A light fighter or lightweight fighter is a fighter aircraft towards the low end of the practical range of weight, cost, and complexity over which fighters are fielded.William Stuart, Northrop F-5 Case Study in Aircraft Design, 1978. Page 7: "This became the Northrop philosophy in the development of the T-38 and F-5 lightweight fighter and trainer aircraft."T. West Hubbard, The Fighter Mafia: Vietnam, the Fighter Jet, and the Future of the Air Force, 2014. Kindle location 1116: "The early flight tests proved extremely successful as both [the F-16 and F-18] light fighters easily outmaneuvered the F-4, exactly as the MiGs had done in Vietnam." The light or lightweight fighter retains carefully selected competitive features, in order to provide cost-effective design and performance.Stuart, 1978, p. 7.James Stevenson, The Pentagon Paradox, Naval Institute Press, 1993. Page 62: "Fighter aircraft like the P-51, F8F Bearcat, and F-16 are examples of fighters that are lighter than their contemporaries, are less expensive, and have greater performance. Because fighter aircraft of lower weight can have increased performance, can cost less, and can create a larger force, these three benefits are embodied in the term lightweight fighter."
A well-designed lightweight fighter is able to match or better a heavier type plane-for-plane in many missions,Sprey, pp. 143–145 and pp. 47–49.Hammond, pp. 97–100. and for lower cost.Sprey, pp. 63–65. The lightweight class can therefore be strategically valuable.Hammond, pp. 98–100 and pp. 107–109.
In attempts to scale this efficiency to still lower cost, some manufacturers have in recent years adopted the term “light fighter” to also refer to light primarily air-to-ground attack aircraft, some of which are modified trainer designs. These lower cost lightweight attack aircraft have become known as light combat aircraft (LCAs), and are sometimes considered to include some multirole light fighters.
From 1926 the light fighter concept has been a regular thread in the development of fighter aircraft, with some notable designs entering large-scale use. From the early interwar period until the early Cold War period, such designs stood in contrast to heavy fighters, which were typically twin-engined, heavier, larger, and more heavily-armed.
Design aims A key design goal of light/lightweight fighter design is to satisfy standard air-to-air fighter effectiveness requirements at minimum cost. These criteria, in order of importance, are the ability to benefit from the element of surprise, to have numerical superiority in the air, to have superior maneuverability, and to possess adequate weapon systems effectiveness.Stevenson, pp. 33–50.Sprey, pp. 48–87.Hammond, p. 36.Spick, 1995, pp. 45–46.Gunston and Spick, 1983, pp. 186–193. Light fighters typically achieve a surprise advantage over larger aircraft due to smaller visual and radar signatures, which is important since in the majority of air-to-air kills, the element of surprise is dominant.Sprey, 1982, p. 48.Gunston and Spick, 1983, p. 188.Stevenson, 1993, p. 33. Their comparative lower cost and higher reliability also allows for greater numbers per budget.Huenecke, p. 31 Finally, while a single engine light fighter would typically only carry about half the weapons load of a heavy twin engine fighter, its surprise and maneuverability advantages often allow it to gain positional advantage to make better use of those weapons.
A requirement for low cost and therefore small fighters first arose in the period between World War I and World War II. Examples include several RAF interceptor designs from the interwar era and French "Jockey" aircraft of the immediate pre-World War II. None of these very light fighters enjoyed success into World War II, as they were too hampered in performance. Similar to the meaning of lightweight fighter today, during World War II the term “small fighter” was used to describe a single engine aircraft of competitive performance, range, and armament load, but with no unnecessary weight and cost.Lee, pp. 30–35
Effectiveness
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. Superiority in the element of surprise, to be aware of the enemy before they are aware of you. 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.Gunston and Spick, 1983, p. 187.
Small fighters like the F-5 with a planform area of about or the F-16 at about , compared to about for the F-15,Sprey, 1982, pp. 88–89. have a much lower visual profile. The small fighter is typically invisible to opposing pilots beyond about , whereas a larger fighter such as the F-15 is visible to about . This is a non-linear advantage to the light fighter opposing a heavy fighter. Additionally, smaller targets take longer to visually acquire even if they are visible.Snyder, Harry, et al., “Air-To-Air Target Acquisition: Factors and Means of Improvement”, Virginia Polytechnic University, July 1979, prepared for USAF School of Aerospace Medicine, p. 15 (p. 18 as read on Adobe), http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA087848 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.Stevenson, pp. 22–36. Once the small fighter sees and turns towards the opponent its very small frontal area reduces maximum visual detection range to about .Schallhorn et al., "Visual Search in Air Combat", Naval Aerospace Medical Research Laboratory and Naval Fighter Weapons School (TopGun), Oct. 1991, p. 6, http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA241347
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 are detectable by a given radar at about 50% further range than the cross section of the light fighter.Sprey, 1982, p. 60. This approximately balances these trade-offs, and can sometimes favor the lightweight fighter. For example, from the front the F-15 actually presents about radar cross sectional area,Sprey, p. 93. 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.Sprey p. 149. Also, airborne fighter radars are limited: their coverage is only to the front, and are far from perfect in detecting enemy aircraft. Although radar was extensively used by the United States in the Vietnam War, only 18% of North Vietnamese fighters were first detected by radar, and only 3% by radar on fighter aircraft.Stevenson, p. 130. The other 82% were visually acquired.Stevenson, 1993, p. 35.
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.
2. 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.Huenecke, p. 31.
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.Sprey, p. 17. For example, as of 2013, total heavy F-15C operating cost is reported at US$41,900 per hour, and light F-16C cost at US$22,500 per hour.See https://nation.time.com/2013/04/02/costly-flight-hours/ for hourly operating cost of USAF aircraft as reported by the USAF.
3. Superior maneuverability, which in maneuvering combat allows getting into superior position to fire and score the kill.Stevenson, pp. 43–47.Sprey, p. 49,52, pp. 67–75.Spick, 1995, p. 46.Gunston and Spick, 1983, pp. 190–191. This is a function of achieving lower wing loading, higher thrust to weight ratio, and superior aerodynamics.Stevenson, p. 28.Burton, Kindle locations 333–370.Spick, 1995, p. 47–48. This is sometimes described colloquially as “wrapping the smallest possible airframe around the most powerful available engine.” Professional analysis through 4th generation fighters shows that among heavier fighters only the F-15 has been generally competitive with lighter fighters, and its maneuvering performance is exceeded by several lighter fighters such as the F-16.Burton, Kindle locations 468–481.Sprey, pp. 98–107, p. 109, 131, pp. 147–149. 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.Sprey, pp. 150–151. Additionally, smaller fighters are lower in inertia, allowing a faster transient response in maneuvering combat.Sprey, p. 156.
4. Weapon systems effectiveness.Sprey, 1982, pp. 48–54.Hammond, p. 36Stevenson, pp. 33–49. 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,Huenecke, p. 26. 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 a 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.Stevenson, p. 47.Sprey, p. 52.
Concept summary