The Douglas F4D Skyray, later redesignated as the F-6 Skyray, is an American carrier-based fighter/interceptor that was designed and produced by the Douglas Aircraft Company.
It was the final fighter produced by the Douglas Aircraft Company before its merger with McDonnell Aircraft to become McDonnell Douglas.
The development of the Skyray began during the late 1940s as the D-571-1 design study, which was a delta wing interceptor capable of a high rate of climb to permit the rapid interception of approaching hostile bombers.
Douglas’ proposal was selected by Navy officials to fulfill a formal requirement issued in 1948.
However, the decision to adopt the Westinghouse J40 turbojet engine to power it led to considerable difficulties later on as this engine was cancelled prior to entering production.
Aerodynamic issues also led to a protracted development cycle, with considerable design changes being made even after the maiden flight of a production standard Skyray in June 1954.
The Skyray was declared ready for fleet introduction in April 1956, permitting its entry to service with both the United States Navy (USN) and United States Marine Corps (USMC) shortly thereafter.
Despite its relatively brief service life, during which it never participated in actual combat, the Skyray was the first carrier-launched aircraft to hold the world’s absolute speed record, having attained a top speed of 752.943 mph (1,211.744 km/h).
It was also the first USN and USMC fighter that could exceed Mach 1 in level flight and set a new time-to-altitude record, flying from a standing start to 49,221 feet (15,003 m) in two minutes and 36 seconds, all while flying at a 70° pitch angle.
The last Skyrays were withdrawn from service in February 1964, although a handful continued to be flown for experimental purposes by the National Advisory Committee for Aeronautics (NACA) up to the end of the decade.
The F5D Skylancer was an advanced development of the F4D Skyray that ultimately did not enter service.
The Skyray was conceived as part of a design study, the D-571-1, conducted by Douglas and funded by the United States Navy (USN).
It was a pure interceptor with exceptional climbing capabilities, utilizing a delta wing configuration and powered by a pair of Westinghouse J34 turbojet engines equipped with afterburners for additional acceleration.
The D-571-1 featured a relatively thick wing with a pod-like cockpit in a forward position, and four 20mm cannons extending forward of the leading edge of the wing.
Alternative armaments included spin-stabilized rockets.
The design study incorporated the research of German aerodynamicist Alexander Lippisch, who moved to the United States after World War II, and was examined by several members of Douglas’ design team.
In June 1947, the Navy awarded a contract to Douglas to proceed with preliminary investigation and engineering works on the concept up to the mock-up stage.
As the design was refined, the wing’s thickness was substantially reduced to increase its high-speed capabilities, and the twin J34 engine arrangement was replaced with a single Westinghouse J40 engine.
The Skyray was equipped with only a single hydraulic system, and measures were taken to permit manual reversion in the event of hydraulic failure.
Rockets became the primary armament, housed in pylon-mounted pods underneath the wing.
A formal operational requirement was issued by the Navy in 1948, with the expectation that the contract would be awarded to Douglas from the onset.
The requirement included the ability to intercept and destroy an enemy aircraft at an altitude of 50,000 ft (15,240 m) within five minutes of the alarm being sounded.
Navy planners were particularly concerned by the threat posed to its carrier battle groups by high altitude Soviet bomber aircraft.
To maximize an interceptor aircraft’s time on station, it was desirable for such an aircraft to possess a relatively high rate of climb so that it could be launched and rapidly reach its operational altitude.
The mock-up review was delayed by almost one year due to numerous design changes, taking place in March 1949.
One criticism produced at this stage was that the nose-up attitude was greater than had been anticipated, necessitating changes to the aircraft’s nose and radome to improve the pilot’s external visibility.
A more pressing issue was the J40 engine intended to power the aircraft.
Douglas’ design team had made accommodations to facilitate the use of other engines as a contingency measure, which proved to be fortunate as the J40 had a particularly troubled development, eventually being cancelled with no production units ever being delivered.
As a temporary measure, the prototype had to be outfitted with an Allison J35 engine instead.
The long-term replacement for the J40 on production aircraft was the Pratt & Whitney J57, a more powerful but considerably larger engine.
As the original inlet design was not a good match for the J57, it had to be redesigned.
