Unlike US Navy and every other air force across the world, USAF has decided to transit to an all-stealth air force.
But due to the Moore’s law, processing power doubles every 18 months – which means not only improvements in sensors that are already very capable of detecting stealth aircraft, but also that, as time passes, stealth aircraft is ever less capable against systems it was designed to counter – namely, active radars.
Stealth vs radar
Stealth relies on processing gain advantage over radar, by reducing return below treshold of what can be detected by radar itself. However, due to the Moore’s law, radars are becoming ever more capable. Further, stealth fighters are designed with minimum nose-on RCS, which means that they are easier to detect by aircraft flying in wall formation. At the same time, jammers benefit from Moore’s law too, which enables fighter-based jammers to rapidly close the effectiveness gap with stealth, or even surpass it.
This purely theoretical thought exercise is not likely to be very relevant, however, as radar – being an active sensor – automatically gives position of aircraft using it away far before it can detect opposing aircraft, meaning that pilots will start shutting it down in combat as soon as losses due to its use start to mount due to radars’ use giving very important advantage of surprise to the opponent. Against both enemy aircraft and SAMs, dedicated jamming aircraft – ranging in size from converted medium-weight fighters to converted heavy bombers – are avaliable, and far more effective since they also protect other aircraft.
Stealth vs IRST
Most discussions about value of IRST against stealth focus on airframe being heated due to air friction. This, however, is wrong for a very simple reason: any time a gas is compressed, it heats. And compression of gasses in front of moving object is a normal, unavoidable occurence – only difference is scale of compression, which depends on object’s speed.
While aircraft do heat up less in rarer atmosphere, less atmosphere also means that more IR radiation – especially of longwave variety – reaches the infrared sensor. Further, at high altitudes – where stealth aircraft are required to operate – temperatures range from -30 to -50 degrees Celzius. At the same time, fighter supercruising at Mach 1,7 creates shock cone with temperature of 87 degrees Celzius. While PIRATE IRST can detect subsonic fighters from 90 km from front and 145 km from rear according to (somewhat outdated) publicly avaliable information, this range is 10% greater against supercruising fighter. At the same time, OLS-35 can detect subsonic fighter from 50 km from front and 90 km from rear. PIRATE’s own range is already comparable to that of fighter radars against 1m2 targets. (Note: Data used for both PIRATE and OLS-35 dates from 2008; it is possible that both have been improved in the mean time). Prototype Russian stealth aircraft PAK FA uses QWIP-based OLS-50M, so it is possible that QWIP technology may find its way into Su-27 family of aircraft. Identification can be carried out at 8 to 10 kilometers.
Parts of aircraft’s exhaust plume are also visible from front, which should present no problem for modern IRSTs that are capable of detecting AAM release due to missile’s nose cone heating.
Some IRST systems have laser rangefinder coupled with them, which means that they can be used to gain gun firing solution without usage of radar. While IRST is mostly immune to “beam turn” used to break radar lock, laser rangefinder may not be. Rangefinder, though shorter-ranged compared to IRST, would also have increased range at higher altitudes. IRST could also use sensitivity model (Atmospheric Propagation Model) to roughly estimate range and velocity of target without using any active sensors.
(Interesting to note is that Soviet MiG-31s were able to target SR-71 by using IRST; at speeds both aircraft were flying at in these situations, MiG-31s front surfaces would heat up to 760 degrees Celzius due to aerodynamic friction. SR-71 was not much better off; fortunately, order to attack was never given).
Astronomic IR telescopes can detect velocity of star down to 1 meter per second. This kind of precision would not be required for air-to-air combat, however, as closure rates between fighters could be up to 1 700 meters per second.
This means that stealth aircraft has no escape – if it attempts to increase effective range of its missiles, it has to increase speed – but this increases IR signature and allows it to be detected from larger distance. If it attempts to avoid detection, it has to reduce speed, which means that it has to come closer to IRST-equipped fighter.
USAF is obviously concerned about it – while IRST-equipped Super Tomcat was slated to be retired in 2008, it was hurriedly retired in 2006 under neoliberal stealth proponent Donald Rumsfeld. Both PAK FA and F-35 have IRSTs, but unlike PAK FA, F-35s IRST is optimised for air-to-ground missions, and is thus operating in appropriate wavelengths, reducing its range against aerial targets.
