<text id=ahf10000><title>North American—F-100 Super Sabre</title>
<history>US Air Force: Aircraft History</history>
<article><hdr>North American—F-100 Super Sabre</hdr><body>
<p>To an entire generation of military aviators, the 'Hun'—the name coined from the North American F-100 Super Sabre's numerical designation—is remembered with respect and a degree of affection. This is despite the fact that, as a type, the F-100 had to overcome great problems, always suffered an accident rate higher than the average of most of its user air forces, and had landing characteristics described as "a controlled crash" by a pilot with 2,000 hours on the type. Its good features were honest flight characteristics, a typically robust airframe and reliable systems, and a sense of fitness for purpose that extended from its sharp-lipped gaping mouth to its variable afterburner nozzle.
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<p>This might all have been expected from an aircraft that, for all its radical features, was a true thoroughbred. North American Aviation had at that time suffered no upheaval in location or management since 1935, the design office being at Inglewood, on the edge of today's Los Angeles International Airport, and the three top men, all giants in every sense except physical stature, were the chairman 'Dutch' Kindelberger, the president J. Lee Atwood, and the vice president engineering (and thus director of design) Ray Rice. This team, plus design leader Ed Schmued, created the Sabre, after having had the sheer nerve to delay the design a full year in order to give it swept wings and tail. Having got the Sabre into mass production in 1949, the restless team looked for new worlds to conquer and decided on a frontal attack on what seemed the likely next generation: a fighter to fly faster than sound.
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<p>It had already made a faulty stab at this with the NA-157, at first called F-86C and later YF-93A, in which the much greater thrust of an afterburning J48 engine fed by flush side inlets was used to propel an enlarged airframe with dual main wheels to handle the greater weight. What killed this line of development were the inherent limitations of the existing Sabre wing, the difficulties associated with the inlets (although they left the nose free for radar) and the fact that switching to a centrifugal-flow engine, even one as powerful as the afterburning J48 (based on the British Rolls-Royce Tay) rated at 8,750-lb (38.92-kN) thrust, seemed to be retrograde. By 1949 Pratt & Whitney had a full go-ahead with their revised JT3 two-spool turbojet that appeared to offer more promise of high thrust and reduced specific fuel consumption, and with USAF agreement Rice's team began again with a clean sheet of paper to create a level supersonic fighter around this wholly new American engine. Colloquially known as the Sabre 45, from the 45-degree sweep angle chosen for the leading edge of the wing (compared with 35 degrees for the Sabre), the new fighter was obviously going to be larger and pose severe structural and aeroelastic problems. So great was the fear of wing twist, and of the consequent aileron reversal, that the decision was taken to mount the ailerons inboard, where wing twist was no problem. This eliminated conventional flaps, so the only way of getting high lift for landing was to have full-span slats along the leading edges of what was inevitably an extremely thin and sharp-edged wing. Another major decision was to use slab tailplanes, then unheard-of for a jet fighter, and after extensive tunnel testing at various heights the best location was found to be at the lowest possible level on the flattened underside of the fuselage.
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<p>It was decided to return to a simple nose inlet, unlike that of the YF-93, although this clearly had to be sharp-lipped for supersonic speeds. Ideally it ought to have had variable area, or auxiliary inlets downstream, and variable internal profile, but in fact reasonable efficiency was achieved with a simple fixed design. The duct bifurcated past the landing gear and cockpit and then went straight over the wing into the big axial-flow engine, which had a long curved bullet fairing over the nose-mounted accessories. Also unlike the YF-93A, the new fighter had single mainwheels but twin nosewheels, the latter being of sufficiently small diameter to lie in a compartment of the same height as the gun armament, which comprised four of the new Pontiac M39 20-mm revolver cannon derived from the German Mauser MG 2134, each with 200 rounds. Structurally, the wing could carry 6,000 lb (2,722 kg) of bombs or other stores on six pylons, but in practice the normal load of the first version was just two 220-Imp gal (1,041-liter) drop tanks of unusual curved profile with cruciform tailfins, cleared for use at supersonic speed. Belly stores were precluded by the large door-type airbrake driven open against air loads by two powerful hydraulic jacks.
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<p>With the help of the NACA (predecessor of NASA) and the company's own supersonic wind tunnel, the design team made rapid progress in 1950, and by the end of that year had firmed up the design as the NA-180. A plan to fit radar was dropped, and after a mock-up review in January 1951 the USAF gave the go-ahead for the aircraft as the F-100, in the role of a day fighter. The number was said to be fortuitous, although it was helped by various prototype designations and the XF-98 and XF-99 missiles (respectively Falcon and Bomarc), so that the new fighter became the first of the 'century' series of supersonic USAF aircraft. These represented a colossal investment in aerodynamic research (backed up by the Bell X-1 series of supersonic aircraft), propulsion, structures, systems and, not least, in giant heavy presses and large machine tools to produce airframes more challenging than any built previously. The bill for USAF presses alone reached $389 million by 1953, then an astronomic figure.
