The General Dynamics (now Lockheed Martin) F-16 Fighting Falcon is a single-engine multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superiority day fighter, it evolved into a successful all-weather multirole aircraft. Over 4,500 aircraft have been built since production was approved in 1976. Although no longer being purchased by the U.S. Air Force, improved versions are still being built for export customers. In 1993, General Dynamics sold its aircraft manufacturing business to the Lockheed Corporation, which in turn became part of Lockheed Martin after a 1995 merger with Martin Marietta. The Fighting Falcon has key features including a frameless bubble canopy for better visibility, side-mounted control stick to ease control while maneuvering, a seat reclined 30 degrees to reduce the effect of g-forces on the pilot, and the first use of a relaxed static stability/fly-by-wire flight control system helps to make it a nimble aircraft. The F-16 has an internal M61 Vulcan cannon and 11 locations for mounting weapons and other mission equipment. The F-16's official name is "Fighting Falcon", but "Viper" is commonly used by its pilots, due to a perceived resemblance to a viper snake as well as the Battlestar Galactica Colonial Viper starfighter. In addition to active duty U.S. Air Force, Air Force Reserve Command, and Air National Guard units, the aircraft is also used by the USAF aerial demonstration team, the U.S. Air Force Thunderbirds, and as an adversary/aggressor aircraft by the United States Navy. The F-16 has also been procured to serve in the air forces of 25 other nations. Development Lightweight Fighter program Experience in the Vietnam War revealed the need for air superiority fighters and better air-to-air training for fighter pilots. Based on his experiences in the Korean War and as a fighter tactics instructor in the early 1960s Colonel John Boyd with mathematician Thomas Christie developed the Energy-Maneuverability theory to model a fighter aircraft's performance in combat. Boyd's work called for a small, lightweight aircraft that could maneuver with the minimum possible energy loss, and which also incorporated an increased thrust-to-weight ratio. In the late 1960s, Boyd gathered a group of like-minded innovators that became known as the Fighter Mafia and in 1969 they secured Department of Defense funding for General Dynamics and Northrop to study design concepts based on the theory. Air Force F-X proponents remained hostile to the concept because they perceived it as a threat to the F-15 program. However, the Air Force's leadership understood that its budget would not allow it to purchase enough F-15 aircraft to satisfy all of its missions. The Advanced Day Fighter concept, renamed F-XX, gained civilian political support under the reform-minded Deputy Secretary of Defense David Packard, who favored the idea of competitive prototyping. As a result in May 1971, the Air Force Prototype Study Group was established, with Boyd a key member, and two of its six proposals would be funded, one being the Lightweight Fighter (LWF). The Request for Proposals issued on 6 January 1972 called for a 20,000-pound (9,100 kg) class air-to-air day fighter with a good turn rate, acceleration and range, and optimized for combat at speeds of Mach 0.6–1.6 and altitudes of 30,000–40,000 feet (9,100–12,000 m). This was the region where USAF studies predicted most future air combat would occur. The anticipated average flyaway cost of a production version was $3 million. This production plan, though, was only notional as the USAF had no firm plans to procure the winner. Improvements and upgrades One change made during production was augmented pitch control to avoid deep stall conditions at high angles of attack. The stall issue had been raised during development, but had originally been discounted. Model tests of the YF-16 conducted by the Langley Research Center revealed a potential problem, but no other laboratory was able to duplicate it. YF-16 flight tests were not sufficient to expose the issue; later flight testing on the FSD aircraft demonstrated there was a real concern. In response, the areas of the horizontal stabilizer were increased 25% on the Block 15 aircraft in 1981 and later retrofitted to earlier aircraft. In addition, a manual override switch to disable the horizontal stabilizer flight limiter was prominently placed on the control console, allowing the pilot to regain control of the horizontal stabilizers (which the flight limiters otherwise lock in place) and recover. Besides reducing the risk of deep stalls, the larger horizontal tail also improved stability and permitted faster