Light fighter

Effectiveness advantages

The modern view of light/lightweight fighters is as a capable weapon intended to satisfy the main criteria of air-to-air combat effectiveness, which in order of importance are:

1. Achieve superiority in the element of surprise, meaning the tendency to surprise the enemy more often than being surprised by the enemy. In past combats surprise advantage has been mostly based upon small visual and radar signatures, and having good visibility out of the cockpit. Surprise is a significant advantage since historically in about 80% of air-to-air kills the victim was unaware of the attacker until too late.

This key advantage is well understood in the literature of the modern fighter. A small fighter like the F-5 with a planform area of about 300 square feet or the F-16 at about 400 square feet, compared to about 1050 square feet for the F-15, has a much lower visual profile. The small fighter is typically invisible to opposing pilots beyond about 4 miles, whereas a larger fighter such as the F-15 is visible to about 7 miles, and much farther if the engines smoke. This is a non-linear advantage to the light fighter in terms of detection area (similar altitude) and even more so in sky volume (if altitudes are different). Additionally, smaller targets take longer to visually acquire even if they are visible. These two factors together give the light fighter pilot much better statistical odds of seeing the heavy fighter first and setting up a decisive first shot. Once the small fighter sees and turns towards the opponent its very small frontal area reduces maximum visual detection range to about 2.0 to 2.5 miles. If not detected by radar (which is often the case when attacking from the rear hemisphere), this allows the light fighter to set up a high reliability short range heat-seeking missile shot by ambush while still invisible to the target (heat-seeking missile range being about 6 to 20 miles depending on the particular missile).

Given similar technology, smaller fighters typically have about two thirds the radar range against the same target as heavy fighters. However, this cannot be counted upon to give the large fighter a winning advantage, as larger fighters with typical radar cross sectional area of about 10 m² are detectable by a given radar at about 50% farther range than the 2m² to 3m² cross section of the light fighter. This approximately balances these trade-offs, and can sometimes favor the lightweight fighter. For example, from the front the F-15 actually presents about 20m² radar cross sectional area, and has been typically defeated by opposing F-16 forces not only in close dogfighting combat, but also in extensive Beyond Visual Range (BVR) trials. Also, airborne fighter radars are limited in coverage zone (front only) and are far from perfect in detecting enemy aircraft. Despite extensive use of radar in the Vietnam War by the United States, only 18% of North Vietnamese fighters were first detected by radar of any kind, and only 3% by air-to-air radar on board a fighter aircraft. The other 82% were visually acquired, which explains why visual signature favoring the light fighter has remained a significant advantage.

The modern trend to stealth aircraft is an attempt to maximize surprise in an era when Beyond Visual Range (BVR) missiles are becoming more effective than the quite low effectiveness BVR has had in the past. The cost of stealth has so far in its history limited it to more expensive heavy fighters, but as it becomes more commoditized and available it will likely become a prominent feature of advanced light fighters as well. For example, as of 2016 India is planning a semi-stealthy version of its cost effective HAL Tejas light fighter.

2. To have numerical superiority in the air, which implies the need for lower procurement cost, lower maintenance cost, and higher reliability. Not even taking into account the sometimes superior combat capability of lighter aircraft based on surprise and maneuverability, the pure numbers issue of lower cost and higher reliability (higher sortie rates) also tends to favor light fighters. It is a basic outcome of Lanchester's laws, or the salvo combat model, that a larger number of less-sophisticated units will tend to be successful over a smaller number of more advanced ones; the damage dealt is based on the square of the number of units firing, while the quality of those units has only a linear effect on the outcome. This non-linear relationship favors the light and lightweight fighter.

Additionally, as pilot capability is actually the top consideration in maximizing total effectiveness of the pilot-aircraft system, the lower purchase and operational cost of light fighters permits more training, thus delivering more effective pilots. For example, as of 2013, total heavy F15C operating cost is reported at $41,900 per hour, and light F-16C cost at $22,500 per hour.

The numbers advantage also allows lighter designs to have the advantage of covering more area. Assuming an aircraft can patrol an area roughly defined by its radar coverage (or visible range in the case of pre-radar designs), and given that in the radar equation range varies with the fourth root of radar power, a larger number of less-powerful radars will provide more coverage than a smaller number of more powerful radars. This same basic outcome also means that response to on-call ground attack missions will be more rapid, as, on average, an aircraft will be closer to the action if there are more aircraft in the air.

The general tendency in air combat is to lose far more aircraft in air-to-ground operations than in air-to-air. Given this reality, when using fast jets for the air-to-ground role, lighter multi-role designs minimize inevitable budgetary losses. For this reason, even when lighter fighters have superior air-to-air capability such as that exemplified by the F-16, they are often favored over heavier and more expensive aircraft in the ground attack role.