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<p>The first USAF contract was received on 1 November 1951, and specified two YF-100 prototypes (numbers 52-5754 and 5755) and 110 production aircraft. In 1952 the design was refined in many ways, the nose becoming broader, flatter and longer, the canopy better streamlined into the fuselage (at some expense in poor rear view) with a dorsal spine joining it to the fin, and the underside of the fuselage made wider and flatter. Later, the canopy was changed from the sliding type to a rear-hinged clamshell, and several major parts were redesigned in the costly new metal, titanium. The changes resulted in the new designation YF-100A, and in early 1953 the new fighter was named Super Sabre.
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<p>The first YF-100A was completed ahead of schedule, and after being taken by road to Edwards AFB was flown by George Welch, chief engineering test pilot, on 24 April 1953. He took two beers from chase pilot Colonel 'Pete' Everest, who had bet that the YF-100A would not go supersonic; it went beyond Mach 1 on the first flight. Bringing in the afterburner, one of the first fully engineered installations on any fighter, resulted in such extra thrust that Welch likened it to "a kick from a well-fed mule." The second prototype flew on 14 October 1953, by which time the Inglewood plant was full of F-100As on the line, the first production machine (52-5756) flying on 29 October, the same day that Everest set a new world speed record in 52-5754. In the following month the 479th Fighter Day Wing began to convert, and all seemed set for the fastest entry to service ever. The F-100A differed from the prototypes mainly in having a cut-down vertical tail.
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<p>Everest was deeply concerned about potential dangerous divergence in extreme flight conditions caused by coupling between roll and yaw, which he considered dangerous. He was overruled, but on 12 October 1954, after a number of F-100s had inexplicably broken up in flight, Welch was killed in just such a break-up. The cause was traced to the roll-coupling, which had turned a hard dive pull-out into an uncontrollable swerve to the right, at the highest possible airspeed. All F-100s were grounded, with 70 already delivered, and another 96 on the line or in flight test. The cure was to go back to the tall fin of the prototypes and also to add 26 in (60 cm) to the wing span. This caused a major disruption to the program, and all aircraft already delivered were rebuilt at their units, most of them at George or Sheppard AFBs.
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<hi style=hdr1>Deliveries Resume</hi>
<p>Deliveries of new F-100As resumed in the spring of 1955, and 203 of this model were delivered, an improved cockpit being introduced at No. 104 (the first F-100A-20). Later in this block, at No. 168, the J57-7 engine was replaced by the J57-39 with afterburning thrust increased from 15,000 lb (66.73 kN) to 16,000 lb (71.17 kN). The F-100A served as a day fighter, some later being passed on to Taiwan and other countries, but they were rather quickly replaced in the USAF by later models.
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<p>The F-100B was a basically more advanced derivative with a larger engine, and which later flew as the F-107. Next on the production line was thus the F-100C, the NA-217, which made full use of the potential attack capability by having a strengthened wing structure, eight pylons installed and the most powerful J57 then available, the J57-21 with afterburning rating of 16,950 lb (75.4 kN) and dry thrust of 11,500 lb (50.27 kN). The first F-100C was rolled out at Inglewood on 19 October 1954 but was hit by the grounding until its test program was permitted to begin, with large tail and long-span wing, on 17 January 1955. By this time further improvements to the F-100C included the addition of radio command guidance for the Bullpup missile and an inflight-refueling probe slanting up from beneath the right wing to a point alongside the pilot. Buddy refueling, using a hosereel in an external pod, was also possible.
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<p>In late 1950 NAA had taken over from Curtiss the large US government plant at Columbus, Ohio, initially to handle US Navy programs such as the FJ-2 Fury, AJ Savage and T-28B. To speed F-100 production Columbus also tooled up to build the F-100C, and eventually a block of 25 F-100C-10-NHs was built in Ohio, the first flying on 8 September 1955, as well as 451 built at Inglewood as F-100C-NAs. On 20 August 1955 Colonel Horace A. Hanes, USAF, set the first world absolute speed record under the new high-altitude rules, and also the first at over Mach 1, the ratified figure being 822.09 mph (1,323.03 km/h). The F-100C was the first model to be flown overseas, using inflight refueling, and the first in Europe hit the concrete at Bitburg on 12 March 1956. Before the end of the year the 8th Fighter Bomber Group was at readiness in Japan.