takeoff rotation. In the 1980s, the Multinational Staged Improvement Program (MSIP) was conducted to evolve the F-16's capabilities, mitigate risks during technology development, and ensure the aircraft's worth. The program upgraded the F-16 in three stages. The MSIP process permitted the quick introduction of new capabilities, at lower costs and with reduced risks compared to traditional independent upgrade programs. In 2012, the USAF had allocated $2.8 billion to upgrade 350 F-16s while waiting for the F-35 to enter service. One key upgrade has been an auto-GCAS system to reduce instances of controlled flight into terrain. Onboard power and cooling capacities limits the scope of upgrades, which often involves the addition of more power-hungry avionics. Lockheed has won many contracts to upgrade foreign operator's F-16s. BAE Systems also offers various F-16 upgrades, receiving orders from South Korea, Oman, Turkey, and the US Air National Guard.In 2012, the USAF assigned the total upgrade contract to Lockheed Martin. Upgrades include Raytheon’s Center Display Unit, which replaces several analog flight instruments with a single digital display. However budget cuts have cast doubt on the USAF's ability to complete the Combat Avionics Programmed Extension Suite (CAPES), which is part of secondary programs such as the Taiwan F-16 upgrade. ACC's General Hostage stated that if he only had money for SLEP or CAPES, he would apply it to SLEP to keep the aircraft flying. Lockheed Martin responded to talk of CAPES cancellation with a fixed-price upgrade package for foreign users, and CAPES was not included in the Pentagon's 2015 budget request. The USAF has said that the upgrade package will still be offered to Taiwan, and Lockheed has said that some of the common elements with the F-35 will keep the unit costs of the radars down. In 2014 the USAF issued a RFI to SLEP 300 C/D model aircraft. Design Overview The F-16 is a single-engine, very maneuverable, supersonic, multi-role tactical fighter aircraft; it was designed to be a cost-effective combat "workhorse" that can perform various missions and maintain around-the-clock readiness. It is much smaller and lighter than predecessors, but uses advanced aerodynamics and avionics, including the first use of a relaxed static stability/fly-by-wire (RSS/FBW) flight control system, to achieve enhanced maneuver performance. Highly nimble, the F-16 was the first fighter aircraft purpose-built to pull 9-g maneuvers and can reach a maximum speed of over Mach 2. Innovations include a frameless bubble canopy for better visibility, side-mounted control stick, and reclined seat to reduce g-force effects on the pilot. The F-16 has an internal M61 Vulcan cannon in the left wing root and has multiple locations for mounting various missiles, bombs and pods. It has a thrust-to-weight ratio greater than one, providing power to climb and accelerate vertically. The F-16 was designed to be relatively inexpensive to build and simpler to maintain than earlier-generation fighters. The airframe is built with about 80% aviation-grade aluminum alloys, 8% steel, 3% composites, and 1.5% titanium. The leading-edge flaps, tailerons, and ventral fins make use of bonded aluminum honeycomb structures and graphite epoxy laminate coatings. The number of lubrication points, fuel line connections, and replaceable modules is significantly lower than predecessors; 80% of access panels can be accessed without stands. The air intake was designed: "far enough forward to allow a gradual bend in the air duct up to the engine face to minimize flow losses and far enough aft so it wouldn't weigh too much or be too draggy or destabilizing." Although the LWF program called for a structural life of 4,000 flight hours, capable of achieving 7.33 g with 80% internal fuel; GD's engineers decided to design the F-16's airframe life for 8,000 hours and for 9-g maneuvers on full internal fuel. This proved advantageous when the aircraft's mission changed from solely air-to-air combat to multi-role operations. Changes in operational use and additional systems have increased weight, necessitating multiple structural strengthening programs. General configuration F-16CJ of the 20th Fighter Wing at Shaw AFB, South Carolina, armed with a mix of air-to-air missiles, anti-radiation missiles, external fuel tanks and support equipment The F-16 has a cropped-delta planform incorporating wing-fuselage blending and forebody vortex-control strakes; a fixed-geometry, underslung air intake to the single turbofan jet engine; a conventional tri-plane empennage arrangement with all-moving horizontal "stabilator" tailplanes; a pair