3. To have superior maneuverability, which in maneuvering combat allows getting into superior position to fire and score the kill. This is a function of achieving lower wing loading, higher thrust to weight ratio, and superior aerodynamics. Light fighters have no inherent aerodynamic advantage for speed and range, but when designed to be as simple as possible they do tend to have lower wing loading and higher thrust to weight ratio. Additionally, a single central engine has lower angular inertia, which combined with lower wingspan allows a higher instantaneous turn rate.

4. Weapon systems effectiveness. This area is one where the light fighter can be at a disadvantage, since the combat load of a single engine light fighter is typically about half of a twin engine heavy fighter. However, modern single engine light fighters such as the General Dynamics F-16 Fighting Falcon and the Saab JAS 39 Gripen generally carry similar cannon and air-to-air missile fighter weapons as heavier fighters. Actual aerial combat in the modern era is of short duration, typically about two minutes, and as only a small fraction of this is spent actually firing, modest weapons load outs are generally effective. The ideal weapons load for a modern fighter is considered to be an internal gun and two to four guided missiles, a load that modern light fighters are fully capable of while maintaining high agility. For example, the JAS 39 Gripen, despite being the lightest major fighter in current production, carries a combat load of an effective 27mm cannon and up to six air-to-air missiles of the same types as carried by heavy fighters. Additionally, combat experience shows that weapons systems "effectiveness" has not been dominated by the amount of weaponry or "load out", but by the ability to achieve split second kills when in position to do so. The light fighter advantages of surprise, numbers, and maneuverability maximizes its odds of getting in position to achieve kills with the more limited load it carries.

Disadvantages

It has been shown that properly designed light and lightweight fighters can match the range and aerodynamic performance of heavy fighters. Given that, there are two real disadvantages remaining to light fighters, which are reduced radar range and lower weapons load-outs.

Given similar levels of technology, single engine light fighters tend to have radar range against a similar target of approximately 70% that of heavy twin engine heavy fighters with twice the thrust and thus the aerodynamic ability to carry radar antennas of twice the cross-sectional area. If the light fighter is also hampered by having only half the radar transmit power, then its relative range will be about 60% that of a heavy fighter with similar technology radar. The reason for this reduction to be relatively modest in the face of significant antenna area and power advantages for the heavy fighter is the non-linear physics of radar range as shown in the radar equation that favors the light fighter. Still, this radar range advantage can sometimes allow the heavy fighter to make a long-range missile shot against a target outside of light fighter radar range. Whether this happens and is successful or not depends on the particular aircraft and their respective radar performances and radar cross sections presented to the opposing fighter, the rules of engagement, and the performance of the available BVR missiles.

At typically half the cost and half the weapons load per fighter, a light fighter force can on a per budget basis put a similar weapons load in the air as the heavy fighter force. However, it has the disadvantage that it takes twice the pilots to lift that weapons load. In a battle of equal budgets, the light fighter air force that adopts a strategy of outnumbering the enemy must train more pilots.

Concept summary

The heavy fighter vs. light fighter argument is one of best strategic use of resources and budget. The case for the heavy fighter has claimed superior range, weapons load, and technology. The range advantage has turned out to be false in theory and in practice, as range is a function of fuel fraction, engine efficiency, and relative drag. So long as the light fighter is not overloaded and is as well designed, it has no disadvantage in these factors. The weapons load issue has also turned out to not have high importance, as the light fighter advantages of surprise and maneuverability generally make up for its lower weapons load. Also, modern high thrust to weight ratio jet engines allow even the light fighter to carry a fairly significant weapons load, one exceeding what is normally used in modern air combat.

Superior technology has often been quoted as a strong factor favoring the heavy fighter. The specific argument usually presented favoring heavy fighters is superior radar range and longer range BVR missiles that take advantage of that range. This radar range advantage is one of the major reasons for the existence of the modern heavy fighter, but it has not turned out to be a significant advantage in air combat history to date for several reasons. A major reason has been because long range BVR missile shots have often been unusable, and often unreliable when they could be taken. Carrying these heavy BVR missiles also reduces performance and range needed to get in position to fire. Due to these factors, between 1958 and 1982 in five wars there were 2,014 missile firings by fighter pilots engaged in air-to-air combat in five wars, but there were only four beyond-visual-range kills. Another reason, as mentioned above, is that the tendency to lower radar cross section for light fighters further reduces the relative ranging difference between light and heavy fighter radars when they face each other. Still another reason has been that modern air combat is often orchestrated by AWAC’s aircraft with far larger radar range than light or heavy fighters, who take their BVR cuing data from the AWAC’s aircraft instead of depending upon their own more limited radars.

