| Guy E. Franklin|
| After about five years of low-key studies, NASA and McDonnell Douglas (by now acquired by Boeing) agreed in 1994 to build an unmanned subscale aircraft to demonstrate technologies for future tailless low-observable (LO) fighter designs. Two vehicles, designated X-36A, were built, and the first one was completed in March 1996. After extensive tests, in which the X-36A was suspended on a cable beneath a helicopter, the vehicle finally made its first free flight on 17 May 1997.
The X-36A, which took off and landed on a conventional retractable tricycle landing gear, represented a notional fighter design at about 28% scale. It had LO design features like aligned edges, a wide flat jet exhaust and no vertical control surfaces. Stability and control was provided by all-moving canards and multiple flying surfaces on the wings' leading and trailing edges, the latter including drag rudders on the wingtips for yaw control. The UAV was powered by a single Williams F112 turbofan, which exhausted through a thrust-vectoring nozzle for additional yaw control. Although the X-36A was also equipped with a GPS-based autopilot, it was essentially always flown via direct remote control by a pilot on the ground. The pilot sat in a fully equipped virtual cockpit, which also included a head-up display, a moving-map display, and video imagery from a camera on the "canopy hump" of the UAV. In case of emergencies, the X-36A could be commanded to deploy a dorsal parachute package for a safe recovery.
NASA's X-36A flight test program lasted until November 1997, and consisted of 31 flights of up to 45 minutes duration. All aspects of the aircraft's operation, its flight-control software, and its full agility envelope were successfully explored. The vehicle was e.g. capable of stable flight at 40° angle-of-attack (AOA), 360° rolls at 15° AOA, and rapid turning/rolling manoeuvers at 35° AOA. The experience gained in the X-36 program probably helped Boeing a lot in the design of their X-45A UCAV (Unmanned Combat Aerial Vehicle) demonstrator.
After the NASA tests were completed, the USAF's AFRL (Air Force Research Laboratory) used the X-36A in 1998 to test its RESTORE (Reconfigurable Control for Tailless Fighter Aircraft) flight control software. RESTORE used neural network algorithms to compensate for inflight changes to the aircraft's aerodynamic configuration (caused e.g. by damage or malfunction of flight control surfaces). Similar technology was also tested around the same time by the NASA/AFRL LoFLYTE project. Two RESTORE test flights were conducted by the X-36 in December 1998, after which the two aircraft were placed in storage.
Data for X-36A:
Length 5.55 m (18 ft 2.5 in)
Wingspan 3.15 m (10 ft 4 in)
Height 0.95 m (3 ft 1.5 in)
Weight 565 kg (1245 lb)
Speed 376 km/h (234 mph) (Mach 0.35)
Ceiling 6160 m (20200 ft)
Endurance 45 min.
Propulsion Williams F112 turbofan; 3.1 kN (700 lb)
09/26/2006 @ 09:57 [ref: 14292]