* The F-86 Sabre incorporated what American aircraft designers had learned from their initial efforts in jet aircraft design, along with captured German research data on advanced jet aircraft concepts. The result was an outstanding aircraft. The Sabre would prove a vital weapon for the US in the skies over Korea. The basic design would also prove adaptable, emerging as the highly modified "YF-93A" fighter, and the "F-86D" single-seat all-weather interceptor.
* By the closing years of World War II, jet propulsion was clearly the way of the future for high-speed combat aircraft. North American Aircraft (NAA) had achieved great success with their P-51 Mustang, one of the best piston-engine fighters of the war, and wanted to take on the challenge of jet propulsion. In late 1944, NAA began a design study under the designation "RD 1265" for the company's first jet fighter, proposing the aircraft to the US Navy. On 1 January 1945, the company received a contract from the Navy for 100 of these fighters; it was given the company designation "Model NA-134" and the Navy designation "FJ-1".
The "XFJ-1", as the prototype NA-134 was designated, flew in late 1946. It was a stubby fat cigar with straight wings and an air intake in the nose, powered by a General Electric (GE) TG-180 / J35-GE-2 turbojet, with 16.7 kN (1,700 kgp / 3,750 lbf) thrust. The first production FJ-1 "Fury" was delivered in early 1948, and was fitted with an Allison-built J35. Some sources claim the J35 was a US copy of the de Havilland Goblin centrifugal-flow engine -- but in fact, the J35 an indigenous American axial-flow design, though it did leverage off British technology. The Goblin was built by Allis-Chalmers as the "J36", but the J36 but was never produced in quantity and never powered an operational aircraft.
The FJ-1's pilot sat in a bubble canopy that was placed high to provide a good all-round view. The little fighter was armed with six 12.7-millimeter (0.50-caliber) Browning machine guns, arranged with three guns on each side of the nose. The fighter featured wingtip drop tanks, with a capacity of 625 liters (165 US gallons) each, though as it turned out the wing wasn't rigid enough to handle them. The FJ-1 had an interesting feature in that it could "kneel" down on its nosewheel. The rationale was said to be to facilitate carrier stowage, but it may have also been done to ease servicing. Although the FJ-1's appearance didn't suggest it, the fighter leveraged heavily off P-51 technology, particularly in the design of its wing.
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NORTH AMERICAN FJ-1 FURY:
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wingspan:
11.63 meters (38 feet 2 inches)
wing area:
20.53 sq_meters (221 sq_feet)
length:
10.48 meters (34 feet 5 inches)
height:
4.52 meters (14 feet 10 inches)
empty weight:
4,100 kilograms (8,845 pounds)
loaded weight:
7,075 kilograms (15,600 pounds)
max speed at altitude:
880 KPH (550 MPH / 475 KT)
service ceiling:
9,750 meters (32,000 feet)
range:
2,410 kilometers (1,500 MI / 1,305 NMI)
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Despite the fact that the FJ-1 won the Bendix Trophy in 1948, it was clearly outdated even as it was being delivered, and the production was cut to a total of 30 machines. One US Navy squadron was equipped with the Fury for about a year, with the aircraft passed on to reserve duty for transition training in 1949.
BACK_TO_TOP* While the Model NA-134 was taking shape in 1945, North American was simultaneously investigating a larger derivative, the "Model NA-140", for the US Army Air Forces (USAAF, which would be split off from the Army to become the independent USAF in September 1947). This resulted in award of a contract in May 1945 for three prototype aircraft with the designation of "XP-86". The USAAF requirements were aggressive, stipulating medium range and a top speed of 965 KPH (600 MPH). The new fighter was to have several advanced features, such as a pressurized cockpit, hydraulically-boosted controls, and a radar-ranging gunsight for the aircraft's six 12.7-millimeter Browning machine guns.
The original NA-140 / XP-86 design strongly resembled the NA-134 / XFJ-1. It had straight wings, the same J35 engine, and the same fit of six Browning machine guns. The major difference was a longer and slenderer fuselage, achieved through the elimination of the structure and gear needed for carrier deck operation. One interesting feature was the use of fencelike wing-mounted air brakes, derived from the A-36A dive-bomber version of the Mustang.
This design got as far as a full-scale partial wooden mockup, unveiled at the NAA Inglewood, California, plant on 20 June 1945. It went no further, since by this time North American engineers knew that there was no way it could meet USAAF requirements. The straight wing couldn't achieve the required speed with the engines available at the time.
