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"Evading Air-to-Air Missiles"
posted by picard578 on August 17, 2013 / defenseissues.net
Missile evasion is a very important part of modern air combat. Yet many people believe it is impossible. But this is false for several reasons.
First reason is that the missile cannot turn tighter than the aircraft. In order to pull as tight turn as a fighter aircraft, the missile has to pull amount of g that is amount of g’s aircraft can pull multiplied by factor of difference in speed squared. For example, the Typhoon can pull 9 g at 360 kts and the IRIS-T missile can pull 60 g at Mach 3 (or 1.984 knots). What this means is that IRIS-T will have 4.5 times as wide a turn diameter. If the target aircraft is pulling 9 g at Mach 0,9, then the IRIS-T will still have 1.7 times as wide a turn diameter. And if target is pulling a sustained 5 g turn at 360 kts, the IRIS-T will have 2.5 times as wide a turn diameter.
Evasion is made easier in some situations by the fact that the missile always attempts to leadthetarget. Thus if the target changes heading, it will be hard pressed to correct. This is the case with Beyond Visual Range (BVR radar-guided) missiles where the target fighter aircraft can turn so that the missile faces its side and only enter a turn once the missile is close.
The probability of a BVR missile hitting is made worse by the fact that it is both faster and capable of pulling less Gs than a Within Visual Range (WVR heat-seeking) missile. The AIM-120 BVR AMRAAM can pull 40 g at Mach 4 (2.646 kts). Which means that it will have 12.2 times as wide a turn diameter as the Typhoon fighter in example above. Even if the Typhoon turns at 5 g (maximum sustained g in AtG configuration), the missile will still have 6.75 times as wide a turn diameter. Also when a missile is tracking a maneuvering target, it bleeds off the energy. [StealthSkater note: However, I have read that some of the newer missiles have thrust-vectoring jets to increase their turning maneuverability.]
The main problem with evading missiles is their speed which makes timing somewhat difficult. However, even that is far less of a problem than commonly assumed as the missile will be closing at 1.200-1.400 meters-per-second in the best case. At 20 kilometers, this means 14-20 seconds to reach the target for a BVR missile or 20-23 seconds for an IR missile.
Thus there are several tactics to evade the missile, some of them very simple. First is a barrel roll. As the missile is unable to track it, it will fly past and loose a lock-on in the process. Second is a simple turn where the pilot forces the missile to follow it through a turn. This turn, however, must be well timed. It is very useful as an end move in more complex maneuvers designed to bleed off the missile’s energy. It is also very useful in a dogfight where rear-aspect shots are far more likely than front-aspect shots.
If missile is fired head-on at BVR range, there are several ways to evade it. First is to turn hard to either the left or right so as to fly at roughly 90 degrees angle to attacking aircraft. This forces the missile to bleed off the energy and to lead the target. As a result, once the target aircraft makes a hard turn to reverse a direction, the missile with its far larger turn circle will be unable to compensate. A variation of this tactic is also useful for head-on WVR launches.
Second tactic, which is also useful at short ranges, is jinking. The aircraft must be positioned so that it is at an angle (30-60 degrees is optimum) relative to missile’s flight path. Diving is recommended so as to keep energy and take advantage of ground clutter.
Once the missile gets closer, the aircraft will make a hard turn in the opposite direction. If the missile follows, the aircraft will immediately reverse the turn. As there is a lag between the aircraft changing the direction and the missile following (for several reasons, most important of which is missile’s inertia), this will cause missile to head in wrong direction until it manages to correct and also to bleed off the energy. Eventually it will fly past the aircraft and miss.
A variation of this maneuver is to continue first turn into a barrel roll. The missile will continue to track the aircraft. But in the end its lower turn rate will mean that it won’t be able to keep up.
Third tactic is to turn away and dive for the ground, gaining speed and putting as much distance as possible between the aircraft and the missile. This tactic is also useful for rear-aspect BVR shots. But it is not useful on its own at shorter ranges. The pilot must evade the missile physically by pulling the aircraft into the turn and forcing the missile to overshoot once the missile comes sufficiently close.
The importance of last part is well displayed in both Gulf wars where Iraqi failures to time the evasion (or even try to outturn the missile) resulted in unusually high missile Pk(probability of kill). A similar situation (but with WVR missiles) happened in the Falklands war.
Fourth tactic, mostly useful at longer ranges, is to climb. Since at long range the missile will have burned out its engine, it will rely on inertia to keep it flying and climbing will mean that it will bleed off energy rapidly. Once the missile reaches a close range (maybe around 1,500 meters), dive for the ground and then pull up. This will allow the pilot to gain energy and using it to evade the missile.
