THE 456th FIGHTER INTERCEPTOR SQUADRON
T PROTECTORS OF S. A. C.
North American F-100B / F-107 "Ultra Sabre"
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First Flight: September 10, 1956
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The F-100 Super Sabre
After the F-100 Super Sabre was in production, the design was reconfigured to meet Air Force requirements for a fighter-bomber capable of delivering a nuclear payload at Mach 2 speeds. The first versions were designated F-100B, but when the U.S. Air Force ordered prototypes, the designation changed to YF-107A (NA-212).
The air intake was located behind the cockpit to permit installation of a fire control radar. The YF-107A was the last fighter North American Aviation built for the USAF, and it flew Mach 2 in its first all-out test flights during 1957.
The three YF-107As provided valuable data for advanced flight research. They were followed by the F-108 (NA-257) Rapier, which entered the design stage as a Mach 3 interceptor, but was never produced.
YF-107A --- "The Ultra Saber" Survivors
By John Weeks
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The F-100 Super Sabre
The F-107A & The F-100
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Note The Intake Is Under The Nose Of The Aircraft
By the early-1950’s, North American Aviation had two very successful fighter jet projects under its belt. The first was the F-86 Saber. Based on the J-47 engine, it could go supersonic in a shallow dive. The F-86 distinguished itself in Korea with a 14 to 1 kill ratio over the agile Mig-15. The F-100 Super Saber was an improved Saber built around the bigger J-57 engine. The F-100 was the first USAF fighter to go supersonic in level flight. The Super Saber would go on to distinguish itself in Vietnam, where it earned the nickname “The Hun”.
The next logical step was a fighter jet that could fly Mach 2 in level flight. The introduction of the larger J-75 engine made a Mach 2 fighter possible, at least on paper. North American started working on such a plane under the designation F-100B. Both the F-86 and F-100 have their air intake in the nose of the aircraft. The F-110B started with this design, but it was soon found that the large radar needed the space in the nose. As a result, NAA moved the air intakes under the fuselage.
A number of events happened in mid-1954. First, the USAF issued a requirement for a tactical fighter bomber that was capable of delivering a nuclear bomb. Second, the USAF gave the go-ahead for the Mach 2 fighter bomber, however, it changed the program name to F-107. A contract for 3 flyable YF-107s was issued. Finally, the USAF gave the go-ahead for the YF-105. The F-107 had competition, and likely would end up in a fly-off.
NAA put the F-107 program into high gear. It was quickly determined that the lower position of the air intake caused problems with dropping the nuclear bomb from the bomb bay. As a result, the intakes were relocated above the fuselage, something that had never been tried before. The first YF-107 flew on September 10, 1956. The YF-107 hit Mach 2 shortly after the first flight.
In the end, there were a lot of problems with the F-107. The same was true of the F-105. The F-107 program lost one plane in flight testing, while the F-105 program lost both of their prototypes. Given time, the problems could have been worked out of the F-107, and it probably would have been a successful program. But the F-105 was selected as the new fighter/bomber. Given the name Thunderchief, the F-105 earned the nickname “Thud” in Vietnam, where almost 400 F-105’s were lost of the nearly 800 that were built.
The YF-107 program was canceled, the two survivors were sent to NASA. NASA found the planes to be so unreliable that they were quickly retired. These two aircraft survive in museums. The lasting legacy of the F-107 is the air intakes located above the cockpit. It is a testament that every problem has solution, even if that solution is unconventional. Pilots feared that they would be sucked into the air intakes if they had to bail out, and gave the airplane the affectionate nickname of the “man-eater”.
The F-100B "Super Saber"
The model series between the F-100A and the F-100C, the F-100B, was conceived as a tactical fighter bomber as well as an air superiority day and night fighter. Three prototypes were built, but they were so extensively redesigned that their intended designation was changed to YF-107A before the first example flew on September 10th, 1956. A unique feature of the YF-107A (powered by a J-75-P-11 axial flow gas turbine engine with afterburner) was the engine inlet duct, located on the upper fuselage behind the cockpit canopy, which incorporated a wedge and a two position ramp to ensure optimum propulsion during high speeds. Another unusual feature of the YF-107A configuration was a logistics pod, proposed by North American to increase the aircraft's ground force support capability. According to North American, the YF-107A airframe's pod cavity could also be used to carry a power plant to start transient aircraft. In mid 1966 the Air Force considered the YF-107A as a possible substitute for the troublesome F-105 being developed by the Republic Aviation Corporation and testing of the three prototypes was accelerated. In February 1957, however, the F-107 program was discontinued because, despite recurring slip pages, the Republic F-105 was still significantly ahead of the North American plane from a production standpoint. The three YF-107As were transferred to the National Aeronautics and Space Administration (NASA) for further research in high supersonic speed ranges.
