Producing a balanced fighter design is a key element of an effective air force. Yet it is also very hard, as tactical capability has to be balanced against strategical capability. “The best is the enemy of good enough” holds true for fighter design as it does for everything else. Fighter design is a balance of compromises, and focusing too much on one side of design leaves gaping holes in the other side of design. Amongst modern fighters, F-22 is tactically an excellent design but is garbage when it comes to strategic capability. F-35 is tactically good for certain ground attack missions (SEAD, DEAD) but worthless for other ground attack missions (CAS) and air superiority, and also strategically worthless. On the other side of the spectrum, original Su-27 and MiG-29 designs were adequate in strategic ability, but were tactically very lacking to say at the least. The only well balanced design in existence is likely Swedish Saab Gripen, with some other designs – F-16, F-18, Tejas and Rafale – being merely adequate.
Situational awareness and emissions stealth
Sensoy suit should be primarily passive. This way, fighter will be able to achieve surprise in aerial combat. Since surprise is number one issue when gaining kills, all active emissions by fighter itself – radar, radio, dana links etc. – should be avoided. Where such emissions are necessary, they should be provided to the fighter by offboard means, such as unmanned aerial vehicles (UAV) and airborne warning and control systems (AWACS). This will allow fighter to achieve surprise, and deny enemy the opportunity to use fighter’s own emissions to find and possibly even target it. Issue with this approach is that IRST has limited rangefinding ability, though its angular resolution is superior to that of the radar. Rangefinding options exist, but passive rangefinding is comparatively imprecise, while active rangefinding warns the opponent. While a degree of surprise is achieved merely by initial detection being passive, even if active rangefinding gives away fighter’s presence, this still limits missile probability of kill as the enemy has time to prepare while a targeting solution is calculated and missile launches and traverses the distance. Completely passive surveillance and targeting avoids that issue, but at the price of more limited situational awareness due to range and scan time issues. IRST also has the advantage of not being easily jammed. Midwave IRST is better for ground attack aircraft due to lower susceptibility to aerosoil, while longwave IRST is better for air superiority fighters as it is less affected by water droplets, and can see straight through thin cloud cover. IRST also allows for detection of stealth fighters at useful tactical distances, and just as importantly, allows for somewhat reliable identification of targets, thus making BVR combat possible. By using PIRATE IRST as a basis, subsonic fighters may be detected at 90-160 km, depending on the altitude and aspect. Supersonic fighters may be detected at 250-500 km distance, again depending on the altitude and aspect.
Radar may be provided either onboard, or through offboard means. If radar is provided in an integrated package, care should be taken that a quest for radar performance does not compromise other fighter’s characteristics, such as size, maintenance or flight performance. However, small fighters are limited by radar’s output and aperture size. For this reason, and due to radar giving away fighter’s presence, an integrated radar is not an ideal solution. Another possibility for an onboard radar is a radar pod. This way, radar is not limited by the size of the fighter’s nose cone, and does not have to be carried by all fighters in a squadron. Radar may also be carried by a command fighter or an AWACS, preferably both. Command fighters would be large, twin-engined, two-seat fighter aircraft with extensive sensory suite. Ideally, they would have nose, cheek and rear sensory arrays – consisting of RADAR and IRST, and possibly LIDAR – as well as standard radar, laser and missile warners, providing a 360* situational awareness. Due to their relative vulnerability, they would be kept back while providing sensory feed to other fighters. Last option is AWACS. This aircraft is even larger and more vulnerable than a command fighter, but also has even more powerful radar. Due to relatively large crew, AWACS is an ideal coordination center, but even so maximum autonomy should be provided to fighter pilots and flights. Overall, a combination of radar pods, command fighters and AWACS aircraft seems to be an ideal solution. A radarless fighter design can be seen here. Offensive fighter however would likely not be able to rely on either AWACS or ground radars, and should thus be equipped with its own onboard radars. Ideally, it would have nose, cheek and tail X-band arrays, and leading edge L-band arrays.
Fighter should also have good cockpit visibility, with bubble canopy and general nose area design optimized so as to provide good over-the-nose, over-the-side and rearward visibility. Canopy would ideally be frameless, though a separate windshield may be provided so as to protect the pilot in the case of mid-air canopy failure (e.g. accidental ejection of the canopy).