Fifth tactic is to place the missile at 3 o’clock or 9 o’clock position and then maintain a sufficient turn to keep the missile there. This tactic (which is also useful against WVR missiles) forces the missile to execute a continuous turn, bleeding the energy entire time, making it easier to outturn the missile once it comes close.
At very close range, the missile will have poor maneuverability as it will not have picked up full speed which means it won’t be able to pull its “official” maximum number of g’s. The pilot of the targeted aircraft will have more time to react than maximum speed of missile might suggest. The missile’s maneuverability peaks at instant before motor burns out as it will have lowest mass while still possessing motor thrust. This state is what is reflected in “official” statistics and only under the assumption that it did not have to maneuver beforehand.
Physically avoiding the enemy missile is not the only option. If missile is radar-guided, hard turns can cause it to loose lock-on and miss regardless of wether it is guided by launch platform or is using its own radar. One of reasons is that most radar-guided missiles track target’s radar centroid (which changes with aspect) and as such the target’s maneuvers can result in LOS jitter and return scillintation.
It is also possible for a fighter to fly out of seeker’s FoV regardless of whether missile uses IR or active radar guidance. This has greatest likelihood of happening if the fighter closes with the missile at an angle. Most modern missiles self-destruct if they have lost the lock.
Maneuvers can cause degradation in performance of the missile’s fuze. If the aircraft is low-flying, terrain can cause activation of proximity fuze.
Jamming can also help evade radar-guided missiles making acquisition of target difficult for the missile. Chaff can also be used to deceive missile’s radar (active-radar missiles are unlikely to use AESA radar due to power and weight requirements) or fuze, forcing either a miss or a premature detonation.
A missile’s effective range is also dependent on altitude and relative speeds. As a rule of thumb, it doubles every 20,000 feet (6,100 meters) above sea level. Speeds also have a major impact. If the target is running away, then every 100 knots in speed advantage for target reduces missile’s range by 5-25% depending on missile’s own speed. A large target speed advantage can also cause acquisition difficulties for Doppler-radar guided missiles fired from the rear.
Readers Comments
1. Segelboot said:
In the “first tactic”, you normally didn’t turn away from the missile but break into it to increase the Target Aspect Angle (TAA) faster, giving the missile less time to react. The rest is quite comprehensive.
BTW: Radar-guided missiles have an inherent small seeker which gives them a very poor angular resolution although MMW Seekers (Ka- or W-Band, 35 older 94 GHz) may overcome this.
2. picard578 said:
If you are talking about the first image, assumption is that you were in a dogfight and the enemy managed to get on your six. Though in that case there is question of whether you have enough energy left for evasion…
Segelboot said:
second image xd
3. Quora said:
I found some helpful links:
4. Juurikas said:
And how is this calculation true? Just for the information/source here. As what I have read from military papers is the claim that missile needs to only pull 2.5-3x of G-forces to out-turn the fighter as a rule of thumb. Meaning that if the fighter pulls 9G, then only 27G is required from missile. Some missiles have a 45-60G turning capability to basically out-turn any fighter in any situation.
This is first time I read about such a high G-force maneuvers required from missiles. For some reason, it does make sense to me. But I just would like to find the source/information for myself.
As a fighter just pulling some loose barrel roll can get missile to totally miss-course if the fighter is doing it steadily instead trying to crank itself up while not really changing the flight path.
5. picard578 said:
Do note that I wrote “in order to pull as tight turn as a fighter aircraft, the missile has to pull amount of g that is amount of g’s aircraft can pull multiplied by factor of difference in speed squared.”
It is basic physics. Of course, the missile often does not need to pull as tight turn as aircraft to hit it whereas sometimes it would need to pull tighter turn than the aircraft did. It all depends on the conditions. The claim that you have cited from the papers is correct in optimal conditions. But conditions rarely are optimal.
A lot depends on the situation. An aircraft that is pulling a sustained turn is far easier to hit than aircraft undergoing erratic maneuvers. The missile might not be launched from optimal distance or position. The attacker might not have managed to get at target’s 6-o’clock. Or he did but is too close or too far. So the missile has no time to accelerate or has spent fuel and is flying on inertia.
Maybe it cannot pull its paper-spec maximum G because it is going too fast, too slow, the air is too rare, or it has fuel left onboard. Maybe it got decoyed by a jammer or blinded by a flare barrage and lost its bearings.
That is why I am skeptical about any claims based on calculations or peacetime testing and prefer to use actual missile performance against certain targets. Note that the AIM-7 radar-guided Sparrow was claimed to have a 90% kill rate. But it was lowered to 70% in operational tests. And even in literally perfect conditions in Desert Storm (i.e., incompetent under-equipped enemy; persistent AWACS presence; BVR engagement allowance etc.), it achieved only a 34% Pk, less than half of what it achieved in operational testing.
