To stealth or not to stealth? That is the question.

The F-35 has sparked intense debates regarding the value of stealth aircraft. Many countries are looking to replace their 4th generation aircraft (F-16, Mirage 2000, Mig-29...) They all end up confronting the question: "Should we buy a 5th generation stealth aircraft or a 4+ generation aircraft? Or both?"

Stealth is about avoiding detection. Stealth is usually restricted to very low observability versus the most common radars. However there are several ways to detect aircraft.

Visual detection 

Doing things the old way. Aircraft can be seen by the naked eye or by camera systems but only at short ranges. Simple AA guns like the common ZU-23-2 are usually just guided by the naked eye. AA guns are powerful enough to destroy nearly all aircraft but they have a very short range. They are however by far the cheapest and most common AA weapon.

Fighter pilots can use their own eyes to detect aircraft but new aircraft are being equipped with camera systems as well.

Infrared detection

Flying fast creates friction and every aircraft has at least one engine. Fighter aircraft are heat sources. This makes detection by infrared systems possible. IR-guided missiles (heat seekers) have been the most effective weapon in air-to-air combat for the last decades. They have a longer range than a simple cannon and were often more reliable than radar-guided missiles.

All of the latest fighters are getting an IRST system. Infra-red detection can be somewhat affected by adverse weather conditions but these systems are definitely improving.

Short range surface-to-air missiles tend to use IR-guidance as well.

Radar

Possibly the best known means of detection. Radars can detect objects at longer ranges than camera or IRST-systems. The power of the radar is relative to the size of it. AWACS aircraft have a large radar. They can detect objects at long range and determine whether it is hostile or friendly. Fighter jets have smaller radars. A radar works by sending out a signal. The object bounces the signal back. This return signal is picked up by the original aircraft. This means that radar is an active system. It works by sending out a signal. Camera and IRST systems are passive. They don't send out signals.

Medium and long range SAM systems use elaborate radars. They normally combine large search radars with smaller tracking and engagement radars.

Signals detection

Aircraft with a radar warning receiver can tell if they are being painted or tracked by a hostile radar. Because radars send out signals, these signal can be detected. Using a radar is sometimes compared to using a flashlight in the dark. You can sweep an area with a flashlight to find something but others can see where the light is coming from.

An aircraft using its radar sends out a signal that has to bounce back. The signal weakens whens bounced back. A radar warning receiver picks up the stronger original signal before it bounces back. This means that RWR can often locate the hostile radar before the radar can detect its target.

AESA radars try to overcome that shortcoming by spreading their signal emissions out across a band of frequencies, which makes it very difficult to detect over background noise.


So while stealth is usually reserved for talking about low observability versus the most common radar systems, all of these detection methods should be kept in mind.

F-117 stealth bomber

VLO aircraft

Radar allows detection at very long ranges and is the most common method for detecting and firing missiles (both A2A and SAM's). That's is why stealth aircraft were developed. They have a special shape and are made of radar absorbing composites to reduce their radar cross section. So basically they absorb the radar signal and try to bounce it away from the receiver. The F-117 was one of the first effective stealth aircraft. It proved to be effective at avoiding radar detection. However it was a pure bomber. It couldn't fight in air-to-air combat. Secondly its stealth coating was difficult and expensive to maintain. 

The USA has continued developing stealth aircraft and the result was the F-22 Raptor and F-35 JSF.

Other countries have joined in and are developing their own stealth designs: 

Russia Sukhoi PAK FA T-50
China Chengdu J-20 Shenyang J-31

South Korea wants to build the KAI KF-X with a reduced RCS.

Japan has built the X-2 prototype.

Usefulness of stealth in air-to-air combat

A2A combat occurs in two situations. Ground or air radar systems may pick up a target and fighters can be send to engage it. Alternatively fighters already in the air can detect or can be engaged by hostile aircraft. 

Ground or air radars will have a harder time detecting stealth aircraft. This means that fighters can rely less on outside information to locate the position of hostile fighters. A stealth aircraft will detect non-stealth fighters earlier than vice versa.

However detection is only part of the kill and live chain.

Engaging a target and firing weapons is done with the assistance of onboard systems (radar, IRST, laser rangefinder, optical system). A second issue to consider is that aircraft don't take out targets. Missiles (or cannon rounds) take out targets. 

It is not enough to detect the target first. You need to clearly identify the target as a friend or foe. You need to lock-on a missile. Your missile needs to defeat any countermeasures or evading actions. Your missile needs to get a kill. You need to assure that you have destroyed the target (and not a decoy). 

