Directory of U.S. Military Rockets and Missiles|
Appendix 4: Undesignated Vehicles
|Copyright © 2004 Andreas Parsch|
In 1995, Accurate Automation Corp. (AAC) was selected by the NASA and the AFRL (Air Force Research Lab) to build the airframe and control system for a sub-scale research UAV called LoFLYTE (Low-Observable Flight Test Experiment). LoFLYTE was to test the low-speed handling characteristics of an airframe optimized for hypersonic flight at Mach 5+, and to develop an automatic stabilization and control system for the vehicle. The LoFLYTE aircraft flew for the first time on 16 December 1996.
The LoFLYTE UAV is a highly-swept flying-wing delta with twin vertical fins, and is powered by a small turbojet engine in a ventral duct. It has a retractable tricycle undercarriage for conventional take-off and landing. The airframe is a so-called "waverider" shape, which can use its own shockwave at hypersonic speeds for optimized lift and drag characteristics. The aircraft is normally flown by a ground-based pilot, but is also equipped with a GPS-based navigation system for autonomous missions. The most important component of LoFLYTE is its Neural Adaptive Controller (NAC) flight control system, also designed by AAC. It is a "neural network" consisting of many interconnected computer "nodes" with a dynamic and self-adapting control logic. This network is supposed to be able to "learn" to keep the aircraft automatically stable similar to the way a human brain learns things by dynamically changing the properties of the connections between its neurons. The basic idea of the LoFLYTE program was that if such a neural network can learn to handle a hypersonic airframe at low speeds (which is one of the most difficult aerodynamic control tasks), it can do that for any other configuration as well. It was actually planned to remove the vertical fins once the flight control system was able to keep the aircraft completely stable.
The LoFLYTE flight tests were conducted by the USAF's 419th and 445th Flight Test Squadrons at Edwards AFB. The first flight had uncovered basic control problems, and flight testing did not resume before June 1997. For the rest of that year, the basic handling characteristics were established, which showed that a Mach 5+ shape could indeed take off and land on a runway at "normal" speeds. These initial tests were not yet flown with the NAC, and used a conventional computerized stabilization and control system instead. Actual flight tests using the NAC began in December 1997 and continued into 1998. The flights also included tests which were to show the ability of the NAC to handle changed airframe configurations and (simulated) damage to the control surfaces. It must be noted that LoFLYTE was never intended to fly at anywhere near the speed suggested by its waverider shape.
From that point on, the history of the LoFLYTE project becomes a bit unclear. NASA's and the USAF's involvement with LoFLYTE probably ended at some time in 1998. However, the tests must have been reasonably successful, because NASA awarded AAC a follow-on contract for the HyFLYTE UAV, later called the "X-43A-LS" (LS = Low Speed). This vehicle was actually built and flown, and tested the low-speed handling of the X-43A Hyper-X Mach 10 configuration using the NAC flight control system. The LoFLYTE itself, of which AAC built a total of three examples, was apparently still used for general research into neural network control systems as late as 2002. Whether this research included actual test flights is unclear.
Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!
Data for LoFLYTE:
|Length||2.54 m (8 ft 4 in)|
|Wingspan||1.58 m (5 ft 2.2 in)|
|Height||0.61 m (2 ft)|
|Weight||32 kg (70 lb)|
|Speed||465 km/h (290 mph)|
|Propulsion||SWB Turbines SWB-3 turbojet; 0.156 kN (35 lb)|
 Kenneth Munson (ed.): "Jane's Unmanned Aerial Vehicles and Targets, Issue 15", Jane's, 2000
 Accurate Automation Corp. Website
 NASA's LoFLYTE™ Program Flown, NASA Langley Research Center, 1997
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