The more general and often misunderstood argument for more technology that has been historically assumed to favor heavy fighters is not just better radar but better systems support for the fighter pilot in other ways as well. Examples include all weather capability, precise electronic navigation, electronic counter-measures, data-linking for improved information awareness, and automation to lighten pilot workload and keep the pilot focused on tasks essential to combat. This was a compelling argument, as the greatest factor in the effectiveness of a fighter plane has always been the pilot. Quoting a prominent reference, “Throughout the history of air combat, a few outstanding fighter pilots, typically less than five percent of the whole, have run up large scores at the expense of their less gifted brethren. The numerical imbalance was such that a large number of high scorers was needed. The quest was on to turn each fighter pilot into an ace, and technology seemed the easiest, and the only way to achieve it. This was the idea underlying the first two American superfighters; the F-14 Tomcat and the F-15 Eagle.”

But, while a high technology advantage for heavy fighters that better supported the pilot may well have been a valid point in the 1970s when the F-14 and F-15 were first fielded, this advantage has not been maintained over time. With continuously improving engine thrust to weight ratio enhancing load carry capability, and ever shrinking electronics to provide that capability, the lightweight fighter pilot from the 1980s onward has enjoyed similar pilot enhancing technical features in his aircraft and its systems. The lightweight fighter carries equally effective weapons including BVR missiles, and has similar combat range and persistence. The modern lightweight fighter achieves these competitive features while still maintaining the classic advantages of better surprise, numbers, and maneuverability. Thus, the lightweight fighter natural advantages have remained in force despite the addition of more technology to air combat.

Due to their lower costs, modern light fighters equip the air forces of many smaller nations. However, as budgets have limits for all nations, the optimum selection of fighter aircraft weight, complexity, and cost is an important strategic issue even for wealthy nations. The budgetary and strategic significance of light fighters is illustrated by the defense investment at stake. As an example where well referenced data is available, though numerous trial and combat references consider the lightweight F-16 to be as good or better on a per plane as the excellent but expensive F-15, fielding and maintaining a light fighter force based on the F-16 is approximately half the cost of the same number of F-15’s. The U.S. Air Force reports the total loaded cost per hour (as of 2013) of operating the F-16 to be ~$22,500 per hour. Numerous authoritative sources report that it takes about 200 to 400 flight hours per year to maintain fighter pilot proficiency. At 250 flight hours per year per plane, maintaining a single light fighter like the F-16 over a 20-year period is an investment of approximately $112M in 2013 US dollars. An air force of 500 F-16’s is an investment of approximately $56 billion. This is course a heavy budgetary burden, but these figures approximately double for heavy fighters, reaching the point of not allowing adequate numbers of fighters even for wealthy nations. These realities illustrate the high strategic importance of understanding weight, complexity, and combat effectiveness trade-offs for fighter aircraft. Light fighters do not always excel heavy fighters for all missions, but for many or possibly most missions they do provide a more efficient means of “packaging” air power.

pre-WWII

The original light fighter class stemmed from concern at the growing size and cost of the frontline fighters in the 1920s. One early light fighter project was the French Air Force's 'Jockey' interceptor program of 1926. Several aircraft, including the Nieuport-Delage NiD 48 and Amiot 110, were trialed without much success as they offered little over aircraft already in production

In the late 1920s the British issued a specification (F.20/27) for a short-range fast-climbing daylight interceptor. The de Havilland DH.77 and Vickers Jockey monoplanes were tendered to meet the specification but neither went into production, the biplane Hawker Fury being preferred.

Despite the failure of their Jockey program, another attempt was made during the late 1930s to expand France's fleet of aircraft to counter a German buildup. This focused on light wooden fighters that could be built quickly without affecting production of other types of aircraft. The most numerous was the Caudron C.714. Delivery began in early 1940, but only about 90 were built before the fall of France.

WWII

There was debate before and during World War II about the optimum size, weight and number of engines for fighter aircraft. During the war, fighters in the light to middle-weight range proved to be the most effective. Properly designed with competitive power to weight and thrust to drag ratios, these aircraft out-performed heavy fighters in combat due to greater surprise and maneuverability. They were also more cost effective, allowing greater numbers to be deployed as a combat advantage. Some single-engined fighters (including the P-51 Mustang and A6M Zero) could also match or beat the range of their heavy twin-engined counterparts.

Germany

The German Messerschmitt Bf 109 entered service in 1937 and became the most-produced fighter in history, with nearly 34,000 built. The design philosophy of the Bf 109 was to wrap a small airframe around a powerful engine using Messerschmitt's "lightweight construction" principle, which aimed to minimize the weight and number of separate parts in the aircraft. By concentrating wing, engine and landing gear weight in the firewall, the structure of the Bf 109 could be made relatively light and simple. The Bf 109 was the second-smallest major fighter aircraft of World War II and the lightest in the European theater. The "E" version used in the Battle of Britain had an empty weight of 2,010 kg (4,431 lb). The more heavily armed and powerful G version used later in the war had an empty weight of 2,700 kg (5,900 lb). In comparison, its main fighter opponents weighed 2,100 kg (4,640 lb) to 5,800 kg (12,800 lb).

