All F-16s are not created equal. The Fighting Falcons rolling out of the factory today are not the Fighting Falcons that rolled out of the factory twenty years ago. Some differences are visible-larger horizontal tails, a wider inlet, a larger head-up display, square landing lights, tinted canopies, a thicker root and cap on the vertical tail, and various antennas, vents, bumps, and blisters. Most differences require more than a naked eye to see-digital electronics, vastly increased computing capacity, structural beef-ups, improved engines, and all the software changes to accommodate new functions, sensors, and weapons.

The original F-16 was designed as a lightweight air-to-air day fighter. Air-to-ground responsibilities transformed the first production F-16s into multirole fighters. F-16s that followed expanded and refined these multiple roles with beyond-visual-range missiles, digital flight controls, infrared sensors, precision-guided munitions, high-speed antiradiation missiles, and a variety of other capabilities. Advanced versions of the F-16 just around the corner build upon these refinements to enhance capability further.

This evolution, however, has not devitalized the fundamental strengths of the original design. At the heart of every Fighting Falcon coming off the line is the lightweight fighter concept championed by John Boyd, Tom Christie, John Chuprun, Harry Hillaker, Chuck Meyers, Pierre Sprey, Everest Riccioni, and other members of what came to be known as the Fighter Mafia. This group favored simple and small fighter designs. Such aircraft can change direction and speed faster than their potential adversaries. Smaller aircraft are harder to detect visually and electronically. The Fighter Mafia advocated designs that are inexpensive to produce, operate, and maintain. They used technology not for the sake of using technology, but to increase effectiveness or to reduce cost. They went so far as to question and thoroughly analyze the basic assumptions that underlie how fighters are judged and compared.

General Dynamics Fort Worth transformed these ideas into reality in the 1970s. The resulting lightweight fighter set new performance standards for fighter aircraft. The basic design combined a host of advanced technologies that had never been used in previous operational fighters. A blended wing-body, variable camber wings, and forebody strakes provided extra lift and control. Fly-by-wire flight controls improved the response time and replaced heavy hydromechanical systems with lighter and smaller electronic systems. Relaxed static stability, made possible by the fly-by-wire system, greatly enhanced agility. Side-mounted throttle and stick, head-up display, thirty-degree seat back angle, hands-on controls, and a bubble canopy improved g-tolerance and situational awareness for the pilot. All of these technologies had been explored in a variety of other aircraft and research programs. But the F-16 prototype, or YF-16, was the first airplane to incorporate them all into one package.

The development of the YF-16 maximized a design for performance. The evolution of the F-16, on the other hand, has been a balance between adding improved capabilities and maintaining the performance levels of the original design. Capability improvements have often come in the form of weapons, pods, and fuel tanks tucked under the wings, attached to the centerline, and affixed to the intake. The airframe itself has been beefed up to handle some of these additions. The good news is that these increases in capability are packed into an airframe still capable of sustaining nine g's. The bad news is that additional weight and drag have accompanied these new capabilities.

The F-16 may have started life as a lightweight fighter, but it hasn't been completely immune to the "pound a day" appetite that applies to all fighters. The empty weight of the Block 10 F-16A is 15,600 pounds. The empty weight of the Block 50 is 19,200 pounds. The increase equates to less than half a pound a day, but it is additional weight nonetheless. (The empty weight of the YF-16 with two AIM-9 missiles was 14,023 pounds. The prototypes, however, did not have a fire control radar and avionics characteristic of an operational airplane.)

Fortunately Pratt & Whitney and General Electric have stepped up to the scale and offset much of the weight and drag gains with some impressive improvements in engine performance. The original Pratt & Whitney engine on the YF-16 developed over 23,000 pounds of thrust. The engines on the Block 50/52 aircraft develop nearly 30,000 pounds of thrust. The next round of engine improvements is expected to boost this figure to as high as 37,000 pounds. So, even though weight has increased, the thrust-to-weight ratio of the F-16 has actually improved over time.

But any Fighter Mafia member will point out that thrust-to-weight ratio is not the only indicator of aircraft performance. The figure doesn't account for the effects of wing loading and aerodynamic drag. A better measure of performance is energy rate (or Ps), which is a function of thrust, weight, velocity, and drag. Every external payload extracts a performance price in aerodynamic drag. And F-16s rarely fly without a few items under the wing.