Stealth fighters have a clear advantage in the detection part. They do not neccesarily have an advantage in the next steps. During the Gulf War, US F-15 were aided by AWACS in the identification of friend of foe. Camera and IRST systems can also help in the identification process. IFF systems can be used by friendlies to disclose their identity. 

Generally speaking a missile fired at long range is easier to evade than a missile fired at short range. 

This site explains it well: explaining A2A missiles Firing a missile to early might result in wasting a weapon and revealing your position. The latest fighter aircraft have radar warning receivers and missile approach warning systems. Aircraft carry chaff to fool radar-guided missiles and flares to fool IR-guided missiles. Modern missiles are less susceptible to flares and chaff. 

Another effective countermeasure against radar-guided missiles is jamming. Fighters acquire a target with their radar and fire a missile. Radar-guided missiles have small onboard radars to track the target themselves. Jammers try to break the radar lock by sending out false signals. Digital radio frequency jamming could be very effective against missiles. Just to be clear, jamming does not work against infra-red guided weapons. Alternatively some missiles have home-on-jam capabilities. Jamming sends out a signal. This signal could possibly be picked up and used for targeting depending on the system and missile technology.

A pilot can also use evading maneuvers to escape from missiles. This works against both radar- and IR-guided weapons. The goal here is to turn the aircraft into the missile at the right time so the missile overshoots (making a tight turn that the missile can't follow). The pilot needs to be aware that he has been fired upon for this to work. Also it is harder to evade a salvo of two of three missiles because the maneuver to evade the first missile can make you an easier target for the 2nd or 3rd one.

Overall stealth aircraft will be able to detect non-stealth aircraft before being detected themselves. 

This gives them the choice to engage or evade enemies. However it is not guaranteed that they will be able to destroy the target before being detected. Stealth technology is rather static. The shape and composite materials of the aircraft are rather fixed. Jamming, missile technology, the development of IRST systems etc are much more fluid. 

Moreover stealth aircraft like the F-35 have to carry their weapons internally to be as stealthy as possible. Carrying external ordnance increases their RCS. Stealth aircraft tend to carry a bit less weapons than 4+ generation conventional aircraft. This means that pilots have have to be more conservative in their use of missiles. The F-35 has four internal weapon stations. 4+ generation aircraft usually carry at least 8 missiles in an air-to-air configuration. This also enables 4+ generation aircraft to carry a more diverse set of missiles (radar homing, infra-red, home on jam). 

The usefulness of stealth in air-to-air combat will depend to a large extent on developments in jamming, IRST systems and missile technology. One can expect that stealth will become less useful over time.

Usefulness of stealth in air-to-ground combat

Ground Control Intercept stations use radars to detect incoming bombers. Medium and long range surface-to-air missile systems also rely on radar to detect and track targets. Stealth aircraft with a reduced RCS definitely have an advantage in avoiding detection by theses systems. The F-117 demonstrated this by performing bombing missions deep inside Iraq. However an F-117 was shot down in Yugoslavia. Apparantly the F-117 flew the same flight route several times in a row. Because of this, the operator knew where to look for it and could shoot it down with his modified S-125 Neva/Pechora SAM when the RCS of the F-117 increased when the bomb bay doors opened.

Stealth aircraft are optimised to be stealthy versus X-band radars, the most common radar. Since the appearance of stealth aircraft, some countries have started looking towards radars operating in other frequencies. X-band radars can be built in very compact designs. Low frequency radars are a lot larger and less accurate. Nonetheless, some would argue that the combination of new radar designs and infra-red systems could reduce the effectiveness of stealth aircraft. It remains to be seen. For now stealth aircraft will have a distinct advantage against the most common radar systems.

However they do have some other drawbacks. Stealth material seems to require some extra maintenance compared to non-stealth aircraft. This may result in lower availability rates of aircraft. The American F-22 is a highly praised air-to-air fighter but it seems to have a rather large downtime for maintenance.  

Secondly stealth aircraft need to carry their weapons internally to be as stealthy as possible. Internal bomb bays are restricted in size. The F-35 for example can carry two bombs and two A2A missiles internally. It could carry a larger amount of small weapons like the GBU-39 Small Diameter Bomb. But smaller weapons are of course less powerful.

To take out a lot of targets you will either need to:

1) have a lot of aircraft.

2) fly a lot of sorties.

3) use the external hardpoints at the cost of losing some stealth.

Until now aircraft protected themselves from SAM's by using jammers and cover from SEAD/DEAD aircraft. The Wild Weasel SEAD aircraft are equipped with jammers and anti-radiation missiles or precision guided weapons. Their job is to jam SAM radars and to engage and destroy them when they pop up. The goal is to allow other aircraft to fulfill their mission without having to worry about SAM's. First in, last out is the name of the game for the Wild Weasels.

