Aerial Attack Study (Chapter 1 - Basic Limitations of AIM-9B against a Maneuvering Target)
Basic Limitations of AIM-9B against a Maneuvering Target
In discussing the employment of AIM-9B against a non-maneuvering target, we indicated that the missile has four basic limitations – IR, range, G, and lambda – and that these limitations forced us to deliver the missile in a cone 60° wide, emanating from the tail of the target aircraft. It was also shown that the length of this cone would vary according to altitude and delta Mach. At high altitude, with a positive delta Mach, the cone (envelope) will be considerably longer than at low altitude. In our discussion of fighter-versus-bomber tactics, we defined this cone in terms of angular velocity (max performance cone). By angular velocity cone, we mean an envelope in which the attacking fighter may deliver AIM-9B without exceeding its maneuvering limitations. We can see, by applying this angular velocity cone to any fighter-versus-bomber or fighter-versus fighter situation, that the purpose of any tactics which we develop will be to place us in this cone. On the other hand, when in a defensive situation, we will attempt to rotate this cone away from a given opponent. By doing this, we prevent him from securing a firing position.
When employing AIM-9B against a maneuvering target, the cone not only diminishes in size, it also changes in shape. In other words, the geometric shape of the maneuvering envelope will be considerably different than a non-maneuvering envelope. To illustrate: When discussing the non-maneuvering envelope, we found that its basic shape was determine by four factors – IR, range, G and lambda. We noted that these envelopes were rather symmetrical in shape. Maneuvering envelopes, on the other hand, are not so symmetrical. The lambda and G-limitations are primarily responsible for this change in shape. The reason for this: Lambda limitation may be exceeded because of a combination of low missile velocity and high angle off. If we launch AIM-9B from long range – within the effective range of the missile – at a maneuvering target, we can expect the target to turn into the attack. His objective is, of course to rotate his angular velocity cone away from the launch aircraft. By doing this, the defender can force the missile to exceed its lambda limit, because the missile is not only slowing down as it approaches the target, but the angle-off is increasing, since the defender is turning into the missile’s line of flight. In other words, the angular velocity generated by the defender forces AIM-9B to turn farther and farther in front of the target to maintain its collision course. This, of course, increases the resultant lambda angle. In addition, the missile is forced to turn even farther in front of the target, because of its continuous decrease in velocity after rocket motor burn-out, producing an extremely large lambda angle. If AIM-9B is launched near its max-effective range and the target turns into the attack, the combination of increasing angle-off and missile deceleration can easily cause the missile to exceed its lambda limitation. If this occurs, the gyro seeker rubs against its mechanical stops, which stops the gyro and the missile loses guidance. The attacker can do two things to avoid exceeding lambda limitation: (1) reduce his range before launch, which results in a higher missile velocity in relation to the target, and therefore, a smaller resultant lambda angle, and (2) reduce angle off. The smaller the angle off, the lower the resulting lambda angle. It is now obvious that the best attack can be initiated from the six-o’clock position at a reduced range. It is also obvious that lambda is the greatest missile limitation against a maneuvering target. To illustrate the magnitude of this limitation, let’s examine figure 18 and 19.
When AIM-9B is launch from a .8 Mach attacker against a 0.8 Mach maneuvering target which is performing a 3-G turn into the attack, we note (from figure 18) that effective missile range is somewhat less than that available against a non-maneuvering target. We also note that max angle off from which Aim-9B may be launched is less than 20°. The reduction in range is necessary because of the 25° lambda limit, while the reduced angle off is caused by a combination of lambda and G-limitations (G-limitations will be discussed later). If the target pulls more than 3 G, the maneuvering envelope will become even smaller.
At 6G, there will be no point from which the attacker can fire the missile and achieve a kill. In other words, there will be no maneuvering envelope at all. If AIM-9B is launched from a Mach-1 attacker against a Mach-1 target, at 35,000 feet, we note the following: When the target performs a 3-G turn into the attack, at missile launch, the attacker must reduce his range by approximately one-third when firing from a six-o’clock position (see figure 19). If the attacker launches at 30° angle-off, he must reduce his range by approximately one-half – as compared to a non-maneuvering target – if he expect to get a kill. Once again, the reason for this reduction in range is lambda limitation. The attacker must reduce his range, by a greater magnitude, at 30° angle-off because missile lambda angle is increase by both high angle-off and increased range. When the angle off is increased, range must be reduced to preclude exceeding lambda limit, hence the difference in range reduction between a zero-degree angle off and a high-angle-off shot against a maneuvering target. Once again, if the target increases G, the maneuvering envelope diminishes in size. At 6-G, there will be no maneuvering envelope, therefore, the attacker cannot achieve a successful launch and kill against a target pulling 6-G.