But technology has come to the rescue again. Advances in electronic miniaturization have significantly reduced aerodynamic drag as well as resulted in lighter and more compact hardware. The latest navigation and targeting pods, for example, are smaller, lighter, and aerodynamically cleaner than the first-generation pods. Further advances have placed infrared targeting and navigation sensors inside the airframe. Electronic countermeasure systems have shrunk through the years and have more recently found their way under the F-16's skin, eliminating even more aerodynamic drag. Weaponeers are hard at work making bombs and missiles smaller, lighter, and more streamlined. Most of these changes, however, have not been made with aerodynamic intentions. Drag reductions have often accompanied efforts to put more systems and weapons on the airplane and to make the airplane stealthier.

While the F-16 has benefited from the electronic revolution, the original designers did not anticipate the revolution. In fact, they kept the aircraft as dense as possible to prevent additional systems-and the extra weight they would bring-from being placed inside the airframe. Technology advances have allowed much more capability to be packed into that same space.

Keeping up with all the varieties of the F-16 through the years is no small task. The fact that most changes were made in groups, or blocks, to track things on the production line simplifies the job. Block is an important term in tracing the F-16's evolution. Basically, a block is a numerical milestone. The block number increases whenever a new production configuration for the F-16 is established. The first production aircraft that followed the two YF prototypes and the eight full-scale development F-16s, for example, were Blocks 1 and 5. Today, the latest F-16s are designated Block 50/52. Block 50 has a General Electric engine. Block 52 has a Pratt and Whitney engine. (From Block 30/32 on, a major block designation ending in 0 signifies a General Electric engine; one ending in 2 signifies a Pratt & Whitney engine.) Block 55 and Block 60 are often used to describe concepts for advanced versions of the F-16, but the terms do not indicate engine selection..

F-16 neophytes note: The A in F-16A refers to a Block 1 through 20 single-seat aircraft. The B in F-16B refers to the two-seat version. The letters C and D were substituted for A and B, respectively, beginning with Block 25. The new letters emphasize the significance of the change that occurred between Block 15 and 25.

Not all F-16s within a given block are the same. They fall into a number of block subsets called miniblocks. These sub-block sets are denoted by capital letters following the block number (Block 15S, for example). Miniblock designations originate for production purposes. However, some of these miniblock capabilities are retrofitted after the airplane leaves the factory. The designation represents a list of changes associated with a particular F-16 block at a certain point in that block's production. All Block 15S aircraft will have the same capabilities and the same technical orders. The latest F-16s are now up to a Block 50H miniblock designation.

The formal process behind these changes is relatively straightforward. Every change that occurs on the F-16 has an engineering change proposal, or ECP, attached to it. The ECP process, which is not unique to the F-16, begins with a form, an advanced change study notice from the Air Force officially requesting a change on the F-16. The vast majority of these requests are for improving capability. The request generates a Lockheed Martin proposal that includes detailed engineering descriptions, development tasks, support impact, costs, and schedules. An ECP number is attached when the proposal is accepted. The ECP process, from the time the study notice is submitted to the actual hardware rolling off the line, takes from a couple of months to two years, depending on the size and nature of the change. ECPs, in turn, affect flight manuals and technical orders for maintaining the F-16.

An ECP can apply to changes ranging from a single wire to an entire structural upgrade involving thousands of parts and complex procedures. The transition of the F-16 from Block 10 to Block 15, for example, is covered by one ECP (ECP 350 to be exact). To date, over 2,200 ECPs have been written for the F-16.

The F-16's evolution predates the ECP process for the airplane. The first major transition from one version of the airplane to another occurred right after the two F-16 prototypes won the lightweight fighter competition and work began on the first of eight full-scale development, or FSD, F-16s. The differences between the prototype and the F-16s that followed are mostly internal. Those who transformed the prototype into an operational fighter wanted to retain the outstanding flying qualities of the original. So, they were careful to make no changes that would degrade its aerodynamics. At the same time, they had to adapt the airplane to amplified air-to-ground requirements that foreshadowed the F-16's transition into a multirole fighter. The changes in shape were, therefore, kept to a minimum. The overall length grew by thirteen inches. The nose, which accounts for about three of those inches, acquired a slight droop to accommodate the Westinghouse APG-66 radar.

