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Glint effects on modern radar guided AAM's


KlarSnow

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Since Glint effects on missile seekers was added to guidance a couple of years ago, there has been a drastic increase in missiles (AIM-7's in particular) just missing their targets for no reason other than glint. This has compounded with the effects of chaff, jamming and the notch to make sparrows of all varieties have a particularly terrible success rate, even when fired with good parameters and doing everything possible to help the missile they still have a very poor success rate.

What is the desired rate of missing implemented by missile glint? I don't know what the implementation goal for this "feature" was, but I can attempt to derive what its actual effect in game is.

It is very hard to specifically quantify because there are so many factors that lead to misses, but I have done the best I can. 

My methodology was take a Hornet vs a veteran Mig-21Bis, remove Chaff and flare from the Fishbed. Set the Fishbed to never use Chaff and Flare, and never use ECM. Both start at 20,000 feet 45 Nautical miles apart. In the hornet I immediately select max AB and accelerate towards the Fishbed straight on, at 16.0 NM I fire one AIM-7M with a loft, and then at 15.0 NM I fire a second one without a loft. Upon second missile away, I immediately dive at a 30-40 degree angle to get underneath the Fishbed to prevent any notch or drop lock behavior while it maneuvers.

In all cases where the bandit does not drag and the missiles themselves did not get notched the missiles guided to a terminal intercept with plenty of energy left to guide to within fuzing distance.

After 24 shots that I have good tracks of(many more since I disregarded all attempts where the Fishbed turned completely cold and kinematically defeated my missiles) 21 of those missiles made it to a terminal intercept successfully

the 3 that I am not counting were: 1 was notched at long range, 1 was out dragged in the vertical, and the final one I'm not sure what happened but it didn't get close enough to have a chance.

A successful result (no glint) was both missiles fuzing on the target, lock was held after first missile impact and on multiple shots you can see the second missile impacting the wreckage after the first. 

Overall results: Of 21 missiles that successfully terminated with the target, 6 missed for no discernable reason. These I can only chalk up to glint causing a random guidance miss.

That is a success rate assuming everything works out perfectly of 71%. With a better than 1/4 odds that an AIM-7M will just randomly miss its target, without chaff, without a notch, and with energy to maneuver.

This is the second time I had run through this methodology, the first time half of my tracks didn't save correctly so I did it all again, the first time through out of 20 missiles, 10 completely whiffed. Combining the 2 sets of data that's 16/41 missiles that missed for no reason other than "glint" or a 61% success rate.

My question/issue is thus. Is this the intended miss rate for glint. I'm not contesting that glint is an issue for AAM's. I'm positing that this is far far too high an incidence rate of non fuzing misses for missiles that were developed in the 70's and beyond.

The declassified Navair 01-245FDB-1T F-4 Phantom Tactical Manual from 1972, lists the expected success rate of an AIM-7E as 85% chance of guiding to within 20 feet (page 1-161 if anybody who has it wants to look). we are currently showing 2-3 times that in failure rate. and that is for the AIM-7E. The AIM-7F has a specified Accuracy of 25 feet according to the SMC documents from 1976 and 1977. Again, if we hold that 85% value, we are still well outside of that.

1972 Navair 01-245FDB-1T page 1-161

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SMC 1976

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SMC 1977

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Why would an AIM-7M do worse than the AIM-7E or AIM-7F is expected to do in this situation.

Finally Glint has been a long studied and researched problem. All of these missiles were designed with Glint as a known issue and with it built into the guidance specifications. If you do some research on proposed glint reduction techniques, every single one pre-1960 generally references it as a filtering problem that is too complex due to the number of calculations required. However every single one of those techniques would immediately become a perfect application for the advent of computerized design in the late 60's and early 70's and you can find several references to exactly that happening.

Papers about Glint reduction theories

https://apps.dtic.mil/sti/pdfs/AD0857647.pdf

https://apps.dtic.mil/sti/pdfs/ADA266509.pdf

Paper about tracking target centroids that specifically deals with glint

https://www.osti.gov/servlets/purl/218705

The other side is that Glint is almost always referenced as a problem resulting in large miss distances for large targets, like bombers, not as much smaller targets like fighters.