The design philosophy behind the Bf 109 was similar to later, more formalised light fighter concepts. It featured low-cost production and simplified maintenance to achieve a high sortie rate. The aircraft remained competitive throughout the war. Like the Japanese Zero, it proved a very light fighter could be effective. Two tradeoffs were that the narrow undercarriage resulted in a high accident rate and the compact nature of the design limited future development.

Japan

The smallest and lightest major fighter of World War II was the Japanese Mitsubishi A6M Zero naval fighter. Entering service in 1940 and remaining in use throughout the war, it had an empty weight of 1,680 kg (3,704 lb) for the A6M2 version, which was extremely light even by the standards of its time. The design team leader, Jiro Horikoshi, intended it to be as light and agile as possible, embodying the qualities of a samurai sword. With Japanese engine technology lagging behind that of the west, but required to out-perform western fighters, the designers minimised weight to maximize range and maneuverability. This was achieved by methods including the use of light weaponry and the absence of armour and self-sealing fuel tanks. Early in World War II the Zero was considered the most capable carrier-based fighter in the world. In early combat operations, the Zero gained a reputation as an excellent dogfighter, achieving a kill ratio of 12 to 1. However, Japan was unable to keep improving the aircraft through the war, primarily limited by lagging engine technology, and by mid-1942 a combination of new tactics and the introduction of better aircraft enabled the Allied pilots to engage the Zero on equal or superior terms.

United Kingdom

The British entered World War II with two modern single-engined fighters forming the majority of the fighter force of the RAF – the Supermarine Spitfire and the Hawker Hurricane. Initially introduced as bomber interceptors, both started with eight machine gun armament but changed to cannon in the course of the war.

The Spitfire, designed by R. J. Mitchell, entered service in 1938 and remained in production throughout the war. The empty weight of the Battle of Britain-era Spitfire IIA was 2,142 kg (4,723 lb), increasing to 2,984 kg (6,578 lb) in a later variant. It was highly maneuverable and was generally a match for its German opponents. Most Spitfires had a Rolls Royce Merlin engine, but later variants used one of the most powerful engines of the war – the Rolls Royce Griffon. The Spitfire was produced and improved throughout the war but was complex to build and had limited range. In other respects it was considered an outstanding fighter.

The Hawker Hurricane played an important role in the Battle of Britain, but its performance was inferior to the Spitfire and during the war was removed from frontline duty as a fighter and used for ground attack. Production ceased in mid-1944. The Hurricane IIC weighed 2,605 kg (5,745 lb) empty.

United States

On the eve of the war, the United States Army Air Corps contracted for several "very light" fighter designs based on the Ranger V-770 engine, an air-cooled inverted V12 engine, that delivered up to 700 hp. Two prototypes were the Bell XP-77 (empty weight 2,855 lb (1,295 kg)) and the Douglas XP-48 (empty weight 2,655 lb (1,204 kg)). Problems with the engine and performance and a perceived lack of need saw both programs canceled. However, they were specifically defined as "light" or "very light" fighter aircraft.

The intense air war over Europe in World War II, which the United States fought against Germany using a variety of fighter aircraft of varying weights, sheds well documented light on the issue of complexity, number of engines, and weight vs. combat effectiveness in the World War II time frame. The American single engine North American P-51D Mustang fighter with empty weight about 7,635 lb (3,463 kg) and costing approximately $51k per aircraft, flew 214,000 sorties and claimed 4,950 air-to-air kills. The heavier single engine Republic P-47 Thunderbolt, empty weight about 10,000 lb (4,500 kg) and costing $85k per aircraft, flew 423,000 sorties and claimed 3,082 air-to-air kills. The heavier twin engine Lockheed P-38 Lightning with empty weight of about 12,800 lb (5,800 kg) and costing $97k per aircraft, flew 130,000 sorties in the ETO and claimed 1,771 air to air kills. All three of these American fighters are regarded as well designed aircraft and were flown by well trained pilots against the same German opposition, providing a statistically valid test of lightweight vs. heavyweight fighter effectiveness. The P-51 scored 0.023 kills per sortie, the P-47 scored 0.0073 kills per sortie, and the P-38 scored 0.014 kills per sortie. The trend is clear for lower weight to result in better combat effectiveness per plane in the within visual range air-to-air mode, with the lowest cost and lightest aircraft, the P-51, achieving about 1.7 to 3.2 times more kills per sortie. On a kills per budget basis, the P-51 shot down enemy aircraft for only 19 percent the cost of the P-47 and 31 percent that of the P-38.