The increased emphasis on air-to-ground capability implied larger payloads. The wing and tail expanded accordingly to carry the extra loads. The wing area grew from 280 to 300 square feet, which is about as much as it could grow without requiring additional bulkheads to lengthen the fuselage. The horizontal tails and ventral fins grew in area by about fifteen percent. The flaperons and speed brakes grew by about ten percent. An additional hardpoint was placed under each wing, giving the aircraft a total of nine. The airframe was structurally strengthened for these new loads as well.

Many other changes brought the FSD aircraft closer to being fully operational. A lighter weight Stencel SIIIS ejection seat replaced the ESCAPAC seats used in the prototypes. A simpler single door was substituted for twin doors on the front landing gear bay. A self-contained jet fuel engine starter was added. The canopy transparency was strengthened to withstand a four-pound, 350-knot bird strike. The radome was hinged to permit easier access to the radar.

Some interesting items were used on the prototypes to keep development costs low. These items included main landing gear tires from the B-58 Hustler, an emergency power unit from the Concorde, an ejection seat from the A-4, a forked air data probe from the SR-71 Blackbird, and servo actuators from the F-111 Aardvark. The actuators in the leading edge flaps were rotary actuators from the F-111 bomb bay doors. The canopy design and the canopy latching system was based on the X-24.

A lot of off-the-shelf equipment, however, did make it onto the FSD aircraft, including a head-up display modified from an A-7 Corsair, nosegear wheel and tire from the F-4, a signal data recorder from the A-10, an oxygen quantity indicator from an F-5E, and a nosewheel steering system from the T-39. The engine, of course, was a modified version of the Pratt & Whitney F100 engine used in the F-15.

Besides winning the lightweight fighter competition, the YF-16 also successfully validated the aerodynamics, propulsion, and handling qualities of the basic design of the airplane. With these major design issues out of the way, engineers could concentrate more on internal details-such as the electrical system, hydraulics, and avionics-with the FSD aircraft. The high readiness and flight rates of the first production F-16s are attributable to the level of maturity achieved with the prototype design.

The FSD aircraft had no block numbers, though they are often referred to as Block 0 F-16s. These earliest F-16s are recognizable in photos by their black radomes and lack of threat warning receiver fairing protruding aft and just below the rudder in production F-16s. The aircraft can also be distinguished by their tail numbers, which range from 0745 through 0752.

The first FSD F-16, which was delivered in December 1976, was used for flutter, propulsion, performance, and flying qualities testing. It was also the first F-16 to fly with the General Electric F101 derivative fighter engine, the forerunner of the F110 introduced at Block 30 (the F101 powers the B-1B). F-16A No. 1, as it is called, is now on display at Wright-Patterson AFB in Ohio. The second FSD aircraft was used for structure and performance tests. It is now being used as a static test article near Fort Worth. The third FSD F-16, which flew for the first time in 1977, was the first F-16 to have a full suite of avionics. It was used for avionics, fire control system, vibration, acoustics, and electromagnetic testing. This aircraft was later converted from a single-seat F-16 to the two-seat F-16XL No. 2. It is now a research aircraft for NASA and flown from Dryden Research Center at Edwards AFB in California.

The fourth FSD F-16 was used for flying qualities, performance, avionics, and weapon separation tests. It is now on display at the USAF Academy. The fifth FSD was used for flying qualities and weapon separation tests. It was later converted into the single-seat F-16XL No. 1, which is also currently being flown by NASA at Dryden. The sixth FSD F-16 was used in climactic tests. It was later converted into the AFTI/F-16, which has pioneered many fighter technologies and which will soon be used to test all-electric actuator technologies for the Joint Strike Fighter program (see the Events section in this issue for more information).