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<p>By far the most important model, and in effect the definitive single-seat version, the F-100D took development even more strongly in the direction of ground attack, although it did nothing to harm air-combat capability. Initially known in NAA as the NA-223 at Inglewood and as the NA-224 at Columbus, the F-100D marked a major advance in mission avionics, with a Minneapolis-Honeywell stick-steering autopilot and the lately developed LABS (low-altitude bombing system) for automatic toss delivery of nuclear weapons from low level in a steep arching trajectory that gave the aircraft time to get away. Other changes included a new wing with a kinked trailing edge with broad slotted flaps inboard and two-piece outer ailerons, as well as outboard fences extending back across the ailerons, and extra integral tanks inboard. The pylons were made jettisonable and cleared to carry up to 7,500 lb (3,402 kg). Other changes included a further increase in height of the fin (with a deeper fuel jettison fairing which later housed the tail-warning receiver), provision for internal ECM, an arrester hook and, at first only in the final block but later fitted as a field modification, local strengthening for two Astrodyne rockets each of 150,000-lb (667.26-kN) thrust for blasting off a zero-length launcher in the so-called Zell technique.
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<p>Inglewood made 940 F-100Ds and Columbus an additional 334. The first F-100D was flown by Dan Darnell on 24 January 1956, and the first at Columbus on 12 June of that year. At Block-60 (serial 56-2903 onwards) the model number switched to NA-235, denoting wiring for Sidewinder missiles; the corresponding Columbus type was the NA-245 (56-335 onwards). About 100 were supplied new to the French Armé de l'Air and the Danish Flyvevaabnet, where they had an extremely long active career.
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<p>The F-100E, an improved F-100D, was not built, and the final new-build model was the two-seat NA-243, at first called TF-100C and later F-100F. The first, a converted F-100C (54-1066), was flown on 6 August 1956. The fuselage was extended 36 in (91 cm) to accommodate the tandem dual-control cockpits, with a one-piece clamshell canopy, the wing was that of the F-100D, and though a 6,000-lb (2,722-kg) underwing load could be carried, there were only two guns. Inglewood delivered all 339 of this version, bringing the total of all models up to 2,294, the last being delivered in October 1959.
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<hi style=hdr1>A Batch of Conversions</hi>
<p>By this time several F-100As had been converted into RF-100A unarmed reconnaissance aircraft with a visibly deeper fuselage ahead of the wing. Other conversions included the NF-100F, 563725 being rebuilt with blown flaps, an enlarged airbrake and an experimental Rohr thrust reverser for short-field tests. Subsequently this aircraft was converted into a DF-100F drone director. There were several DF models, and several other NF variants, although not with the short-field features. Many variants remained projects only, notably the F-100s with the afterburning Spey 250 turbofan.
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<p>From 1957 the 'Hun' equipped 16 USAF wings, and in Vietnam various models flew with such intensity that by 1969 four wings alone (the 3rd, 31st, 35th and 37th) had exceeded the number of missions flown by the 15,000-plus Mustangs in World War II. The 'Hun' proved equally proficient at top cover and low attack, and, after progressive updating with Bullpups, Sidewinders, ECM, IFF, ILS and secure voice communications, they did a tremendous job. This included the RF conversions, as well as many two-seaters used for 'fast-mover FAC' forward air control duties, and others, converted as EW (electronic warfare) and 'Wild Weasel' aircraft with special sensors for detecting, locating and analyzing enemy radio and radar emissions, notably those of the 'Fan Song' SAM guidance radars.
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<p>By 1970 'Huns' were fast being replaced by McDonnell Douglas F-4s and General Dynamics F-111s, the last regular units at Cannon AFB, New Mexico, and RAF Lakenheath, England, not converting until 1972. Even then, with an amazing average of 5,100 hours on the airframes, the 'Huns' soldiered on with Air National Guard units until 1980. By far the largest secondhand user was the Turkish air force. Taiwan's F-100As were updated close to F-100D standard, the French F-100Ds and F-100Fs gradually faded from 1972 until 1980, and in Denmark the three squadrons of F-100Ds and F-100Fs were not replaced until the General Dynamics F-16 arrived between 1979 and 1982.
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<hi style=hdr1>Specification</hi>
<hi style=hdr2>North American—F-100D Super Sabre</hi>
<item><hi format=bold>Powerplant:</hi> one Pratt & Whitney J57-P-21A turbojet rated at 16,000 lb thrust with afterburner
<item><hi format=bold>Performance:</hi> maximum speed 892 mph at 35,000 ft; service ceiling 40,000 ft; range 1,200 miles
<item><hi format=bold>Weights:</hi> empty 20,638 lb; maximum take-off 38,048 lb
<item><hi format=bold>Dimensions:</hi> wing span 38 ft 9 in; length 54 ft 21/2 in; height 16 ft 21/2 in; wing area 400 sq ft
<item><hi format=bold>Armament:</hi> four 20-mm M39 cannon in forward fuselage; up to 7,040 lb of external stores on underwing hardpoints, including bombs, rocket pods, Bullpup and Sidewinder missiles