The ensuing delays to the program led to several other aircraft, such as the North American F-100 Super Sabre and the Mikoyan-Gurevich MiG-19, beating it into operational service, costing the Skyray the status of being the world’s first supersonic interceptor.
During June 1954, the first flight of a production standard Skyray occurred, after which an intense period of flight testing and remedial design work followed.
The aft section needed to be reprofiled to eliminate undesirable buffeting as well as to reduce drag.
In September 1955, initial carrier suitability trials were performed onboard USS Ticonderoga.
No production aircraft were delivered until early 1956, and it was declared ready for fleet introduction in April of that year.
A total of 419 F4D-1 (later designated F-6 under the unified designation system) aircraft were produced prior to the end of production in 1958.
The Skyray was a wide delta wing design with long, sharply swept, rounded wings, named for its resemblance to the manta ray.
The thick wing roots contained the air intakes that fed its single turbojet engine.
Fuel was contained both in the wings and the deep fuselage.
Leading edge slats were fitted for increased lift during take-off and landing, while the trailing edges comprised mostly elevon control surfaces.
Additional pitch trimmers were fitted inboard near the jet exhaust and were locked upwards on take-off and landing.
The Skyray’s unique design for the era was a key factor in it becoming one of the best-known early jet fighters, affectionately known as the “Ford” (after the “Four” and “D” of its designation).
During 1953, Edward H. Heinemann was awarded the Collier Trophy in recognition of his design work on the F4D. Variants XF4D-1 Prototypes; redesignated YF-6A in 1962, two built. F4D-1 Single-seat fighter aircraft, production model; redesignated F-6A in 1962, 420 built. F4D-2 Re-engine F4D-1 with the J57-F-14, 100 on order cancelled. F4D-2N F4D-2 version with extended nose housing twin radar scanners, the project only evolved into the F5D Skylancer. F5D Skylancer The F5D Skylancer was derived from the F4D and intended to be a Mach 2 capable successor to the Skyray. Although four prototypes were built and flown, the project was cancelled as being too similar in mission parameters to the F8U Crusader and also to reduce dependence upon Douglas Aircraft, which was also producing several other aircraft for the U.S. Navy. This decision effectively removed Douglas from active fighter development. Specifications F4D-1 Crew 1 Length 45 ft 3 in (13.79 m) Wingspan 33 ft 6 in (10.21 m) Height 13 ft 0 in (3.96 m) Wing area 557 sq ft (51.7 m2) Airfoil Root NACA 0007-63/30-9.5 Tip NACA 0004-5 63/30-9.5 Empty weight 16,024 lb (7,268 kg) Gross weight 22,648 lb (10,273 kg) Max take-off weight 27,116 lb (12,300 kg) Powerplant 1 × Pratt & Whitney J57-P-8, −8A or −8B afterburning turbojet engine, 10,200 lbf (45 kN) thrust dry, 16,000 lbf (71 kN) with afterburner. Performance Maximum Speed 627 kn (722 mph, 1,161 km/h) Range 610 nmi (700 mi, 1,130 km) Ferry range 1,040 nmi (1,200 mi, 1,930 km) Service ceiling 55,000 ft (17,000 m) Rate of climb 18,300 ft/min (93 m/s) Wing loading 41 lb/sq ft (200 kg/m2) Thrust/weight 0.71 Armament Guns 4 × 20 mm Colt Mk 12 cannon, Two on each wing just aft of the leading edge, Mid-wing, underside, with 65 rounds/gun Rockets 6 pods of 7 2.75 in (70 mm) unguided rockets
Or 4 pods of 19 2.75 in (70 mm) unguided rockets Missiles 4 × AIM-9 Sidewinder air-to-air missiles Bombs 2 × 2,000 lb (907 kg) bombs Avionics APQ-50A radar Aero 13F fire-control radar.
Sources
Charles Daniels Photo Collection
The National Museum of the U.S. Air Force
McDonnell Douglas aircraft since 1920: Volume I-René J Francillon.
Naval Fighters No.13, Douglas F4D Skyray-Nick Williams & Steve Ginter.
Douglas F4D-1/F-6A Skyray-Nicholas M. Williams.
Warpaint Series 117, Douglas F4D Skyray & F5D Skylancer-Tony Buttler.