The seventh FSD F-16, the first two-seater FSD aircraft, was used for maintenance training and reliability testing. It was also the first F-16 to be modified with the larger tail surfaces associated with the transition to Block 15 aircraft. This aircraft is now on display at Edwards. The eighth FSD F-16, also a two-seater, was also used for maintenance training and reliability testing. It was modified in 1980 to accept the General Electric J79-GE-119 engine, a derivative of the engine that powers the F-4 Phantom and several other military aircraft. The engine mod was later removed and the airplane was used extensively, until very recently, by company test pilots to develop technologies for close air support, night vision, off-boresight weapons, color displays, and a variety of other capabilities. It is now in flyable storage in Fort Worth.

All of the FSD F-16s were used extensively in tests that went well beyond the scope of the original FSD program. Even the two prototypes flew for many years as platforms for a number of development programs that improved the capability of the operational fleet. Today, these testing duties are performed primarily by more advanced versions of the F-16.

After the prototype and full-scale development programs, the first Block 1 F-16 flew for the first time in August 1978 and was delivered to the Air Force that same month. From there, it succeeded to a number of wings and groups before finding a resting place. This first operational F-16 was first assigned to the 388th Tactical Fighter Wing at Hill AFB, Utah. It later became an interceptor fighter with the 125th Fighter Interceptor Group in Jacksonville, Florida. After that assignment, the aircraft joined the 158th Fighter Interceptor Group in Burlington, Vermont. It then flew with the 127th Tactical Fighter Wing at Selfridge Air National Guard Base in Michigan and was eventually sent to Lowry AFB in Colorado as a student trainer. The F-16 is now on display at Langley AFB in Virginia.

Ninety-four Block 1 and 197 Block 5 F-16s were manufactured through 1981 for USAF and for four European air forces. Most Blocks 1 and 5 aircraft were upgraded to a Block 10 standard in a program called Pacer Loft in 1982. New production Block 10 aircraft (312 total) were built through 1980. The differences between these early F-16 versions are relatively minor, involving improvements to make the airplane more reliable and more easily maintained. Both FSD and Block 1 F-16s are distinguishable in photos by their black radomes. All operational aircraft eventually were retrofitted with lower visibility gray noses. Production F-16s have ACES II ejection seats, the USAF standard for all of its fighters. Blocks 1, 5, and 10 can be distinguished from later F-16A models by a single UHF communications blade antenna below the inlet and by smaller horizontal tails. Several air forces, however, have retrofitted larger tails onto their early model F-16s.

The 330th production F-16 was the first of 983 Block 15 aircraft built in five countries and on three production lines. The production of the Block 15 spanned fourteen years. Of the more than 3,600 F-16s manufactured to date, Block 15 aircraft represent the most numerous version.

The transition from Block 10 to Block 15 resulted in two hardpoints added to the chin of the inlet that were designated stations 5R and 5L. The larger horizontal tails are the most noticeable difference between Block 15 and previous F-16 versions. The tails grew in area by about thirty percent. These larger control surfaces offset the shift in center of gravity brought on by the weight of two additional hardpoints on the inlet chin and their associated sensor pods and structure. The larger tails also provide better stability and control authority, especially at higher angles of attack.

Block 15 saw some structural improvements. It had internal provisions for the AIM-7 Sparrow air-to-air missile as well. The last production Block 15 rolled out of the factory in 1996 and was delivered to Thailand. Eleven other countries fly Block 15 aircraft.

Block 15 aircraft received an operational capability upgrade, or OCU. This upgrade added a data transfer unit and a radar altimeter. It also improved the radar, expanded the fire control and stores control computers, allowed Block 15 aircraft to fire the AGM-119 Penguin antishipping missile, the AGM-65 Maverick air-to-ground missile, and the AIM-120 advanced medium-range air-to-air missile, or AMRAAM. The first F-16 to have these upgrades installed on the production line was delivered in January 1988. Block 15 aircraft built from 1988 on had OCU, larger head-up displays, and the Pratt & Whitney F100-PW-220 engine. Most Block 15 aircraft produced before 1988 also received OCU in a retrofit program that began that year.