of ventral fins beneath the fuselage aft of the wing's trailing edge; and a tricycle landing gear configuration with the aft-retracting, steerable nose gear deploying a short distance behind the inlet lip. There is a boom-style aerial refueling receptacle located behind the single-piece "bubble" canopy of the cockpit. Split-flap speedbrakes are located at the aft end of the wing-body fairing, and an arrestor hook is mounted underneath the fuselage. A fairing beneath the rudder often houses ECM equipment or a drag chute. Later F-16 models feature a long dorsal fairing along the fuselage's "spine", housing additional equipment or fuel. Aerodynamic studies in the 1960s demonstrated that the "vortex lift" phenomenon could be harnessed by highly swept wing configurations to reach higher angles of attack, using leading edge vortex flow off a slender lifting surface. As the F-16 was being optimized for high combat agility, GD's designers chose a slender cropped-delta wing with a leading edge sweep of 40° and a straight trailing edge. To improve maneuverability, a variable-camber wing with a NACA 64A-204 airfoil was selected; the camber is adjusted by leading-edge and trailing edge flaperons linked to a digital flight control system (FCS) regulating the flight envelope. The F-16 has a moderate wing loading, reduced by fuselage lift. The vortex lift effect is increased by leading edge extensions, known as strakes. Strakes act as additional short-span, triangular wings running from the wing root (the juncture with the fuselage) to a point further forward on the fuselage. Blended into the fuselage and along the wing root, the strake generates a high-speed vortex that remains attached to the top of the wing as the angle of attack increases, generating additional lift and allowing greater angles of attack without stalling. Strakes allow a smaller, lower-aspect-ratio wing, which increases roll rates and directional stability while decreasing weight. Deeper wingroots also increase structural strength and internal fuel volume. Early F-16s could be armed with up to six AIM-9 Sidewinder heat-seeking short-range air-to-air missiles (AAM), including rail launchers on each wingtip. Some F-16s can employ the AIM-7 Sparrow medium-range AAM; more recent versions can equip the AIM-120 AMRAAM. It can also carry other AAM; a wide variety of air-to-ground missiles, rockets or bombs; electronic countermeasures (ECM), navigation, targeting or weapons pods; and fuel tanks on 9 hardpoints – six under the wings, two on wingtips, and one under the fuselage; two other locations under the fuselage are available for sensor or radar pods. Negative stability and fly-by-wire F-16C of the South Carolina Air National Guard in-flight over North Carolina equipped with air-to-air missiles, bomb rack, targeting pods and Electronic Counter Measures pods The F-16 was the first production fighter aircraft intentionally designed to be slightly aerodynamically unstable, also known as "relaxed static stability" (RSS), to improve maneuverability. Most aircraft are designed with positive static stability, which induces aircraft to return to straight and level flight attitude if the pilot releases the controls; this reduces maneuverability as the inherent stability has to be overcome. Aircraft with negative stability are designed to deviate from controlled flight and thus be more maneuverable. At supersonic speeds the F-16 gains stability (eventually positive) due to aerodynamic changes. To counter the tendency to depart from controlled flight—and avoid the need for constant trim inputs by the pilot, the F-16 has a quadruplex (four-channel) fly-by-wire (FBW) flight control system (FLCS). The flight control computer (FLCC) accepts pilot input from the stick and rudder controls, and manipulates the control surfaces in such a way as to produce the desired result without inducing control loss. The FLCC conducts thousands of measurements per second on the aircraft's flight attitude to automatically counter deviations from the pilot-set flight path; leading to a common aphorism among pilots: "You don't fly an F-16; it flies you." The FLCC further incorporates limiters governing movement in the three main axes based on attitude, airspeed and angle of attack (AOA); these prevent control surfaces from inducing instability such as slips or skids, or a high AOA inducing a stall. The limiters also prevent maneuvers that would exert more than a 9 g load. Flight testing has revealed that "assaulting" multiple limiters at high AOA and low speed can result in an AOA far exceeding the 25° limit, colloquially referred to as "departing"; this causes a deep stall; a