Douglas F4D Skyray
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The Douglas F4D Skyray (later redesignated F-6 Skyray) is an American carrier-based supersonic fighter/interceptor designed and produced by the Douglas Aircraft Company. It was the last fighter produced by the Douglas Aircraft Company prior to its merger with McDonnell Aircraft to become McDonnell Douglas.
Development of the Skyray was started by Douglas during the late 1940s as the D-571-1 design study. It was a delta 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 fulfill a formal requirement issued in 1948. The decision to adopt the Westinghouse J40 turbojet engine led to considerable difficulties, as this engine would be cancelled prior to entering production, and the aircraft was redesigned to accept the Pratt & Whitney J57 instead. Aerodynamic issues led to a protracted development cycle; considerable design changes were made after the maiden flight of the first production standard Skyray in June 1954. The Skyray was declared ready for fleet introduction in April 1956 and entered service with both the United States Navy (USN) and United States Marine Corps (USMC) shortly thereafter.
The Skyray had a relatively brief service life and never saw combat. Despite this, it was the first carrier-launched aircraft to hold the world's absolute speed record, having attained a top speed of 752.943 mph,<ref name="Enzo92">Angelluci 1987, p. 92.</ref><ref name = "caygill 175">Caygill 2006, p. 175.</ref> (1,211.487 km/h).Template:Sfn It is widely reported as the first naval fighter to break the speed of sound in level flight rather than in a dive.<ref name=Supersonic/> The Skyray also set a new time-to-altitude record, flying from a standing start to Template:Convert 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 The last Skyrays were withdrawn from service in February 1964, although a handful continued to be flown for experimental purposes by National Advisory Committee for Aeronautics (NACA) up to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.
Design and development
The Skyray originated within a design study, the D-571-1, performed by Douglas and funded by the United States Navy (USN). It was a fast-climbing pure interceptor aircraft with a delta wing, powered by a pair of Westinghouse J34 turbojet engines, which were equipped with afterburners for bursts of additional acceleration.<ref name = "thomason 129143">Thomason 2008, pp. 129, 143.</ref> 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 the leading edge of the wing; alternative armaments consisted of spin-stabilized rockets.<ref name = "thomason 143"/> The design study had harnessed the designs and research of the German aerodynamicist Alexander Lippisch, who moved to the United States following the end of World War II, and whose work had been examined by several of Douglas's design team.<ref name = "caygill 157">Caygill 2006, p. 157.</ref> 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.<ref name = "thomason 143">Thomason 2008, p. 143.</ref>
As the design was refined, the wing's thickness was substantially reduced to increase its high speed capabilities.<ref name = "thomason 143144">Thomason 2008, pp. 143–144.</ref> The twin J34 engine arrangement was also swapped out for a single Westinghouse J40 engine. Only a single hydraulic system was incorporated and measures to permit manual reversion in the event of hydraulic failure were included.<ref name = "thomason 144"/> Rockets would be the primary armament, 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, it was a foregone conclusion from the outset that Douglas would win the contract.<ref name = "thomason 144"/> 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.<ref name="Enzo91">Angelluci 1987, p. 91.</ref> At the time, Navy planners were particularly concerned by the threat posed to its carrier battle groups by high altitude Soviet bomber aircraft; as early jet aircraft were fuel-hungry and had limited endurance, it was necessary for an interceptor to climb very quickly to its operational altitude to attain the time on station the Navy desired.<ref name = "thomason 128129143">Thomason 2008, pp. 128–129, 143.</ref>
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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.<ref name = "thomason 146">Thomason 2008, p. 146.</ref> 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.<ref name = "thomason 146"/> A more pressing issue would be the J40 engine. Douglas' design team made accommodations for other engines as a contingency measure;<ref name = "thomason 152">Thomason 2008, p. 152.</ref> this approach proved to be quite fortunate as the J40 had a particularly troubled development and was eventually cancelled with no production units delivered.<ref name = "thomason 129">Thomason 2008, p. 129.</ref> As a temporary measure, the prototype had to be outfitted with an Allison J35 engine instead.<ref name = "caygill 157"/>
The long-term replacement for the J40 on production aircraft was the Pratt & Whitney J57, a more powerful but considerably larger engine.<ref name = "thomason 151152">Thomason 2008, pp. 151–152.</ref> 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.<ref name = "caygill 157"/>
On 5 June 1954, during its maiden flight, the first production F4D-1, bureau number (BuNo) 130740, reportedly became the first naval fighter to exceed the speed of sound in level flight.Template:Sfn According to Flight, this was achieved during the aircraft's acceptance flight between the Douglas plant in El Segundo, California, and Edwards Air Force Base, flown by test pilot Bob Rahn.<ref name=flight_intel>Template:Cite magazine</ref> An intense period of flight testing and remedial design work followed, as there had been inadequate time to evaluate the J57 during the prototype stage. To address an engine stalling problem at near-supersonic speeds above Template:Cvt of altitude, the air intake geometry had to be changed, and an airflow baffle plate added in front of each intake. The aft section of the fuselage was reprofiled to eliminate undesirable buffeting and reduce drag.<ref name = "thomason 151152"/>Template:Sfn In September 1955, initial carrier suitability trials were performed onboard USS Ticonderoga.