The Air Defense F-16 is a variant of the Block 15 OCU F-16 equipped with some additional systems for the air-to-air role. It has an improved APG-66A radar, an APX-109 identification friend or foe interrogator, ARC-200 high-frequency radio, standard flight data recorder, and a 150,000-candlepower spotlight mounted on the left side of the forward fuselage. The Air Defense F-16 can fire the AIM-7 Sparrow air-to-air radar-guided missile using continuous wave illumination from the radar. Like later F-16 versions, the air defense version can fire the AIM-120 AMRAAM radar-guided missile. The airplane is distinguishable by its four-bladed "bird-slicer" antennas just forward of the canopy and under the engine inlet and by the blistered tail root. The blisters were required to make room for the high-frequency radio equipment.

Two-hundred and seventy Block 15 airframes were converted to the air defense configuration in the late 1980s and early 1990s. All of the aircraft went to the Air National Guard. The first air defense variant was delivered in early 1989. An Air Defense F-16 unit from Fargo, North Dakota, proved the airplane's prowess when it won the William Tell air-to-air competition in 1994. Five ANG units still operate the Air Defense F-16. The Royal Jordanian Air Force is scheduled to receive Air Defense F-16s later this year.

The transition of the F-16 from Block 15 to Block 25 marks the evolution from the F-16A/B to the F-16C/D models. Block 25 added in production the ability to carry AMRAAM to the F-16 as well as night/precision ground-attack capabilities. An improved fire control computer, an improved stores management computer, and a USAF-standard inertial navigation system was added as well as multifunction displays, data transfer unit, radar altimeter, anti-jam UHF radio, and provisions for future electronic warfare systems.

The Block 25 F-16 also received an improved radar, the Westinghouse (now Northrop-Grumman) AN/APG-68, with increased range, better resolution, and more operating modes. Block 25 got a larger head-up display, two head-down multifunction displays, and new up-front controls. All Block 25s were originally powered by the Pratt & Whitney F100-PW-200, but they have since been upgraded to the -220E configuration.

The first of 244 Block 25 F-16s flew in June 1984 and was delivered to the Air Force in July. Block 25 is the only F-16 to be employed exclusively by USAF. An F-16 Block 25 aircraft is distinguishable by its larger tail root with a small blade antenna on the leading surface. The extra space in the tail root was intended for an airborne self-protection jamming system. The space is being used for electronic countermeasure systems by some subsequent F-16 blocks.

Block 30/32 added two new engines-the Pratt & Whitney F100-PW-220 and the General Electric F110-GE-100-to the F-16 line. Block 30 designates a GE engine, and Block 32 designates a Pratt & Whitney engine. A larger inlet was introduced at Block 30D for the GE-powered F-16s, which are often called "big-mouth" F-16s. The larger inlet, formally called the modular common inlet duct, allows the GE engine to produce its full thrust potential at lower airspeeds.

The smaller inlet is called a normal shock inlet and has not changed for the -220 and subsequent Pratt & Whitney engines. A Pratt & Whitney F100-PW-229 engine now powers the VISTA/F-16, which has the larger inlet. This is the only F-16 with a large inlet and a Pratt & Whitney engine. The engine bays are common to both engines.

The smaller inlet is called a normal shock inlet and has not changed for the -220 and subsequent Pratt & Whitney engines. A Pratt & Whitney F100-PW-229 engine now powers the VISTA/F-16, which has the larger inlet. This is the only F-16 with a large inlet and a Pratt & Whitney engine. The engine bays are common to both engines.

Block 30/32 can carry the AGM45 Shrike and the AGM-88A high-speed antiradiation missiles or HARM. Like the Block 25, it can carry the AGM-65 Maverick air-to-ground missile. Changes at Block 30D allowed the aircraft to carry twice as many chaff/flare dispensers. The aircraft has provisions for the ALR-56M advanced radar warning receiver. Forward radar warning receiver antennas were relocated to the leading edge flap at Block 30D. These "beer can" antennas have since been retrofit onto all previous F-16C/D aircraft. Block 30/32 has a crash-survivable flight data recorder, voice message unit, and expanded memory for the multifunction displays. The first of 733 Block 30/32 F-16s was delivered in July 1987; the airplane was manufactured through 1989.