* Aircraft engineers knew that a thin swept wing could greatly reduce drag and delay the onset of compressibility problems, but such a wing also led to troublesome stability problems at low speed. The hard data needed to resolve the issue was not available until early 1945, when the Allies captured research data on swept-wing flight from the Germans.
The Germans had conducted wind-tunnel tests on small swept-wing aircraft models as far back as 1940. By 1944, their work had demonstrated that swept wings offered substantial performance benefits. The main difficulty was that any swept wing that was efficient at high speeds tended to be unstable at low speeds. They experimented with a number of ways to deal with this problem, one of the most promising being a "slat" on the leading edge of the wing, an auxiliary airfoil that could be raised to change the airflow and generate more lift.
After the end of the war, aviation engineer George Schairer of the Boeing Company went to Germany to examine German aviation research. He was accompanied by the well-known Theodore Von Karman of the California of Technology, and Robert Jones of the US National Advisory Committee on Aeronautics (NACA, the main precursor organization of the modern US National Aeronautics & Space Administration / NASA). Schairer was extremely enthusiastic about the data he found on swept-wing flight, and not only proposed that Boeing use it on their new XB-47 long-range bomber, but that the information be provided to other US aviation firms.
Larry Green of NAA studied the materials, and came to the conclusion that a swept wing was the answer to improving the performance of the XP-86; he determined that a slat attached to the wing's leading edge and automatically extended at low speeds would solve the low-speed stability problem. Green and other NAA engineers convinced the president of NAA, "Dutch" Kindelberger, that the swept wing was the way to go, and on 18 August 1945, Kindelberger approved further studies on the concept. Within a few weeks, NAA engineers were performing wind tunnel tests on a 1/23rd scale model of an XP-86 with wings swept at 35 degrees. The results were extremely promising. After further tests, the USAAF approved development of the swept-wing XP-86 on 1 November 1945.
* Models were one thing, a flying aircraft another. Engineering the slats was troublesome, and in fact the NAA team went so far as to obtain slatted wings from the German Messerschmitt Me 262 jet fighter to get ideas. The first seven aircraft would actually use some Me 262 slat hardware.
As the work progressed, more changes were made to the design. The wing was lengthened, and the tail, which originally was to have remained straight, was swept back 35 degrees as well. Three hydraulically-operated speed brakes were fitted on the rear fuselage, replacing the wing-mounted "fence" airbrakes. The fuselage was split just behind the wing, allowing the aircraft to be pulled apart to give access to the J35 engine.
The XP-86's relationship to the FJ-1 Fury was still apparent. The new aircraft had an air intake in the nose, straddled by three 12.7-millimeter Browning guns on each side, with a high-sitting plexiglas bubble canopy that slid backwards to open. However, the XP-86 was as sleek as the FJ-1 Fury was tubby, with the new aircraft giving the impression of a flying shark. The USAAF was so enthusiastic when they saw the design that on 20 December 1946 the service ordered 33 production P-86As, even though the prototype hadn't been completed.
BACK_TO_TOP* The first XP-86 prototype was rolled out on 8 August 1947, and made its initial flight on 1 October 1947. It was powered by a Chevrolet-built J35-C-3 engine with 16.7 kN (1,700 kgp / 3,750 lbf) thrust. This was only intended as an interim engine fit, with production aircraft to use the more powerful GE TG-190 / J47 engine, an improved derivative of the J35.
The pilot was George "Wheaties" Welch, North American's chief test pilot and one of the colorful test pilots of the early days of jet aviation. He was at Pearl Harbor when the Japanese attacked on 7 December 1941, and was one of the few pilots to get a Curtiss P-40 into the air to fight back. Welch then flew with the USAAF over the Pacific until 1944, attaining the rank of major and scoring 16 kills, and joined NAA in 1944 as a test pilot. He would remain there until 1954, when he was killed ejecting from a North American F-100 Super Sabre that broke up in flight.
The first flight in the XP-86 was uneventful, until it came time to land and Welch found that the nosewheel leg wouldn't lock down. Welch made a nose-up landing, and the nosewheel snapped into place after the main wheels hit the runway. Welch muttered over the radio: "Lucky! Lucky!"