near-freefall at 50° to 60° AOA, either upright or inverted. While at a very high AOA, the aircraft's attitude is stable but control surfaces are ineffective; the pitch limiter locks the stabilators at an extreme pitch-up or pitch-down attempting to recover, this can be overridden so the pilot can "rock" the nose via pitch control to recover. Unlike the YF-17, which had hydromechanical controls serving as a backup to the FBW, General Dynamics took the innovative step of eliminating mechanical linkages between the control stick and rudder pedals, and the aerodynamic control surfaces. The F-16 is entirely reliant on its electrical systems to relay flight commands, instead of traditional mechanically-linked controls, leading to the early moniker of "the electric jet". The quadruplex design permits "graceful degradation" in flight control response in that the loss of one channel renders the FLCS a "triplex" system. The FLCC began as an analog system on the A/B variants, but has been supplanted by a digital computer system beginning with the F-16C/D Block 40. The F-16's controls suffered from a sensitivity to static electricity or electrostatic discharge (ESD). Up to 70–80% of the C/D models' electronics were vulnerable to ESD. Cockpit and ergonomics F-16 ground trainer cockpit (F-16 MLU) A key feature of the F-16's cockpit is the exceptional field of view. The single-piece, bird-proof polycarbonate bubble canopy provides 360° all-round visibility, with a 40° look-down angle over the side of the aircraft, and 15° down over the nose (compared to the common 12–13° of preceding aircraft); the pilot's seat is elevated for this purpose. Furthermore, the F-16's canopy lacks the forward bow frame found on many fighters, which is an obstruction to a pilot's forward vision. The F-16's ACES II zero/zero ejection seat is reclined at an unusual tilt-back angle of 30°; most fighters have a tilted seat at 13–15°. The tilted seat can accommodate taller pilots and increases G-force tolerance; however it has been associated with reports of neck ache, possibly caused by incorrect head-rest usage. Subsequent U.S. fighters have adopted more modest tilt-back angles of 20°. Due to the seat angle and the canopy's thickness, the ejection seat lacks canopy-breakers for emergency egress; instead the entire canopy is jettisoned prior to the seat's rocket firing. The pilot flies primarily by means of an armrest-mounted side-stick controller (instead of a traditional center-mounted stick) and an engine throttle; conventional rudder pedals are also employed. To enhance the pilot's degree of control of the aircraft during high-g combat maneuvers, various switches and function controls were moved to centralised "hands on throttle-and-stick (HOTAS)" controls upon both the controllers and the throttle. Hand pressure on the side-stick controller is transmitted by electrical signals via the FBW system to adjust various flight control surfaces to maneuver the F-16. Originally the side-stick controller was non-moving, but this proved uncomfortable and difficult for pilots to adjust to, sometimes resulting in a tendency to "over-rotate" during takeoffs, so the control stick was given a small amount of "play". Since introduction on the F-16, HOTAS controls have become a standard feature on modern fighters. The F-16 has a head-up display (HUD), which projects visual flight and combat information in front of the pilot without obstructing the view; being able to keep his head "out of the cockpit" improves a pilot's situational awareness. Further flight and systems information are displayed on multi-function displays (MFD). The left-hand MFD is the primary flight display (PFD), typically showing radar and moving-maps; the right-hand MFD is the system display (SD), presenting information about the engine, landing gear, slat and flap settings, and fuel and weapons status. Initially, the F-16A/B had monochrome cathode ray tube (CRT) displays; replaced by color liquid crystal displays on the Block 50/52. The MLU introduced compatibility with night-vision goggles (NVG). The Boeing Joint Helmet Mounted Cueing System (JHMCS) is available from Block 40 onwards, for targeting based on where the pilot's head faces, unrestricted by the HUD, using high-off-boresight missiles like the AIM-9X. Fire-control radar The F-16A/B was originally equipped with the Westinghouse AN/APG-66 fire-control radar. Its slotted planar-array antenna was designed to be compact to fit into the F-16's relatively small nose. In uplook mode, the APG-66 uses a low pulse-repetition frequency (PRF) for medium- and high-altitude target detection in a low-clutter environment, and