Assessing the SAM Threat
posted by picard578 on February 15, 2015 / defenseissues.net
Introduction
SAMs are the new boogeyman of the USAF, one which they are also using in their political games. They want the F-35 because they saythat current legacy aircraft are “unsurvivable”. They want to retire the A-10 Warthog and leave ground troops without any support because they say it is unsurvivable. But how much truth there is in their assertions?
Historical overview
During the Vietnam War, Surface-to-Air Missiles (SAMs) saw extensive usage. They were used primarily to defend key targets but were also deployed in the field. Many were also mobile (though level of mobility they had does not even begin to compare with modern SAMs thanks to excessive times necessary to either deploy or pack up).
The next table addresses heavy radar-guided SAMs performance during the Vietnam war:
Year / SAMs launched / U.S. aircraft lost / Pk1965 / 194 / 11 / 5.7%
1966 / 1,966 / 31 / 1.6%
1967 / 3,202 / 96 / 3.0%
1968 / 322 / 3 / 0.9%
1972 / 4,244 / 49 / 1.2%
As it can be seen, kill probability has danced up and down but always stayed below 6%. Total gives 190 aircraft lost to 9,928 SAM launches or a Pk of 1,9% (or 1/4 of what radar-guided AAMs achieved). Many SAMs were crewed by Russian crews.
SAMs did have a major indirect impact. Since the USAF predominantly used thin-skinned “multirole” aircraft for air superiority as well as ground attack (including SEAD/DEAD missions), this meant that the aircraft were exceedingly vulnerable to AAA (anti-aircraft fire) during low altitude attacks on SAMs. The NVA used SAMs as baits drawing U.S. aircraft into overlapping AAA fire. Since most of the AAA used was optically-aimed, there was no warning until they opened fire. In the first DEAD mission of the War, 6 aircraft were lost out of 50 present – all of them to AAA. And all of them thin-skinned sluggish F-105 Thunderchiefs.
SAMs were also effective at their primary mission -- i.e., shooting down (useless) strategic bombers. B-52s flew 724 sorties in the North Vietnam losing 15 aircraft – a loss rate of 2.1%, just at or slightly above the limit for sustainable operations (for comparison, B-17s had a loss rate of 6% during 1943 World War 2). To achieve this, over 2,000 Soviet SA-2s were fired – a probability of kill of 0.75%.
Still, the B-52 attrition rate was still 10 times higher than the overall attrition rate in the Vietnam War which was 0.35% in the 1966 and 0.15% in the 1968. By the end of the War, North Vietnam had mostly run out of their SAM stocks.
North Vietnamese also used some 100 MHz (VHF band) radars which could not be attacked by anti-radiation missiles (such as the Shrike). They were not used for SAM guidance, however.
During the 1973 Yom Kippur War, Israel lost between 98 and 280 aircraft. An IAF officer (Cohen) admitted 15 losses in air-to-air combat although the figure might be as high as 21 (Dupuy). Zaloga in “Soviet Air Defence Missiles” p.240 quotes ‘Israeli sources’ as stating that the Sa-7 caused 2 losses, 4 possible losses, and 28 hits which did not result in losses. Since 5,000 SA-7 missiles were launched, this equals a Pk of 0.04-to-0.12%. Main dangers were the SA-6 and the ZSU-23 anti-aircraft gun.
There were several factors playing into SAMs' successes. The Israelis were surprised and had to go after priority targets (attacking ground troops) with no time left to organize SAM supression. SAMs were fired in large salvos (often of 20-or-more missiles).
An obvious answer to the SAM threat is to go below the SAM's envelope. And that is what Israelis did. However, since they had no proper CAS (close air support) aircraft, they had to use fast thin-skinned fighter jets for ground attack which made them vulnerable to AAA fire.
The Israelis also had no previous experience in dealing with SAMs and had in fact ignored the problem altogether. The Soviet SA-6 Gainful missile was effective in particular shooting down 36 aircraft on a first day because of 3 factors.
Israeli electronic countermeasures were designed to counter the SA-2 and SA-3 and were useless against the SA-6. As a result, the ALR-36 RWR (rear warning receiver) used by the Israeli Air Force was unable to pick up any radar emissions from the SA-6.
Israeli aircraft also had no missile approach warners which meant that pilots had to pick up SAMs visually. This, however, was hard to do. The main Israeli aircraft were the F-4 Phantom and the A-4 Skyhawk. Both aircraft with very bad cockpit visibility and low to moderate cruise speeds (510 kts/Mach 0.87 and 420 kts Mach 0.62 respectively).
After RWRs were modified to detect the SA-6 launches, losses dropped sharply since evasive maneuvers were typically effective against it despite the aircrafts’ less-than-ideal maneuvering performance (F-4 had a very high wing loading while A-4 had low thrust-to-weight ratio).