Realizing the advantages of the P-51's low weight, designers attempted to lower its weight still further while increasing its power. The P-51H of 1944 had an empty weight of 6,586 lb (2,987 kg). An even lighter "J" version with reduced armament of four 0.50 (12.7 mm) machine guns was tested in April 1945. This had an empty weight of 5,749 lb (2,608 kg). The planned production run of 1,000 P-51H aircraft was cancelled at the end of the war after 555 were delivered. The "J" version never entered production.

The United States Navy, also made aware of lightweight advantages by combat results, ordered a lighter version of the Grumman F6F Hellcat, which at 9,238 lb (4,190 kg) empty weight had limited maneuverability and rate of climb. The planned Grumman F8F Bearcat replacement used the same engine, but with empty weight reduced to 7,070 lb (3,210 kg) had excellent performance. It entered production too late to see combat in World War II. Postwar, it equipped 24 fighter squadrons in the Navy and a smaller number in the Marines. The U.S. Navy considered the Bearcat to be "the quintessential lightweight fighter".

USSR

The Soviet Yakovlev Yak-3, which entered service in 1944, was an attempt to develop the smallest and lightest fighter around the 1,600 hp (1,200 kW) V-12 Klimov M-107 engine. As this engine was not available in time, the 1,300 hp (970 kW) Klimov M-105 was substituted, with a resulting empty weight of 2,100 kg (4,640 lb). Despite the reduced power, the Yak-3 had a top speed of 655 km/h (407 mph). The Yak-3 could out-turn the German Bf 109 and Fw 190. German pilots were ordered to avoid dogfights with the Yak-3 at low level.

The Soviet Yakovlev Yak-9 was also a lightweight fighter, initially using the M-105 engine. With an empty weight 2,350 kg (5,170 lb), it was among the lighter major fighters of World War II. A development of the Yakovlev Yak-7, it entered combat in late 1942 and was the Soviet Union's most-produced fighter with 16,769 built. At low altitudes, the Yak-9 was faster and more maneuverable than the Bf 109. However, its armament of one cannon and one machine gun was relatively light.

Early light jet fighters

The Luftwaffe's He 162A of 1945 was a very deliberate attempt at producing an effective light jet fighter. It was a low cost emergency fighter aimed at defending the Third Reich in the late stages of the war. With an empty weight of 1660 kg ( 3,660 lbs), it was very light even for the time. The He 162A was powered by a BMW 003 engine. With a top speed of 790 km/h (491 mph) at normal thrust at sea level, and 840 km/h (522 mph) at 6000 m (19,680 ft), it was about 130 kph (80 mph) faster than Allied fighters. Test pilots reported it to be a fine handling and conceptually well designed aircraft, and considered its problems to be rushed delivery more than any fundamental design flaws. It never formally entered operational service, and did not receive the benefit of being flown by well trained pilots using a well considered operational plan. Only 320 were built, and it scored only a few kills in experimental use before the war ended.

Although not considered a light fighter by the Germans, the twin-jet Messerschmitt Me 262's empty weight of 3,795 kg (8,366 lb) was less than some contemporary World War II single-engined propeller fighters.

The Mikoyan-Gurevich MiG-15 was a Soviet jet fighter developed shortly after World War II. It weighed 3,630 kg (8,003 lb) empty and was one of the first successful jet fighters to use swept wings for high transonic speeds. It first saw service in the Chinese Civil War. In combat during the Korean War, it outclassed straight-winged jet day fighters. Some 18,000 were produced.

The North American F-86 Sabre, a transonic jet fighter manufactured from 1949, was the United States's first swept wing fighter. With an empty weight of 5000 kg (11,000 lb) it was nearly 40 per cent heavier than the MiG-15, but light compared with today's fighters. The F-86 had a bubble canopy, small size, moderate cost, high maneuverability, and an armament of six .50 in (13 mm) calibre machine guns. It could turn faster than any modern fighter. It saw combat against the Mig 15 in high-speed dogfights during the Korean War. Considered (with the MiG 15) as one of the best fighters in the Korean War, it was the most-produced Western jet fighter, with total production of 9,860 units. It continued as a front-line fighter in numerous air forces until 1994.

The Folland Gnat was a British private venture design for a light fighter and was the product of "Teddy" Petter's theories about fighter aircraft design. Although only adopted by the UK as a trainer, the Gnat served successfully as a fighter for the Indian Air Force and was in service from 1959 to 1979. India produced an improved derivative of it, the HAL Ajeet. With an empty weight of 2,177 kg (4,800 lbs) it was the lightest successful post-World War II jet fighter, though at the cost of shorter range compared to other fighters. The Gnat is credited as having shot down seven Pakistani F-86's in the 1965 war, for the loss of two Gnats downed by PAF fighters. During the Indo-Pakistani War of 1971, Indian Gnats shot down several Pakistani F-86s without loss. The Gnat was successful against the capable F-86 flown by well-trained Pakistani pilots because its smaller size allowed a superior level of surprise and greater agility in dogfighting.

