The Douglas X-3 Stiletto was an experimental jet aircraft with a slender fuselage and a long tapered nose, manufactured by the Douglas Aircraft Company.
Its primary mission was to investigate the design features of an aircraft suitable for sustained supersonic speeds, which included the first use of titanium in major airframe components.
It was, however, seriously underpowered for its purpose and could not even exceed Mach 1 in level flight. The Douglas X-3 Stiletto was the sleekest of the early experimental aircraft, but its research accomplishments were not those originally planned.
The goal of the aircraft was ambitious - it was to take off from the ground under its own power, climb to high altitude, maintain a sustained cruise speed of Mach 2, then land under its own power.
The aircraft was also to test the feasibility of low-aspect ratio wings, and the large-scale use of titanium in aircraft structures.
The X-3 rolled as expected, but also pitched up 20 degrees and yawed 16 degrees. The aircraft gyrated for five seconds before Walker was able to get it back under control. He then set up for the next test point. Walker put the X-3 into a dive, accelerating to Mach 1.154 at 32,356 feet (9,862 m), where he made an abrupt left roll.
The aircraft pitched down and recorded an acceleration of -6.7 g (-66 m/s²), then pitched upward to +7 g (69 m/s²). At the same time, the X-3 side-slipped, resulting in a loading of 2 g (20 m/s²). Walker managed to bring the X-3 under control and successfully landed.
For the X-3, the roll coupling flight was the high point of its history. The aircraft was grounded for nearly a year after the flight, and never again explored its roll stability and control boundaries. Walker made another 10 flights between September 20, 1955, and the last on May 23, 1956.
The aircraft was subsequently retired to the US Air Force Museum. Although the X-3 never met its intention of providing aerodynamic data in Mach 2 cruise, its short service was of value. It showed the dangers of roll coupling, and provided early flight test data on the phenomena. Its wing planform was used in the F-104, and it was one of the first aircraft to use titanium. Finally, the X-3's very high take off and landing speeds required improvements in tire technology.
Video 1: Douglas X-3 Stiletto
Video 2: Douglas X-3 Stiletto
(This text was adapted from http://www.wikipedia.org/ )(GFDL)
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