in the pocket area and titanium and electroformed nickel leading edges for abrasion resistance. The spars for all three blades are made of annealed 6 A1 - 4Va titanium sheet which is cold brake formed into a constant diameter cylindrical shape. The seam is plasma-arc welded in a single pass without the use of filler to produce a high quality joint. The total assembly is then simultaneously hot formed to the desired airfoil shape and annealed in ceramic dies. This paper discusses the manufacturing research and development that lead to this unique construction technique as well as the very important tooling concepts and fabrication techniques now being used in the production of the blade.