In the early 1950s, the NATO NBMR-1 competition for a cheap "light weight tactical strike fighter" able to carry conventional or tactical nuclear weapons led to designs including the French SNCASE Baroudeur, Breguet Taon and Dassault Étendard VI, the Italian Aeritalia G.91 and Aerfer Ariete. Other competitors included the Northrop F-5A. The British chose to continue production of the Hawker Hunter, while the French decided to work independently of the competition. Italy produced the Fiat G.91 while the competition was underway and, in 1957, this was selected as NATO's standard strike fighter. With an empty weight of 3,100 kg (6,830 lbs) it was very light for a jet fighter. The G.91 entered service with the Italian Air Force in 1961, with the West German Luftwaffe, in 1962, and later with the Portuguese Air Force. It was in production for 19 years, with production ceasing in 1977 with 756 aircraft built.

In the mid-1950s, it was realized that fighter costs were escalating to possibly unacceptable levels, and some companies sought to reverse the trend to heavier and more expensive fighters. A prominent result was the Mach 1.3 to Mach 1.6, 4335 kg (9,558 lb) Northrop F-5. Smaller, cheaper and simpler than the contemporary F-4 Phantom, the F-5 had excellent performance and was popular on the export market. It was perhaps the most effective US-produced fighter in the 1960s and early 1970s, with a high sortie rate, low accident rate, high maneuverability, and an effective armament of 20mm cannon and heat-seeking missiles. Though the United States never procured the F-5 for main line service, it did adopt it as an opposing forces (OPFOR) "aggressor" for dissimilar training role because of its small size and similarity in performance to the Soviet MiG-21. It also participated in large scale trials of aircraft and missile effectiveness. In the extensive 9 month long AIMVAL/ACEVAL trial at Nellis AFB in 1977, the F-5 "Red Force" was quite effective against the considerably larger F-14 Tomcat naval fighter and F-15 Eagle single seat fighters making up the "Blue Force". These modern aircraft are approximately five to ten times more expensive than the various versions of the F-5. The final result was the F-5 fighting the more modern fighters to an effective plane for plane draw, which was a significant budgetary win for the F-5 in that given a similar budget the F-5 force would have attritted the more modern fighters to zero. The ability of the F-5 to win over large modern fighters is mostly due to the element of surprise, numbers, and superior sortie generation rates. Just under 1000 of the F-5A Freedom Fighter were sold worldwide, and another 1,400 of the updated F-5E Tiger II version. As of 2016 the F-5 remains in service with many nations.

The light middleweight Saab 35 Draken was a second to third generation Mach 2 fighter produced from 1955 to 1974 and in service for 45 years, with empty weights from 6,577 kg (14,500) to 7,440 kg (16,400 lbs). It was a double-delta wing single-engine fighter. Its steeply swept inner delta wing allowed for a high cruise speed. The double-delta, with a shallower rake at the outer wing, improved maneuverability. It was designed to be cheap enough for small countries and simple enough to be maintained by conscripted mechanics. Its high acceleration, light wing loading, and extreme maneuverability enabled it to be an excellent dogfighter. However, it had an overly complex fire control system. It remained in service until 2005.

The French Dassault Mirage III is another late 2nd/early 3rd generation delta wing Mach 2 fighter. Stemming from a French requirement for a lightweight all-weather interceptor, it has been in service since 1961. With an empty weight of 7,076 kg (15,600 lbs) in the "E" version with added ground attack capability, the Mirage III is a light fighter by modern standards (though twice as heavy as initial Mirage I). Its maneuverability, modest cost, reliability and armament of 30mm cannons and heat seeking missiles proved effective. It served the French Air Force and was exported to many countries. It performed well for Israel in the Six-Day War of 1967 and Yom Kippur War of 1973.

Similar in size to the F-5, the Russian Mikoyan-Gurevich MiG-21 entered service in 1959, was produced until 1985, and is still in widespread use today. The late Generation 2 to Generation 3, Mach 2 MiG-21 has an empty weight of 4535 kg (10,000 lbs), and has served nearly 60 nations. It shot down 37 to 104 US Phantoms, in the Vietnam War, with the Phantoms shooting down 54 to 66 MiG-21s in return. In December 1966 the MiG-21 pilots of the 921st FR downed 14 F-105s without any losses. Its weaknesses include poor visibility and relatively short range, but has otherwise proven to be a capable fighter.

