Missile performance tuning overview

[OlWilly 122]

While playing around I noticed that missiles (BVRs mostly) behave quite unrealistically. I have a bad habit of flying low and slow, and this is the worst place kinematics wise for BVR combat, yet, I have little problem scoring hits. Granted, AI doesn't know how to defend with maneuver, but it is still wrong. Similarly, when I am on the receiving side, no defensive maneuver seems to help - missile will still get me. The only way is to abuse the game's engine and go below 50 meters when AI loses all means of attacking me - even with guns.

Checking out the missile performance shines the light on the problem. First example, R-24R - I launch on pursuit course, while going at 0.7M at target above me and going with the same speed. Missile accelerates to 3.7M on upward swing and even gains velocity during the entire 30 or so km flight path. R-40, while checked in MRS, shows the range of 160km while launched at 2.8M from 15k meters. And the crazier ones, AIM-47 shows the range of above 1200km (!) at the speed of 14M (!) while launched from 15k meters at 3M. Both AIM-47 and R-33 have weird 240 second sustainer times.

What this means is that missiles are barely energy limited, and the max effective launch is limited only by the statement in DATA file. Your kinematic performance barely matters.

This turned out easy to correct.

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The missile performance is governed by few statements in the DATA file.

Booster acceleration and booster time govern the max acceleration of missile. Acceleration is measured in Gs which are roughly 35km/h. The time says for how long the booster works. Thus, If we have acceleration at 5 and time at 10, we get 5x10x35 = 1750km/h of default acceleration - with no account of drag and launch platform velocity.

Sustainer works by the same logic.

Then we have subsonic and supersonic drag which determine mostly how quickly missile runs out of energy. Supersonic drag is the most relevant here of course.

The obligatory tool to deal with missiles is MRS:

Now, keep in mind that missile performance you find online is usually its best performance - meaning launch from good altitude at a good platform speed.

For the sake of simplification, let's assume the altitude as 15k meters. You may tailor it more accurately by ceiling of known aircraft, but I keep it at 15k.

The platform speed will be close to max M number of given aircraft or aggregate of various aircraft using a given missile.

As an example, I show the process for R-40 missile as it is very dependent on launch platform kinematic state.

First we have to set up the launch state. MSR has no altitude setting but it could be st by IAS/TAS ratio. For 15k meters it will be around 0.6.

MiG-25 will launch it at 2.8M. The speed of sound at 15k is around 1060km/h. Thus, 2.8x1060=2968km/h. Then we convert it to m/s - the factor for this is 3.6. So, 2968/3.6=~824m/s. We input this into the init speed.

Weight and diameter of missile could be picked from DATA file. Thus, 475kg and 0.31m.

Now we had to deal with the booster and sustainer. R-40 has no sustainer, so both values at 0.

For R-40 we are lucky and we know the default acceleration - around 2.2M and the max speed - around 4.5M. We pick the first value.

2.2Mx1060km/h=2332km/h. Then we divide the given speed at G value - 2332/35=~67. Let's say we give it a 4 second booster - so 67/4=16.75.

This way, we have booster acceleration at 16.75 and booster time at 4.

We press SIMULATE and get 300km range (statement Length) with max velocity 1455m/s (~4.9M). Speed is almost there, but the range is out of whack. We forgot about the drag.

Now, we experimentally adjust the drag to bring missile range close to its real value. For R-40 this should be around 50-60km. Drag has two windows, first is subsonic, second is supersonic. Second is the most important here, keep the first below it.

Input 0.6 for subsonic and 1.2 for supersonic. This gives us 56km range and drops velocity to 1353m/s (4.5M). This looks really good. Check out the energy loss curve too.

Now we can check how missile will perform at subpar kinematic state of the platform. Set IAS/TAS to 0.95 and init speed to 350 (this is going at 1M at 2k meters). We get pitiful 11km range and 845m/s (2.4M) velocity. This is close to how the missile should perform at such launch parameters.

I strongly recommend to extend the duration in DATA file too, make it so missile lives longer

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R-40 was easy as we know both default and max speed, as well as the parameters of launch platform (MiG-25 and MiG-31 behave similarly). What about missile when we know only the max speed?

Sparrow for example, it has max speed of 4M. But if we use 4M for booster calculation, we get values far above 4M.

Take the max missile speed at retract 70-80% of the optimal speed of launch platform from it. Assume we mind Phantom launching from 2M, so we set up 4M-1.5M=2.5M of default acceleration.

