A Retrospective Of 3600 Composite Blades

Since 1976 AH-I Cobra helicopters have been fitted with Kaman K747 composite blades. The K747 blade was designed to replace the then-current metal blade and to take maximum possible advantage of the potentials of composites. Structural tailoring for long life, dynamic properties matching and weight control was an easily attainable basic requirement. The more challenging requirements were ballistic survivability, low radar signature, world-wide environmental consideration, maintainability, repairability, increased performance and, most challenging of all, affordable cost. Design, test, development and aircraft integration proceeded at a rapid pace with all objectives met in a very successful program. The first blades were fielded in 1978. Over the next few years the K747 blade attracted a following in the Army based on performance, ruggedness and low maintenance. As time went on other factors. largely environmental in nature. presented themselves and resulted in changes and improvements. Also apparent were reactions, positive and negative, at the operational level to the new structural material from which the blade was made. An operational incident involving severe tree impact demonstrated blade ruggedness. A blade failure due to extreme temperature environment resulted in a redesign and test evaluation. Even the circumstances of blade storage presented unique problems to the metal parts. From this body of experience a large number of lessons have been learned. The objective of this paper is to relate the interesting array of problems and concerns associated with a successful composite product and tell how they have affected design practices and procedures for the generation of composite products which follow. Issues dealt with include design, testing, manufacturing, performance and field operations.