AIM-54 Probability of Kill – III – The Altitude Factor

While we look forward to the AIM-54 overhaul that should happen as soon as ED allows HB to rework the missile guidance model during its whole envelope, we continue the analysis of the current implementation of the AIM-54 Phoenix in DCS.

In the second article of this series we analysed the performance of the AIM-54 at an altitude of 1,000ft. Predictably, at constant altitude and increasing range, the PK of the AIM-54 went down, sometimes dramatically (AIM-54C Mk47, Notching scenario).

This article “capsizes” (pun about the Navy fighter totally intended 🙂 ) the approach by studying the evolution of the PK at constant range but different altitude. Particularly, the worst performer range is considered from the previous tests (25nm) and at:

  • 1000ft;
  • 7000ft;
  • 15000ft;
  • 25000ft.

The goal is finding the “sweet spot” where the PK becomes consistent even when the aspect of the target is disadvantageous. This information allows the RIO to assess the situation and command his pilot in the most appropriate way.

I’m not posting raw data in this article due to their length, I will release them along with other results later. The following instead is the data already elaborated into more readable tables:

rio13-AIM-54-PK-altitude-effect-results-exp


rio13-AIM-54-PK-altitude-effect-results

Results evaluation

At 25,000ft the AIM-54A Mk60 has an incredibly high PK. The reason is apparent as we look at a track sample from Tacview:

rio12-AIM-54-PK-hit-C-25nm-25000-ntch-su27-dive
[HIT] AIM-54A Mk60, 25nm, 2500ft, DIVE vs F/A-18C

The AIM-54 hit the target at the impressive speed of mach 3.6, after reaching an altitude peak of 30,000ft at mach 4.5. The missiles covered the 25nm in less than 40 seconds, leaving virtually no escape to the target. The AIM-54A was still accelerating when it turned towards the target. This great amount of energy allows the missile to perform above the expected even in the Notching and Flanking scenarios.

The AIM-54C Mk47 instead proves to be quite unreliable when the target is not Hot, achieving a hit rate of 45% at both 15,000ft and 25,000ft.
These are tacview images of defeated AIM-54C Mk47 at 25,000ft:

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Curious behaviour

What happens at 15,000ft is worth of attention: the hit rate, rapidly increasing from 1,000ft to 7,000ft, suffers a drastic suspension for both versions of the missile, whereas at 25,000ft the trend resumes. This is worth noting for the RIO because it shows how climbing from 7,000 to 15,000ft doesn’t offer tangible benefits whereas climbing to 25,000ft greatly increases the PK. On the other hand, climbing from 18,000ft means investing a considerable amount of energy so the RIO has to decide the best course of actions: for instance, if it is better to turn cold and change the F-14 approach to the target or, instead, reduce the distance.
This topic is subject to an infinite amount of tactical considerations but let’s imagine two simple scenarios: if the target is an older generation aircraft armed with obsolete weapons then the RIO can command his pilot to commit and get closer in order to increase the PK. If the target is a modern aircraft, armed with longer range weapons (such as AIM-120 or R-27 ER/ET), getting closer can expose the F-14 to response, such as either a snapshot or maddog, therefore turning cold, gaining distance and later re-commit may be the better option.
Considerations such as the above are the very reason why I am doing this series of articles. Unfortunately I have no real life military experience in aviation so if someone more knowledgeable is willing to provide suggestions, he’s more than welcome 🙂

Charts and in-depth Analysis

As usual, visualizing data helps to better understand the results.

Hit rate

The following chart represents the combined Hit Rate. The results of each of the 4 scenarios for the MiG-29S, the Su-27 and the F/A-18C are included.
rio13-AIM-54-PK-altitude-effect-chart-hitrate-overall
This chart is the least useful. As we concluded in the previous article, the Energy of the missile has a great impact on the Hit rate so combining the results can drive to erroneous conclusions.
Nevertheless, the beneficial impact of the less dense air if clear, especially for the AIM-54C Mk47, equipped with a less powerful rocket motor.

Defeated missiles

As expected, the AIM-54C Mk47 benefits greatly from the thinner air of higher altitudes.
rio13-AIM-54-PK-altitude-effect-chart-miss
The most considerable gain is between 1,000ft and 7,000ft. As noticed before, between 7,000ft and 15,000ft the performance improvement almost stops. It resumes at 25,000, where the AIM-54C Mk47 is almost “free” from the energy issues.

Hit rate per Aspect: Relative

This chart represents the hit rate of each aspect relative to the total Hits scored. In other words, it shows in which target Aspect scenario more Hits have been scored.
rio13-AIM-54-PK-altitude-effect-chart-hitrate-relative
Due to the Energy issues that affected the AIM-54C Mk47 at low altitude, it is obvious how most of the scored hits come from the scenario that is less energy-dependant: Hot. As the Energy factor becomes less cumbersome due to the thinner air, the hit rates become closer and finally stabilize.
The Flanking scenario still makes the Phoenix-C pay a toll in terms of results, no matter the thinner air present at higher altitudes.

Hit rate per Aspect: Normalized

This chart is definitely more interesting. It represents the hit rate normalized and relative to the Aspect of the target.
rio13-AIM-54-PK-altitude-effect-chart-hitrate-normalized
The “energy-induced gap” shrinks when at an altitude higher than 7,000ft, to the point that the hit rates of both the AIM-54C Mk47 and AIM-54A Mk60 are comparable. This does not happen in every scenario: it is clear how the energy gained (“saved” would be more precise) thanks to the higher altitude is not sufficient to close the “gap” in the Flanking scenario. It is interesting to note how the results of such curves become flat, a clear demonstration that a performance limit has been reached whereas the Hot scenario still improves.

As mentioned before, the AIM-54A Mk60 shows something interesting at 25,000ft. The hit rate for Hot targets increases to an astonishing 97% whereas the Flanking results are stable. How come? As mentioned before, the AIM-54A Mk60 hits the target incredibly fast in the Hot scenario, leaving little escape margins to the target. Nevertheless, it doesn’t really help against countermeasures as the seeker of Phoenix-A should be much more sensible to such defences.

Conclusions

I have already touched most of the interesting points whilst I analyzed the charts: the AIM-54C Mk47 benefits more than the AIM-54A Mk60 from the higher altitude since it was suffering the most at ground level. Both versions of the missiles score comparable results in the Hot scenario whereas the Flanking is still owned by the AIM-54A Mk60, thanks to its more powerful rocket motor. It looks like the AIM-54C Mk47 hits its energy limits at 15,000ft.
The behaviour of both missiles at 15,000ft is indeed interesting and it’s something the RIO has to take into account because trading energy for altitude doesn’t seem to be worth and the PK can probably be drastically increased by closing the range. As mentioned above, this fact opens a great number of considerations.


As we know, the Phoenix can kill a target at a range greater than 100nm. How come that its performance is sometimes so abysmal? How can a missile that barely scores a 50% Hit rate at 25nm, reach and kill a target that far?
Something else comes into play and it will be analyzed in the next article: Medium to Long range.


Building the AIM-54 PK Model

Now that the first 1440 results have gathered, equally split between the AIM-54A Mk60 and the AIM-54C MK47, we can start drawing the first sketch of the AIM-54 PK Model. This sketches report only the combined Hit rate, later they will be split depending on the Aspect of the target. Due to the “short” number of samples, I used a histogram, later on it will be integrated by more and different charts.

AIM-54C Mk60 – 720 Samples

rio13-AIM-54-PK-model-1440-C

AIM-54A Mk47 – 720 Samples

rio13-AIM-54-PK-model-1440-A

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