The F-16N manufactured for the US Navy is a variation of the Block 30. It is powered by the GE F110-GE-100 engine and has the small inlet associated with early Block 30 production. The F-16N also has the APG-66 radar of the F-16A models and minor structural differences for meeting Navy requirements. The aircraft has no cannon. Twenty-two F-16Ns and four TF-16Ns (two-seaters) were built from 1987 to 1988. They were used for dissimilar air-to-air training at three Navy adversary squadrons and at the Navy's Fighter Weapons School (Top Gun). The F-16Ns were retired from Naval service in 1994 for budget reasons.

With the Block 40/42, the F-16 gained capabilities for navigation and precision attack in all weather conditions and at night. The F-16 traded its analog flight controls for a digital system and new core avionics. The landing gear of the Block 40/42 was beefed up and extended to handle the LANTIRN pods and more extensive air-to-ground loads. The landing gear bay doors bulge slightly by design to handle the larger wheels and tires. The LANTIRN pods also forced the landing lights to move forward from the struts of the main landing gear to the leading inside edge of the nose landing gear door. A larger head-up display accompanied the LANTIRN system as well.

The precision weapons incorporated by the Block 40/42 include the GBU-10, GBU-12, GBU-24 Paveway family of laser-guided bombs as well as the GBU-15 glide bomb. Block 40/42 also saw the addition of the APG-68(V) radar, automatic terrain following (part of the LANTIRN system), global positioning system, a new positive-pressure breathing system to improve g tolerance for the pilot, full provisions for internal electronic countermeasures, an enhanced envelope gun sight, and a capability for bombing moving ground targets. Some foreign versions of the aircraft can carry the AIM-7 Sparrow missile.

Block 40/42 production began in 1988 and ran through 1995. Twenty-one more Block 40s will be built for Egypt from 1999 to 2000. Bahrain is considering more Block 40s to equip a second squadron. The 744 Block 40/42 aircraft produced to date can be distinguished externally from previous F-16 blocks by their landing lights and by the bulged landing gear doors. Any USAF F-16 carrying a LANTIRN pod is a Block 40/42.

Some USAF Block 40 aircraft are now equipped and flying missions with night vision goggles and with a data link system called Sure Strike. This system receives highly accurate position information from a forward air controller on the ground. The system then inputs the data into the weapon system computer and displays it as a waypoint on the head-up display. Sure Strike was integrated into the F-16 in about two months with off-the-shelf equipment. The data link is also used on the Apache helicopter. An upgrade program to Sure Strike, called Gold Strike, is adding two-way imagery transmission. This system will be operationally tested this year. The data link capability will become standard equipment on new F-16s.

Block 20 refers to new-production F-16As that incorporate significant avionic enhancements, including a modular mission computer that replaces three other computers, takes up almost half the space of the hardware it replaces, weighs over fifty-percent less, has faster processing and large growth capacity, and uses almost forty percent less power. The processing speed of the computer is over 740 times faster than the computer in the original F-16. It has over 180 times the memory. An improved version of the APG-66 radar in the Block 20, the APG-66(V2), has many new features, including increased detection and tracking ranges and the ability to track more targets.

These F-16s also have an improved data modem, a ring laser inertial navigation system, a miniaturized global positioning system, a digital terrain system, an advanced interrogator for identifying friendly aircraft, wide-angle head-up display, color multifunction cockpit displays, up-front controls (a set of programmable pushbuttons placed just below the head-up display), and Block 50-style sidestick and throttle controllers. Cockpit lighting is compatible with night-vision systems. MLU will also have provisions for microwave landing systems and helmet-mounted displays.

These features are also being added to over 300 F-16A/B aircraft in the Mid-Life Update program for Belgium, Denmark, the Netherlands, and Norway. These aircraft are also being structurally upgraded so they can meet an 8,000-hour airframe lifespan in a program called Falcon UP (for unos programmum). In addition to these European countries, several other current and potential F-16 customers are considering the upgrade as well. USAF is also planning to incorporate some of these systems, such as the modular mission computer and color multifunction displays into new-production Block 50/52 aircraft. USAF has plans to retrofit Block 40 and Block 50/52 with these systems as well. With its color displays, modular mission computer, and other features, the Block 20 represents one of the most advanced versions of the F-16 being produced today.

The latest version of the F-16C/D is the Block 50/52. The Block 50/52 F-16 is best recognized for its ability to carry the AGM-88 HARM in the suppression of enemy air defenses, or SEAD, mission. The AGM-88 is a second-generation air-to-ground antiradiation missile. The F-16 can currently carry two HARMs, though four-HARM loads are being flight-tested at Eglin AFB.

