| F4D (F-6) Skyray | |
|---|---|
 | |
| General information | |
| Type | Fighter aircraft |
| Manufacturer | Douglas Aircraft Company |
| Status | Retired |
| Primary users | United States Navy |
| Number built | 422 |
| History | |
| Manufactured | 1950–1958 |
| Introduction date | April 1956 |
| First flight | 23 January 1951 |
| Retired | February 1964 |
| Developed into | Douglas F5D Skylancer |
TheDouglas F4D Skyray (later redesignatedF-6 Skyray) is an Americancarrier-based supersonicfighter/interceptor designed and produced by theDouglas Aircraft Company. It was the first naval fighter to exceed the speed of sound in level flight and the last fighter produced by theDouglas Aircraft Company prior to its merger withMcDonnell Aircraft to becomeMcDonnell Douglas.
Development of the Skyray was started by Douglas during the late 1940s as theD-571-1 design study. It was adelta wing interceptor capable of a high rate of climb as to permit the rapid interception of approaching hostile bombers. Douglas' proposal was selected by Navy officials to fulfil a formal requirement issued in 1948. The decision to adopt theWestinghouse J40turbojet engine to power it would lead to considerable difficulties later on as this engine would be cancelled prior to entering production. Aerodynamic issues would also lead to a protracted development cycle, considerable design changes being made even after themaiden flight of a production standard Skyray having taken place in June 1954. The Skyray was declared ready for fleet introduction in April 1956, permitting its entry to service with both theUnited States Navy (USN) andUnited States Marine Corps (USMC) shortly thereafter.
The Skyray had a relatively brief service life, during which it never participated in actual combat. Despite this, it was the firstcarrier-launched aircraft to hold the world's absolute speed record, having attained a top speed of 752.943 mph,[1][2] (1,211.744 km/h).[3] It also 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 The last Skyrays were withdrawn from service in February 1964, although a handful continued to be flown for experimental purposes byNational Advisory Committee for Aeronautics (NACA) up to the end of the decade. TheF5D Skylancer was an advanced development of the F4D Skyray that ultimately did not enter service.
The Skyray originated within a design study, theD-571-1, performed by Douglas and funded by theUnited States Navy (USN). It was a fast-climbing pure interceptor that used adelta wing configuration and powered by a pair ofWestinghouse J34turbojet engines, which were equipped withafterburners for bursts of additional acceleration.[4] The D-571-1 had a relatively thick wing with no conventional fuselage save for a pod-like cockpit in a forward position. A total of four 20mm cannons extended forward of theleading edge of the wing; alternative armaments consisted of spin-stabilized rockets.[5] The design study had harnessed the designs and research of the GermanaerodynamicistAlexander Lippisch, who moved to the United States following the end ofWorld War II, and whose work had been examined by several of Douglas's design team.[6] In June 1947, the Navy issued a contract to Douglas to proceed with preliminary investigation and engineering works on the concept up to the mockup stage.[5]
As the design was refined, it was decided to reduce the wing's thickness substantially to increase its high speed capabilities.[7] The twin J34 engine arrangement was also swapped out for a singleWestinghouse J40 engine. Only a singlehydraulic system was incorporated, thus measures to permit manual reversion in the event of hydraulic failure were also included.[8] Rockets also became the primary armament, which were housed in pylon-mounted pods underneath the wing. A formal operational requirement was issued by the Navy in 1948, however, according to aviation author Tommy H. Thomason, that the contract would be awarded to Douglas from the onset was an apparently foregone conclusion.[8] Specifics of this 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.[9] At the time, Navy planners were particularly concerned by the threat posed to itscarrier battle groups by high altitudeSoviet bomber aircraft; furthermore, as early jet aircraft were fuel hungry and had limited endurance, to maximise an interceptor aircraft time on station the Navy desired for such an aircraft to possess a relatively high rate of climb so that it could be launched and rapidly reach its operational altitude.[10]
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On account of the numerous design changes, the mockup review was delayed by almost one year, taking place in March 1949.[11] 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 andradome to improve the pilot's external visibility.[11] A more pressing issue would be the J40 engine intended to power the aircraft. Douglas' design team had decided to make accommodations to facilitate the use of other engines as a contingency measure;[12] this approach proved to be quite fortunate as the J40 had a particularly troubled development, being eventually cancelled with no production units ever being delivered.[13] As a temporary measure, the prototype had to be outfitted with anAllison J35 engine instead.[6]
The long-term replacement for the J40 on production aircraft was thePratt & 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.[14] The ensuing delays to the programme led to several other aircraft, such as theNorth American F-100 Super Sabre and theMikoyan-Gurevich MiG-19, beating it into operational service.[6]
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.[12] The aft section needed to be reprofiled to eliminate undesirable buffeting as well as to reducedrag. In September 1955, initial carrier suitability trials were performed onboardUSSTiconderoga.[12] No production aircraft were delivered until early 1956, it was declared ready for fleet introduction in April of that year.[12] A total of 419F4D-1 (later designatedF-6 under theunified designation system) aircraft would be produced prior to the end of production in 1958.
The Skyray was a wide delta wing design with long, sharply swept, rounded wings. It was named for its resemblance to themanta ray.[15] The thick wing roots contained the air intakes that fed its singleturbojet engine. Fuel was contained both in the wings and the deep fuselage.Leading edge slats were fitted for increased lift during takeoff and landing while thetrailing edges comprised mostlyelevon control surfaces.[8] Additionalpitchtrimmers were fitted inboard near the jet exhaust, and were locked upwards on takeoff and landing. It had a relatively unique design for the era, which was a key factor in the Skyray becoming one of the best-known earlyjet fighters. It was affectionately known as the "Ford" (after the "Four" and "D" of its designation).[16] During 1953,Edward H. Heinemann was awarded theCollier Trophy in recognition of his design work on the F4D.[17]
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During April 1956, VC-3 became the first squadron to attain operational status with the F4D-1.[1] This unit was later redesignatedVFAW-3 and assigned toNORAD, becoming the onlyUnited States Navy fighter squadron in what was predominantly aUnited States Air Force (USAF) andRoyal Canadian Air Force (RCAF) organization. VFAW-3 was permanently based atNAS North Island in San Diego.
TheUnited States Marine Corps (USMC) also operated the Skyray. When theDepartment of Defense adopted auniform aircraft designation system patterned on the USAF's aircraft designation system during September 1962, the F4D was redesignated as theF-6A Skyray. TheF4D (old designation) should not be confused with theF-4D (new designation) – the latter being the "D" variant of theMcDonnell Douglas F-4 Phantom II operated by the USAF.[18]
The Skyray was designed exclusively for the high-altitude interception role, with a high rate and angle of climb. It 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.[1] As a dedicated interceptor, the F4D was unsuited to the multi-mission capabilities that became increasingly in demand, thus the type had a relatively short career in both USN and USMC service. In addition to multiple Navy and Marine Corps squadrons, Naval Air Reserve and Marine Air Reserve squadrons VF-881, VF-882 andVMF-215 also flew the Skyray. The last operational squadron wasVMF(AW)-115, which flew the Skyray until February 1964. A total of four aircraft were used for experimental purposes by theNational Advisory Committee for Aeronautics (NACA) (which was later renamedNASA) until 1969.[19]
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 theF8U Crusader and also to reduce dependence upon Douglas Aircraft, which was also producing several other aircraft for the U.S. Navy.[19][20] This decision effectively removed Douglas from active fighter development.[21]
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