This is still a very valid tactic in nearly all situations. It is only for deep strikes in a territory defended by an extensive integrated air defense network that you will run into problems. An integrated air defense network comprises several layers or anti-air weapons comprising everything from simple anti-aircraft guns to long range SAM's like the S-300 and everything in between. The most important assets will be defended the best. Less important assets will be less defended.

For striking targets deep inside an IADS you will need either stealth aircraft or cruise missiles (or both). For targets at short and medium range and close air support, non-stealth aircraft will do fine. If stealth aircraft are used for these tasks, it will probably be more efficient to use the external pylons as well. In short stealth aircraft are only really worth it when used against high value targets and for deep strike missions.

One could opt for a complete stealth fleet and use the external hardpoints when fit. One consideration that I do have is the following. Tanker aircraft, AWACS, command and control aircraft, ISR planes and transport planes are not stealth aircraft. When confronted only with stealth fighters , SAM crews will be tempted to shut down their radars until they get an opportunity to target these vulnerable assets. There will be a large risk to pop-up threats for a very long time. When confronted with a mixed fleet of stealth and non-stealth fighters, SAM crews will be more eager to go active to engage non-stealth targets. This provides opportunities to locate and destroy SAM's. 4+ generation aircaft stand a much better chance versus SAM's than tankers. In a similar way, one could use non-stealth aircraft as bait to lure hostile fighters in a trap of stealth fighters.

The unknown future

Drone technology is a big thing now in aviation. People are starting to say that the 6th generation of fighters will be unmanned. I don't think that it al will go so fast. However I think that drones could become an effective countermeasure against SAM systems. Some aircraft like the Brtish Typhoon are equipped with a towed decoy. A towed decoy sends out signals to lure a radar guided missile away from the aircraft. As a result the missile hits the decoy instead of the aircraft. I imagine that in the near-future we will see drone decoys appearing. Drone decoys could create a lot of fake targets in the airspace. SAM systems could be overwhelmed with targets. Instead of being stealthy, hiding amongst decoy drones could be an interesting future development.

Despite the effort put in developing stealth aircraft, the US is actually leading this drone decoy development with the MALD. The advantage of drone decoys is that they can provide camouflage for all aircraft, not just fighters. Decoy drones can also be upgraded and adjusted. The shape and composite materials of stealth aircraft are rather fixed for their entire lifetime.

Why I prefer a mixed fleet of stealth and non-stealth aircraft

By now is might be clear that I personally prefer a fighter fleet of both stealth and non-stealth aircraft.

Non stealth fighters tend to be a bit cheaper and easier to maintain and operate. They usually have more hardpoints and can carry large payloads. 4+ generation aircraft are survivable enough for most missions.

The stealthy fighters are fit for deep strikes against high value targets. They can also serve as SEAD/DEAD aircraft. They could use their stealth to hunt aerial tankers and AWACS and to thin out and scare the hostile airforce.

Stealth aircraft can improve the survivability of non-stealth aircraft versus SAM's and hostile fighters. Likewise non-stealth fighters can protect stealth fighters who have run out of missiles or fuel. Non-stealth fighters tend to have higher availability rates. They will ensure a large enough force presence at anytime.

30-40% stealth fighters and 70-60% non-stealth fighters is probably a good mix. Technically speaking one could have an all-stealth fleet with 60% operating with external stores but this might be a more expensive option considering maintenance costs and downtime. As I wrote above, having both types presents more tactical options to lure out SAM's and fighters.

If we consider a theoretical airforce of 1000 aircraft, I would consider:

100 F-22 Raptors
400 F-35 JSF (or 300)    carrier version available
400 Rafale (or 500)        carrier version available
100 A-10 Warthog

These four aircraft bring all the necessary capabilities with the stealth fighters making up the high end and the Rafale and Warthog making up the low end.

Smaller countries like Belgium can't operate fleets of multiple aircraft. They will have to chose one role and count on allies to fulfill the other. Generally speaking, the role of none-stealth aircraft will be more suited for them.

What happens in the real world?

The UK and Italy will have both the Typhoon and F-35. Some European  countries like Norway and the Netherlands have selected the F-35 while Germany and France have the Eurofighter and Rafale.

Russia is taking the Sukhoi SU-30SM, Su-35S and Su-34 is service, while developing the PAK FA.

China is developing the J-20 and J-31 but has taken a large amount of Sukhoi derivatives in service.

So far the US seems to favour a stealth only approach with the F-22 and F-35 but I wouldn't be surprised if a large number of F-15's and F/A-18 Super Hornets stay in service.