Douglas F4D / F-6 Skyray High-Altitude Carrier-borne Interceptor Aircraft
The Douglas F4D Skyray was the quintessential jet fighter of the 1950's, appearing in limited service though possessing an impressive rate-of-climb.
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The F4D Skyray (affectionately nicknamed the "Ford" for its "F", "Four" and "D" used in the designation) stemmed from a 1947 United States Navy requirement to field a competitive Mach 1-capable, high-altitude interceptor. Not to be outdone by their Air Force counterparts developing their North American F-100 Super Sabre program and the competing Soviets and their Mikoyan-Gurevich MiG-19 "Farmer" design, the USN set about to find an equal force for in defense of their carrier battle groups.
The design of the Skyray indirectly had its origins in German World War 2 delta-wing research and, in particular, the work of one German engineer, Alexander Lippisch. Lippisch had relocated to the United States after the end of the war in 1946 and his work did not go unnoticed by the United States Navy. Douglas Aircraft Company's legendary designer Ed Heinemann was an astute admirer of Lippisch's work centering on the concept of a tailless delta-wing aircraft. Lippisch's work produced the well-known, single-seat, rocket-powered Me 163 Komet interceptor for the German Messerschmitt firm in the latter years of the war. His ground-breaking research furthered the envelop of aircraft design, especially as turbojet technology began to evolve into more capable powerplants with sufficient output for new and better airframe types. The tailless delta wing concept was one of Lippisch's revolutionary forays that sought to contain the violent reactions encountered by objects traveling past the speed of sound. The stability and aerodynamic capabilities inherent with a high amount of surface area held some innate benefits for any design regardless of the chosen powerplant. In theory, this would play well into the burgeoning world of jet-powered aircraft design, considering the field of jet technology was still essentially in its infancy.
On June 17th, 1947, the Douglas Aircraft Corporation was ready with its proposal for the delta wing concept, a unique concept which the US Navy began to favor. The initial Douglas D-571-1 plan was selected for further development, producing the D-571-4. The D-571-1 featured a more straight wing delta while the D-571-4 differed in featuring the rounded delta wing edges consistent with production Skyrays. The USN granted a contract to Douglas for two XF4F-1 prototypes on December 16th, 1949 - by this time the designation of "Skyray" was affixed to the aircraft based on its resemblance to the ocean-going manta ray. The prototype first flew on January23rd, 1951 and proved a promising endeavor.
The XF4D-1 was initially designed around the temperamental Westinghouse J40 series engine though engineering foresight on the part of Douglas engineers made sure that the airframe could accept a variety of powerplants as needed. Though development of the XF4D-1 airframe progressed nicely, the Westinghouse J40 proved a whole other matter. The Westinghouse J40 eventually floundered (leading to accidents surrounding it and the F3H Demon series) despite a good amount of support from the US Navy forcing the Skyray to accept the now USN-approved Pratt & Whitney J57 turbojet for the aircraft - an individual decision that most likely saved the aircraft from becoming a forgettable - and possibly cancelled - Cold War design. Though the Pratt & Whitney J57 proved a larger powerplant than the intended Westinghouse, the extra space afforded by Douglas designers from the beginning ensured that the J57 was a proper fit for the airframe and the Skyray program progressed without much delay.
Performance for the Douglas product eventually yielded a top speed of 722 miles per hour. As sustained Mach 1 speeds were part of the USN requirement, the Skyray excelled. Throughout its service life, the Skyray was fitted with several Pratt & Whitney engines including the J57-P-8, J57-P-8A and the J57-P-8B models. Dry thrust from these engines was reported at 10,200lbf and this rose to an impressive 16,000lbf with the use of afterburner. A range of 700 miles was possible with a ferry range of 1,200 miles. A service ceiling of 55,000 feet was reported, falling well in line with the early USN requirements. Most important, however, was in the Skyray's impressive 18,300 feet-per-minute rate-of-climb. The concept of a slow-climbing interceptor was not a consideration in the jet-age (or any age for that matter) and the Skyray did not disappoint in this performance category.
The Skyray itself was constructed with a semi-stressed skin incorporating aluminum alloy. Despite its large wing area, every effort was made to rid the design of excess weight. This is the area where Douglas designer Ed Heinemann shined. The delta wing concept as applied to the Skyray proved most efficient in both construction methodology and in high speed performance. In the center of the design was the sleek fuselage, integrated into two thick wingroots each containing a split triangular air inlet for the single Pratt & Whitney J57 series afterburning engine. The wings extended out from the roots and, as a whole, provided for a very solid structural base. The wings gave the aircraft its identifiable and definitive shape with its sharply swept leading edges that rounded out nicely at the wing tips. Being a tailless delta wing concept, the Skyray made no use of rear-mounted tailplanes consistent with conventional aircraft designs (as these were essentially absorbed as part of the large delta wing surface) and featured a single large vertical tail surface extending out over the engine and rearward portion of the fuselage.