In our discussion of the above envelopes, we assume that there has been no diminution of target speed in any of his maneuvers. If speed decay occurs, the attack conditions will change and the attack will no longer be co-speed. As a result, missile velocity will be higher in relation to the target, and the resultant lambda angle will be smaller, since velocity varies inversely with lambda angle (at a given range and angle-off). This means that if the attacker has a positive delta Mach, rather than a co-speed relationship, he can launch at a greater range without exceeding lambda limitation. On the other hand, if the attacker is forced to launch against a maneuvering target which is traveling faster than the attacker, missile velocity, in relation to the target, is smaller. Result: The attacker must launch at a shorter range to preclude lambda limitation.
In view of the above relationships, we can see that the best attack is one in which the attacker has a positive delta Mach and a low angle-off on his initial approach to the target. This will provide greater freedom of maneuver and the opportunity to launch at longer ranges. On the other hand, the worst possible attack is one in which the attacker has a negative delta Mach and a high angle-off. This will restrict his freedom of maneuver and force him into a position from which the target can easily defend against this attack.
If AIM-9B is launched from an attack executed in the vertical plane overhead or underside attack – the maneuvering target will be forced to turn into the attack. Once again, by turning into the plane of the attack, the target will generate max angular velocity and force the missile to operate near its limiting parameters. In an overhead attack, this means that the attacker will not only be concerned with lambda limitation, but also with the same limitations encountered in an attack against a non-maneuvering target – IR and G. These limitations force the attacker to diminish his range until he can discriminate between IR background clutter and target signal and/or avoid exceeding the lambda limitation. This means that in a .9 Mach co-speed attack against a maneuvering target, the attacker will be forced to fire at less than 20° angle-off, otherwise, he will exceed his 2G limitation (see figure 20). Remember, in an overhead attack, the difference between total and radial G is considerably less than in the high-side or the underside attack (Gt = Gr + Cosθ), therefore, to stay within the 2G limitation, the attacker must launch from longer ranges (at a given angle-off). For example, if an attacker performs an overhead .9-Mach co-speed attack – to prevent himself from exceeding the 2G launch limitation at 30° angle-off – he must launch from a range of at least 10,450 feet. Under the same conditions, he can launch from a range of 6,840 feet at 30° angle-off in a high-side or level attack. In an underside attack, he can launch as near as 4,130 feet at 30° angle-off and still be within the 2G launch limitation.
From the above analysis, it is apparent that the overhead attack is the worst possible because of the limitations imposed by IR, G and lambda. Unlike an overhead attack against a non-maneuvering target, the attacker will find it difficult to acquire the low angle-off necessary for launch. Instead, since the target is turning into the attack, the angle-off will increase and the opportunity to launch will be lost. On the other hand, there is a slight advantage since the target is forced to turn into the attack – he will be forced to pull up and will consequently experience speed decay. The attacker will have a positive delta Mach and a higher missile velocity in relation to the target, and, therefore, a greater range from which he can launch AIM-9B before lambda limit is reached. This advantage is not a real advantage however, because the attacker can still be forced to exceed the IR and G parameters. We know, from our study of AIM-9B, that if we force the missile to exceed any one of the four parameters – IR, range, G or lambda – a kill will be unlikely. From a tactics standpoint, while on the defensive, the attack most easy to defend against is an overhead attack with a negative delta Mach. In this situation, we force the attacker to exceed a greater number of his limiting parameters than in any other attack.
The underside, or six-o’clock-low attack is the best possible attack which we can execute against a maneuvering target. It was noted in our analysis of this attack against a non-maneuvering target that we acquired advantage in IR, G, surprise, and performance. When attacking a maneuvering target, we retain these advantages, but acquire a disadvantage from lambda limitation. The lambda disadvantage is however, overridden by the advantages. This is true because the advantages of IR and G allow the attacker to launch at relatively shorter ranges at high angles-off, without exceeding the 2G launch limitation. (Remember, in an underside attack, radial G is greater than total G.) In other words, the attacker receives the benefit of 1G gravity, thus allowing him to position himself closer to the target at a higher angle-off without exceeding his 2G limitation (total G). This means that the attacker can reduce his range to stay within the lambda limitation and still be within his 2G launch limitation. In effect, the attacker is provided greater freedom of maneuver to successfully launch AIM-9B. In an underside attack, this freedom of maneuver is greater than in any other attack. From the defender’s viewpoint, it is certainly the most difficult attack to defend against. In summary we may say: The best attack for AIM-9B is the underside attack and the worst attack is the overhead attack – especially if the attacker has a negative delta Mach.