The Douglas F4D Skyray (later redesignated F-6) was the first carrier-based fighter to break the world's absolute speed record and was the first Navy fighter capable of exceeding Mach 1 in level flight. Although it served with the Navy for only a short time and never fired its weapons in anger, it is still fondly remembered as an extremely attractive airplane. The Skyray also has the distinction of being the only Navy interceptor ever to be assigned to the North American Air Defense command, serving with VFAW-3, an all- weather interceptor unit based at NAS North Island, San Diego.
The Douglas F4D Skyray was the result of a 1947 Navy design competition for a new aircraft based on delta wing planforms. Analysis of the studies carried out by Dr. Alexander Lippisch on delta winged aircraft in Germany during the war attracted a considerable amount of interest on the part of both the US Army Air Forces and the US Navy, since such aircraft offered particular promise in the design of fast-climbing interceptors.
Several manufacturers submitted proposals for interceptor aircraft to the Navy that embodied a delta-winged format. On June 17, 1947, the US Navy Bureau of Aeronautics (BuAer) selected the Douglas proposal as being the best of the lot, and a contract was awarded for a preliminary design study.
Douglas engineers E. H. Heinemann and C. S. Kennedy directed the preliminary design study. Very early on, the pure delta planform was abandoned in favor of a tailless aircraft with a pair of mid-mounted, thin, low aspect-ratio, highly-sweptback wings with round tips. The single turbojet was fed by a set of lateral air intakes located in the wing roots. The deepened fuselage provided additional space for fuel, whereas the wing itself had leading edge slats and trailing-edge elevons. A set of trimmers were installed on the inboard trailing edges of the wing next to the jet engine exhaust. These trimmers were to be locked full-up on takeoff to provide a strong nose-up moment, leaving the larger outboard elevons in their most-effective neutral position. The outer wing panels folded hydraulically for carrier stowage. The tricycle undercarriage had to be supplemented by a small retractable tailwheel mounted under the rear fuselage because of the aircraft's high angle of incidence during takeoff and landing. The tailhook extended from the base of the tailwheel assembly. The armament was to be four 20-mm cannon, the guns being mounted in the wing roots just outboard of the main wheels, their muzzles being located slightly below and behind the wing leading edges. The cockpit was situated well forward in the nose and was equipped with a Douglas- designed ejector seat.
The engine was to be the afterburning Westinghouse J40 turbojet, which was the powerplant of choice for the next generation of high-performance Navy aircraft such as the McDonnell F3H-1 Demon, the Grumman F10F Jaguar, and the Douglas A3D Skywarrior. With this engine, it was estimated that the Douglas design should be able to achieve a maximum speed in level flight slightly greater than Mach 1, and would have an initial climb rate exceeding that of all other contemporary fighters. However, Ed Heinemann was not all that confident in the ultimate success of the J40, and he provided ample space in the engine bay of his new design so that a different engine could be installed if needed. It turned out that Heinemann's caution was well-founded.
On December 16, 1948, Douglas was awarded a contract for the construction and testing of two prototypes. The designation XF4D-1 was assigned. The BuAer serials were 124586 and 124587.
The airframe was completed in 1950, but the 7000 lb.s.t. Westinghouse XJ40-WE-6 engine that was intended for the XF4D-1 had experienced serious development delays and was not yet ready for flight. Rather than wait until the J40 was completed, Douglas decided to install a 5000 lb.s.t. Allison J35-A-17 turbojet in the two XF4D-1 airframes for the initial testing. XF4D-1 BuNo 124586 took off on its maiden flight on January 23, 1951, test pilot Robert Rahn being at the controls. The similarly-powered second prototype flew shortly thereafter. The first prototype had a clamshell-type canopy, whereas the second had a rearward-sliding canopy. The clamshell canopy was adopted for the production version. The Navy ordered an initial production batch of 12 F4D-1s in February of 1951.
With the J35, the XF4D-1 was seriously underpowered. Nevertheless, with the exception of a few minor control problems, the XF4D-1 was highly maneuverable and had a good climb rate. The XF4D-1 prototypes were both re-engined with the 7000 lb.s.t. non- afterburning XJ40-WE-6 when it finally became available. This engine made it possible for the XF4D-1 to exceed the speed of sound.
In the spring of 1952, a production order was issued for 230 production F4D-1s They were to be built in a formerly government-owned plant in Torrance, California.
In the automn of 1953, the afterburning XJ40-WE-8 was finally available, and examples were installed in both prototypes. The thrust of the engine was 11,600 lb.s.t. with afterburning. The XJ40 turbojet was highly temperamental and was prone to sudden inflight failures, but it did enable the high-speed performance profile of the XF4D-1 to be explored. On October 3, 1953, BuNo 124587 flown by Navy Lt-Cdr James B. Verdin set a new world's air speed record of 752.944 mph over a three-kilometer course above the Salton Sea in California. This was the first time in history that the world air speed record had been captured by a carrier-based aircraft. On October 16 of that year, Douglas test pilot Bob Rahn used the same aircraft to set a 100-km closed course speed record of 728.11 mph over Muroc Dry Lake.
In the meantime, the problems with the J40 were beginning to get very serious. The engine would not deliver the expected thrust output, and was notoriously unreliable, being subject to sudden inflight failures, fires, and explosions. By March of 1953, the J40's problems were beginning to make the Navy very nervous, and in that month the decision was made to adapt the Skyray to the Pratt & Whitney J57 axial flow turbojet as insurance in case the J40 project should fail. The J57 was not only more reliable than the J40, it was also more powerful. However, it was also quite a bit larger and heavier than the J40, requiring that up to 80 percent of the airframe be modified in order to accommodate it.
It was a good thing that this decision to replace the J40 was made, because the J40's problems proved to be insoluble, and the entire J40 program had to be cancelled. The J40 episode was a sorry experience for all concerned, especially for Westinghouse, which was driven out of the jet engine manufacturing business altogether.
In October of 1953, while work on the J57-powered production F4D-1 was getting underway, the XJ40-WE-8-powered XF4D-1 was used for carrier qualification trials aboard the USS *Coral Sea*. The tests were carried out by LtCdr James Verdin in fairly foul weather. These conditions made it possible to test the aircraft's low-speed stability on approach with its leading-edge slats.
The second XF4D-1 (BuNo 124587) was loaned to General Electric in 1956 for use as a test bed for the J79 turbojet and later for the CJ805-3 turbojet which was intended for the Convair 880 commercial jet transport.
124587 is now on display at NAWC China Lake, California, restored in its original configuration. 124586 was destroyed during fire-fighting practice back in the 1980s.
BuNo 124586 and 124587 Douglas XF4D-1 Skyray