Clash of the cancelled Round 2: North American YF-107A versus Vought XF8U-3 Crusader III
History chewed out and spat out some incredible aeroplanes. We drag these rotting morsels out of the compost mulch of history and drag them to our laboratory/fight-club for autopsy. To assist us in our morbid analysis is Hush-Kit’s tamed scientist and engineer Jim ‘Sonic’ Smith (a key figure in the Typhoon and UK JSF programmes among others). To further our thrills we shall pit these dead aeroplanes against each other!
What a fabulous pair of aircraft these are. The souped-up F-100 development chasing a requirement eventually won by the F-105 Thunderchief, and the Crusader on steroids that eventually lost out to the F-4 Phantom II. The thing that grabs you about both aircraft is simply the look. The YF-107A with its ‘over the top’ variable ramp supersonic intake and recessed, nuclear-capable, weapons bay, and the Crusader 3 with its shark-mouth intake and large twin dorsal fins, which had to be folded up to the horizontal for a successful landing. Just Wow!
North American YF-107A
The YF-107A was a development of North American’s successful F-100 Super Sabre, intended to be a versatile fighter bomber aircraft, capable of missions ranging from air defence to nuclear strike. Initial development centred on a design with a chin intake, like that of the F-8 Crusader, to accommodate a nose mounted radar. This was later changed to the signature dorsal intake design when the Air Force indicated a desire that the aircraft be capable of delivering a tactical nuclear weapon.
Other innovative features of the design included an all-moving fin for yaw control, as used later, on the A-5 Vigilante, and a supersonic variable area inlet duct, later used on the XB-70. Although the wing planform was essentially the same as the F-100, roll control dispensed with ailerons, and used spoilers instead. The 16, 950 lb thrust J-57 engine of the Super Sabre, was replaced by a more powerful 24,500 lb thrust J-75 engine, and the YF-107A was able to demonstrate a maximum speed of Mach 2.0.
The aircraft was armed with 4 20mm cannon, and could also carry up to 10,000 lb of external stores. Following completion of its flight test program, the Air Force conducted a fly-off between the YF-107A and the Republic F-105 Thunderchief, which was narrowly won by the latter. The F-105 was a bigger, heavier aircraft, almost equally dramatic in appearance, which after a difficult development period went on to a long and distinguished career with the USAF. Its particular forte, towards the end of its USAF career, was serving in a SEAD (Suppression of Enemy Air Defences) role as a ‘Wild Weasel’ in the Vietnam war.
Vought XF8U-3 Crusader III
In the mid-1950s, the F8U Crusader had been successful in a US Navy competition for a supersonic shipboard fighter. McDonnell’s proposal in that competition did not make the short list for selection. Displeased by this, McDonnell proposed to the Navy a highly capable twin-engine attack aircraft, the AH-1. In parallel, Vought proposed to the Navy a follow-on development of the F8U, designed around a single J-75 engine, the XF8U-3 Crusader 3.
The Crusader 3 was projected to deliver Mach 2.3+ capability, and would be armed with 4 x 20 mm cannon and 3 air-to-air missiles. The US Navy looked favourably on this proposal, and ordered five prototypes, the first of which flew on June 2, 1958.
Meanwhile, the US Navy had indicated to McDonnell-Douglas that they were no longer interested in the AH-1, but (influenced by the XF8U-3 proposal) were now looking for 2-seat long-range all-weather interceptor to be armed only with air-to-air missiles, targeted using the aircraft’s radar system. This aircraft was to be designated the F4H-1, and made its first flight on May 24, 1958.
The US Navy was now in a position to choose between the fast, manoeuvrable, F8U-3 single-seat, single-engine interceptor, and the larger and heavier McDonnell F4H, with two engines, two crew, all-weather radar, and missile armament.
By the end of 1958, the Navy had selected the McDonnell F4H Phantom II, and over years of development and service with many air arms, this proved to be one of the greatest Naval aircraft of all time. The relatively large, low aspect ratio wing of the Phantom, coupled with its twin J79 engines, provided a capable and versatile platform, and the aircraft is still in service today in small numbers.
What of the Super Crusader? Well, the performance of the aircraft as a Naval interceptor was probably unmatched in terms of speed and handling qualities, but compared to the Phantom, it was disadvantaged by having a less capable weapons system, and by being a single-seat, single-engine configuration. The maximum speeds claimed for the XF8U-3 vary, but the aircraft was capable of at least Mach 2.3, and had outstanding manoeuvrability. One of the most distinctive features of the Crusader 3 was the large twin ventral fins carried under the rear fuselage. These were linked to the undercarriage, so that they were deployed downward when the undercarriage was up, and retracted to a horizontal position when the undercarriage was lowered for landing.
The 5 aircraft built were transferred to NASA, and operated from Patuxent River, where they were said to have routinely defeated USN Phantoms in mock dogfights, to the annoyance of the USN.
YF-107A and XF8U-3
Two sensational-looking aircraft, which eventually lost out to two outstanding and versatile competitors, the F-105 Thunderchief and the F4H Phantom II.
The YF-107A and the XF8U-3 were both more manoeuvrable than the aircraft which were favoured with production orders, but the latter proved to be versatile, capable, and impressive performers with long service lives. Both the F-105 and the Phantom II were eventually used in roles which had not been envisaged in their design, and the Phantom, in particular, made a rare, and successful transition for a Naval aircraft, to serve not only with the USAF, but many other land-based air arms.
Both the YF-107A, with its dorsal intake, and the XF8U-3 with its shark-mouth intake and retractable ventral fins, appeared futuristic. Both succeeded in meeting their design objectives and were flown successfully, and both missed out in the procurement game to worthy competitors.
It is really difficult to pick between these two spectacular and relatively successful designs, neither of which ever made it into service. The YF-107A might well have been a better fighter than the F-105, but the F-105 later excelled as a heavy strike aircraft and made the SEAD role a speciality. Similarly, the XF8U-3 was a better within-visual-range fighter than the A4H, but lacked the all-weather capability and versatility of the latter. My choice goes to the XF8U-3 Crusader 3 as the better loser, but this is a judgement based on aesthetics rather than analysis.
North American YF-107A and Vought XF8U-3 – Air Combat Comparison
These aircraft were designed to quite different requirements. The XF8U-3, although only really a day fighter, was heavily armed, with 4 20 mm cannon and 3 air-to-air missiles. It was also very fast, at Mach 2.3+, had a lower wing loading than the YF-107A, and a greater thrust to weight ratio.
The YF-107A was intended to have greater flexibility, and, indeed, to have a tactical nuclear strike capability. It lacked the missile armament of the XF8U-3, but had the same cannon armament, and would also have been a fast and manoeuvrable aircraft, although not to the same degree as the XF8U-3.
In air-to-air combat, the XF8U-3 would be expected to have the edge in sustained and instantaneous turn rate, and in energy manoeuvrability. It would also, in principle, have been able to engage at greater range using its air-to-air missiles.
On sortie generation, there seems little to choose between the aircraft, which both used variants of the same engine. The folding ventral fins of the XF8U-3 are an additional element, but this might be offset by the slightly more difficult to access engine of the F-107.
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In regards to the F105: “ Its particular forte, towards the end of its USAF career, was serving in a SEAD (Suppression of Enemy Air Defences) role as a ‘Wild Weasel’ in the Vietnam war.”
Not sure I would call it a forte, as the 105 was withdrawn from Wild Weasel operations due to its high loss rate.
Where is it documented that the Crusader III had a cannon armament?