in downlook employs a medium PRF for heavy clutter environments. It has four operating frequencies within the X band, and provides four air-to-air and seven air-to-ground operating modes for combat, even at night or in bad weather. The Block 15's APG-66(V)2 model added a more powerful signal processor, higher output power, improved reliability and increased range in cluttered or jamming environments. The Mid-Life Update (MLU) program introduced a new model, APG-66(V)2A, which features higher speed and more memory. The AN/APG-68, an evolution of the APG-66, was introduced with the F-16C/D Block 25. The APG-68 has greater range and resolution, as well as 25 operating modes, including ground-mapping, Doppler beam-sharpening, ground moving target, sea target, and track-while-scan (TWS) for up to 10 targets. The Block 40/42's APG-68(V)1 model added full compatibility with Lockheed Martin Low-Altitude Navigation and Targeting Infra-Red for Night (LANTIRN) pods, and a high-PRF pulse-Doppler track mode to provide continuous-wave (CW) target illumination for semi-active radar-homing (SARH) missiles like the AIM-7 Sparrow. Block 50/52 F-16s initially used the more reliable APG-68(V)5 which has a programmable signal processor employing Very-High-Speed Integrated Circuit (VHSIC) technology. The Advanced Block 50/52 (or 50+/52+) are equipped with the APG-68(V)9 radar, with a 30% greater air-to-air detection range and a synthetic aperture radar (SAR) mode for high-resolution mapping and target detection-recognition. In August 2004, Northrop Grumman were contracted to upgrade the APG-68 radars of Block 40/42/50/52 aircraft to the (V)10 standard, providing all-weather autonomous detection and targeting for Global Positioning System (GPS)-aided precision weapons, SAR mapping and terrain-following (TF) modes, as well as interleaving of all modes. The F-16E/F is outfitted with Northrop Grumman's AN/APG-80 Active Electronically Scanned Array (AESA) radar. Northrop Grumman developed the latest AESA radar upgrade for the F-16 (selected for USAF and Taiwan Air Force F-16 upgrades), named the Scalable Agile Beam Radar (SABR). In July 2007, Raytheon announced that it was developing a Next Generation Radar (RANGR) based on its earlier AN/APG-79 AESA radar as a competitor to Northrop Grumman's AN/APG-68 and AN/APG-80 for the F-16. Propulsion The initial powerplant selected for the single-engined F-16 was the Pratt & Whitney F100-PW-200 afterburning turbofan, a modified version of the F-15's F100-PW-100, rated at 23,830 lbf (106.0 kN) thrust. During testing, the engine was found to be prone to compressor stalls and "rollbacks," wherein the engine's thrust would spontaneously reduce to idle. Until resolved, the Air Force ordered F-16s to be operated within "dead-stick landing" distance of its bases. It was the standard F-16 engine through the Block 25, except for new-build Block 15s with the Operational Capability Upgrade (OCU). The OCU introduced the 23,770 lbf (105.7 kN) F100-PW-220, later installed on Block 32 and 42 aircraft: the main advance being a Digital Electronic Engine Control (DEEC) unit, which improved reliability and reduced stall occurrence. Beginning production in 1988, the "-220" also supplanted the F-15's "-100", for commonality. Many of the "-220" engines on Block 25 and later aircraft were upgraded from 1997 onwards to the "-220E" standard, which enhanced reliability and maintainability, unscheduled engine removals were reduced by 35%. The F100-PW-220/220E was the result of the USAF's Alternate Fighter Engine (AFE) program (colloquially known as "the Great Engine War"), which also saw the entry of General Electric as an F-16 engine provider. Its F110-GE-100 turbofan was limited by the original inlet to thrust of 25,735 lbf (114.5 kN), the Modular Common Inlet Duct allowed the F110 to achieve its maximum thrust of 28,984 lbf (128.9 kN). (To distinguish between aircraft equipped with these two engines and inlets, from the Block 30 series on, blocks ending in "0" (e.g., Block 30) are powered by GE, and blocks ending in "2" (e.g., Block 32) are fitted with Pratt & Whitney engines.) The Increased Performance Engine (IPE) program led to the 29,588 lbf (131.6 kN) F110-GE-129 on the Block 50 and 29,160 lbf (129.4 kN) F100-PW-229 on the Block 52. F-16s began flying with these IPE engines in the early 1990s. Altogether, of the 1,446 F-16C/Ds ordered by the USAF, 556 were fitted with F100-series engines and 890 with F110s. The United Arab Emirates’ Block 60 is powered by the General Electric F110-GE-132 turbofan, which is rated at a maximum thrust of 32,500 lbf (144.6 kN), the highest developed for the F-16.