So I’ve recently learned how to make custom missiles and used it to do quite a decent bit of testing with this new ability, which I’ve primarily used for 2 things, testing varied/optimized loft profiles and verifying the effect of missing altitude adjusted thrust (AAT) for the AIM-54.
I’ll start with the big one;
As I’ve previously suggested, rocket motors in War Thunder do not model increase in thrust from decreases in atmospheric pressure. Rocket motor thrust in WT is constant, as verified using WTRTI and an Me163:
Spoiler
Me163 at takeoff (TRST: 3730lbf)
Me163 at 9000m (TRST: 3730lbf)
This is not much of an issue for smaller rocket motors due to the in-game missing portion of the rocket thrust equation having the exit area of the rocket motor’s exhaust nozzle as a modifying variable, which indicates that the increase in thrust from altitude is proportional to the area of the rocket exhaust nozzles exit. The math can be seen below:
Rocket Thrust Equation:
“deltaF = (Phigh - Plow) * Area” being what is used to determine the missing thrust by altitude.
Source 1 (Stanford)
Source 2 (NASA)
Source 3 (DTIC Paper)
Following this confirmation, I went about modeling Altitude Adjusted Thrust (AAT) versions of the AIM-54C in WT to verify the effect this missing thrust has on the missile. The graph of which can be seen below, as compared to the AIM-120A.
AIM-54C with AAT vs AIM-120A with AAT peak velocity:
Disclaimer: Inaccuracies due to how I modeled AAT for the missiles
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Rocket motor area was determined using the diameter of the missile body (AIM-54C: 380mm / AIM-120A: 178mm).
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Rocket motor AAT was hard coded for a specific altitude by preemptively calculating the increase in thrust for a given altitude, and adding it directly in the missile code before performing the test.
Justification:
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This was done simply due to the fact that I could not find specific info on rocket motor dimensions and therefore had to simplify to some degree, and results in a notable increase in the “Area” term in the equation, and therefore a notable increase in AAT.
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I am unfortunately unaware of a method to make an adaptive thrust in WT due 2 issues. Lack of access to the real-time altitude of the missile (which could be used to determine the atmospheric pressure at the missile’s current location) and the inability to use mathematical equations for the rocket motors thrust code. This results in a decrease in AAT during the tests, as both missiles tested loft (increase in altitude → increase in thrust)
Generally speaking though, the tests were meant more to demonstrate a general trend and offer a somewhat roughly accurate visual representation of the negative effect of the missing AAT on the AIM-54 in-game, which I believe is achieved despite the inaccuracies from the modeling.
There’s a few noteworthy things that can be identified from these graphs:
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The AIM-54C is hit brutally hard by the missing AAT due to its larger motor area (~0.11m^2) compared to the AIM-120A (~0.025m^2), with the largest difference between AAT and in-game thrust being M1.5 for the AIM-54C (at 10 000m) and M0.43 for the AIM-120A (at 14 000m).
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The AIM-54C’s AAT peak velocity runs into what appears to be an in-game issue/limitation above 10000m altitude. Between roughly 5400-5500kph, missiles struggle immensely to accelerate, which is why the AIM-54C’s AAT peak velocity breaks from its trend and flattens out above 10000m. If this “wall” did not exist, it would likely continue following the trend.
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This “wall” does not appear to be a function of drag, altitude, missile dimensions, coded speed limit, or any other variable I can identify, and seems to be an issue with the game itself.
War Thunder Hypersonic Research Institute (ie: Testing The Wall):
I did some testing specifically regarding “The Wall”, in which I tested what it would take to go beyond it. Here are some of the results:
AIM-54C “GO FASTER”:
Thrust: 50000N, dragCx: 0.018 → 0.08, launch conditions: 14km M2.8.
Results: unable to surpass “The Wall”, tops out around 5489kph before dropping like a rock back down to the ~5400-5410kph range BEFORE motor burnout:
AIM-120A “Basicly Zeus’ Lightning Bolt At This Point”:
Thrust: 100000N, Motor burn time: 30 sec, dragCx: 0.018 → 0.08, launch conditions: 14km M2.8. Max speed: 1500m/s → 1800m/s
Results: Missiles thrust is so excessive, it immediately breaks M5.0 leaving the rail, and takes ~5.8 seconds to go from 5400kph up to 5500kph. Once cleared of 5500kph, it begins RAPIDLY accelerating, increasing from 5500kph to its 6480kph speed limit in 14.5 seconds.
From a 4000m launch, both missiles once again hit the 5400kph mark and struggled to go any faster as well, suggesting it is not realistic drag imposed speed limit, nor is it a thrust limitation, but a game modeling one gaijin will need to fix:
To touch on what peak velocities the AIM-54C is expected to hit between 10000 - 14000m, I did use the trend from 2000 - 8000m to extrapolate values for 10000 - 14000m, resulting in the following estimated values, of which the 1000m value is similar to the one found in-game:
Spoiler
Do note that the AIM-54C has a hard limit of 1800m/s(6480kph), which is M6.1 above ~11km altitude.