The XP-86 differed from most other aircraft with tricycle landing gear in that the nose gear pivoted forward, instead of backward. This had been done because of a mechanical conflict with the intake ducting. The nosewheel hadn't gone down because the hydraulics weren't strong enough to push the leg forward in the face of air resistance. The hydraulics were quickly strengthened. Following tests went smoothly. The climb rate was unsatisfactory, but the design team believed the more powerful J47 engine intended for production aircraft would solve that problem. Even with the J35 engine, the aircraft's speed was extremely impressive, roughly 150 KPH (93 MPH) faster than any other operational USAF fighter.
Welch flew the first prototype through the sound barrier in a shallow dive on 19 October 1947, making it the first non-experimental aircraft to exceed Mach 1. In fact, although Chuck Yeager had put the X-1 through the sound barrier on 14 October 1947, it is very possible that Welch had exceeded Mach 1 before Yeager. The XP-86's flight instruments were not capable of determining if the aircraft was moving faster than Mach 1, and so supersonic speed had to be confirmed by ground-based measurements. However, Welch had been making high-speed dives for some time before 19 October, and there was every reason to believe that some had exceeded Mach 1.
It mattered not. As far as formal records go, Yeager broke Mach 1 in level flight, not in a dive; and more importantly, establishing a record meant following procedures established by the Federation Aeronautique Internationale and properly documenting the event. Since there was a considerable cloak of secrecy over the XP-86 at the time, nobody was interested in telling the world about how fast it was, and everyone who knew about the 19 October supersonic flight was told to be quiet about it. Yeager would rightfully be recorded as the first man to break the sound barrier.
* The USAF remained very keen on the XP-86. On 16 October 1947, in addition to the 33 P-86As already in the queue, the service ordered 190 P-86s with strengthened landing gear for rough field operation, to be designated "P-86B". However, development of new high-pressure tires and improvements in the P-86A design resulted in landing gear that was perfectly capable of meeting the rough field requirement. On 17 December 1947, the order was changed to specify 188 P-86As, and two examples of a drastically modified "deep penetration" variant, the "P-86C", discussed later. No "B" variant would ever actually be built.
The Air Force began their own flight tests of the XP-86 in early December 1947. The service was thoroughly impressed, finding the aircraft substantially faster than the straight-winged Republic F-84 Thunderjet, which was also powered by the J35 engine. Major Ken Chilstrom, the USAF test pilot, concluded that "the Air Force now had the very best jet fighter developed to this date, anywhere in the world."
The second and third prototypes were delivered for flight testing in early 1948. The third prototype differed from the first in many ways, and was closer to production specification. One of the biggest differences was that the number 3 prototype was fully armed, fitted with the six 12.7-millimeter machine guns as specified in the original requirement. Each gun had a rate of fire of 1,100 rounds a minute, and the aircraft carried 267 rounds per gun.
Production avionics were fitted, including an "identification friend or foe (IFF)" system, a radio compass system, and a Sperry Mark 18 gyroscopic lead-computing gunsight with manual ranging. Another big difference was that while the number 1 prototype had three air brakes -- one on each side of the rear fuselage and one on the bottom, hinged on the rear -- the number 3 prototype had two air brakes, one on each side of the redesigned rear fuselage, and hinged on the front.
On 26 April 1948, a visiting British pilot put the XP-86 through Mach 1 and broadcast the fact through his radio channel. Although the pilot was disciplined for this breach of security, the secret was out, and was announced in the 14 June 1948 issue of AVIATION WEEK.
BACK_TO_TOP* The first P-86A flew on 20 May 1948. It was powered by a General Electric J47-GE-1 engine with 21.6 kN (2,200 kgp / 4,850 lbf) thrust. The USAF placed an order for a third batch of 333 P-86As at the end of the month, bringing the total ordered to 554. In June 1948, the USAF redefined their aircraft designation system, changing the prefix "P" for "pursuit" to "F" for "fighter". The P-86A became the "F-86A".
With the more powerful engine, top speed and ceiling of the new fighter increased significantly, and the rate of climb almost doubled. The F-86A was fitted with a T-4E-1 ejection seat, the canopy being manually jettisoned before ejection, plus a self-destruct charge to keep the aircraft from falling into enemy hands.