Pilot is the most important part of the aircraft, and thus pilot training is the most crucial for performance, including survivability. Pilot training heavily outweighs any technical concerns. In war, 10% best pilots score 60-80% of all kills. During Battle of Poland in1939., a few Polish pilots became aces in 225 mph open cockpit biplanes while fighting against 375 mph Me-109 modern monoplane fighters. Meanwhile, during 1940 Battle for France, French and British pilots did poorly despite their fighters being as good as German ones, due to using incorrect tactics. Later Battle for Britain was not lost because of fighter production, but because Germans were incapable of recovering pilot losses: while 50% of British pilots shot down were recovered safely, all German pilots were lost due to fighting over a hostile territory. Likewise, air war against Germany in late 1944 was won because Germans were not able to replace fighter pilots at adequate rate.
Training is made easier by simulators, but live training in actual aircraft is still irreplaceable. Consequently, pilot has to be able to fly regularly, and often – one hour per day or more. To fulfill this requirement, aircraft has to have several characteristics. It has to have low maintenance downtime, low operating cost and high system reliability. Peacetime availability has to be high to very high, which is achieved by having adequate ground crews as well as an excess of spare parts and fuel available. Ideally, there would be an excess number of fighter aircraft compared to pilots, for two main reasons. First, such a situation would mean that pilots are not limited in training and combat by their machines. If a fighter aircraft is not available due to damage or maintenance, pilot simply uses a spare one. Second, it would provide a pool of spare fighters to be cannibalized if spare parts are not available for whatever reason. This situation should be avoided as much as possible, but expecting it to never happen is moronic. To achieve this however, fighter aircraft has to have both low procurement cost and low operating cost, combined with high reliability. All these requirements lead to a final requirement for a small, simple fighter design. Fighter should also be single-role, as single-role aircraft and especially single-role pilots are far superior in their designed role than aircraft and pilots carrying out multiple roles.
In order to simplify both training and operation, allowing pilot to focus on tactics instead of managing the aircraft, interface has to be simple and intuitive. This can be achieved through usage of design utilizing large touch screens with as few switches and buttons as possible. Another important factor is the ability to optimize HUD/HMD symbology so as to avoid cluttering. This would ideally include the ability to quickly switch between different programmed HUD layouts, as required by the situation. Layouts themselves should be as minimalist as possible. This would reduce the amount of information forced onto the pilot by the aircraft systems, allowing him to focus on actual combat. Each pilot should be given possibility to personalize HUD and screen layouts. Information should be presented in a graphic form as much as possible, with numbers and letters being used only where absolutely necessary.
Aircraft should have as low visual, IR and EM signature as possible. Visually, this means that fighter itself should be small, less than 15 meters in length and 10 meters in wingspan. It should also be painted light gray, and have as few protrusions as possible. Care should be taken to ensure that engines have as little smoke emissions as possible, regardless of the operating conditions, as smoke can increase visual detection distance by a factor of 3 to 5. As noted before, situational awareness should be provided primarily through passive means, and aircraft should have an option of IR BVRAAM.
While internal weapons carriage is not an option due to other concerns, radar cross section should also be minimized. There are several approaches which can minimize RCS on conventional fighters. First, airframe should be optimized so that there is a minimum number of unnecessary protrusions – everything should be flush with the airframe. Refueling probe can be internal, or else aircraft could use boom refuelling so that fighter itself has no protrusions. Missiles should be carried conformally, with ideally two wingtip stations and two to four body stations allowing for conformal carriage. This way, missile rail as well as a gap between the missile and aircraft’s airframe would be eliminated. Missiles themselves should have retractable wings, which would eliminate scattering from the missiles as well as the possibility of missile wings acting as corner reflectors. Aircraft’s wings and canards should both be canted – downwards for wings, upwards for canards – not only to achieve adequate separation for aerodynamic purposes, but also to avoid forming a corner reflector with vertical stabilizer. This approach would also prevent missile winglets, if conventional missiles are carried on wingtip stations, from forming a corner reflector with coplanar radar source.
