June 01, 2007

F-16 Fighting Falcon

The F-16 Fighting Falcon is a multirole jet fighter aircraft developed by General Dynamics and Lockheed Martin for the United States Air Force. Designed as a lightweight fighter, it evolved into a successful multirole aircraft.
F-16 Fighting Falcon image 1The Fighting Falcon is a superb dogfighter with innovations including a frameless, bubble canopy for better visibility, side-mounted control stick to ease control while under high g-forces, and reclined seat to reduce the effect of g-forces on the pilot. It was also the first fighter aircraft to be deliberately built to sustain 9g turns. It is also one of the few jets with a thrust-to-weight ratio greater than one, giving the Falcon excellent acceleration.

The Falcon's versatility is a paramount reason it was a success on the export market, serving 24 countries. The F-16 is the largest Western fighter program with over 4,000 aircraft built since production started in 1976. Though no longer produced for the US Air Force, it is still produced for export.

During the 1960s the U.S. Air Force and Navy both concluded that the future of air combat would be determined by increasingly sophisticated missiles. Future "fighters" would be designed primarily for long range, high speed, and equipped with extremely large radar systems in order to detect opposing fighters at long range. This made them much more like interceptors than classic fighter designs. In the early 1960s both the Air Force and Navy expected to use the F-111 (then still in development as the TFX) and F-4 Phantoms for their long and medium range needs complemented by several single-engine designs including upgraded F-100 Super Sabres, F-104 Starfighters, and F-8 Crusaders. Future twin-engine fighter programs were getting underway and the Air Force began a replacement for its single-engine fighter designs to maintain its high-low mix of air superiority aircraft.

Real-world experience in the Vietnam War showed the continued need for the 'high-low' fighter matrix system. Soviet-bloc fighters over Vietnam were proving to be more of a problem than expected for US designs. Even though the US had very large kills to losses ratio in its favor, combat revealed some shortcomings. Missiles of this era still had notable reliability issues, and restrictions on how they were used functionally.

Combat invariably closed to short ranges where air-combat maneuverability and short range air-air weapons became critical. Dedicated interceptors like the F-102 Delta Dagger had also been tested in combat which revealed certain shortcomings. Although US training, doctrine and air control more than made up for these disadvantages, it was nevertheless clear to some in the Air Force that the all-missile doctrine was seriously flawed. Both aircraft of the future High-Low mix for the USAF would have guns (F-15 and F-16).

In May 1971 the US Congress released a report that was highly critical of both the F-14 and F-15 programs. They proposed funding the LWF with $50 million and an additional $12 million the next year. Several companies submitted proposals, but General Dynamics and Northrop had such a head start that they were both asked to produce prototypes for head-to-head testing. These were ready in 1974, and in extensive testing General Dynamics' YF-16 proved somewhat better all-round, winning the LWF contest.

By this time a number of countries were looking for a multi-role replacement for their existing F-104Gs and other older designs. Up to this point, the LWF was merely an evaluation program with no plans to purchase models, but the possibility of a European order lead the Pentagon to reconsider. The Air Force was now seeking a multi-role fighter to replace the F-105, so the program was renamed the Air Combat Fighter (ACF). In September 1974, the Air Force announced plans to purchase 650 ACF's. On 13 January, 1975, Secretary of the Air Force John McLucas announced the selection of the YF-16, beating out Northrop's YF-17.

Design characteristics
The F-16 is a single-engined, multi-role tactical aircraft. It is equipped with an M61 Vulcan cannon in the left wing root, and was almost always armed with two AIM-9 Sidewinder missiles, one on each wingtip on a dedicated rail.

From the very beginning, the F-16 was intended to be a cost-effective "workhorse" that could perform various kinds of missions and maintain around-the-clock readiness. It is much simpler and lighter than its predecessors, but uses advanced aerodynamics and avionics (including the first use of fly-by-wire, earning it the nickname of "the electric jet") to maintain good performance.

More recent versions can be equipped with the AIM-120 AMRAAM on these rails instead. It can also be armed with a wide variety of air-to-air missiles and air-to-ground missiles, rockets or bombs, carried on a number of hardpoints under the wings.