The F-86A also had a stores pylon under each wing that could each carry a 782-liter (206.5 US gallon) drop tank or a 450-kilogram (1,000-pound) bomb. Internal fuel capacity was 1,650 liters (435 US gallons). Four zero-length stub rocket launchers could be installed under each wing, with each launcher carrying two 12.7-centimeter (5-inch) "High Velocity Air Rockets (HVAR)" for a total of 16 rockets. Unfortunately, without the drop tanks the combat radius fell from about 530 kilometers (330 miles) to 80 kilometers (50 miles). In effect, the only armament of the F-86A was its machine guns -- and so, in the beginning, it was not very useful for close support.
The first production batch of 33 aircraft was designated "F-86A-1". The second production batch of 188 was designated "F-86A-5", and featured a number of enhancements. While the F-86A-1 had a rounded front windscreen, the F-86A-5 had a flat front armor glass windscreen, and the canopy was now jettisoned using pyrotechnic charges. An improved leading-edge slat scheme was introduced, and there were a number of minor internal changes.
The third batch of 333 aircraft was also designated F-86A-5, but featured further improvements. The most significant was the replacement of the gyroscopic sight by the A-1B radar sight and its AN/APG-5 ranging radar. Although the radar sight had some reliability problems, when it was working it could lock accurately onto a target at long range. Optical sighting still had to be used at low altitudes, since the radar could not pick a target out of ground clutter.
F-86A-1s and early production F-86A-5s actually had little doors that sealed off the muzzles of the six 12.7-millimeter Brownings; the doors opened automatically in a twentieth of a second for firing. This feature was abandoned at some time during F-86A-5 production because of potential reliability problems.
Up to this time, the USAF hadn't publicly demonstrated the capabilities of their new fighter, and felt it was time to show it off. On 15 September 1948, an F-86A set a world air speed record of 1,080 KPH (671 MPH), which was 32 KPH (20 MPH) faster than the pre-existing record. Unfortunately, that fall technical problems with the J47-GE-1 engine halted F-86A production until General Electric managed to get the difficulties under control in late December 1948, and began delivering the improved J47-GE-7, with 23.7 kN (2,420 kgp / 5,340 lbf) thrust.
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NORTH AMERICAN F-86A SABRE:
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wingspan:
11.31 meters (37 feet 2 inches)
wing area:
26.75 sq_meters (288 sq_feet)
length:
11.43 meters (37 feet 6 inches)
height:
4.5 meters (14 feet 9 inches)
empty weight:
4,780 kilograms (10,535 pounds)
loaded weight:
7,360 kilograms (16,220 pounds)
max speed at altitude:
965 KPH (600 MPH / 520 KT)
service ceiling:
14,630 meters (48,000 feet)
combat radius:
530 kilometers (330 MI / 285 NMI)
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* The first two operational F-86As were delivered to the USAF on 15 February 1949. The crews quickly staged a contest to give their new aircraft a name, and the F-86 became the "Sabre", which the news media tended to render as "Sabrejet". By the end of 1949, two fighter groups had been equipped with the type, and another was converting to it.
While the Sabre was being delivered to USAF fighter squadrons, new improvements were added. Late production featured the improved A-1CM radar gunsight, resulting in the designation "F-86A-6"; some had both the A-1CM gunsight and the longer-ranged AN/APG-30 ranging radar, and were designated "F-86A-7". A total of 554 F-86As of all subtypes was built.
There were also field upgrades of F-86As to the uprated J47-GE-13 engine, with 24.2 kN (2,470 kgp / 5,450 lbf) thrust; these aircraft were not redesignated. Another field change resulted in moving the pitot tube, used to measure airspeed, from the air intake to the right wingtip. Positioning the pitot tube in the air intake had led to false readings due to the additional airflow drawn into the intake.
BACK_TO_TOP* On 25 June 1950, North Korea crossed the 38th parallel and invaded South Korea in a massive ground offensive, driving South Korean and American forces back in confusion. Although the North Koreans were powerful on the ground, their air assets were weak and antiquated, consisting of Soviet piston aircraft such as the Yak-9 fighter and Il-10 Shturmovik ground-attack aircraft. The USAF had few air assets on the spot to resist the offensive, but long-range North American F-82 Twin Mustangs were able to reach the war zone from bases in Japan and provide air cover for long periods of time. Lockheed F-80 Shooting Star fighters were also able to reach Korean airspace, but their endurance was very short.