In IR spectrum, aircraft should be capable of supercruise so as to minimize the need for afterburner. This should be reinforced by having high thrust-to-weight ratio, even on dry thrust. Consequently, engine should be capable of achieving high percentage of total thrust without afterburner, pointing to a low bypass ratio, possibly even a turbojet. Engine woud have dual nozzles, with outer nozzle hiding the hotter inner nozzle as well as the hottest portion of afterburner. Additional cooling channel may also be provided, coupled with the outer nozzle. This cooling channel would utilize cool air from the boundary section layer, instead of the hotter air provided by the engine itself. Aircraft should be aerodynamically well designed and small, so as to minimize the engine emissions necessary. Air exhaust for the electronics cooling would lead into the engine air duct, so the hot air would be ejected with already superheated engine exhaust.
For a multirole fighter, acoustic stealth is also important. This means limiting the aircraft size, weight and thus engine power. Aerodynamic design should also be with as few protrusions as possible in order to eliminate irregularities in the air flow.
Weapons should allow both quick reaction during close combat and silent kills during long-range combat. As a result, normally used weapons would be 30 mm revolver gun, short-range IR missile, medium-range IR and dual mode RF/anti-radiation missiles, and long-range dual mode RF/anti-radiation missiles. Missile ranges should be in brackets of 25, 50, 100, 150, 300 and 500 kilometers. Going with noted, IR missile option should be present for missile ranges of 25, 50 and 100 kilometers, with RF/AR missiles being available for ranges of 50 kilometers and greater. Usage of IR missiles would result in improved reliability as well as reduced vulnerability to countermeasures.
Fighter should have at least one onboard kill in adverse conditions. Assumed probability of kill used here are 0,31 for revolver cannon, 0,26 for rotary gun, 0,15 for IR WVRAAM, 0,11 for IR BVRAAM and 0,07 for RF BVRAAM against uncooperative targets. Against cooperative targets, Pk values assumed will be 1 for gun, 0,73 for IR WVRAAM, 0,59 for IR BVRAAM and 0,46 for RF BVRAAM (pilot training and situational awareness are the primary determinants of aircraft’s ability to avoid the missile). With four conformal stations – two wingtip and two body stations – and four wing stations being assumed, fighter should be able to carry eight missiles, plus 6 gun bursts to allow for two kills. In “stealth” configuration, with two IR WVRAAM and two IR BVRAAM, total number of kills is 2,38 against uncooperative targets and 8,64 against cooperative targets. If normal configuration is assumed to be two IR WVRAAM, two IR BVRAAM and four RF BVRAAM, total number of kills should be 2,66 against uncooperative targets and 10,48 against cooperative targets. BVR missiles overall have limited effectiveness against fighter aircraft, and are mostly useful against large targets such as AWACS or transport aircraft. They are useful when pursuing a retreating target due to longer range, and can be used to force the enemy into unfavourable situation for the merge. It should also be noted that the missile effectiveness noted here is for visual range only; at BVR, BVRAAM Pk is halved compared to the values noted.
In order to maximize kill probability at beyond visual range, BVRAAM should be of a ramjet design, so as to maintain thrust during the terminal phase. Long-range BVRAAMs could combine ramjet primary missile with solid-fuel rocket secondary stage, coasting in a ballistic path until close enough to target. Unless this is done, there is no chance of a BVR missile hitting an aware target outside the visual range, as it will lack energy and maneuvering capacity to do so – probabilities of kill noted earlier are all achieved within visual range. Probability of kill at altitude is low even with maneuvering ability intact. A missile that pulls 40 g at sea level will only pull 13 g at 10.000 meters and 2,85 g at 20.000 meters, unless 40 g is a structural limit. AIM-9 for example can pull 40 g at SL and at 10.000 ft, and 35 g at 20.000 ft. At 40.000 ft, AIM-9 should be able to pull no more than 13 g. Meanwhile, F-16 for example can sustain 9 g at up to 10.000 ft, and Rafale can sustain 9 g at 40.000 ft. In terms of more relevant (for missile evasion) instantaneous turn performance, F-16 can pull 9 g at altitudes up to 35.000 ft; at 40.000 ft, maximum limit is 7 g, and 5 g for most of the envelope. Missile on the other hand needs at least five times the g performance of a fighter aircraft to achieve a hit, possibly even more (lowering the speed of a missile does not improve turn rate as missiles typically operate well below their corner speed). As it can be seen, even AIM-9 is very unlikely to hit a maneuvering F-16 at 20.000 ft, and basically impossible to hit it at 40.000 ft. As a consequence, fighter aircraft should carry a large number of missiles and be able to fire them in pre-programmed salvos if goal is a BVR engagement. If fighter is optimized for visual-range combat, it should be able to carry missiles conformally, and fire them even from high off-bore angles, as well as to maintain missile lock during rapid maneuvers so that pilot can fire off a missile immediately upon achieving a desired position.
