Superfortresses and Rocket Planes

The United States developed the first rocket-propelled, transonic research aircraft after World War II. Bell Aircraft developed the X-1 under contract to the Army Air Force. Douglas Aircraft developed the D-558-II Skyrocket under contract to the Navy. Due to the low power of the jet engines available at the time, both research aircraft were to be powered by rocket engines built by Reaction Motors Incorporated. The Bell X-1 used the XLR-11 and the Douglas Skyrocket used the nearly identical XLR-8. Each rocket was composed of four combustion chambers that could be individually toggled on and off. Each combustion chamber produced about 1,500 pounds of thrust, with a combined total thrust of about 6,000 pounds. The fuel used by these rocket engines was ethyl alcohol mixed with water. The oxidizer was liquid oxygen. The general configuration of the X-1 was established by May 1945. The fuselage had an ogive profile inspired by a 50-caliber bullet, because the bullet was known to be stable in supersonic flight. The Army Air Technical Service Command dictated that the design should have a straight wing. It was 30 feet 11 inches long with a wing span of 28 feet. In August 1945, the National Advisory Committee for Aeronautics (NACA) and the Navy requested Douglas to study a design for the D-558-II with a 35-degree swept wing. It was 42 feet long with a wing span of 25 feet. It was equipped with retractable landing gear mounted in the fuselage and would take off from the ground. It was to be powered by an XLR-8 rocket engine with 6,000 pounds of thrust and an engine burn time of 100 seconds. The propellants would be fed to the rocket engine by two hydrogen peroxide- powered turbopumps. The rocket engine would be augmented with a 3,000-pound thrust Westinghouse 24C (later designated J34) turbojet engine. The jet provided extra power on take-off, conserved rocket fuel on the climb to altitude, and powered the airplane following the exhaustion of the supply of rocket fuel.