My position is thus that glint effects are drastically overstated in DCS in the developing API, especially for all missiles that IOC'd in the 1970s. And that especially after 1980 there really should be no effect on the guidance of a missile that puts it outside of fuzing distance due to Glint. If out of those 41 missiles I had fired, 5-6 had missed (an 85% success rate) , I would consider that an acceptable failure rate, and within design specifications. However almost half to a quarter of the missiles just avoiding the target terminally is unacceptable. This level of random miss stacks with all of the other guidance issues missiles have to deal with to get to their target and results in ridiculously ineffective missiles. 

All 12 of the tracks and all 22 of the Tacviews for my tests are uploaded for anyone to take a look at. I specifically checked each one for end game notching, and for kinematics, there were missiles that pulled 8G's at .9-.85 Mach to make the intercept happen, so if a missile just missed on a 200 foot pass while only pulling 3G's and it had the ability to pull 4-5 more... then that's another problem that needs to get looked at.

GlintTracks.7z Glint repeat Tacviews.7z Glint whiffs.7z

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On 6/5/2022 at 2:41 AM, KlarSnow said:

My position is thus that glint effects are drastically overstated in DCS in the developing API, especially for all missiles that IOC'd in the 1970s. And that especially after 1980 there really should be no effect on the guidance of a missile that puts it outside of fuzing distance due to Glint.

Good work.

Glint should have an effect when the aircraft (or missile) maneuvers - the glint effect becomes more intense as the distance to target decreases (as opposed to other miss-distance factors!) and there are filters and other methods to deal with it.

My position is this:  AMRAAM has demonstrated the ability to repeatedly directly impact low-flying cruise missiles.   Physically, that is a small target.  If the missile had maneuvered, there would be a chance for a miss (but within fuze limits) due to glint.   We don't know the real numbers behind all of this beyond your AIM-7 report, but the point here is, that the effect of glint in DCS IMHO should be this:

1) If the target performs a maneuver (this to include a prop-powered aircraft potentially changing rotor RPM) like even a simple roll

2) If the target is flying near clutter

In both cases:

  * Immediately increase miss distance from the minimum.   This can be proportional or random, and the MAXIMUM (and minimum) would be based on knowledge about the missile era/technology capability

  * Once the target is stable again (including any form of steady acceleration) the miss distance penalty will begin to decrease, down to its minimum based on current conditions.  How fast it decreases would depend on the missile's technology.    Note, this is called seeker settling, though glint is not the only factor that affects it.

  * IN case 2, after a certain technology is introduced to a missile (probably digital filtering?) this should only raise the minimum miss distance and probably not too much.

  * ECM and Chaff.   You make your counter-measure money here 🙂


Edited by GGTharos
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1 hour ago, GGTharos said:

Good work.

Glint should have an effect when the aircraft (or missile) maneuvers - the glint effect becomes more intense as the distance to target decreases (as opposed to other miss-distance factors!) and there are filters and other methods to deal with it.

My position is this:  AMRAAM has demonstrated the ability to repeatedly directly impact low-flying cruise missiles.   Physically, that is a small target.  If the missile had maneuvered, there would be a chance for a miss (but within fuze limits) due to glint.   We don't know the real numbers behind all of this beyond your AIM-7 report, but the point here is, that the effect of glint in DCS IMHO should be this:

1) If the target performs a maneuver (this to include a prop-powered aircraft potentially changing rotor RPM) like even a simple roll

2) If the target is flying near clutter

In both cases:

  * Immediately increase miss distance from the minimum.   This can be proportional or random, and the MAXIMUM (and minimum) would be based on knowledge about the missile era/technology capability

  * Once the target is stable again (including any form of steady acceleration) the miss distance penalty will begin to decrease, down to its minimum based on current conditions.  How fast it decreases would depend on the missile's technology.    Note, this is called seeker settling, though glint is not the only factor that affects it.

  * IN case 2, after a certain technology is introduced to a missile (probably digital filtering?) this should only raise the minimum miss distance and probably not too much.

  * ECM and Chaff.   You make your counter-measure money here 🙂

 

GGTharos, as always DTIC has a paper for that.

https://apps.dtic.mil/sti/pdfs/ADA213452.pdf
 

from 1987 and very illuminating on miss distance and what factors affect what. Key note relating to glint….

2B658B7F-86EC-4AD2-B9BE-D48EC4DAEC2F.png

So 8 foot miss expected inherent to glint alone on a 32 foot wide (or long object) and yes this is why all of these shots were taken against a maneuvering target. Glint should not be much of a factor on steady state targets. Maneuvering targets are where glint can start to become more of an issue.

 

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