A HARM avionics launcher interface computer allows the F-16 to launch the HARM missile. The F-16 has quietly and competently taken over the Wild Weasel SEAD role formerly conducted by the F-4G. The HARM is usually combined with a targeting pod mounted on the right intake hardpoint. The pod contains a super-sensitive receiver that detects, classifies, and ranges threats and passes the information to the HARM and to the cockpit displays. With the targeting system, the F-16 has full autonomous HARM capability. F-16s have, however, conducted joint exercises with RC-135 Rivet Joint aircraft, which can help sort and prioritize targets in dense threat environments.

The Block 50/52 is the first F-16 version to integrate the AGM-84 Harpoon antishipping missile. The aircraft can launch the Harpoon in line-of-sight, bearing-only, and range/bearing modes. The addition of the Harpoon gives the F-16 a significant standoff range antishipping capability. When the Harpoon is combined with optional 600-gallon fuel tanks, the Block 50/52 has an unmatched maritime patrol and attack capability.

The Block 50/52 F-16 is equipped with the APG-68(V5) radar, which offers longer range detection against air targets and higher reliability. The radar has a programmable signal processor that employs very high-speed integrated circuit technology. The F-16 is the first US military aircraft to employ this VHSIC technology. The Block 50/52 also includes a ring laser gyro inertial navigation system, a global positioning system receiver, a larger capacity data transfer cartridge, an improved data modem, the ALR-56M advanced radar warning receiver, the ALE-47 threat adaptive countermeasure system, a digital terrain system data transfer cartridge, a cockpit compatible with night vision systems, and an advanced interrogator for identifying friendly aircraft. An upgraded programmable display generator has four times the memory and seven times the processor speed of the system it replaces. New VHF/FM antennas increase reception ranges. The Block 50/52 is powered by increased performance engines-the General Electric F110-GE-129 and the Pratt & Whitney F100-PW-229-each rated to deliver over 29,000 pounds of thrust in afterburner.

New production Block 50/52 aircraft ordered after 1996 will also include color multifunction displays, a three-channel video tape recorder, and the modular mission computer. The throughput of the new computer dramatically increases the processing power of the F-16 and will allow the airplane to continue to grow indefinitely. All four international versions of the Block 50/52 will have LANTIRN capability.

The first Block 50/52 was delivered to USAF in 1991. Over 300 have been delivered so far from three production lines in Fort Worth, Korea, and Turkey. All three production lines are producing Block 50/52s today. These F-16s have no features that easily distinguish them from Block 40/42 aircraft. An HTS pod under the inlet or a HARM attached to the wing, however, indicates a USAF Block 50/52. Block 52 aircraft are distinguishable by the black exhaust leaves of the Pratt & Whitney Increased Performance Engine. The Block 50/52 is the newest and most advanced fighter in the USAF fleet.

The engines that power the F-16 have improved in more ways than maximum thrust. Engines used in early F-16s took from six to eight seconds to spool up from idle to afterburner. Since then, electronic controls have replaced hydromechanical systems. The changes allow current engines to go from idle to full afterburner in as few as two seconds. This responsiveness has a huge payoff in performance and aircraft handling. Engine reliability and ease of maintenance have also been improved significantly. Today's F-16 engines can be expected to deliver eight to ten years of operational service between depot inspections.

Digital engine controls, first introduced on Pratt & Whitney powered F-16s in 1986, have also improved performance. Older hydromechanical controls had to be trimmed to operate at the most challenging point within the F-16's flight envelope. Digital engine controls automatically adjust to the operating environment, so that they optimize engine performance at all points within the flight envelope. This optimization has increased thrust by more than ten percent in some areas of the F-16 flight envelope. All engines being built today for the F-16 have second-generation digital engine controls.

With all the varieties of the F-16 produced through the years, it comes as no surprise that USAF is trying to standardize its F-16 fleet to simplify logistics, maintenance, and training. The service will soon be flying only Block 40/42 and Block 50/52 F-16s in its active-duty units. Block 25 and Block 30/32 will be concentrated in Air National Guard and Air Force Reserve units with a few exceptions for those already flying more advanced versions of the F-16.