North American F-107A
The F-107A was originally designed as a tactical fighter-bomber version of the F-100, with a recessed weapon bay under the fuselage. However, extensive design changes resulted in its re-designation from F-100B to F-107A before the first prototype flew. Special features included an all-moving vertical fin; a control system which permitted the plane to roll at supersonic speeds; and a system (Variable Area Inlet Duct) which automatically controlled the amount of air fed to the jet engine.
On Sept. 10, 1956, the No. 1 F-107A made its initial flight, attaining Mach 1.03 (The speed of sound, Mach 1, is about 760 mph at sea level). The aircraft first achieved Mach 2 (twice the speed of sound) in tests on Nov. 3, 1956. Three F-107As were built as prototypes and were test flown extensively, but the aircraft did not go into production, the Republic F-105 having been selected as the standard fighter-bomber for the Tactical Air Command. In late 1957, Nos. 1 and 3 were leased to the National Advisory Committee for Aeronautics (NACA) for high-speed flight research.
TYPE Number built/Converted Remarks F-107A 3 was F-100B; S/N 55-5118/5120
Span: 36 ft. 7 in.
Length: 60 ft. 10 in.
Height: 19 ft. 8 in.
Weight: 41,537 lbs. max.
Armament: Four 20mm cannons, 108 2.75 in. rockets and up to 4,000 lbs. of bombs
Engine: Pratt & Whitney J75 of 23,500 lbs. thrust (with afterburner)
Maximum speed: Mach 2-plus
Cruising speed: 600 mph.
Range: 1,570 miles
Service Ceiling: 48,000 ft.
Curtest of the US Air Force Museum
North American F-100B/F-107
BY JOE BAUGER
The F-100B was originally going to be the follow-on to the F-100A. It was pictured as a faster version of the F-100A day fighter, optimized to take maximum advantage of the power offered by the J57 jet engine.
The F-100B project began in 1953 as company design NA-212 for an improved F-100A. On March 4, 1952, North American Aviation management had asked their design team for an estimate of engineering requirements for the F-100B. The F-100B retained the original swept wing planform of the F-100A but had a thinner wing cross section with a 5 percent thickness/chord ratio rather than the 7 percent of the F-100A. An upgraded J57 engine was provided, and the aircraft was to be fitted with a variable-area inlet duct and a convergent-divergent exhaust nozzle. Total thrust of this new engine was to be 16,000 pounds. Dual landing-gear wheels were to be provided which would make operations from unprepared airfields possible. The fuselage was to be area-ruled and was to have an increased fineness ratio. The fuel load was to be carried in integral wing tanks, no provisions being made for the carrying of external fuel tanks. The F-100B was to expected to be approximately the same size and weight as the F-100A, and with the increased power and the aerodynamic refinements that would be made available, a maximum speed of Mach 1.80 at high altitude was anticipated. Production was expected to begin in 1955.
At the same time, North American began to study the feasibility of adapting the Super Sabre as an all-weather interceptor. The project became known as the "F-100I" (I for *Interceptor*) or "F-100BI", although these designations were not official USAF designations. This aircraft was similar in overall configuration to the F-100B except that it had a modified cockpit and was fitted with a nose radome. In order to accommodate the radome, the forward fuselage had to be redesigned so that it had an under the nose variable-area air intake. Provision were made for underwing drop tanks, and the wing leading edges were to be heated to prevent icing. An all-rocket armament was to be fitted. The F-100BI was intended to bear much the the same relation to the F-100A as the F-86D did to the F-86A.
On October 20, 1953, the factory designation NA-212 was assigned to the project. Work began on wind-tunnel studies and a detailed cockpit mockup was built. Work was started on a full aircraft mockup.
In November of 1953, North American started to give some consideration to adapting the NA-212 to a fighter-bomber role. Six hardpoints were added underneath the wing, and the wing structure, controls, and cockpit were revised accordingly. Single-point refuelling capability was provided and the windshield and canopy were revised to improve the pilot's view. A retractable tailskid was installed and the flight control system was upgraded by the addition of pitch and yaw dampers.
Neither the F-100B nor the F-100BI attracted all that much interest on the part of the Air Force. Consequently, on January 15, 1954, the program was cut back drastically at the request of NAA president Lee Atwood. Plans to undertake full production were abandoned, and the program was scaled back to a comprehensive engineering study.