<ref name = "thomason 152"/> No production aircraft were delivered until early 1956 when the F4D was declared ready for fleet introduction in April.<ref name = "thomason 152"/>Template:Sfn A total of 419 F4D-1 (later designated F-6 under the unified 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 the manta ray.<ref name="Gunston67">Gunston 1981, p. 67.</ref> 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 takeoff and landing while the trailing edges comprised mostly elevon control surfaces.<ref name = "thomason 144">Thomason 2008, p. 144.</ref> Additional pitch trimmers 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 early jet fighters. It was affectionately known as the "Ford" (after the "Four" and "D" of its designation).<ref name="Gunston70">Gunston 1981, p. 70.</ref> During 1953, Edward H. Heinemann was awarded the Collier Trophy in recognition of his design work on the F4D.<ref>"Collier Trophy awards." Template:Webarchive National Aeronautic Association. Retrieved: 27 February 2008.</ref>
Supersonic capability
Thomason disputes the commonly accepted claims that the Skyray achieved supersonic speed in level flight and was the first naval aircraft to do so. He notes that the formal Navy report from the F4D-1 acceptance trials explicitly states that the aircraft "does not have level flight supersonic capability", and that Heinemann and Rahn never mention this capability in their memoirs, with Rahn mentioning only that the Skyray was supersonic in a dive. Thomason further notes that the Skyray's speed-record flight was conducted when the ambient temperature was unusually high at Template:Convert, delaying the onset of transonic drag; although the speed of sound is Template:Cvt at standard temperature and pressure, it rises to Template:Cvt at 37Template:Nbsp°C, so the Skyray's speed during the record-setting flight was equal to only 0.95 Mach. Thomason writes that, according to U.S. Navy records, the first naval aircraft to exceed the speed of sound in level flight was a Grumman F11F Tiger prototype.<ref name=Supersonic>Template:Cite web</ref>
Operational history
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During April 1956, VC-3 became the first squadron to attain operational status with the F4D-1.<ref name="Enzo92"/> This unit was later redesignated VFAW-3 and assigned to NORAD, becoming the only United States Navy fighter squadron in what was predominantly a United States Air Force (USAF) and Royal Canadian Air Force (RCAF) organization. VFAW-3 was permanently based at NAS North Island in San Diego.
The United States Marine Corps (USMC) also operated the Skyray. When the Department of Defense adopted a uniform aircraft designation system patterned on the USAF's aircraft designation system during September 1962, the F4D was redesignated as the F-6A Skyray. The F4D (old designation) should not be confused with the F-4D (new designation) – the latter being the "D" variant of the McDonnell Douglas F-4 Phantom II operated by the USAF.<ref name = "thomason 266">Thomason 2008, p. 266.</ref>
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 Template:Convert in two minutes and 36 seconds, all while flying at a 70° pitch angle.<ref name="Enzo92"/> 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 and VMF-215 also flew the Skyray. The last operational squadron was VMF(AW)-115, which flew the Skyray until February 1964. A total of four aircraft were used for experimental purposes by the National Advisory Committee for Aeronautics (NACA) (which was later renamed NASA) until 1969.<ref name="Gunston73">Gunston 1981, p. 73.</ref>
F5D Skylancer
Template:Main 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.<ref name="Gunston73">Gunston 1981, p. 73.</ref><ref name = "thomason 230231">Thomason 2008, pp. 230-231.</ref> This decision effectively removed Douglas from active fighter development.<ref name = "thomason 262">Thomason 2008, p. 262.</ref>
Variants
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- 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-engined F4D-1 with the J57-F-14, 100 on order cancelled.
- F4D-2N
- F4D-2 version with extended nose housing twin radar scanners, project only evolved into the F5D Skylancer.
Operators
Aircraft on display
- XF4D-1
- 124587 – In front of the main gate of Naval Air Weapons Station China Lake, California. It is on loan from the National Naval Aviation Museum, Naval Air Station Pensacola, Florida.<ref>Template:Citation</ref>
- F4D-1 (F-6A)
- 134748 – Pima Air and Space Museum adjacent to Davis–Monthan Air Force Base in Tucson, Arizona. It is on loan from the National Naval Aviation Museum.<ref>"F4D Skyray/134748." Template:Webarchive Pima Air and Space Museum. Retrieved: 27 January 2015.</ref>
- 134764 – Naval Air Station Patuxent River in St. Mary's County, Maryland. It is on loan from the National Naval Aviation Museum.<ref>"F4D Skyray/134764." aerialvisuals.ca Retrieved: 27 January 2015.</ref>
- 134806 – National Naval Aviation Museum at Naval Air Station Pensacola, Florida.<ref>"F4D Skyray/134806." Template:Webarchive National Naval Aviation Museum. Retrieved: 27 January 2015.</ref>
- 134836 – Intrepid Sea, Air & Space Museum in New York City. Originally on display at the New England Air Museum before relocating to Intrepid in 2021.<ref>"Intrepid Museum Skyray." Intrepid Sea, Air & Space Museum. Retrieved: 24 April 2022.</ref>
- 134936 – Pueblo Weisbrod Aircraft Museum at Pueblo Memorial Airport, Colorado.<ref>"F-4D Skyray/134936." Template:Webarchive Pueblo Weisbrod Aircraft Museum. Retrieved: 29 February 2008.</ref>
- 134950 – Aviation Heritage Park at Naval Air Station Oceana in Virginia Beach, Virginia. It is on loan from the National Naval Aviation Museum.<ref>"F4D Skyray/134950." aerialvisuals.ca Retrieved: 27 January 2015.</ref>
- 139177 – Flying Leatherneck Aviation Museum at Marine Corps Air Station Miramar in San Diego, California. It is on loan from the National Naval Aviation Museum.<ref>"F4D Skyray/139177." Template:Webarchive Flying Leatherneck Aviation Museum. Retrieved: 27 January 2015.</ref>
Specifications (F4D-1)
See also
References
Citations
Bibliography
Further reading
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External links
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