There were some vigorous debates about what configuration the research plane should take. The navy, naturally enough, leaned toward an aircraft with military oriented features, so that derivatives of it could be used in combat. NACA, on the other hand, preferred a strictly research vehicle. I agreed with the latter, since there was salient concern for learning what we were up against in the transonic area. We had to identify the problems inherent in this regime before building combat machines to operate within it. 3
The initial D-558s would be designed around the General Electric TG-180 turbojet, the most powerful engine then available. 4 Named Skystreak, the D-558-1 had a straightforward design that featured a cylindrical-section fuselage with a nose air intake, a small canopy over the forward-positioned cockpit, and short, stub wings mounted low on the fuselage. Two 50-gallon wingtip tanks could be fitted to supplement the 230 gallons of fuel carried in the fuselage. The initial aircraft were fitted with the J35-A-11 turbojet, an Allison-built version of the TG-180.
The first D-558-1—painted bright red—took off from the Muroc Dry Lake (later Edwards Air Force Base) on 15 April 1947, flown by a Douglas test pilot. On 20 August, Commander Turner Caldwell reached 640 mph, setting a world speed record. This flight marked the first time since 1923 that a Navy aircraft exceeded an Army speed record—by 17 mph. Five days later Marine test pilot Major Marion Carl broke Caldwell's mark, pushing a Skystreak to 650.796 mph.
The two D-558-1 aircraft flown by Navy, Marine Corps, and Douglas pilots were subsequently turned over to the NACA for further research flights. A third D-558-1 was delivered to NACA. The second aircraft crashed on takeoff on 3 May 1948, killing NACA test pilot Howard C. Lilly, the first committee test pilot to die in the line of duty.
The third D-558-1 aircraft continued in NACA service, being used to develop data for handling high-speed subsonic aircraft. Its last flight was on 10 June 1953. (The first D-558-1 was used by NACA to provide spares for the other aircraft.) Meanwhile, Douglas responded to an August 1945 request by the Navy to begin design studies for a more advanced research aircraft that would be capable of supersonic speeds.
This project became the D-558-2 Skyrocket. The aircraft would have both turbojet and rocket engines, the latter with sufficient fuel for two minutes of operation to provide supersonic flight. While Douglas initially looked at a swept-wing variant of the D-558-1 aircraft, it soon became obvious that a complete redesign was needed to accommodate the composite power plant. In January 1947 the Navy approved the change of the last three D-558-1 Skystreaks to be produced as D-558-2 Skyrockets.
Again, Ed Heinemann would supervise the project, with Kermit E. Van Every leading the design team. The D-558-2 had a larger circular-section fuselage with mid-mounted swept wings. The pilot sat in a jettisonable compartment in the nose of the aircraft. As initially configured, the D-558-2 would have a Westinghouse J34-WE-40 turbojet and a Reaction Motors XLR-8-RM-5 four-chamber rocket engine. The turbojet's air intakes were fitted aft of the cockpit, low in the fuselage.
The initial flights were without the rocket engine. On 4 February 1948 a Douglas pilot lifted the first D-558-2 from Muroc on its maiden flight. According to aviation historian Ren?
Francillon, the initial test flights "indicated that with only the turbojet installed the aircraft had a sluggish performance, particularly on take-off, that visibility from the cockpit was poor, and that directional stability was inadequate." 5
Modifications were made to the aircraft, and the first D-558-2 was restricted to subsonic tests until mid-1949 when the rocket engine was installed. From the first flight with a composite power plant in October 1949, the aircraft was flown only by Douglas and, on one occasion in 1956, by NACA pilots. (That plane was officially retired in March 1957.)
The second D-558-2, also sans rocket engine, was delivered in late 1948 and began a rigorous flight-test program by Douglas and NACA pilots. It was then returned to Douglas for installation of the rocket motor. The third aircraft began flight tests on 8 January 1949. During the manufacturer's tests, it exceeded Mach 1 on 24 June 1949.
By this time the Navy and Douglas decided that air-launch of the D-558-2 would be more efficient, and the two later aircraft were modified to be carried aloft by a P2B-1S, a modified B-29 Superfortress, and released in flight (as was the Bell XS-1). The first air launch, with a Douglas pilot at the controls, was by the second D-558-2 from an altitude of 24,850 feet, on 8 September 1950. It had been extensively modified, with the turbojet removed and a more powerful XLR-8-RM-6 four-chamber rocket installed.
Flown by Douglas test pilot William B. Bridgeman, the second D-558-2 set several records, reaching Mach 1.88 on 7 August 1951, and 74,494 feet on 15 August. Then, it too was turned over to NACA for continued flight testing, with advisory committee and service pilots at the controls.
Marion Carl reached a record 83,235 feet in that aircraft on 21 August 1953, and three months later, on 20 November, NACA's Scott Crossfield pushed the D-558-2 into a dive from 72,000 feet and reached Mach 2.005—1,291 mph—the first vehicle to exceed Mach 2. (A month later the Air Force's Bell X-1A exceeded that speed.) The Skyrocket continued flying until 20 December 1956.
At Douglas, studies were begun on a follow-up research aircraft, sometimes referred to as a D-558-3 or Douglas Model 671. This aircraft was intended to explore hypersonic flight. In a ballistic trajectory the aircraft was envisioned to reach an altitude of about 700,000 feet and on the return to earth attain hypersonic speeds, possibly as high as Mach 9. The lack of funds and the availability of the North American X-15 to explore high-speed flight, however, led to cancellation of that project.
Rene Francillon summarized the Douglas effort: "the D-558 programme in general and the D-558-2 in particular were both highly useful and truly spectacular. While very different in nature from the better known Douglas achievements, they contributed most brilliantly to the Douglas share in the development of aviation." 6
1. Yeager reached Mach 1.015—670 mph at an altitude of 42,000 feet—flying a Bell XS-1 rocket-propelled aircraft. The aircraft was released in flight from a B-29 Superfortress over Muroc, California.
2. Mach numbers express aircraft speed as the ratio of the velocity of a moving body to the local velocity of sound. Thus Mach 1 equals 760.98 mph at sea level at 59?? F. The term is named for Dr. Ernest Mach.
3. Edward H. Heinemann and Rosario Rausa, Ed Heinemann: Combat Aircraft Designer (Annapolis, MD: Naval Institute Press, 1980), p. 143.
4. A comprehensive description of the D-558 project is found in Ren?
J. Francillon, McDonnell Douglas Aircraft since 1920 (London: Putnam, 1979), pp. 434-439, 447-455.
5. Francillon, p. 449.
6. Francillon, p. 455.