Understanding that flying higher, where the air is thinner; and flying faster, so the missile departs with a higher initial speed, is quite elementary. These two elements combined improve the reach of the missile and are usually recommended to new players to improve the success rate of their missiles.
However, there is another fundamental factor, often more important than the two just mentioned, that is usually overlooked: how the target presents itself from the point of view of the fighter. This parameter is the Target Aspect angle (TA – US Navy, Marines), sometimes indicated by its supplementary angle, the Aspect Angle (AA – US Air Force).
The Target Aspect is defined as “The angle from the bearing line of the fighter to the nose of the target“, and the reason why it is often omitted is probably because it is less intuitive: flying high and fast is understandable. Considering how an aircraft appears from the fighter’s point of view is not really complex, but the implications are indeed less immediate.
Comparing how a missile behaves as the Target Aspect changes to a football match may help to visualize the those implications: imagine you are a defender trying to stop an attacker running towards your goal: if he’s coming in your direction you run straight into him. However, if he’s running perpendicularly to you, you don’t run towards him, but you try to cut his path, running in a direction where he is not at the moment, but he will be later, in a moment in time where you will be there as well. On top of that, it forces you to run for longer than in the first.
How do you tell where the attacker is running? By looking at how his body presents itself: in the first example, you see the whole figure, in the second, you probably see the side of the head, and almost only one arm and leg.
Back to aviation
How these examples transpose to fighter jets? The simplest way to visualize the Target Aspect is by using images, to this purpose I picked four photos from the Wiki page about fighter aircraft.
(Notes: the point of view of the photographer is considered equal to the point of view of the fighter. The TA values are approximated).
The Target Aspect matters!
The concept of “Aspect” should be now more clear. But why is it important? Back to the two scenarios mentioned before, it should be clear why the first scenario is preferable: the Closure Rate (VC) is higher and if you are exactly on the path of the attacker, he will run straight into you, meaning you do not have to spend energy chasing him. The second example instead requires you to run following a certain path (Collision Course), and in some cases requires you to run faster than the attacker to stop him from reaching his objective.
Moreover, consider what happens if the attacker tries to evade you: in the first scenario, since you are in his path, it is hard for him to avoid you, as he can’t turn instantaneously without losing control of his body and / or the ball. In the second, he may increase the angle between him and you to the point that for you reaching him becomes impossible.
The explanation above is directly applicable to simple Air-to-Air scenarios with at least four significant differences:
- Altitude: a football field is plain (at least professional ones are. The one at the oratory where I group up was… peculiar ¯\_(ツ)_/¯ ), an aerial fight is a 3D business: different altitude also means thinner or ticker air and other differences, impacting the performance of missiles and aircraft;
- Energy is not unlimited: although you may run for a while, the missile can’t. Besides more modern missiles able to throttle and conserve energy, the missiles in DCS usually burn their rocket motors immediately (some “loft”, trading energy for altitude and then diving on the target). The battery powering the electronics also runs out in a relative short amount of time;
- The “field” is not unlimited: although the maps and the Areas of Operations are not unlimited, a defending aircraft may run towards friendly positions and their SAM umbrella, forcing you to spend precious fuel in the process.
- Countermeasures: aircraft can defend themselves by using Counter Measures such chaffs, flares, jammers and the Target Aspect can improve the efficiency of the countermeasures.
The following is an example you can recreate in a couple of minutes thanks to the Mission Editor: two MiG-23 are set as passive targets (no defensive manoeuvres, no Chaff used, similar to the settings I used in the previous article of this series) and flying from initial TA0 and TA48. They also fly at the same speed and altitude.
As you can see, the missile, an AIM-54A Mk47, fired at a range of 35nm has enough energy to be a threat only in the first scenario. In the second scenario, the TA is increasing over time, forcing the missile to keep turning into the target and wasting precious energy and further reducing the Probability of Kill (PK). This is evident when the TAS (True Air Speed) of the Phoenixes at the moment of hitting the target is compared: 719kts vs 490kts. Eventually, the second AIM-54 hit the MiG-23 only because the target was not defending at all.
Moreover, the second missile has to be supported for a longer period, and this is critical when launching in STT (so the Phoenix behaves as a SARH missile) or, for example, to avoid enemy air defences.
Guidance and Countermeasures
The Aspect also have a concrete influence to the guidance and countermeasures resilience. This is a brief overview of common radar and guidance modes in DCS:
Pulse Doppler Radars
Pulse Doppler radars have a blind spot coinciding with zero relative speed (“notching“) because the target is filtered by the same filter that removes the unwanted terrain returns (Main Lobe Clutter filter). Depending on the technology used, the interval in which the Pulse Doppler radar is blind can be more or less wide, but it is understandable how the closer the Aspect is to 90°, the higher are the changes of it disappearing from the radar.
The Target Aspect is important for another reason: the lower the TA, the higher the VC making the target more clear to the radar, the faster the missile approaches and fewer manoeuvres are required by it in order to hit the target.
PD radars have higher resistance to Chaffs than older radars: the chaff in fact is as fast as the aircraft as soon as it is released, but it loses its energy in a matter of fractions of seconds. A fairly modern radar can therefore understand which one is the decoy and which return is the aircraft.
The countermeasure used to distract an IR missile is the Flare. It is a source of heat that hopes to distract the missile from your aircraft. The aspect is again important because if the target’s exhausts are visible to the missile’s seeker, the task of the Flares becomes much more complex.
Countermeasures & “DCS the Weirdo”
A note of warning about DCS: although a new CM system is being developed, at the moment the countermeasures are like a saving throws from D&D or WH: roll a die, if you hit the number greater than a certain parameter, the missile is fooled. Countermeasures are not physical objects at the moment, so chaffs deployed 10″ before can still fool a PD-guided missile. This is not realistic, but it’s what we have, unfortunately but ED has acknowledged the problem, and they are working on it. Nevertheless, the Aspect seems to have an impact on the CM so what has been said so far it is still applicable.
Measuring and Using the Target Aspect
Now that we have a slightly better idea of what the Target Aspect is, the question rises: “how do we measure it?”.
Modern aircraft use a visual indication on their attack display (such as the HAFU) whereas others (e.g. the F-14A/B) rely on mental Maths or eyeballing and estimations. Explaining how it’s done is way beyond the scope of this article, if you want to know more, have a look at the Intercept Geometry discussion in Procedures & Ops.
Proper manipulation of the Target Aspect requires a more profound understanding of the geometry, but there are some tools we can use “out of the box”. This is, for instance, the simplest intercept I managed to put together uses the Collision Course. I later realized it is somewhat similar to some real procedures in use 20 years ago, with the difference that the missile is not employed from Collision. Keep in mind, however, that the Collision Course does not reduce the Target Aspect, it actually stabilizes and maintains it; therefore you can use this procedure when the TA ≤ 30°-35° top. Otherwise, you can place the target close to the gimbal limits and reduce the distance and the Target Aspect until you are happy to shoot.
To reiterated again, this is a very simplified approach, but it should be good enough if you are new and in need of a starting point.
I hope you have found this article interesting. If you have questions or feedback, give me a shout!