Thursday, November 5, 2009

The Bell X-2 "Starbuster

The Bell X-2 "Starbuster was a research aircraft built to investigate flight characteristics in the Mach 2-3 range.
Providing adequate stability and control for aircraft flying at high supersonic speeds was only one of the major difficulties facing flight researchers as they approached Mach 3. For, at speeds in that region, they knew they would also begin to encounter a "thermal barrier", severe heating effects caused by aerodynamic friction. Constructed of stainless steel and a copper-nickel alloy, and powered by a two-chamber XLR25 2,500 to 15,000 lbf (11 to 67 kN) sea level thrust throttleable rocket engine, the swept-wing Bell X-2 was designed to probe this region.
Following launch from a modified B-50 bomber, Bell test pilot Jean "Skip" Ziegler completed the first unpowered glide flight of an X-2 at Edwards Air Force Base on 27 June 1952. Ziegler and aircraft #2 were subsequently lost on 12 May 1953, in an inflight explosion during a captive flight intended to check the aircraft's liquid oxygen system.[1][2]

Lt. Col. Frank K. "Pete" Everest (1920-2004) completed the first powered flight in the #1 airplane on 18 November 1955 and, by the time of his ninth and final flight in late July the following year, he had established a new speed record of Mach 2.87 (1,900 mph, 3050 km/h). The X-2 was living up to its promise, but not without difficulties. At high speeds, Everest reported that its flight controls were only marginally effective. High speed center of pressure shifts along with fin aeroelasticity were major factors. Moreover, simulation and wind tunnel studies, combined with data from his flights, suggested that the airplane would encounter very severe stability problems as it approached Mach 3.

A pair of young test pilots, Captains Iven C. Kincheloe and Milburn G. "Mel" Apt, were assigned the job of further expanding the envelope and, on 7 September 1956, Kincheloe became the first pilot ever to climb above 100,000 ft (30,500 m) as he flew the X-2 to a peak altitude of 126,200 ft (38,466 m). Just 20 days later, on the morning of 27 September, Mel Apt was launched from the B-50 for his first flight in a rocket airplane. He had been instructed to follow the "optimum maximum energy flight path" and to avoid any rapid control movements beyond Mach 2.7. Flying an extraordinarily precise profile, he became the first man to exceed Mach 3 that day, as he accelerated to a speed of Mach 3.2 (2,094 mph, 3,370 km/h) at 65,500 ft (19,960 m). The flight had been flawless to this point, but, for some reason, shortly after attaining top speed, Apt attempted a banking turn while the airplane was still well above Mach 3 (lagging instrumentation may have indicated that he was flying at a slower speed or perhaps he feared he was straying too far from the safety of his landing site on Rogers Dry Lake). The X-2 tumbled violently out of control and he found himself struggling with the same problem of "inertia coupling" which had overtaken Chuck Yeager in the X-1A nearly three years before. Yeager, although exposed to much higher vehicle inertial forces, as a result of extensive experience flying the X-1 was very familiar with its character, was able to recover. Unlike Yeager, Apt was unable to recover and both he and the aircraft were lost.

While the X-2 had delivered valuable research data on high-speed aerodynamic heat build-up and extreme high-altitude flight conditions, this tragic event terminated the program before the National Advisory Committee for Aeronautics could commence detailed flight research with the airplane, and the search for answers to many of the riddles of high-Mach flight had to be postponed until the arrival, three years later, of the most advanced of all the experimental rocket planes, the North American X-15.

Flight test program

Two aircraft completed a total of 20 flights (27 June 1952 - 27 September 1956).
  • 46-674: seven glide flights, 10 powered flights, crashed 27 September 1956[2]
  • 46-675: three glide flights, destroyed 12 May 1953
General characteristics
  • Crew: one, pilot
  • Length: 37 ft 10 in (11.5 m)
  • Wingspan: 32 ft 3 in (9.8 m)
  • Height: 11 ft 10 in (3.6 m)
  • Wing area: 260 ft² (24.2 m²)
  • Airfoil: 2S-50 bicon
  • Empty weight: 12,375 lb (5,600 kg)
  • Loaded weight: 24,910 lb (11,300 kg)
  • Max takeoff weight: 24,910 lb (11,300 kg)
  • Powerplant: 1× Curtiss-Wright XLR25 rocket engine, 15,000 lbf (67 kN)at sea level
  • Maximum speed: Mach 3.196 (2,094 mph, 3,370 km/h)
  • Service ceiling: 126,200 ft (38,466 m)

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