On April 16, NAA decided to settle on the general configuration of the F-100B as being basically that of the F-100BI interceptor. However, later that month, NAA learned that the Air Force was interested in the fighter-bomber configuration of the NA-212. On May 16, 1954, North American directed that all work on the F-100B interceptor project be terminated and that all efforts now be concentrated on the fighter-bomber adaptation. The nose radome and the chin intake of the interceptor version were, however, to be retained.
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In the meantime, NAA engineers had discovered that low-speed handling properties could be improved and landing speeds lowered by about 30 mph if an inboard blown flap were used for boundary layer control. These were incorporated into the design at an early stage. The F-100A had been designed without any wing flaps at all.
Among the changes needed to adapt the F-100B as a fighter-bomber was the change from a 7.33 to an 8.67 load factor, the installation of a maneuvering autopilot, the mounting of an AN/APW-11A radar beacon, a Low-Altitude Bombing System (LABS), an AN/ALF-2 chaff dispenser, an AN/APS-54 radar warning system, a plotting board and a cockpit computer. Larger and heavier wheels and brakes had to be designed, and provision had to be made for electric fuseing of external stores.
On June 11, 1954, the USAF authorized a contract for 33 F-100B fighter bombers. On July 8, 1954, the Air Force notified NAA that the designation for the project had been officially changed to F-107A, the USAF concluding that since this aircraft was so vastly different from the original F-100A it deserved a completely new fighter designation. On August 4, 1954, the contract was cut back to only nine service test aircraft under the designation YF-107A. USAF serials were to be 55-5118/5126.
Late in 1954, the Air Force issued General Operational Requirement 68, calling for a tactical fighter-bomber and an air-superiority day and night fighter. North American apparently responded to this requirement, but it is not quite sure how the F-107A fits into GOR-68. In any case, work continued on the F-107A at a feverish pace. In the meantime, Pratt & Whitney had developed the J75 turbojet, a newer and more powerful adaptation of the J57. NAA enthusiastically embraced this engine as the powerplant for the F-107A.
North American engineers redesigned the vertical tail of the F-107A fighter-bomber as a single-piece, all-moving slab. A similar innovation was adopted for the North American A3J (later A-5) Vigilante carrier-based strategic bomber. A complex spoiler-slot-deflector system on the wings provided lateral control. The wing leading edge was similar to that of the F-100A and had automatically-actuated slats, but the wing trailing edge was made up entirely of tabbed and slotted flaps. There were no ailerons, lateral control being provided by a set of spoilers above and below the wing. The aircraft had an early fly-by-wire control system known as the Augmented Longitudinal Control System (ALCS). It used air data system inputs to provide a command of pitch rate. The major offensive load was to consist of a nuclear weapon carried semi-submerged in the fuselage belly on the centerline.
Unfortunately, wind tunnel tests showed that there would be major problems with weapon release and separation caused by airflow interference from the nose radome and chin air intake. In order to correct this problem, it was decided to move the air intake from the nose to the top of the fuselage just behind the cockpit. This intake was fitted with a complex system of variable inlet ramps to adjust for optimal airflow to the engine at various speeds. A two-position (3.25 degrees and 12 degrees) engine inlet duct system was installed in the first two prototypes for the initial flight tests. This system incorporated a vertical wedge-shaped splitter in the middle of the intake, with four hydraulically-powered doors attached to the sides of the wedge inside the intake which would extend or contract as needed to adjust the intake throat area for optimal airflow to the engine. In the third prototype, the system was made fully automatic and the doors were continuously adjustable.
The main landing gear was attached to the fuselage (rather than the wing as in the F-100) and retracted forwards into bays in the fuselage. The dual-wheeled forward landing gear retracted forwards into the fuselage. There was a retractable tailskid underneath the rear fuselage to prevent damage during inadvertent high-angle landings.
The YF-107A was to be equipped with the NAA Autonetics Division XMA-12 integrated fire control system in the nose. This system was to be capable of detecting airborne targets, selecting a victim, and calculating a lead pursuit course for attack with guns or rockets.
Because of the unusual location of the air intake, it was necessary for the canopy to open straight up rather than to open in the usual clamshell fashion. In an emergency, the pilot could eject right through the canopy without having to jettison it first.
On January 1, 1957, the YF-107A contract was amended to provide for only three flying examples, plus one static test airframe.
