The significance of the Douglas D-558-2 was that it was the first airplane to reach twice the speed of sound. The Skyrocket (Fig. 1.10) was sponsored by the NACA and the US Navy, and there was keen competition with the NACA/USAF team and their X-1 program to be the first with this milestone. To accomplish it, pilots and engineers spared no effort. By adding nozzle extensions, waxing the wings, and chilling the alcohol fuel to increase its density, it was hoped that the Skyrocket could be the first to reach Mach 2. NACA test pilot Scott Crossfield reached this goal on November 20, 1953, just a little over 6 years after Chuck Yeager pierced Mach 1 in the X-1. This milestone was accomplished at an altitude of 72,000 ft.
The Douglas Skyrocket used the same engine as that of the X-1, with its own Navy designation (XLR-8), but it had a 35° swept wing rather than the straight wing of the X-1. Its wing area was 175 sq ft, compared to 130 sq ft for the X-1. Three Skyrockets were built for the USN, and together they made 313 flights during the 8-year test program. The Skyrocket was both jet- and rocket-powered. The first Skyrocket was initially powered only by a 3,000-lb thrust turbojet and carried 260 gallons of aviation gasoline. This was later replaced by the 6,000-lb thrust rocket engine. The second Skyrocket had the rocket engine only. And the third vehicle used both jet and rocket engines at the same time. Rocket propellants were LOX and diluted ethyl alcohol. The third Skyrocket, which flew 87 times, was able to carry 260 gallons of aviation gasoline, 179 gallons of LOX, and 192 gallons of rocket fuel.8
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