The pilot was afforded the best seat in the house, with the cockpit placed well ahead of the main body. The cockpit featured relatively heavy framing but still allowed for good views outside. The canopy was contoured as such that the cockpit was seamlessly integrated into the aircraft's aft fuselage. The nose extended out just a bit forward of the cockpit. Cockpit avionics included the APQ-50A series radar system. The undercarriage was of a conventional tricycle design with the two main gears recessing under the wings and a nose wheel gear retracting under the forward fuselage.
Standard armament consisted of 4 x Mk 12-0 series 20mm cannons. Two of these systems were fitted into the underside of each wing leading edge with 65 projectiles to a gun. As the Skyray design was mostly all-wing, it was expected that the wings mount a good amount of ordnance for the workload ahead. As such, the Skyray could field unguided rocket pods on up to six hardpoints depending on the pod size (and thus weight). 6 x 2.75" rocket pods of seven rockets each could be carried or 4 x 2.75" rocket pods of nineteen rockets each. The Skyray could sport 2 x 2,000lb bombs or equivalent as well. More importantly to a Cold War interceptor, the F4D could also be fitted with a pair of AIM-9 Sidewinder short-range, air-to-air missiles. Fire control was handled by the Aero 13F series fire-control radar system.
Make no mistake, however, that the F4D was a US Navy answer to an all-performance platform. The Skyray was an interceptor through-and-through, which explains the short-lived service life incurred by the type. The Skyray was not in the same category as follow-up designs that were more of a robust fighter-bomber, multi-role design philosophy. The F4D was specifically built for speed for the USN and in that way it did not disappoint, becoming a one-of-a-kind yet revolutionary step for the service branch. At any rate, it was a solid evolution in design for future USN fighter implementations.
On October 3rd, 1953, a Douglas Skyray set a new world airspeed record of 752.9 miles per hour, proving the design as a sound high-level performer. The combination of the delta wing and a powerful engine yielded tremendous results, particularly in the category of rate-of-climb. The Skyray set another aerial record by reaching 49,221 feet within 2 minutes and 36 seconds and the aircraft would hold no fewer than five such records during its operational life.
The first production F4D-1 set a new standard for the world (and essentially itself) on June 5th, 1954 as it became the first aircraft to sustain Mach 1 speed in level flight, proving the delta-wing design as sound with the potential to achieve great performance specifications. However, this next generation design was not without its faults. It was soon proven that the aircraft suffered from a potentially lethal high-speed stall occurring at altitude that could have disastrous results to pilot and airframe alike. As such, the program was stalled for several years before the problem was remedied and the design approved for USN service.
The Skyray would enter service as the F4D-1 with the United States Navy's VC-3 squadron (later becoming the VFAW-3) in April of 1956. At its height, seventeen USN and USMC squadrons, along with three reserve elements were fielding the aircraft. At least 419 F4D-1 models were produced in total, making it the most numerical and essentially the only major Skyray model in service. All F4D-1 models became F-6A designations after 1962. Likewise, the two XF4D-1 prototype designations were now updated to the YF-6A designation. Production of all Skyrays ran from 1950 through 1958.
The F4D-2 was a proposed Skyray variant fitted with the J57-F-14 series of engines. Though at least 100 were on order, the order was eventually cancelled in full. The F4D-2N became another proposed Skyray variant. These aircraft would have featured a longer nose section for the implementation of two radar scanners. Though this model went on to become the F5D Skylancer, the project was never fully developed with only four examples produced.
The Skyray was utilized by both the United States Navy and the United States Marine Corps, the latter, however, once the aircraft became the F-6. Despite its promising design and stellar performance, the interceptor-only mode of operation was steadily leaving the picture of modern aerial warfare. More capable platforms were on the horizon or arriving yearly that exhibited more in the way of true fighter-bombers than the Skyray could ever hope to achieve in its limited design philosophy. As such, the Skyray served just a few short years as a frontline operational fighter. All Skyrays were officially retired by 1964. The USN and the USMC were truly the only two operators of the aircraft as no global sales were sought or secured. Such was the speed of the changing technological front. The last operational squadron fielding the Skyray became the VMF-542 in 1964. Beyond that, the NACA (forerunner to NASA) utilized four examples for testing.
Despite its inherent limitations, Ed Heinemann earned himself the coveted Collier Trophy for his design work on the Skyray, a testament to the groundbreaking fighter design (the Collier Trophy is yearly award in the field of aviation recognizing achievements in both astronautics and aeronautics beginning in 1911. Winners have included Glenn Martin for his work on the Martin B-10 bomber, the Rutan Voyager team and the F-22 Raptor team ). The F4D/F-6 Skyray was never to see combat service during its tenure for it arrived too late for use in the Korean War (though development was underway during the conflict) and was wholly outclassed by the time of the Vietnam War. The F4D was still a beautiful aircraft to look at and a new memorable chapter in USN aircraft design, opening the doors for the next generation of jet-powered multi-role aircraft to take the lead.