Gun is most likely to be used against large, undefended targets such as AWACS or transport arircraft in order to avoid wasting missiles. Other scenario is usage against targets that are too fleeting to achieve a missile lock, or are within missile’s minimum engagement distance. As a result, premium is placed on damage output in quick bursts. Firing opportunities in a dogfight are brief, and length of a burst is never longer than 1,5 seconds. This means that gun has to pump out as much damage as quickly as possible, which in turn requires quick acceleration and high HE-I content of the shell. Overall, the best choice is a high-calibre (30 mm) revolver cannon.
Aircraft should be capable of supercruise, so as to minimize the infrared signature while supersonic, as well as extending the time it can spend at supersonic speeds. This would allow the pilot to surprise the enemy from the rear, and avoid getting surprised himself. It would also allow it to dictate the terms of the engagement, avoiding the unfavourable engagements. Supercruise speed goal should be at least Mach 1,5 with six conformal missiles and no external fuel tanks. Fighter should be able to spend at least 20 minutes at that speed in the combat zone. Combat radius calculations should include the supercruise as well as combat. For defensive purposes, fighter should be assumed to operate without external fuel tanks, while in offensive purposes normal load would be six missiles and two to four external fuel tanks. Therefore, 300-400 km combat radius with 20 minute supercruise on internal fuel would be acceptable performance. This will likely lead to fuel fraction of 0,35-0,45, depending on the aircraft performance, aerodynamics, engines and size. For a dedicated offensive design, target combat radius would be 500-800 km with 20 minute supercruise on internal fuel.
Fighter should have 9 g turn capability in both instantaneous and sustained turn. If possible, 11 g instantaneous turn capability should be pursued as normal performance, with 13 g in override. Roll onset should be very rapid in order to allow fast transients, both in level flight and during the turn (at angle of attack). This is important for both dogfight and missile evasion purposes, as missile guidance lags behind an aircraft. Climb capability should be at least 300 m/s when clean at sea level, >350 m/s if possible. Ideally, turn rate would be above 30 deg/s instantaneous, 24 deg/s sustained and 300 deg/s roll rate. Fighter should be able to both gain and lose speed quickly, to allow outmaneuvering the opponent in a dogfight, as well as missile evasion. For this, moderate-to-high sweep tailless delta is a best choice. Engine should be turbojet in order to allow for quick changes in fan rotation rate and thus engine output – larger diameter of turbofan engine leads to comparatively more sluggish response. Just as importantly, turbojet engine should be capable of achieving higher thrust-to-weight ratio, especially at dry thrust. This would reduce the need for afterburner, leading to improved persistence even though fuel consumption at same engine setting will likely increase. Fighter’s combat weight should be low in order to reduce inerta and allow quick transients that are key to winning an air engagement. Reduction of roll inertia specifically can be achieved through single-engined configuration, low wing span, and locating heaviest ammunitions as well as most fuel as close to the aircraft centre as possible. Offensive design however would do well with two engines so as to ensure backup in the case of a failure or a hit by a SAM or AAA, in order to get the pilot back to the friendly territory.
Despite the name “air craft”, modern aircraft – especially fighter jets – are less air craft and more air hoppers. Fighter aircraft in particular spend only a portion of time in the air – no more than a third, and many far less. Most of the time is spent on the ground, undergoing maintenance, repair, refit and refuelling. As a result, ground survivabilty is a crucial aspect of aircraft survivability. To achieve this, fighter should be capable of operating from road bases. Minimum takeoff and landing distances should be less than 500 and 400 meters, respectively. Wingspan should also be less than 8,75 meters for a defensive design. A dedicated offensive fighter would likely have to have larger wingspan as well as longer takeoff and landing distances, thus placing emphasis on dirt strip performance. Logistics requirements should also be low, in particular in terms of spare parts and fuel. Low fuel usage means that fighter itself should be relatively small. Easy repairability in field would mean usage of aluminium alloys instead of composites, though decision should be made after taking into account impact on aircraft performance.