Let's make the same tuning for AIM-7M

Speed is almost here, but range is not enough. As we know, AIM-7M had sustainer, so we can use it here to extend the range. Sustainer acceleration at 4 and duration at 10. I also drop booster to 17

And once again, subpar kinematic state check:

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What this does in-game is that your kinematic performance now matters. If you want extended engagement ranges, you had to go higher and faster. And missiles now actually lose energy. I am not sure if missiles in-game lose energy during maneuvering (hard to check since AI doesn't defend) but I hope so.

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Now, this doesn't quite apply to lofted missiles like AIM-54 since they have very different flight profile, and this MSR has no loft settings. I guess you can set them up to have reduced range and velocity and then check in-game if they perform correct while being lofted.

Likewise, I currently don't know how this tool could be used to tune SAMs since their flight profile is radically different.

Edited July 18 by OlWilly

[OlWilly 122]

After some testing, I came up with a routine to tune SAMs and SRMs as well.

For SAMs, the data you can find online is usually given for a high-altitude target - where the air is thinner and missile could accelerate better, having more range. To get the low-level performance, for simplicity sake, we may assume that it is the half of maximum range (which is often close to reality, check MIM-23 for example) and reduced max speed.

And this is all we need.

Weight and Diameter as in DATA file. Init speed at zero which would mean launching from a non-moving platform.

Next, we will check the missile performance at higher altitude. Again, to keep things simple, let's assume 15k meters - IAS/TAS ratio at 0.6. Here, aim for more range and speed as stated online - because you had to account for missile actually getting there and MRS doesn't do this.

Then, check missile performance at lower altitudes, which would be IAS/TAS ratio of 0.8, or around 5k meters. The range should drop approximately in half and max speed below the one stated online. Speed of sound at this altitude is around 1150km/h or 319m/s for the reference. 

SAMs nearly universally have booster stages, so they had to be enabled in data file for the required performance.

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For SRMs, the process is a bit different. SRMs follow the same energy rules as all other missiles, but they are in fact limited by their seeker - the max lock-on range, plus heatseekers leading algorithms are inferior to radar seekers, and they don't lead in the most optimal way. Purely ballistically, one could lob AIM-9 at  well over 20km with no problems, but you would be unlikely to lock on anything at that range.

Thus, as SRMs are designed for maneuver combat at close ranges, we simply pick the lesser energy state of the launch platform.

For simplicity, this would be 5k meters (IAS/TAS ratio of 0.8) and Init speed at 1 Mach, or 319m/s. Tune the missile so it would have the speed close to what you can find online, and range somewhat below it.

The game doesn't have good algorithms for heatseeker operation, and many vanilla SRMs have crazy lock-on ranges - it was not uncommon to lock and shoot with something like Python-3 or AIM-9M from 20km at target that doesn't even have the afterburners on. In my install I arbitrarily capped all SRM at certain ranges to prevent this.

[simonmiller416 1,197]

This thread is very useful, thanks! I will come back here when I get tired of A2A missiles that still fly 3 march at beyond 200 km.

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Regarding the "lofted missiles" part, I would like to share my point, although it may not be completely correct.

Many modern missiles claim to have a range of 160-200 km, such as the AIM-120D-P3 and PL-15. Obviously, as you said, these range data are achieved under a very ideal state, such as launching from 30000 feet, lofting, and then diving at a target aircraft that is almost motionless, at low alttitue and flying towards the missile carrier fighter.

Therefore, I will run the range simulation with the maximum range in their theoretical "no escape zone".

I put this into practice in the test of overhauling PL-15. When I ran the simulation, I considered the maximum range to be 80KM. So in the actual game, if I want to hit a target 150 km away, I have to climb to more than 20,000 feet and launch the missile at a speed of Mach 1.3.The missile has almost lost most of its kinetic energy when it finally reaches the target.For me, it is an ideal state.

Sadly, SF2's AI really doesn't seem to react too much to incoming AHMs (I don't know if that's possible),sometimes they don't even move ,therefore, it still has a higher probability of hitting.

If I attack a target at 10,000 feet, 150 km away, and im flying tangentially from below 5,000 feet and at less than Mach 1, my missiles will hit almost nothing.

 

Edited Friday at 05:44 AM by simonmiller416

[orsin 157]

Honeyfox and i found this issue 10+ years ago and that was why he put his time to code the missile range simulator.

The tool is very much a SF1 level simulation (which altitude effect is not gradual)

It still works on SF2 and can get a close enough result though. 

In general all stock missile range have problem. Start with those AA missiles.