F-16 Fighting Falcon image 2

Ergonomics and visibility
The pilot sits high in the fuselage with the canopy support-bow behind him, out of his field of view. This and the bubble canopy give the pilot an unobstructed field of view, a feature vital during air-to-air combat. The seat is reclined 30 degrees (other seats are typically inclined around 13 degrees) to help the pilot endure high accelerations (g-forces). The control stick is mounted on the right armrest rather than between the legs as is traditional, to aid in maneuvering during high g-force turns. In addition, a Heads-Up Display (HUD) displays vital information in the pilot's field of view.

It has been suggested that the actual benefit in terms of g capability is very close to zero, and the real reason for the large incline was to make the seat fit into the aircraft. The canopy itself has the problem of having to be much thicker than in most aircraft, where only the portion between the cockpit frame and nose have to be thick enough to guard against bird strikes. The F-16's canopy has to be much thicker overall, and as a result is quite heavy.

It is worth noting that some of these features have been used on newer aircraft design. The F-22 uses a single-piece canopy like the F-16, although the F-35 and Eurofighter Typhoon do not. Seat angles have universally been less than the F-16, normally around 15 degrees. The F-22 and F-35 both have deeper forward fuselages than the F-16, which must be very shallow to avoid negatively impacting airflow into the chin-mounted intake.

Fly by wire
F-16 Fighting Falcon image 3The F-16A/B uses a fly-by-wire flight control system with no mechanical linkages between the control stick and the flight surfaces. The flight control system began as an analog computer and switched to a digital computer on the C/D models. Computer control is necessary for flight as a result of the inherent negative stability of the aircraft, a trait which trades stable flight for increased maneuverability.

This lack of mechanical linkages between the control stick and the flight surfaces led to an unusual characteristic in the design of the control stick: originally, it did not move. The control stick instead detected pressure applied by the pilot and translated that pressure into control of the aircraft. This arrangement proved uncomfortable and difficult for pilots to adjust to, so the control stick was given a small amount (less than a quarter of an inch (6 mm) in any direction) of play.

The onboard computer makes thousands of calculations and corrections each second to keep the plane flying, freeing pilots to concentrate on tasks necessary to fulfill their intended role. The enhanced computer oversight also provides automatic flight coordination, utilizing all control surfaces (including the rudder) to keep the aircraft from entering performance hurting or even potentially dangerous situations such as unintentional slips or skids. This led to a common refrain heard from pilots: "You don't fly an F-16; it flies you".

Wing and strake configuration
Aerodynamic studies in the early 1960s demonstrated that the phenomenon known as “vortex lift” could be beneficially harnessed by the utilization of highly swept wing configurations, such as found in the Concorde supersonic aircraft and the Swedish Viggen canard configured aircraft. These favorable effects affected the aircraft’s lift capability and allowed the close-coupled wing to be extended to create higher angles of attack through use of a strong leading-edge vortex flow of a slender lifting surface. The leading edge of the wing’s blended forebody would thus increase the strength of the vortices and give the aircraft additional lift.

The exploitation of this aerodynamic phenomenon shaped the design of the F-16, which boasts cropped delta wings and long wing-body strakes, and is considered to be one of the significant elements responsible for its enduring success as a highly maneuverable fighter.

Negative static stability
F-16 Fighting Falcon image 4An aircraft with negative static stability will, in the absence of control input, depart from level and controlled flight. Most aircraft are designed with positive static stability, where a plane tends to return to its original attitude following a disturbance. However, positive static stability hampers maneuverability, as the tendency to remain in its current attitude opposes the pilot's effort to maneuver; therefore, a plane with negative static stability will be more maneuverable. With a fly-by-wire system, such a plane can be kept in stable flight, its instability kept in check by the flight computers.

The YF-16 was the world's first aircraft to be slightly aerodynamically unstable by design. This feature is officially called "relaxed static stability." At subsonic speeds, the airplane is constantly on the verge of going out of control. This tendency is constantly caught and corrected by the FLCC (Flight Control Computer) and later the DFLCC (Digital Flight Control Computer), allowing for stable flight. When supersonic, the airplane exhibits positive static stability due to aerodynamic forces shifting aft between subsonic and supersonic flight.

From Wikipedia, the free encyclopedia

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