Numbers in the air
In order to carry out all the task, fighter force has to be able to launch enough sorties – best weapon in the world is useless if it cannot cover all necessary areas, and planet is a large place. Larger number of aircraft than the enemy’s also allows for tactical (as well as operational and strategic) flexibility, allowing one portion of the force to engage the defending fighters while remainder goes after crucial targets that had been left without cover. This means that fighter’s procurement and especially operating cost should be low, as well as its logistics requirements. Again, this leads to requirement for a small, easily maintained fighter aircraft.
Ease of maintenance
Aircraft should have a simple and maintenance-friendly design. Number of individual components should be kept to minimum, and all important components should be placed so as to allow easy access from the outside. Components themselves should be grouped into easily replaceable modules – which themselves should be repairable in the field. Minimum number of parts should be used in construction.
Logistical support is the most vulnerable element of any force. If supply chain is disrupted, the entire combat force is quickly rendered impotent. For this reason, minimizing logistical footprint for any given force is mandatory. Chain itself consists of several main elements. First one is the producer, albeit it is not always relevant in the war. Items produced in the factory are stored in the depots at home, and then shipped to military bases – which, in the case of expeditionary military forces such as the US military, are often overseas, requiring shipping over large distances. Once transferred over the sea, they are unloaded at port, and either stored there or transferred to inland supply depots. From there, items are transferred to military units and bases that require them (not all bases are large enough to function as supply depots on their own). In a specific case of fighter aircraft, the chain consists of manufacturers (aircraft parts, weapons, fuel), supply depots and air bases at home, supply depots / large air bases abroad, and forward operating bases (e.g. road bases).
Supply footprint of a fighter unit is not limited to fighter aircraft themselves, but also to any and all support elements – AWACS, tankers, air bases themselves, ground forces providing security for said air bases. Most modern fighter aircraft are large and complex machines, requiring dedicated air bases for operation. Such fighters themselves already have high logistical footprint due to complex maintenance and high fuel usage. Footprint is only increased by the equally complex tools required for maintenance – especially when it comes to stealth fighters such as the F-35. Further, air bases themselves require constant maintenance. Not only tools for fighter maintenance have to be maintained, but also the aircraft runway (FOD walks!), hangars, living quarters for pilots and ground crews. Dedicated air bases themselves are very vulnerable to attacks, and are also very lucrative targets. This means that they require security in the form of extensive missile and air defense systems, as well as powerful ground forces for defense against ground assaults. These forces require massive supplies as well, which typically means usage of large transport aircraft. Due to importance, vulnerability and obviousness of these air bases, they are typically situated far behind the front line. As a result, fighter aircraft have to traverse long distances to the combat zone, requiring tanker support to reach their targets, further increasing their logistics footprint.
For this reason, fighter aircraft has to be able to operate from FOBs (Forward Operating Bases). That way, fighters would be close to friendly ground troops, increasing the time spent in the combat zone, and thus reducing the size of the force necessary for the effect. These bases should be very small, holding no more than a few fighters each (ideally, a pair or a flight of four). Fighters and everything else present would be camouflaged with the use of multispectral camouflage nets, making finding them more difficult. Crews would live in tents, which would be camouflaged the same way. In the case some are discovered and attacked, wide dispersal of forces achieved in this way would limit damage compared to attack agaist conventional air bases. Due to necessarily small size of such bases, any fighters used from there have to have small logistics footprint, and ground forces present would also be small. All of this would result in very small logistics footprint of each base, as well as reduced footprint of the force as a whole. Small logistics footprint required would necessarily mean a light (5-7 metric tons empty) single-engined fighter design, however measures could be taken to reduce footprint of larger aircraft as well – specifically, dirt strip / open field capability.
As it can be seen, fighter design may change in major ways depending on its role and expected environment. However, most basic things are common for all fighters, and it would be a mistake to ignore them.