QWIP IRST such as PIRATE or OSF has some very useful advantages over “legacy” IRST. Aside from longer range, they can be tuned for sensitivity in certain IR band. While normal IRST operates in microwave to longwave IR bands, QWIP IRST can operate in very longwave bands, allowing for easy detection of objects that are only slightly hotter than the background, with difference being in single digit degrees of Cenzius. It can also use several bands in paralel, getting “best of the both worlds”.
While F-22 was designed to operate at high altitudes, as high as 15-20 kilometers, clouds only go up to 14 kilometers in some cases, with majority being below 4 500 meters – and even that only in tropics. All other stealth air superiority aircraft are similarly expected to operate at high altitudes.
Ground radars have to be above any obstacles to radar beam, which means that areas such as small valleys and canyons are usually not covered. Anti-radiation missiles and cruise missiles are very reliable against stationary radar sites; ARMs are better against mobile radars, as there is no radar that can pack up and leave in the time that ARM requires to reach it. SAMs are no different in that regard, and as such they can be kept shut down by use of anti-radiation missiles.
Without these two factors, however, stealth aircraft can be detected easily enough by long-wavelength radars, which completely ignore any practical amount of stealth coating, and are far less affected by stealth shaping measures than shorter-wavelength radars. These, then, can be used to guide IR SAM or IRST-equipped aircraft close enough for their IR systems to detect stealth aircraft.
Numerical issues are probably the worst drawback of stealth. Stealth aircraft cost more and are harder to maintain than non-stealth ones. To demonstrate the actual impact, I will compare F-22 to two twin-engined aircraft designed to carry out similar mission to F-22s, but without stealth.
While F-22 costs 250 million USD per aircraft flyaway, cost for Tranche 3 Typhoon is 121,5 million USD, and cost for F-15C is 108,2 million USD. As such, 50 billion USD gives 200 F-22s, 411 Typhoons or 462 F-15Cs.
Sortie rate stands at maximum of 0,52 sorties/aircraft/day for F-22, 1,2 sorties/aircraft/day for F-15 and 1,2 – 2,4 sorties/aircraft/day for Typhoon (later value only assuming that design goals have been met). Thus, force bought would be able to support 104 sorties/day for F-22, 554 sorties/day for F-15C and 493 – 986 sorties/day for Typhoon.
Historically, quality of aircraft was always unable to compensate for force disparity once latter was above 3:1. As such, it can easily be seen that F-22 is, strategically, worse choice than Typhoon or F-15. And while all numbers are not yet avaliable, it cannot be expected that F-35 will perform any better in this crucial area relative to Gripen and F-16 than F-22 did relative to Typhoon and F-15. Me-262, while by any measure a revolutionary aircraft, was not used in large enough numbers to have impact against Allied fighters. In the end, Me-262 shot down no more than 150 Allied fighters, with 75 of them being lost in turn, in large part due to Allied superior numbers allowing them to catch Me-262 on take-off or landing.
Stealth aircraft are built under assumption that BVR radar-based combat trumps WVR combat. However, that assumption is unproven; neither AMRAAM or other BVR missiles were ever used beyond distance of 40-50 kilometers. In case of AMRAAM, usage was against aircraft with no radar, no IRST, no radar warners, no ECM, with badly trained pilots that were in most cases unaware they were under attack (and were not maneuvering as a consequence). Yet even in such perfect conditions, AMRAAM achieved 6 kills in 13 BVR launches, or Pk of 0,46.
During Desert Storm, in conditions identical to above, USAF F-15s launched 12 Sidewinders for 8 kills, for Pk of 0,67. For same F-15s, AIM-7 Sparrow achieved 23 kills in 67 shots, for Pk of 0,34.
