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The helicopter's unique ability to transport large work crews and heavy equipment to remote areas quickly, cheaply, and efficiently will become increasingly important and useful as easily accessible resources are depleted. The introduction of large helicopters into operation will result in increased capabilities and expanded application of helicopter transport. Because costs prohibit certifying a new large helicopter, updating and adapting existing machines, developed under military programs is a very desirable approach. The Boeing Vertol CH-47 “Chinook” helicopter is a prime candidate for this opportunity due to its successful history in the U.S. Army as well as with foreign users.

In this decade we are witnessing the transition from all metal to all composite helicopter rotor blades. One such helicopter is already in full scale production. A driving factor is structural reliability and guarantee against catastrophic failure. Low crack propagation rate and the nature of failures in composite structures are the characteristics which make this quality product superior to metal structures for rotor blades. The ability to economically tailor blades aerodynamically and dynamically offer important advances in performance, flying qualities, low stress levels, and low vibratory forces.

This paper is a summary of the characteristics and development program for the U.S. Army heavy lift helicopter (HLH) fly-by-wire flight control system. The evolved control system consists of a triple channel direct electrical linkage which replaces the mechanical controls between the cockpit and the rotor control actuators and a triplex digital automatic flight control system. The direct electrical linkage has been successfully tested in a demonstration helicopter. The test helicopter utilized triple hydraulic driver actuators to control existing power actuators. In the HLH, the driver and power functions will be integrated into a single rotor control actuator consisting of a triple control stage and dual power stage. Transmission-driven dual hydraulic systems at each rotor head supply the two power stages and two of the control stages. A separate electrically driven hydraulic pump supplies the third section of the triplex control stage.