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Weapons & Countermeasures Modeling in Falcon 4.0:
Interview with Realism Patch Group's "Hoola"
by Paul Stewart[Paul] Id like to talk a bit about IR missiles. Could you explain how IR seekers work, what bands they cue off of, and what the principle difference are between 1st, 2nd, 3rd and 4th gen IR missile seekers?
[Hoola] Most IR seekers (other than new missiles like AIM-9X and ASRAAM) are what is called reticle scan seekers. They do not actually see a target, but rather sense the heat source. The seeker consist of a detector and a rotating reticle that "chops" the IR signal. Based on where the heat source is moving, this creates an error signal in the seeker, by shifting the phase of the tracking signal. The missile then guides by steering towards the direction of target motion so as to reduce the error signal.
The sensitivity of the seeker depends on the material. Some materials are more sensitive to the lower wavelength IR emissions that is more typical of afterburner temperatures, while some are more typical of military thrust temperatures. The earlier missiles are more sensitive to the lower wavelength IR emissions, and hence they need to see the tail pipe before they can track. For newer missiles such as AA-11 and AIM-9M, they are more sensitive to the higher wavelength IR emissions more typical of diffused exhaust plume from the engine, which is visible in the frontal sector.
AA-11 “ARCHER” IR ALL-ASPECT IR Missile
[Paul] There is also the matter or IRCCM of missiles. In Realism Patch 4.0, the oldest generation missiles bascially love going after expendable flares, but 2nd-3rd have "mediocre" IRCCM (like the AA8) and then the latest gen (AA11 and AIM(m) have superior IRCCM. How is it that missile become better at "flare rejection?"
[Hoola] It depends on how the guidance system is programmed. Missiles basically will track a heat source, the issue is how to make it distinguish between what is a flare and what constitutes a target. There are various schemes of implementing IRCCM, some of which are more robust than others. IRCCM is a guarded field, which I cannot discuss much about :-) Suffice to say that some schemes can be defeated quite easily, due to the lack of robustness in the tracking system that allows this exploitation. Generally, as electronics become more sophisticated, it becomes easier to incorporate the logic and programming required to implement more sophisticated IRCCM.
What I did in F4 was to tune the "flare chance" of the missile based on flare release from the target, and determine approximately the number of flares as well as flare dispensing frequency, that will decoy the missile. Nothing classified was used and the sources are all public.
F16 Deploying Decoy Flare
[Paul] Yes...also I believe you modeled ground clutter and other variables as affecting IR acquisition?
[Hoola] Yes, I did. The main thing is ground clutter. Tested by flying against targets in look-down low altitude scenarios, as well as look up with the sun in the background. Microprose did a pretty good job and I just made use of the underlying data structure to tune it.
[Paul] On the subject of IR detection, you recently modeled individual IR signatures and visual signatures for each aircraft in the simulation. Tell us how you did all this, and what factors you considered when arriving at the values that you did?
[Hoola] For IR signature, I took into account typical engine exhaust temperatures, presence of IR suppressors, propellers and rotor blades, bypass ratio, etc. Based on the temperature of each engine type, I compared the IR spectral emissions and then adjusted accordingly. You can find examples of this in the USN Radar and EW engineering handbook.
With respect to Visual Signature, this was done with Sylvain's help of course, to wire the signatures into the data files. For visual signature, it is based on visual acuity of the human eye. We determine the length and size of each airplane, and base on the visual resolution, we determine the range at which each airplane can be seen. For example, if the human can make out an object of 2 mils at a distance of 4 nm, then for a larger or smaller object, I worked out the range at which this object will become 2 mils to the human eye. The final number is adjusted for camouflage paint, atmospheric distortion and haze, etc., and of course, the ultimate judge is to pass this through real pilots in the RP Group (like John Simon) for a sanity check, as they know best the range at which they can spot a plane.
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