The YF-23A Advanced Tactical prototype Fighter was a revolutionary statically unstable, twin engine aircraft that cruised at supersonic speeds without afterburner and was designed to out maneuver opponents at subsonic and supersonic speeds. Combining these capabilities into a chosen aircraft configuration demanded a flight control hydraulic system of unprecedented power and performance. Increased system reliability, and reduced maintenance also presented a challenging system design.
The YF-23A's unique flight and maneuvering envelope required high surface rates and large actuator excursions at low flight speeds, as well as power to generate increased hinge moments at supersonic speeds. To achieve these specifications, Northrop developed a hydraulic system that utilized flow conservation and prioritization techniques.
The hydraulic system configuration was maintained by using hydrologic, as well as electronic control. The control electronics for the YF-23A's hydraulic management system were housed within quad redundant Vehicle Management Computers (VMCs). The computers were developed from derivative flying hardware and were constrained in size and power dissipation.
The system was fully tested and verified over thousands of hours in Northrop's Vehicle Management System Laboratory (VMSL). The laboratory contained a complete Iron Bird facility that was fully representative of the real aircraft. The hydraulic system also underwent rigorous flight testing on two flying prototypes at Edwards Air Force Base (EAFB). The complete test
program demonstrated and validated that all system functions performed as designed.


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