Two relatively new programs will further increase the combat capability of the F-16, reduce operation and support costs, and help standardize the Air Force fleet. The first will retrofit all Block 50/52 aircraft with two four-inch color cockpit displays and the modular mission computer, developed for the Mid-Life Update Program.

The second program, called the Common Configuration Implementation Program, adds the color displays, common missile warning systems, and the modular mission computer to Block 40/42 F-16s as well as an advanced data link to both Block 40/42 and Block 50/52 aircraft. The datalink, called Link 16, will be the standard for US and NATO aircraft. A helmet-mounted cueing system is also being considered for this upgrade. This system will work with the high-off-boresight AIM-9X air-to-air missile as well as with other slewable sensors. Over 200 Block 50/52 and 450 Block 40/42 aircraft are involved in the two programs. F-16s from both Guard and active units are scheduled to be modified with the first of the upgraded aircraft operational in the year 2004.

F-16s will soon be the first aircraft to field a new family of smart weapons, which include the CBU-103/104/105 Wind-Corrected Munitions Dispenser, the AGM-154 Joint Stand-Off Weapon, and the GBU-31/32 Joint Direct Attack Munition. Software for these weapons is to be released in mid-1999 for Block 50/52 F-16s.

While the actual evolution of the F-16 to this point is impressive, the potential remains revolutionary. Electronically scanned array radar technology, as used in the F-22, improves the aircraft's ability to detect and track more ground and air targets. The radar also reduces radar cross section, provides several new operating modes, and allows interleaving (simultaneous operation of more than one radar mode). Internal sensor suites and countermeasure systems reduce drag significantly. More and larger color displays improve upon an already exceptional interface between pilot and plane. Interior and exterior lighting makes the F-16 fully compatible with night-vision systems. Conformal tanks increase range and free up hardpoints for additional weapons. Thrust vectoring enhances dogfighting abilities and eliminates angle-of-attack restrictions. Many of these systems and capabilities have already been demonstrated in the F-16.

A tail-less version of the F-16XL has been proposed for a flight test program. This program, however, has not been funded. All-electric flight controls being tested on the AFTI/F-16 for the JSF program could find their way into new production F-16s.

Research at Lockheed Martin into unmanned F-16 variants represents the more radical end of the spectrum. These aircraft are being called uninhabited combat air vehicles or UCAVs. As a first step in the development of UCAVs, the company is proposing to convert an F-16 into an UCAV configuration as a demonstration platform. The airplane would be used to prove autonomous vehicle control, to demonstrate up-link command technologies, and to develop operational requirements. Another proposed F-16 UCAV has a sixty-foot wingspan and 22,000 pounds of internal fuel capacity. The configuration could maintain an unrefueled, eight-hour presence on a nominal combat air patrol mission. A prototype could be built and flying in less than two years.

Other studies have shown that F-16s could be easily modified to become remotely piloted drones. These aircraft would be much less expensive to maintain and operate than USAF's current QF-4 and QF-106 drone fleet. Like these Q-planes, a QF-16 could be piloted from the ground or from the cockpit.

The YF-16 flew for the first time in 1974 at Edwards. The first production F-16 rolled out of the factory in Fort Worth in August 1978. Since then, over 3,600 F-16s have rolled off assembly lines in five countries. Nineteen air forces fly the Fighting Falcon. Several are planning follow-on buys. A dozen other countries are considering the fighter to modernize their fleets. F-16 production is expected for another ten years and front-line service will extend beyond the year 2020.

The long production run and the F-16's low cost have given the airplane latitude to expand its capabilities. The F-16 has grown extensively within the external lines of the first F-16. The limited external changes are a tribute to the optimization of the original design and huge advancements in avionics. The airplane continues to grow, mainly through software changes, to accommodate new weapons and sensors.

The present state of the F-16 covers a broad range. While some F-16s perch atop poles for public display, others test the latest weapon technology. Those rolling out of the factory and being modified by European air forces represent the most advanced operational fighter produced today. Even though the F-16 has been around for over twenty years, its evolution continues to build on the fundamental strengths of the original design.