By early July, North American F-51D Mustangs were flying close-support missions from forward airfields in Korea to slow down the North Korean offensive. The US Navy was performing carrier-based close-support missions on the enemy rear, and British and other UN forces were contributing air power as well. By August, the USAF was hitting the enemy rear areas hard with B-26 Invader and B-29 Superfortress bombers in an attempt to relieve the pressure on US and South Korean forces boxed in around the city of Pusan, in the southeast corner of Korea.
On 15 September 1950 General Douglas MacArthur, commander of United Nations forces in the theatre, conducted an amphibious landing at Inchon, near the South Korean capital of Seoul, cutting the supply lines of North Korean units to the south. Within a month, the North Koreans had been driven out of South Korea, and the UN forces had moved above the 38th parallel, intending to finish off the enemy for good.
* The Chinese government warned that such a drive north would lead to their intervention, and on 26 November Chinese troops made contact with the UN forces, sending them falling back south. The Chinese ground offensive was followed by the appearance of a new threat in the air: the Soviet-made swept-wing MiG-15, which was more than a match for anything the UN had in the field in Korea. The MiG-15 was a heavily armed interceptor that had been developed at the same time as the Sabre under a Soviet crash program, and had flown for the first time only 13 weeks after the initial flight of the XP-86.
The first encounters between MiGs and UN aircraft were in early November. For the moment, UN pilots were able to cope with the faster MiGs. Unknown to the UN, they were mostly flown by Soviet pilots at the time. Many of these pilots had relatively little experience compared to their UN adversaries, who were often able to escape or even turn the tables on the MiGs. However, the Soviets were bound to learn, and the good luck of UN pilots could not last indefinitely. The MiG-15 outclassed the main USAF jet fighters in the field in Korea, the F-80 and the Republic F-84 Thunderjet, and the USAF needed to get the F-86 into combat immediately.
On 10 December 1950, the escort carrier USS CAPE ESPERANCE arrived in Tokyo Bay with a load of F-86As of the USAF 4th Fighter Wing. Unfortunately, due to the haste in which the Sabres were sent over the ocean, they had not been adequately conditioned for the trip, and most were in need of repairs for corrosion damage. Seven were in good enough condition for immediate action, and four went into combat from an advanced Korean airfield on 17 December. On that mission, one of the pilots, Lieutenant Colonel Bruce Hinton, shot down the first MiG-15 to fall victim to the Sabre.
* On paper, the F-86A and the MiG-15 were well matched. The Sabre was somewhat underpowered and the MiG-15 could outclimb it. The Soviet aircraft also was more heavily armed, with two 23-millimeter and one 37-millimeter cannon. The MiG's cannon had a relatively low rate of fire, but it only took a few hits from them to kill a Sabre, while the F-86's six 12.7-millimeter guns lacked hitting power. One Soviet MiG-15 pilot who fought in Korea described them contemptuously as "pea-shooters", and USAF pilots reported expending all their ammunition on a MiG, only to watch it fly away. Soviet pilots felt with good reason that their machine was more rugged, and believed that many of their aircraft that were credited as "kills" by the Americans actually returned to base and were able to fly again.
The MiG-15 does have something of a modern reputation for being a beast to fly, but it appears this is more or less a myth, traceable back to Chuck Yeager. Yeager evaluated a MiG-15 and said in his best-selling autobiography that it was dangerously unstable in a dive, adding that on a visit to the USSR several Soviet pilots agreed with him. However, modern Russian sources said that when this comment got back to those particular pilots, they responded loudly: "BULLSHIT!" A Russian writer suggested that it was Yeager's co-author taking liberties with the facts; the Russian appeared to be unaware of Yeager's notorious windiness, and baffling inclination to exaggerate accomplishments that would seem impressive enough not to require it.
On the plus side, the F-86 was well-crafted, and turned and rolled better than the MiG, though it could by no means fly rings around it. The F-86's radar gunsight was much superior to the MiG's eyeball gunsight -- the Soviets would copy a captured example of the radar -- and if the Sabre's guns were of relatively small caliber, they were accurate, well focused, and had a high rate of fire. Sabre pilots also had an excellent field of view, sitting high up in a prominent bubble canopy, while MiG pilots sat deeper in their machines. This did give the MiG pilots an advantage of greater protection in air combat, but at the cost of a poorer field of view, compounded by the fact that parts of the MiG-15's canopy were prone to fogging.
The MiG's cockpit ergonomics were in general inferior to the Sabre's; in particular, Soviet pilots were unhappy that there was only one ejection lever. If they were wounded in one arm, they would have to reach across with the other to eject, which put them in a posture that made an ejection injury very possible.