The US's Vought F-8 Crusader used in Vietnam weighed 8000 kg (17,500 lb), as compared with 13,750 kg (30,300 lbs) for an F-4 Phantom. It was a simple, supersonic, single engine, gun- and heat-seeker armed fighter in front-line service from 1957 to 1976. It had no radar except a simple ranging gunsite radar. The US claims the Crusader (up to 1968) shot down six enemy aircraft for every loss, compared with 2.4 for every Phantom lost. The three F-8s shot down in air-to-air were all lost to MiG-17 cannon fire.

The first few decades of the jet fighter era showed a combat history similar in general trend to that of the propeller fighters of World War II. So long as lighter fighters are of sufficient power-to-weight ratio and airframe sophistication, and flown by similarly skilled pilots, they tend to dominate over heavier fighters using surprise, numbers, and maneuverability. However, one significant difference did emerge in design strategy in the early jet fighter era. In World War II fighter design was strongly influenced by the seeking of higher speeds that were valuable in combat in order to close with the enemy or to escape. This trend was instinctively continued in some jet fighters through the 3rd generation (F-4 at Mach 2.23) and into the 4th generation (F-14 at Mach 2.35 and F-15 at Mach 2.5+). The aerodynamic requirements to operate at such speeds add considerable complexity, weight, and cost to the airframe. But, these Mach 2 and above class speeds have zero utility in combat. Combat speeds never exceed Mach 1.7 and seldom 1.2, for two reasons. First, it requires extensive use of the afterburner, which typically increases fuel consumption by about a factor of three or even four, and rapidly reduces operational radius. Second, speeds even above about Mach 0.7 to Mach 1 (depending on circumstances) so widen the turn radius in maneuvering combat that the fighter is thrown too wide to get a tracking solution on an opponent. Speed had reached the limit of its practical combat value, such that optimum fighter design required understanding the penalties the endless search for higher speed was imposing, and sometimes deliberately choosing not to accept those penalties.

Modern light jet fighters

In the 1960s and 1970s, a US-based "Fighter Mafia", led by colonels John Boyd , Everest "Rich" Riccione and analyst Pierre Sprey advocated for production of a 4th generation light fighter. Despite heavy fighter losses in the Vietnam War, most senior US Air Force leaders still opposed the light fighter concept. After much debate, General Dynamics designed the successful F-16. Its competitor, the Northrop YF-17, led to the successful McDonnell Douglas F/A-18 Hornet Navy fighter as cheaper alternative to the F-14. The F-16 offered excellent air-to-air combat performance due partly to its fly-by-wire control system, which made it agile. When not burdened by heavy air-to-ground weapons, the F-16 had the longest range of any US fighter at the time. The F-16 and F-18 later added significant weight to become multirole fighters with strong air-to-ground capabilities, pushing them towards the "middleweight" range of modern fighters.

The Soviet counterpart to the F-16 and F-18, the Mikoyan MiG-29, was originally part of the Perspektivnyy Lyogkiy Frontovoy Istrebitel (LPFI, or "Advanced Lightweight Tactical Fighter") program.

In the 1980s the privately developed F-5G, later renamed the Northrop F-20 Tigershark, aimed to correct weaknesses in the aging F-5 while maintaining small size and low cost. Its empty weight was 6,000 kg (13,150 lbs). Its General Electric F404 engine produced 60 per cent more power than the F-5, and it had a higher climb rate and acceleration, better cockpit visibility, and more modern radar. Chuck Yeager, test pilot and the first man to break the sound barrier, referred to the F-20 as "the finest fighter" of the mid 1980s. Despite its high performance and cost effectiveness, the F-20 lost out for foreign sales against the similarly capable, more expensive F-16, which was being procured in large numbers by the US Air Force and was viewed as having greater support. The Tigershark was cancelled having made no sales.

The HAL Tejas has an empty weight of 6,500 kg (14,300 lbs), and is the second-lightest fighter behind the JAS 39 Gripen among current production light fighters. Introduced into service in 2014, it was the lowest-cost fighter aircraft with competitive air-to-air capability in production at that time, at an equivalent cost of USD $27 million. Several hundred aircraft are planned to enter service with both the Indian Airforce and Indian Navy. As of 2016, 123 aircraft had been ordered, with production rates of approximately 18 aircraft per year. The design is similar to the JAS 39 Gripen, being a light tailless delta-wing single-engine fighter with ground attack capability. It is armed with a 23mm cannon, heat-seeking missiles enhanced with electro-optical imaging, and radar-guided missiles. The HAL Tejas Mark 3 is a planned upgrade with limited stealth capability.

The French Dassault Mirage 2000 was designed for the French Air Force (Armée de l'Air)in the late 1970s as a lightweight single engine fighter. It was based on the Mirage III, entered service in 1982, and has since evolved into a multirole aircraft. In heavier multirole form it has empty weight of 7,400 kg (16,300 lb). More than 600 were built and it has served nine nations.