TLDR; The real most likely cause for the AIM-54’s underperformance in top speed is neither loft profile, nor drag, but missing thrust due to gaijins inadequate and oversimplified modeling of rocket motor thrust, which hits larger missiles like the AIM-54’s particularly hard.
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Next, I tested multiple different loft profiles and their effect on the AIM-54’s performance, the graph for which can be seen below.
Spoiler
@dark_claw 's graph for all other ARH’s for comparison:
Loft codes:
In-game AIM-54C:
EM:
IMPL (Dark_claw’s loft code):
MP:
MP2:
MP3:
One notable detail is that the addition of the AIM-120A’s energy management code (timeToHitToGain code, added to the “AIM-54C EM”) with no other changes to the missile appears to have been an improvement at nearly all ranges for the AIM-54C, and likely benefits it even more against a maneuvering target (though I did not test against a maneuvering target, so this is an unverified claim).
Secondly, as can be seen from the graph that changes in loft profiles, even large changes, do not have a significant impact on time to impact. The largest difference (between the IMPL loft profile and the MP3 loft profile), is ~6.4 seconds out at 80km, with the in-game AIM-54C sitting somewhere between the 2 at 74.6 seconds.
What modified loft profiles do affect significantly though, is impact velocity at ranges beyond ~40km, where the in-game AIM-54’s impact velocity falls like a rock while all other tested loft profiles follow a more gradual curve as expected of a missile with the AIM-54’s stated range. All other tested loft profiles impact velocity at 80km+ being similar to those seen by the current in-game AIM-54C at 50km, which is a significant increase in long range performance with negligible impacts at all ranges the AIM-54’s are currently used at in-game.
Most noteworthy points when comparing my AIM-54C graph to that of other ARH’s (and the R-27ER):
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All other ARH’s outperform it in impact velocity below ~25km
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All other ARH’s outperform it in TTI below ~40km
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R-27ER outperforms it in impact velocity below ~27km
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R-27ER outperforms it in TTI below ~50km
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R-27ER with a 30° manual loft outperforms it in impact velocity at 65km
The R-27ER comparison is the most important though in my opinion. Without manual loft, the R-27ER outperforms the AIM-54C in TTI at all reasonable combat ranges (<50km launch) seen in WT. With a 30° manual loft, the R-27ER outperforms it in impact velocity even out to 60km. This, along with the R-27ER having 1/3rd the motor burn time (and therefore visibility) of the AIM-54, along with more than 2x the max G limit, and datalink, make the R-27ER effectively better in every conceivable way to the AIM-54’s in a 1 on 1 engagement as currently modelled in-game.
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Finally, not test related, but I did find this document while perusing the DTIC website, with the following information regarding the AIM-54C:
Spoiler
There’s some pretty great information in this document regarding some specifics of the AIM-54C modification.
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AIM-54A was considered inadequate vs highly maneuverable targets at high altitudes
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AIM-54A was considered inadequate against very low altitude targets
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AIM-54A was considered inadequate vs groups of targets that were tightly packed (stream raid)
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New inertial guidance system, modeled in-game by reduced inertial guidance drift speed being dropped from 10 → 2 (unit of measurement is unclear, likely m/s?))
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More complex and optimized trajectories permitted, improving performance vs high altitude targets that are actively defending when compared to the AIM-54A (not modeled in-game, 54A and 54C loft trajectories and autopilots are copy pastes)
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New transceiver with linear frequency modulation, believed to improve performance against beaming targets, cold targets, and groups of targets (not modeled in WT, AIM-54C’s radar and notch angles are complete copies of the AIM-54A’s)
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New proximity fuse for improved performance vs small targets at extremely low altitudes (irrelevant in WT due to the hypercrutch that is gaijins excessive multipath modeling)
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New test missile shot (M1.55 11000m vs M0.9 9000m target, 160km launch)
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Increased radiating power from missiles GSN transmitter (likely referring to the AIM-54C+/AIM-54C ECCM/Sealed upgrade)
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New fragmentation warhead providing improved performance. This is likely the new WDU-29/B Directional fragmentation warhead I’ve previously discussed and is currently seen in-game on the AIM-54C, but only has a negative impact on the missile performance in-game seeing as gaijin modeled the reduction in TNT equivalent, but did not model the increase in warhead lethality (estimated between 20-30% by all previously stated sources in this thread).
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Development of a frequency synthesizer for the GSN Transceiver allowing it to be more frequency agile (might indicate MPRF for the AIM-54C+/AIM-54C ECCM/Sealed? would fit with the known capabilities of the AIM-120A along with the development timeframe).
This document, though only an analysis of Russian and public sources available at the time to Lt Col Mikhaylov, fills in the blanks for some known modifications to the AIM-54C and ECCM/Sealed variants we’ve already discussed here, and further reinforce the theory of the completely inadequate modeling of the AIM-54C in WT, which at the moment remains an outright downgrade in all ways except inertial drift speed to the AIM-54A.
