XCOR Aerospace EZRocket

One of the newest rocketplanes is the liquid-fueled EZ-Rocket. It was converted into a rocketplane by a team at XCOR Aerospace in Mojave, California, from a Rutan Long-EZ. Test pilot Dick Rutan flew it for the first time on July 21, 2001. The rocketplane burns isopropyl alcohol fuel and LOX in a pressure-fed Kevlar-shielded engine, with the composite pressurized fuel tank slung beneath the fuselage. The oxidizer is stored internally in an insulated aluminum tank. Two regeneratively cooled 400-lb thrust engines power the EZ-rocket, with chamber pressures of about 350 psi and specific impulse of some 250-270 s, better than either the Bell X-1 or the Mercury Redstone. A 20-s 1,650-foot takeoff roll lifts the fully fueled EZ-rocket into the air, whereupon it can fly 10 miles in as many minutes, or climb at 6,000 ft/min. Because the pusher-prop has been removed and replaced with a rocket engine, the EZ-Rocket is aerodynamically "cleaner" than the original Long-EZ, increasing its glide range. On December 3, 2005, Dick Rutan established a point-to-point world record for the EZ-Rocket by flying 16 km in less than 10 min in a flight from the Mojave Spaceport to California City, California. This set a new world record for ground-launched rocket-powered aircraft. Recall that the NACA rocketplanes and NASA lifting bodies were all air-launched.

The EZ-Rocket has an engine burn time of min, a best rate of climb speed (V) of 145 knots, and a never-exceed speed (Vne) of 195 knots. The maximum speed is determined by stresses on the airframe rather than by engine capability. Climbing at 145 knots gives the best performance - faster climb speeds would just create more drag on the airframe. The greatest altitude flown by the EZ-Rocket was 11,500 ft. During its 4^-year test program, the EZ-Rocket flew 26 times, including twice at Oshkosh 2002, and three times at the Countdown to the X-Prize Cup in Las Cruces, New Mexico, in 2005. These flights lasted up to 10 min, including the glide portion.

The EZ-Rocket accomplished many "firsts" in rocket aviation. In addition to the world distance record mentioned above, it was the first ground-launched rocketplane to demonstrate restart of its rocket engine in flight, the first to perform touch-and-goes, and the first to arrive at Mojave Spaceport, which it did on its last flight, December 15, 2005, returning from California City. The EZ-Rocket has a ground crew of just five and a cost per flight of only $900. A large portion of this expense is in the fuel-pressurizing system, which uses helium gas. This cost will come down when XCOR installs its in-house-developed piston-pumps in future rocketplane models, such as the X-Racer (Fig. 1.20).23

Fig. 1.20 Artistic impression: fleet of rocket racers over the mountains (courtesy Rocket Racing League)

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