As of mid-2001 the X-39 designator was apparenty unassigned, but it is reported to be reserved for use by the Air Force Research Laboratory. The designation may be intended for subscale unmanned demonstrators planned under the Future Aircraft Technology Enhancements (FATE) program, which was sponsored by Wright Laboratory (WL) in Dayton, Ohio.
FATE develops revolutionary technologies that will become the foundation for next generation warfighters. It will be these new systems that will provide the US with air and space superiority into the 21st century. Examples of FATE technologies include affordable low-observable data systems, active aeroelastic wing, robust composite sandwich structures, advanced compact inlets, photonic vehicle management systems, self-adaptive flight controls and electric actuation. Each of the major airframers has performed a long-range study on next-generation aircraft.
A subset of the national Fixed Wing Vehicle (FWV) Program, FATE was structured with three phases:
- FATE I, Phase I: Define a set of aircraft technologies that must be flight test validated in a new air vehicle to meet FWV Phase I program goals for a fighter attack class of aircraft, including both inhabited and uninhabited aircraft.
- FATE I, Phase II: Develop preliminary vehicle design concepts, a demonstrator system, and demonstration plans.
- FATE II: Develop, build and flight-test a demonstrator vehicle to achieve program goals.
FATE I, Phase I was used as a jump start for the Unmanned Combat Air Vehicle Advanced Technology Demonstration [UCAV ATD] that will replace the FATE activity.
In the past, tailless aircraft directional control has been provided by spoilers or drag rudders. This was done to decouple the control system as much as possible. Unfortunately, spoilers and drag rudders have high attendant actuator requirements (a result of large hinge moments) and provide inadequate control power at high AOA. With quantum advances in throughput capabilities of digital processors, it is now possible to take advantage of advanced integrated/adaptive flight control techniques that make a decoupled control effector a requirement. As a result, more efficient aerodynamic controls, like the all-moving wing tip or spoiler-slot-deflector, can now be used for tailless aircraft lateral-directional control. Integration of these effectors reduces control suite weight fraction 5%, reduces hydraulic power requirements 45% (because hinge moments are much less than those of conventional surfaces), and vastly improves high-AOA flying qualities. All of these factors contribute to improved agility. Advanced flight control technologies that enable these unconventional effectors also reduce FCS complexity and cost and will reduce loss-of-control related accidents and mission-critical vulnerability.
The Future Aircraft Technology Enhancements Program was sponsored by Wright Laboratory (WL) FI in Dayton, Ohio, and originally led by Captain Mark Cherry, the program manager. Captain Cherry subsequently was replaced by a new program manager Mr. Tom Black, who also serves as chief engineer. Program tasks were authorized and performed under Contract No. F33615-97-C-3804 from June through October 1997. FATE was performed to "develop revolutionary technologies that will become the foundation for next generation warfighters."
Thrust vectoring is not required for the FATE vehicle to fly throughout the majority of its flight envelope; it is only required in high AOA conditions. If it is desired to fly the FATE vehicle at a high AOA, an axisymmetric vectoring nozzle could be used instead. The IHPTET program will perform a ground demonstration of a conformal fluidic nozzle. However, the nozzle and the engine will not be representative of flight hardware and are not representative of the engine/nozzle combination required for the FATE vehicle. A ground demonstration with an F404 engine must be performed to prepare the conformal fluidic nozzle for the FATE Program. This project is currently unfunded. If the conformal fluidic nozzle technology is not ready in time for FATE, a fixed nozzle without thrust vectoring can be installed in the FATE aircraft.
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