Sabres performed better at low altitudes, MiGs at high. For this reason, fights tended to be brief, since the adversaries would quickly seek the ground where they had the most advantage. The Sabre had been designed primarily for the air superiority role, while the MiG-15 had been designed primarily as a high-altitude bomber destroyer. Each was very well suited to the mission for which it had been specifically designed.
The close balance between the F-86 and the MiG-15 meant that the critical factor in the air battle was pilot training and skill. Even Yeager admitted as much, claiming in his biography that he took on a less skilled pilot in a mock dogfight, first flying the Sabre against the MiG, then the MiG against the Sabre, and won in both cases. While there were many skilled Soviet pilots, the Soviets were hampered by the decision to rotate entire units through combat, meaning each new unit had to learn the game all over again. The Americans were in general experienced, and rotated individuals into combat with the help of those that knew the game.
Chinese and North Korean pilots were absolutely no match for the Americans. They had little flight experience, and Soviet pilots who worked with them believed many of their Asian counterparts suffered from malnutrition. Some American pilots reported MiG pilots ejecting rather than face combat -- which sounds windy, but becomes more plausible if these pilots were barely able to fly a MiG, much less take it into combat.
* Encounters between Sabres and MiGs were rare at first. The Chinese ground offensive seemed unstoppable, and by January 1951 the disorganized UN forces had been thrown back south of the 38th parallel. UN resistance then began to stiffen, while air strikes hammered Chinese combat units and their supply routes. MiGs finally began to come out in force to attack UN strike aircraft, and air combat began in earnest.
In early January, F-86s were forced to withdraw from their forward Korean air bases back to Japan by the Chinese advance. The Chinese overran Seoul and got well into South Korea when their offensive, overstretched and hammered by air strikes, finally ran out of steam on 22 January. UN forces began a counteroffensive in early March that pushed the Chinese back north of the 38th parallel. After savage fighting, the battle line more or less stabilized along the parallel. The war of movement was over, and the rest of the war would be a static battle of attrition. The UN had the firepower, but the Chinese were willing to accept horrendous losses, and so the war dragged on.
The North Korean push south forced the Sabres to withdraw to Japan in January 1951 when their Korean air bases were overrun. The abrupt reversal of the war in March allowed the F-86s to return and renew the battle. Sabre successes against the MiG-15 were so impressive that the Chinese effectively abandoned serious air operations in December 1951, in order to regroup.
The Chinese returned in May 1952, with improved tactics. The US reacted by offering a $100,000 USD bounty for any enemy pilot who defected with a MiG. The effort was codenamed Operation MOOLAH, "moolah" being obscure antique American slang for "big money" -- a Russian author, understandably baffled, later mistranslated this as Operation MULLAH, which must have seemed almost as bizarre. The offer was publicized by leaflet drops over airfields. This effort would eventually be rewarded on 21 September 1953, when North Korean Lieutenant No Kum-Suk flew his MiG-15 south and landed it on an American airstrip, allowing the US to perform a detailed investigation of the aircraft.
BACK_TO_TOP* While the Sabre was engaged in heavy combat across the Pacific, the design was being updated back in the States. Design work on the "NA-157" or "XP-86C" was begun in late 1947, in response to a USAF requirement for a "deep penetration" fighter. North American's XF-86C, as it was redesignated in 1948, won the competition against the Lockheed "XF-90" and the McDonnell "XF-88" (which would eventually evolve into the F-101 Voodoo), with the Air Force ordering two prototypes.
The XF-86C had a bigger and longer fuselage than the F-86A. The increased size was to accommodate 5,909 liters (1,561 US gallons) of internal fuel to meet the range requirements, while the increased length was to allow fit of a Pratt & Whitney J48-P-6 engine. The J48 was an improved, afterburning version of the Rolls-Royce Nene centrifugal-flow turbojet, manufactured in Britain as the Tay, providing 27.8 kN (2,835 kgp / 6,250 lbf) dry thrust and 35.6 kN (3,625 kgp / 8,000 lbf) afterburning thrust. The J48's exhaust had a two-piece clamshell variable-size outlet.