The first F-107A (serial number 55-5118) took off on its maiden flight on September 10, 1956 at Edwards AFB, with NAA test pilot Bob Baker at the controls. It went supersonic on its first flight, although there was some minor damage upon landing when the drag chute malfunctioned and the aircraft overran the end of the concrete runway and ended up in a ditch. The aircraft was quickly repaired and flew again three days later.
55-5118 achieved its first Mach 2.0 flight on November 3, 1956.
55-5119 flew for the first time on November 28. It was equipped with the armament of four 20-mm cannon and was assigned the job of carrying out performance and integrated control system testing, and was to check out the separation characteristics of the centerline store.
55-5120 flew for the first time on December 10. It was the first YF-107 to have the fully-automatic variable area inlet duct. Unfortunately, the variable-geometry duct did not live up to its expectations. In spite of repeated attempts at steady climbs at subsonic or supersonic speeds and even zoom climbs from maximum speed at 35,000 feet, 55-5120 was never able to get above 51,000 feet. This was blamed on problems with the variable-geometry intake duct and with the J75 engine, both of which were relatively new at the time. In addition, there was an annoying "buzz" in the variable air intake at high speeds, which was traced to instability of the airflow at the inlet.
55-5118 was asssigned the taks of exploring the zoom climb characteristics. Test pilot Al White was able to start off at 39,000 feet at Mach 2.1, and was able to reach a maximum height of 69,000 feet.
55-5119 was assigned the job of evaluating the weapons delivery system. It was the only one of the three F-107 prototypes to be fitted with the four 20-mm M39 cannon. Wind tunnel tests had suggested that there might be problems with the release of weapons from the streamlined centerline container at supersonic speeds. After some initial problems, on February 25, 1957, test pilot Al White finally successfully delivered the weapon store while flying at Mach 1.87 over the Naval test range at China Lake.
The F-107A found itself in direct competition with the Republic F-105 Thunderchief for production orders. In March 1957, the USAF decided to go with the F-105, and the F-107 was relegated to aerodynamic testing duties. The first and third F-107As were turned over to NACA for high speed flight testing work.
The first F-107A (55-5118) reached NACA at Dryden on November 6, 1957. It was given the NACA number of 207. However, it was so mechanically unreliable that it was grounded by NACA after only four flights and was scavenged for spare parts to keep the other one flying.
The third F-107A (55-5120) reached NACA at Dryden on February 10, 1958. The flight testing of the variable geometry intake of the aircraft was cut short because of its mechanical problems. Eventually, NACA gave up on the F-107A's variable-geometry inlet altogether and it was bolted fixed in position, limiting top speed to Mach 1.2. This aircraft also experienced buffeting problems at high angles of attack. 55-5120 completed some forty test flights for NACA/NASA during 1958-59. On the basis of F-107 flight testing, North American refined the design of the side-stick planned for the X-15. 55-5120 was damaged on September 1, 1959 when test pilot Scott Crossfield was forced to abort a takeoff because of control problems. Both tires blew and the left brake burst into flames. Crossfield was uninjured, but the resulting damage to the F-107A was deemed to be too severe for economical repair, and NASA decided to scrap the aircraft. It was cut up and its fuselage shipped to Sheppard AFB in Texas where it was used for as a fire fighting training aid.
The other two F-107As still survive. After being retired by NASA, F-107A number 55-5118 was turned over to the Pima Air Museum in Tucson, Arizona, where it is now on display. F107A number 55-5119 is in the Air Force Museum at Wright-Patterson AFB in Ohio.
Serials of North American YF-107A:55-5118/5126 North American YF-107A 5121/5126 cancelled.
Engine: One Pratt & Whitney YJ75-P-9, 17,200 lb.s.t. dry and 24,500 lb.s.t. with afterburning. Performance: Maximum speed: 890 mph at sea level, 1295 mph at 36,000 feet. Initial climb rate: 39,900 feet per minute. Service ceiling 53,200 feet. Normal range 788 miles, maximum range 2428 miles. Dimensions: wingspan 36 feet 7 inches, length 61 feet 10 inches, height 19 feet 8 inches, wing area 376 square feet. Weights: 22,696 pounds empty, 39,755 pounds gross, 41,537 pounds maximum takeoff. Total internal fuel capacity was 1260 US gallons, carried in fuselage tanks and in two wing cells. Additional fuel could could be carried in a recessed centerline external tank, as well as in drop tanks carried underneath under-wing hard-points. Armament consisted of four 20-mm cannon M39 cannon with 200 rounds per gun (fitted only to 55-5119). A centerline position was provided for a recessed store. Six underwing pylons could be attached which could carry a total external load of 10,000 pounds.
BY JOE BAUGER
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