General Dynamics F-16 Fighting Falcon Design

The General Dynamics F-16 Fighting Falcon is a multirole jet 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 4,400 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 is a fighter with numerous innovations 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 that makes it a highly nimble aircraft. The F-16 has an internal M61 Vulcan cannon and has 11 hardpoints for mounting weapons and other mission equipment.  Although the F-16's official name is "Fighting Falcon", it is known to its pilots as the "Viper", due to a perceived resemblance to a viper snake as well as after 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.

Design

The F-16 is a single-engined, very maneuverable, supersonic, multi-role tactical aircraft. The F-16 was designed to be a cost-effective combat "workhorse" that can perform various kinds of missions and maintain around-the-clock readiness. It is much smaller and lighter than its 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 can pull 9-g maneuvers and can reach a maximum speed of over Mach 2.

The Fighting Falcon includes innovations such as 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 11 hardpoints for mounting various missiles, bombs and pods. It was also the first fighter aircraft purpose built to sustain 9-g turns. It has a thrust-to-weight ratio greater than one, providing power to climb and accelerate vertically.

Early models 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 11 hardpoints – six under the wings, two on wingtips and three under the fuselage.

General configuration

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; a single-piece, bird-proof "bubble" canopy; 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 a short distance behind the canopy. Split-flap speedbrakes are located at the aft end of the wing-body fairing, and an arrestor hook is mounted underneath the fuselage. Another fairing is situated beneath the bottom of the rudder, often used to house ECM equipment or a drag chute. Several later F-16 models, such as the F-16I, also have a long dorsal fairing "bulge" along the "spine" of the fuselage from the cockpit's rear to the tail fairing, it can be used for additional equipment or fuel.

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 an aircraft 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. Since introduction, changes in operational usage and additional systems have increased aircraft weight, necessitating several programs to strengthen its structure.

Wing and strake configuration

Aerodynamic studies in the early 1960s demonstrated that the phenomenon known as "vortex lift" could be beneficially harnessed by the adoption of highly swept wing configurations to reach higher angles of attack through use of the strong leading edge vortex flow off a slender lifting surface. Since the F-16 was being optimized for high agility in air combat, 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, which is lower when fuselage lift is considered.

The vortex lift effect is increased by extensions of the leading edge at the wing root (the juncture with the fuselage) known as a strake. Strakes act as an additional elongated, short-span, triangular wing running from the actual wing root 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, thereby generating additional lift and thus allowing greater angles of attack without stalling. The use of strakes also allows a smaller, lower-aspect-ratio wing, which increases roll rates and directional stability while decreasing weight. Deeper wingroots also increase structural strength and increase internal fuel volume.

Negative stability and Fly-by-wire

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.[46] 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 aircraft must overcome its inherent stability in order to maneuver. 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 changes in aerodynamic forces.

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 that govern movement in the three main axes based on current attitude, airspeed and angle of attack (AOA), and 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. Although each axis of movement is limited by the FLCC, flight testing 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 cause 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 and the aircraft's pitch limiter locks the stabilators at an extreme pitch-up or pitch-down attempting to recover; the pitch-limiting 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, Grumman took the innovative step of eliminating mechanical linkages between the 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

One feature of the F-16 for air-to-air combat performance is the cockpit's 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 more 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 seat angle was chosen to improve pilot tolerance of high g forces and reduce susceptibility to gravity-induced loss of consciousness. The seat angle has been associated with reports of neck ache, possibly caused by incorrect use of the head-rest. Subsequent U.S. fighters have adopted more modest tilt-back angles of 20°. Due to the seat angle and the canopy's thickness, the F-16's ejection seat lacks steel 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 the Block 40/42/50/52 aircraft to the (V)10 standard, providing the F-16 with all-weather autonomous detection and targeting for Global Positioning System (GPS)-aided precision weapons. It also adds 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, making it only the third fighter to be so equipped. Northrop Grumman is continuing development upon this latest radar, to form 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 powerplant first selected for the single-engined F-16 was the Pratt & Whitney F100-PW-200 afterburning turbofan, a slightly modified version of the F100-PW-100 used by the F-15. Rated at 23,830 lbf (106.0 kN) thrust, 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, which was also installed on Block 32 and 42 aircraft: the main advance being a Digital Electronic Engine Control (DEEC) unit, which improved engine reliability and reduced stall occurrence. Added to the production line 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 mid-1997 to the "-220E" standard, which enhanced reliability and engine 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.

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