The fuselage was designed using the new "area ruling" concept developed by NACA engineers, which specified that changes in an aircraft's cross-sectional area should be minimized to ensure smooth airflow at high speeds; this meant that the fuselage was "pinched" slightly along the wing roots. The result was a somewhat inelegant machine compared to the F-86A, with a porpoise-like body and fat appearance. In fact, the aircraft was so clearly different that the USAF redesignated it the "YF-93A" in 1948.
The nose intake was replaced with air intakes at the sides, leaving the nose available for SCR-720 radar, and the new aircraft was armed with six 20-millimeter cannon instead of six 12.7-millimeter Brownings, with 225 rounds per cannon. The YF-93A's greater weight required reinforced landing gear, with dual wheels on the main gear. The twin air brakes of the Sabre were replaced with a single large air brake under the fuselage.
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NORTH AMERICAN YF-93A:
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wingspan:
11.86 meters (38 feet 11 inches)
wing area:
28.43 sq_meters (306 sq_feet)
length:
13.43 meters (44 feet 1 inch)
height:
4.77 meters (15 feet 8 inches)
empty weight:
6,370 kilograms (14,035 pounds)
loaded weight:
9,800 kilograms (21,610 pounds)
max speed at altitude:
1,000 KPH (620 MPH / 540 KT)
service ceiling:
14,630 meters (48,000 feet)
range, no drop tanks:
3,165 kilometers (1,970 MI / 1,710 NMI)
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The YF-93A had excellent performance and range, and it could be fitted with stores pylons for external tanks to give even greater range, or to carry up to 900 kilograms (2,000 pounds) of bombs, rockets, or other stores. The Air Force ordered 118 production F-93As in 1948.
The first YF-93A prototype performed its initial flight in January 1950, again with George Welch at the controls. Only two were built, neither being armed; the contract had been canceled a year earlier, since the USAF's new Boeing B-47 bomber was so fast that it didn't really need fighter escort, and money was tight anyway. Mid-air refueling would soon kill the "penetration fighter" concept completely. The two YF-93A prototypes were finished as test articles, and flown in this role by NAA, the USAF, and NACA, eventually ending up as NACA property. They were used in various experiments into the late 1950s, in one case fitted with scoop-type air intakes instead of the original flush intakes, and then scrapped.
BACK_TO_TOP* Even while the Air Force had building up fighter groups with the F-86A, work was proceeding on an interceptor variant of the F-86. Development of the big Northrop "F-89 Scorpion" interceptor on which the USAF was resting their hopes had been delayed, and the USAF was desperate to get an aircraft to defend North America from Soviet bombers. The service decided to obtain a derivative of the Lockheed T-33, to become the "F-94 Starfire", and a derivative of the Sabre as interim interceptor solutions.
Development of the first Sabre interceptor variant, originally designated the "F-95A", was initiated in early 1949, with rollout of the first of two prototypes, lacking armament and combat avionics, in November 1949, and first flight on 22 December 1949. Once again, George Welch was at the controls, and once again the nosewheel wouldn't go down. This time it didn't pop open at the last minute, and Welch had to pancake the prototype onto the runway, damaging the aircraft.
The second prototype first flew in September 1950, and was fitted with a Hughes E-3 fire-control system (FCS). By this time, the aircraft had a new name. The F-95A was an almost complete redesign of the original F-86, with only about 25% commonality. However, the US Congress would not approve new aircraft at the time; a modification of an existing aircraft wasn't such a problem, and so the aircraft was redesignated the "F-86D" in the summer of 1950 to ensure funding.
The prototypes were redesignated "YF-86D". The first production "F-86D-1" was rolled off the Inglewood assembly line in March 1951, with first flight in June. 37 were built. This was followed by the "F-86D-5", featuring the definitive Hughes E-4 FCS, with much longer range radar than the E-3. The first was flown in July 1952, though the new FCS proved unreliable and operational delivery of the subtype was protracted. NAA built a total of 26 F-86D-5s.
* The F-86D had only a general resemblance to an F-86A, the most noticeable difference being the F-86D's big nose radome, and modified air intake to accommodate the radome. Of course, this arrangement required a complete redesign of the Sabre's forward airframe. The big nose gave the F-86D a faintly cartoonish appearance. Although the F-86D prototype had a standard F-86A sliding canopy, production F-86Ds had a clamshell canopy and a flat armor-glass windscreen. The F-86D also had a "slab" all-moving tailplane with no elevators.
