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Design & Development
On his return to the United States, Johnson immediately started the design of just such an aircraft. In March his team was assembled, and they studied several aircraft designs, ranging from small designs at 8,000 pounds (3.6 t), to fairly large ones at 50,000 pounds (23 t). The L-246 remained essentially identical to the L-083 Starfighter as eventually delivered.
The design was presented to the Air Force in November 1952, and they were interested enough to create a new proposal and to invite several companies to participate. Three additional designs were received: the Republic AP-55, an improved version of its prototype XF-91 Thunderceptor; the North American NA-212 which would eventually evolve into the F-107; and the Northrop N-102 Fang, a new General Electric J79-powered design. Although all were interesting, Lockheed had an insurmountable lead, and was granted a development contract in March 1953. The prototype was given the designation XF-104.
Work progressed quickly, with a mock-up ready for inspection at the end of April, and work starting on two prototypes late in May. At the time, the J79 engine was not ready; so, both prototypes were instead designed to use the Wright J-65 engine; a licensed version of the Armstrong Siddeley Sapphire. The first prototype was completed by early 1954, and started flying in March. The total time from design to first flight was about two years, a very short time even then, and unheard of today, when several years is more typical.
In order to achieve the desired performance, Lockheed chose a minimalist approach: a design that would achieve high performance by wrapping the lightest, most aerodynamically efficient airframe possible around a single powerful engine. The emphasis was on minimizing drag and mass.
Structure
Wings
The F-104 featured a radical wing design. Most jet fighters of the period (and to this day) used a swept-wing or delta-wing planform. This allowed a reasonable balance between aerodynamic performance, lift, and internal space for fuel and equipment. Lockheed's tests, however, determined that the most efficient shape for high-speed, supersonic flight was a very small, straight, mid-mounted, trapezoidal wing. The new wing design was extremely thin, with a thickness-to-chord ratio of only 3.36% and an aspect ratio of 2.45. The wing's leading-edges were so thin (0.016 in / 0.41 mm) and sharp that they presented a hazard to ground crews, and protective guards had to be installed during ground operations. The thinness of the wings meant that fuel tanks and landing gear had to be contained in the fuselage. The motors driving the control surfaces had to be only one inch (25 mm)-thick to fit. The wings had both leading- and trailing-edge flaps. The small, highly-loaded wing resulted in an unacceptably high landing speed, so a boundary layer control system (BLCS) of blown flaps was incorporated, bleeding engine air over the trailing-edge flaps to improve their lift. The system was a boon to safe landings, although it proved to be a maintenance problem in service, and landing without the BLCS could be a harrowing experience.
Tail surfaces
The stabilator (horizontal tail surface) was mounted atop the fin to reduce inertia coupling. Because the vertical tailfin was only slightly shorter than the length of each wing and nearly as aerodynamically effective, it could act as a wing on rudder application (a phenomenon known as Dutch roll). To offset this effect, the wings were canted downward, given 10° anhedral.
Fuselage
The Starfighter's fuselage had a high fineness ratio, i.e., tapering sharply towards the nose, and a small frontal area. The fuselage was tightly packed, containing the radar, cockpit, cannon, all fuel, landing gear, and engine. This fuselage and wing combination provided extremely low drag except at high angle of attack (alpha), at which point induced drag became very high. As a result the Starfighter had excellent acceleration, rate of climb and potential top speed, but its sustained turn performance was very poor, described by some as more like a milk truck than a fighter. It was sensitive to control input, and extremely unforgiving of pilot error.
NACA wind tunnel tested a model of the F-104 to evaluate its stability, and found it became increasingly unstable at higher angles of attack, to the point that there was a recommendation to limit the servo-control power that generated those higher angles, and shake the stick to warn the pilot. In the same report, NACA stated that the wingtip tanks, possibly because of their stabilizing fins, reduced somewhat the model's instability problems at high angles of attack.
Engine
The F-104 was designed to use the General Electric J79 turbojet engine, fed by side-mounted intakes with fixed inlet cones optimized for supersonic speeds. Unlike some supersonic aircraft, the F-104 does not have variable-geometry inlets. Its thrust-to-drag ratio was excellent, allowing a maximum speed well in excess of Mach 2: the top speed of the Starfighter being limited more by the aluminium airframe structure and the temperature limits of the engine compressor than by thrust or drag (which gives an aerodynamic maximum speed of Mach 2.2). Later models used uprated marks of the J79, improving both thrust and fuel consumption significantly.
Ejection seat
Early Starfighters used a downward-firing ejection seat (the Stanley C-1), out of concern over the ability of an upward-firing seat to clear the tailplane. This presented obvious problems in low-altitude escapes, and some 21 USAF pilots failed to escape their stricken aircraft in low-level emergencies because of it. The downward-firing seat was soon replaced by the Lockheed C-2 upward-firing seat, which was capable of clearing the tail, although it still had a minimum speed limitation of 90 knots (170 km/h). Many export Starfighters were later retro-fitted with Martin-Baker zero-zero ejection seats (having the ability to successfully eject the pilot from the aircraft even at zero altitude and zero airspeed).
Avionics
The initial USAF Starfighters had basic AN/ASG-14T ranging radar, TACAN, and the AN/ARC-34 UHF radio. The later international fighter-bomber aircraft had much more advanced Autonetics NASARR radar, a simple infrared sight, a Litton LN-3 inertial navigation system, and an air data computer.
In the late 1960s, Lockheed developed a more advanced version of the Starfighter, the F-104S, for use by the Italian Air Force as an all-weather interceptor. The F-104S received a NASARR R21-G with moving-target indicator and a continuous-wave illuminator for semi-active radar homing missiles, including the AIM-7 Sparrow and Selenia Aspide. The missile-guidance avionics forced the deletion of the Starfighter's internal cannon. In the mid-1980s surviving F-104S aircraft were updated to ASA standard (Aggiornamento Sistemi d'Arma, or Weapon Systems Update), with a much improved, more compact Fiat R21G/M1 radar.
Armament
Basic armament of the F-104 was the M61 Vulcan 20 mm Gatling gun. The Starfighter was the first aircraft to carry the new weapon, which had a rate of fire of 6,000 rounds per minute. The cannon, mounted in the lower part of the port fuselage, was fed by a 725-round drum behind the pilot's seat. It was deleted in all the two-seat models and some single-seat versions, including reconnaissance aircraft and the early Italian F-104S; the gun bay and ammunition tank were usually replaced by additional fuel tanks. Two AIM-9 Sidewinder air-to-air missiles could be carried on the wingtip stations, which could also be used for fuel tanks. F-104C and later models added a centerline pylon and two underwing pylons for bombs, rocket pods, or fuel tanks. The centerline pylon could carry a nuclear weapon; and a "catamaran" launcher for two additional Sidewinders could be fitted under the forward fuselage, although the installation had minimal ground clearance and made the seeker heads of the missiles vulnerable to ground debris. The F-104S models added a pair of fuselage pylons beneath the intakes available for conventional bomb carriage. The F-104S had an additional pylon under each wing, to give a maximum of nine.
M61 cannon installation of a Luftwaffe F-104G. (Michael Wolf photo)
Several two-seat training versions of the Starfighter were produced. They were generally similar to the single-seater, but the additional cockpit required removing the cannon and some internal fuel (very early versions of the F-104B did have a cannon fitted but it became impractical for many reasons). The nose landing gear bay was repositioned and the strut retracted rearwards. Two-seaters were combat-capable with Sidewinder missiles, and, despite a slightly larger vertical fin and increased weight, had similar performance to the early model single-seat aircraft
Sources:
Wikipedia: F-104 Starfighter
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