Modus Operandi
The said goal is harder to achieve than expected. “Go high”, is euphemistically reductive. How high? Is it worth pushing a few thousand feet more? If yes, when is an impact appreciable and when do we land in the realm of diminishing returns? To answer these questions, I collected a few tens of thousands of data points about a fairly predictable missile capable of reaching reasonable speeds and range. Predictability means taking lofting missiles out of the pool. One of the few useful results is, therefore, the R-27ER.
I initially collected speed readings every second, but I observed changes of hundreds of knots between two readings. Ergo, I needed more granularity, and I collected values every 250 ms.
Altitude-wise, I started at 1000ft, or circa 300m, up to 50,000ft, or over 15.2km, at intervals of 1000ft.
The next question is: “what do we measure?”. The acceleration is interesting, but fairly static, so to speak. I required something less related to the missile itself. For this reason, I measured the deceleration of the R-27ER for a period close to the battery life.
Results
The following charts show the results of the recorded missile speed, expressed as TAS, or True Air Speed and measured in knots, from 500 kts to 2750kts. On the ordinate, we have the altitude in feet, and the time in seconds on the abscissa. Let’s see what these charts tell us, starting from Altitude [ft] vs Time [s].
The representation of the results tracks the speed as the altitude changes. For example, the R-27ER decelerates to 750kts at 10,000ft after 30s. However, at 20,000ft, the missile is still flying at 750kts after circa 40s. Therefore, the missile is losing less speed if the launching aircraft is higher. If we put it into numbers, a 50% increase in altitude corresponds to a circa 25% gain in terms of energy retention.
The just discussed relation is, however, not applicable throughout the envelope: as the chart shows, in fact, the curves follow different patterns, with the majority appearing as logarithmic functions between 0 and 1. The interesting part is that a “flatter” curve indicates a lower deceleration, ergo, better energy retention across altitudes.
It is also worth noting how missiles reach much higher speeds as the altitude increases. This is why certain values, such as 2750 kts or 2500 kts, are missing below certain altitudes. So, not only do missiles lose less energy, but they also fly faster, making them much more dangerous and harder to defeat.
To answer another question asked at the beginning of this discussion, is gaining altitude worth it? Generally speaking, yes, of course. However, there can be situations where this is not tactically feasible, might delay the engagement, thus costing the element of surprise, or perhaps it may come at a severe cost in terms of speed or fuel.
For example, let’s consider the altitude between ground and 10,000ft, or 3km. As we can see, the curves tend to be almost orthogonal to the abscissa. Therefore, the speed retention is rather poor even as we climb, and especially for speeds above 1,000kts, which corresponds to circa M1.5. In other words, the missile loses a lot of energy anyway. So, is it worth climbing 10,000ft to have your missile maintain the same speed for 3-5 seconds more? If possible, sure. If there are possibly adverse consequences, perhaps not necessarily.
Let’s see another example, 1500kts, equivalent to circa M2.3. Between ground and 10,000ft, there is basically no change in terms of energy retention. What about 25,000ft and 35,000ft instead? Here, the picture changes drastically. Here, the Mach-equivalent speed is M2.5, a respectable speed. Such a high speed is retained for 10 additional seconds, which is circa 4-5nm. It might not sound like a lot, especially for us, F-14 fans, but it is not irrelevant at all, especially for a non-lofting missile.
Let’s now discuss the second chart, representing speed versus time, and each series is an altitude dataset. There appears to be a gap in the series, but that’s just Google Drive running out of colours.
The first noticeable peculiarity is that the curves are stacked. Since the ordinate is the kTAS, it means that launching at higher altitudes immediately grants better performance to the missile. Moreover, as we climb, we see that the lines tend to be more “spaced”, so to speak. This behaviour is probably connected to the last point I raised when I discussed the previous chart.
The second observation concerns the “shape” of the curves. At low altitudes, the curves appear similar to the letter “L”. Ergo, the missile loses a considerable amount of energy until it reaches a point where the speed is better retained. The “elbow” of the curve corresponds to circa 800 kts, which is circa M1.2 at low altitude, or the upper boundary of the transonic region.
High up, instead, the curve approximates more and more a straight line. The bend is missing because the missiles run out of battery before fully entering the transonic region, which sits at circa 700 kTAS, at 50,000ft.
Considering only the supersonic part of the curves, we can clearly see how the deceleration is linear but happens at vastly different ratios. Approximating those intervals with straight lines, we can see how their angular coefficient is diverse. In particular, the steeper the line, the greater the deceleration.
Fun fact: what has been mentioned so far applies to aeroplanes as well. However, an in-depth discussion is beyond the purpose of this discussion. If you would like to know more, I recommend checking the plethora of Thrust-to-Weight ratios, performance videos and articles I made between the end of 2024 and 2025.
Altitude vs Top Speed
The next point to discuss is the maximum speed. The chart shows the top speed reached, measured as TAS in knots, as a function of the altitude. The trend is almost linear, with a slight convexity. To make the values more understandable, the top speed of the R-27ER at 1,000ft was circa M3.3. At 25,000ft, it was M4.4, and at 50,000ft it was M5.2.
Without entering into the specifics of missile rocket motors’ efficiency as a function of the altitude, which is way beyond my expertise, if we take the results as a black box, it is clear how altitude plays a considerable role in determining the top speed of a missile, on top of the energy retention. And once again, a fast missile reaches farther, sooner, and it is harder to defeat.
Lofting missiles
The quasi-linear trajectory of the R-27ER has been great to show how the characteristics of the atmosphere affect the behaviour of a missile. Several modern missiles use lofting as a technique to reach farther distances. How would such weapons compare to what we have seen so far? Intuitively, we can expect a pattern that tends to be orthogonal to the curves, at least during the cruising phase, as the speed changes relatively slowly as the missile dives.
To verify my assumption, I twice tested an AIM-54A Mk47 at 50,000ft against a target flying at 40nm. The first run used standard employment, the second, a non-lofting Phoenix. Both missiles connected, which is quite surprising in the latter case. On top of that, I added an AIM-120C-5 launched following the same parameters.
This is the resulting chart. Keep in mind that these missiles have been introduced in the span of many years. The 54A is from the early 1970s, the R-27ER from the late 80s and 90s and extremely rare, and the AIM-120C-5 is from the 2000s.
The blue and green dashed lines represent the two AIM-54s. The blue curve represents the standard employment, and the green the non-lofting test. The thrust of the Phoenix’s rocket motor is not particularly explosive performance-wise, but it allows the missile to reach well over 100nm, especially at such a high altitude.
The white dashed line is the AIM-120C-5. This missile is more comparable to the R-27ER than the Phoenix. It is a perfect showcase of how lofting allows missiles to “borrow” the characteristics of the atmosphere at higher altitudes, with all the associated benefits that, by now, should be clear.
As a side note, manually lofting a missile usually helps to achieve or improve the performance of a missile by exacerbating the initial climb.
Conclusions
I hope you have found this discussion about the characteristics of the atmosphere in DCS, and how it affects the performance of missiles in the game, useful. As with many aspects of the game, it is not as “one-sided” as it may appear, and intricacies and effects are indeed quite complex.
Lastly, a shoutout to Jack, who contacted me a few months ago to discuss the behaviour of the atmosphere in DCS and inspired me to dive into this topic.
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