Processing Of Titanium Tubes An Approach To Helicopter Blade Spar Manufacturing

Sikorsky Aircraft has designed, built, and fatigue tested an Improved Rotor Blade (IRB) for CH-53 helicopters. The IRB is a high-performance blade, consisting essentially of a one-piece 32-foot long titanium spar structure, a fiberglass skin, and a reinforced plastic honeycomb core. The spar is made of annealed titanium 6A1-4V tapered thickness sheet, which is fabricated into a cylindrical shape by cold brake forming. The cylindrical preform is joined to a tube shape by longitudinal butt plasma arc welding. A forged titanium 6A1-4V flange is friction welded to the root end of the welded tube to complete the one-piece spar construction. The tube assembly is simultaneously hot formed and annealed to its desired air foil shape in a ceramic die. Shot peening and a Picatinny process surface pre-treatment for subsequent bonding of fiberglass components complete the titanium spar fabrication cycle. This paper discusses alternative spar fabrication methods and describes the method selected by Sikorsky to produce titanium spars for the CH-53 Improved Rotor Blade.