South Korea's KAI T-50 Golden Eagle designed by Lockheed Martin with Korea Aerospace Industries is based on the F-16 multirole-fighter. Its latest variant, the FA-50 Fighting Eagle, is designated as a light fighter and trainer. It uses the same air frame as the T-50 advanced trainer introduced in August 2002. It is now deployed with South Korean Air Force and the Philippine Air Force.

The CAC/PAC JF-17 Thunder light fighter was developed by China's Chengdu Aircraft Corporation in the early 2000s in cooperation with Pakistan. it was inducted into the Pakistan Air Force in February 2010. At least 66 aircraft have been delivered to Pakistan. More aircraft are scheduled to be introduced in 2018. A twin-seater variant was undergoing flight testing as of late 2015.

The JAS 39 Gripen is a single-engine light fighter manufactured by the Swedish aerospace company Saab. With an empty weight of 5,700 kg (12,600 lbs) it is the lightest fighter in production as of 2016. Though primarily an air superiority fighter, the design has effective air-to- ground capability as well. Its delta wing offers high cruise and super-cruise (above Mach 1 without using after-burner), low wing-loading and high maneuverability. It can operate from short airstrips and 800m (800 yard) sections of road, can be serviced by moderately trained mechanics, and has high sortie rates. Among Western 4th generation fighters the Gripen has the lowest operating cost at about $4,700 per flight hour (as of 2012). The next best is the F-16 at about $7,000 per flight hour. The Gripen has relaxed stability fly-by-wire flight controls for maximum agility, a top speed of Mach 2, a 27mm cannon, heat-seeking missiles, and radar-guided missiles.

Future of light fighters

The issue of where a fighter is best positioned on the weight, cost, and complexity curve is still a contentious issue. Stealth technology (airframe and engine design that strongly reduce radar and heat signatures) seeks to emphasize the most important feature of fighter effectiveness, the element of surprise. So far it has been featured only on heavier and more expensive fighters, specifically the F-22 Raptor and F-35 Lightning II. These fighters are not only stealthy, but also have information or combat awareness advantages due to active electronically scanned array (AESA) radars, and data linking for external cuing of enemy position and friendly force status. Their combination of near invisibility, superior combat awareness, networking, and reliable Beyond Visual Range (BVR) missiles, enables them to get deep inside the enemy's OODA loop and destroy enemy fighters before their pilots are even aware of the threat.

However, due to Lanchester's laws such superiority on a unit basis does not always translate to winning wars. For example, late in WWII the greatly superior German Messerschmitt Me 262 jet fighter, flown by the finest pilots Germany had left, many of them very high scoring aces with kill counts far in excess of Allied pilots, in its relatively small numbers suffered heavy losses and was unable to fundamentally alter the air war over Germany. This could be a harbinger of things to come if a greatly numerically inferior force of expensive stealth heavy fighters ever enters into mass combat against a larger force of lower cost but well designed light to middleweight fighters that are competently flown and led.

Though the advantages of stealth have so far been applied only to heavy and expensive fighters, it is possible for light fighter technology to also adopt most of these features to keep pace while maintaining its cost advantages. Modern lower cost fighters like the JAS 39 Gripen and F-16 are already datalink- and network-equipped with integrated electronic suites, and are being equipped with AESA radar as well. India is introducing stealth into the advanced lightweight fighter with its HAL Tejas Mark 3.

Fighter drones (see Unmanned combat aerial vehicle) are a likely future development, driven by the same tactical and cost effectiveness principles of light fighters. If their software allows them to match or excel the most skilled of human fighter pilots, they may well become the most effective type of fighter aircraft. The advantages of unmanned fighters would include not only cost and numbers, but the fact that their software based "pilot" does not require years of training, is always at the same peak effectiveness for each aircraft (unlike the human pilot case where the top 5% of pilots have historically scored about 50% of all kills), is not physiologically limited, and does not have a life to lose if the aircraft is lost in combat. Of these factors the elimination of the variation in pilot skill, replaced with a fast acting artificial intelligence that makes very few tactical mistakes, is probably the most significant in terms of combat effectiveness. If every software pilot is "ace caliber" with a decision and reaction time measured in milliseconds, this automation of air combat could improve total force effectiveness by an order of magnitude or more. Though there is cultural resistance to replacement of human fighter pilots and also concerns about entrusting life and death decisions to robot software, the military effectiveness advantages are so compelling that unless restricted by treaty they are almost certain to eventually be implemented.

Going into the future the basic principle of maximum tactical efficiency per unit of budget that has driven light fighter development mostly remains the same as it has been throughout the history of military aviation. However, new technology such as stealth and further software automation are added to the issues to be considered, and are likely to have a dominant impact.