Thus we have to take a look back at Vietnam. Why Vietnam? Simply because it was the last time US have fought somewhat competent opponent in the air. Even experience with IR missile suggests that Pk in combat against competent opponent will be far lower than above: AIM-9B achieved Pk of 0,65 in tests, which fell to 0,15 in Vietnam, to be improved to 0,19 with AIM-9D and J, whereas G model does not offer large enough sample for drawing conclusions. Yet even this was better than Pk for BVR missiles. While majority of AIM-7 shots were taken within visual range, during 1971-1973 in Vietnam, 28 BVR shots were made, resulting in 2 kills, one of which was a fratricide against an F-4 – a Pk of 0,071, as opposed to predicted Pk of 0,9 or more. During entire war, AIM-7D achieved 8% Pk, AIM-7E achieved 10% Pk and AIM-7E2 achieved 8% Pk. At the same time, guns had Pk of 0,28.
In fact, summary by Burton of kills made during Cold War has found that, out of 407 missile kills he studied, 73 were made by Sparrows in 632 firings, a kill rate of 11%. Sidewinder achieved 308 kills in around 1 000 firings. Out of all radar-guided missile kills, only four were made at BVR – two already described shots in Vietnam that were carefully staged outside of combat, and two similarly staged shots by Israeli air force. His summary of these 407 shots concluded that most targets were unaware and fired from the rear, and that there were almost no head-on BVR shots due to high closing rates. Only way to positively identify the target was by the eye.
When we take a look at the data above, a clear pattern begins to emerge: while Pk against incompetent opponent is significantly higher than against competent one, by a factor of almost five, relative weapons’ effectiveness remains unchanged: IR missiles achieve half the Pk of gun, and radar-guided missiles achieve half the IR missile’s Pk. Further, visual identification of target is still important, and is likely to remain so. In fact, during First Gulf War, majority of US casualties were due to the friendly fire, while in 1973 war Israeli pilots considered an on-board radar “essentially useless”, with Sparrow achieving one or no kills in that war.
This situation will even worsen for BVR-oriented aircraft in the future, as IRIS-T has capability to intercept and destroy BVR missiles. While it definetly will not be perfect, it will reduce number of missiles aircraft actually has to evade.
Time has also shown that maximum simplicity weapons and countermeasures, such as guns and flares/chaff, are usually most effective. This is unlikely to change.
Pilot competence was always dominant issue in Air to Air combat. During German invasion of Poland, several Polish pilots became aces in 362 kph open cockpit fighters, when fighting against 603 kph Me-109, an early warning about importance of pilot skill. This was again shown when German fighters fought outnumbered in invasion of France, when higher-performance Spitfires and equal-performance Hurricanse fared poorly against Me-109s, which were flown by far more experienced pilots using tactics derived from actual combat as opposed to air shows and unrealistic peacetime exercises. Late in the war, Luftwaffe was unable to mount serious opposition not due to the lack of air frames – Allied bombing did not have major effect on German industry – but due to the lack of pilots.
Yet stealth aircraft’s large maintenance downtime prevents pilots from becoming familiar with their aircraft, and training enough in them. Modern fighters are also more complex than World War II ones, so lack of fighters is a very real possibility. AIMVAL tests, despite bias towards BVR, have also shown that ground controller assistance was more important to more complex and automated aircraft, and off-boresight missiles offered only slight improvement in results.
Stealth aircraft are expensive, and do not provide bang for the buck, in good part due to them being built on flawed reasoning and inaccurate assumptions. While they can be very useful against backward coutries, even in these cases larger numbers of cheaper aircraft will perform better. Assumptions behind stealth ignore lessons of combat to date, including the fact that pilot skill tended to dominate air combat (especially when combined with numerical superiority), as well as existing counter-stealth technologies.
Game-changing technologies were always simple in idea and execution, as relatively inexpensive. For comparision, stealth F-22 has cost of 12 690 USD per kg, F-35A costs 14 812 USD per kg, F-15C costs 8 504 USD per kg, F-16C costs 8 168 USD per kg, and Eurofighter Typhoon costs 10 942 USD per kg in its most expensive variant. It should be noted that F-22 lacks IRST and some of Typhoon’s systems, whereas F-35A is most loaded with electronics of aircraft listed. As such, stealth requirements add – without counting weight increase – 1 000 – 3 000 USD per kg. If the fact that F-22 is heavier than F-15C at least 7 000 kg is counted, stealth coating itself likely cost around 50 million USD, almost as much as my estimated flyaway cost of Gripen NG. IRST, on the other hand, costs around 1 million USD, and is far more useful than radar stealth.