The F-86D was fitted with the J47-GE-17 afterburning turbojet, with 22.3 kN (2,270 kgp / 5,000 lbf) dry thrust and 29.6 kN (3,015 kgp / 6,650 lbf) afterburning thrust, plus an electronic fuel-control system. The prototypes had been fitted with developmental J47-GE-17 engines, with about 10% less thrust. The rear fuselage was widened and lengthened to accommodate the new engine, with some changes in the design between the prototype and production aircraft.
The J47-GE-17 gave the F-86D impressive performance for the time. In late 1952, an F-86D set a world speed record of 1,124.6 KPH (698.505 MPH), and in July 1953, another F-86D established a new record of 1,152.3 KPH (715.7 MPH).
The F-86D had no guns. Its armament consisted of 24 70-millimeter (2.75-inch) unguided "folding-fin air rockets (FFAR)", stored in a belly tray that could be lowered in half a second. The rockets could be fired in salvos of 6, 12, or 24 at intruding bomber formations. Each rocket had a range of over 4 kilometers (2.5 miles) and a warhead weighing 3.4 kilograms (7.5 pounds).
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NORTH AMERICAN F-86D:
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wingspan:
11.31 meters (37 feet 1 inch)
wing area:
26.75 sq_meters (288 sq_feet)
length:
12.27 meters (40 feet 3 inches)
height:
4.57 meters (15 feet)
empty weight:
6,125 kilograms (13,500 pounds)
loaded weight:
8,240 kilograms (18,150 pounds)
max speed at altitude:
990 KPH (615 MPH / 535 KT)
service ceiling:
16,900 meters (55,400 feet)
range, no drop tanks:
890 kilometers (555 MI / 485 NMI)
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By the standards of the time, the F-86D was an electronic marvel. Most radar-equipped aircraft were two-seaters, carrying a pilot and a radar operator. The F-86D was a single-seat aircraft. Although early concepts for the aircraft had envisioned a two-seat machine, this led to reductions in performance and range, and new developments in electronics encouraged NAA and the Air Force to think that advanced technology could replace the "back-seater" in guiding the pilot to the target.
In operation, the pilot would be directed to the vicinity of a target by a "Ground-Control Intercept (GCI)" operator. At a range of about 50 kilometers (30 miles), the pilot would acquire the target with the aircraft's AN/APG-7 radar. The E-4 fire-control system, which integrated the radar with an AN/APA-84 electronic analog computer system, would provide a course to intercept the target. At the appropriate time, the E-4 would indicate that rockets should be fired as the two paths intersected, the F-86D streaking past the target from the side or front. The E-4 would also provide a warning if there were danger of a collision. The F-86D had a manual lead-computing gunsight as a backup.
In reality, dumping the workload normally handled by a pilot and a radar operator in a two-seat interceptor on a single man proved challenging. Despite the fact that the electronics were intended to take up much of the load, the F-86D was said to require the most training of any contemporary USAF plane, even more than the Boeing B-47 bomber.
* The small batch of F-86D-5s was followed by another small batch of 36 "F-86D-10s", featuring a power-actuated rudder with no trim tab. Earlier Sabre variants had used a manually-actuated rudder with a trim tab. This led in turn to a long sequence of other subvariants with generally minor changes:
* The F-86D was known as the "Sabre Dog" or "Dogship". It seems that these two names were not entirely affectionate, and the second undoubtedly led to a cruder nickname when things weren't going well. The advanced technology used in the interceptor led to painful teething troubles.
The leading-edge afterburning J47 engine proved to be unreliable. Delivery of the E-4 fire-control system was delayed, and when it did arrive, it was plagued by manufacturing defects. At one point, the delays in delivering acceptable fire-control and other electronic subsystems were so bad that there were 320 F-86Ds lined up on the field outside the North American manufacturing plant, awaiting arrival of the boxes needed to complete them.
Problems continued to plague the F-86D after it was delivered. A rash of 13 fires and explosions grounded them all in late 1953, until changes in the electronic fuel-control system were implemented. Then, in early 1954, another streak of 19 accidents occurred, and the Sabre Dogs were grounded again. The answer was Project PULLOUT, in which the Air Force, working with North American, implemented a comprehensive set of fixes to the 1,000-plus F-86Ds in service, bringing them up to F-86D-45 standard. The refit took 18 months and cost $100 million USD. After the update, the Sabre Dogs proved much more satisfactory in service. They were deployed in large numbers in the US, Europe, and Far East.
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