[EVALUATING] ASP for A-2-A gun use incorrect / Radar

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DCS: MiG 21BIS - Make the most out of the ASP Optical Sight and Sapphire Radar

A video tutorial showing how easy it would be to aim the Gsh-23 gun if the ASP used the Sapphire to get precise range to target rather than "fixing" it at .3km

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It would appear "300m" is the minimum firing distance, not maximum --i.e. you shouldn't be engaging targets below that distance so I am not sure why the ASP auto-gyro function is 'locked' at 300 meters.

Also, the ASP system should not jump when switching from 'auto' to 'manual'. So if you're tracking an air target in 'auto' and have radar lock on the target or fixed-beam pointed at it, the range slider should move and the angular correction knob should move as necessary and when you point the nose up to fire the cannon at the aircraft and lose radar lock, the distance and other settings shouldn't jump.

This makes perfect sense to me. Also they shouldn't 'reset' when you switch back to manual, the distance and angular correction settings should 'remember' their position.

This would aid in using the cannon and I don't believe the Russian designers would have the thing 'locked' to the minimum safe firing distance.

"Here you can see the ammunition being loaded. The aircraft's [su-25] now being fitted out with ammo. The gun fires over 2,000 rounds per minute. It can fire from a range of 300m to 2km. The minimum distance is set to avoid [getting hit by] its own debris. 300m is the MINIMUM firing range."

Also of note, the radar doesn't seem very good at picking out A-10s.

Even with the 'LST' filter engaged.

Considering their extra wingspan and all that... It's almost as if the radar were 'tweaked' to not pick 'em up.

I agree for small targets near the ground like attack helicopters this'd be a great tweak to stop newbs just targeting Ka-50s near the ground, flying near trees, from 100 miles away... but the A-10 pilots don't really need that kind of help. They have RWR, chaff etc. The Ka-50 has nothing.

And the radar... seems to return ground clutter noise even at altitude which is strange. If I point a laser at a mirror, the laser point only hits me in the face if I'm 90 degrees in front...

So I'm not really sure why the ground clutter returns such high values at a <= 45 degree angle.

I'd understand if the terrain was rugged, with a lot of hills and I was flying quite low. It'd be returning a bit more noise... but this particular radar seems to return more noise than anything else.

ps:

... However it even returns this ground clutter return when I've set it to +1.5 degrees... which means the antenna isn't even pointed at the ground... It just makes no sense to me.

The MiG-21bis RL operating manual that's been floating around for a while (one source) claims that the real MiG's gyro gunsight is indeed locked to 300m, and that best results are obtained between 250m and 350m firing range.

300m must be a minimum distance for the 30mm gun of a Su-25 engaging ground targets. And it makes sense. Engaging an airborne target you can fire even at 100m distance.

Shark, Your posts above are a bit confusing. Which of the things You mentioned are wrong and You can back it up and which You THINK are wrong?

As Fish mentioned above, when working in Aerial+Gun+Gyro mode ASP sight did have a fixed 300 m distance dialed in automatically. It's not because of minimum safe firing distance, but rather the only realistic distance you can hit any maneuvering thing with a cannon. Sure it can be used to hit stationary ground targets much further than that, but hitting a moving airplane is another "kettle of fish".

The aforementioned manual covers the whole topic of estimating speeds and lead angles needed during close range aerial combat, with a note that "the highest target hit probability is obtained in traversing firing [...] at ranges of 400-200 m". It also states, that if you used radar for range measurement and for some reason the radar was unable to lock the target (or the lock was broken) the sight was automatically jumping to a fixed 600 m range.

The altitude, at which ground clutter becomes an issue is quoted to be in the 2000-3000 m range, and although attacking techniques below these levels are described, it's clear they required lots of hocus-pocus with using built-in radar filters.

Another source posted in "Beczl era" of MiG development stated that RP-22 radar had an 0 to 500 m "dead zone", which I believe should be taken into account when trying to use it for air-to-air range aquisition.

I admit I haven't tested Leatherneck rendition of both sight and radar so thoroughly to see how precisely they do (or don't) match the data from archive documents, but the basic functionality seems to be OK.

Art-J wrote: "It's not because of minimum safe firing distance, but rather the only realistic distance you can hit any maneuvering thing with a cannon."

In a turning dog-fight perhaps, but a slower moving target moving in a straight line, an A-10, perhaps or an AH-64.

Remember it's an Interceptor! And it works on ground targets but whatever way it was put in the game makes using it against air targets extremely tricky!

When I use the labels to get range (because idiotic radar can't find the target) and setting the required distance on ASP (up to 1.2km) certainly works just fine (against said A-10/AH-64). Labels aren't available in multi-player however --nor real life.

So it works, it's just the A-2-A settings that are crazy. If I were head of a Russian design team and someone came up with the system working in this way... I'd have them shot for treason. ;-) The MiG-21 is designed for A-2-A combat.

I just find it curious why the radar can't do this ranging for me.

Art-J wrote: "Another source posted in "Beczl era" of MiG development stated that RP-22 radar had an 0 to 500 m "dead zone", which I believe should be taken into account when trying to use it for air-to-air range aquisition."

Yes. Exactly. The radar expansion/emission cone is quite limited at close range. I uploaded a visual reference for this because I noticed it straight away.

MiG-21BIS - RP-22SMA "Sapphire" Radar Visual Reference Chart v1.1

http://www.digitalcombatsimulator.com/en/files/921515/

It's interesting that tipping the nose up slightly will lose radar contact with a target (correct) but for some magical reason the radar returns show ground clutter even with the nose pointed up or with it not pointing at the ground at all (wrong)... And the magical invisible A-10s don't seem to show up even with their clunky, sub-sonic architecture.

And even pointing the radar at the ground it wouldn't reflect 100% of signal back because it would be refracted just like any signal. I'm a layman, but I'm also a savant, handy thing to know things without knowing how. %) It just seems wrong to me. :-)

Of course there would be reports of radar-returns at variable altitudes because they'd have probably pointed the radar-cone at a nearby mountain or something! :-P

If objects do not 'refract' radar emissions then these old stealth aircraft are an impossibility.

Art-J wrote: "I admit I haven't tested Leatherneck rendition of both sight and radar so thoroughly to see how precisely they do (or don't) match the data from archive documents, but the basic functionality seems to be OK."

It is awesome. :-) Don't get me wrong, I love it.

However, just like with the Ka-50... when you have such a complex flight model, adding to its difficulty with things that probably shouldn't be as difficult.. Not impressed with that. Especially with the gun-sight, when the ASP is meant to make using it that much easier. And did I mention it's an Interceptor?

I'm not sure what this 'authentic flight manual' is because all I've got access to were the documents that came with the game which are stated as having every component explained in detail, so please forgive me for not having 'authentic' flight manuals to compare to.

Fishbreath wrote: "The MiG-21bis RL operating manual that's been floating around for a while (one source) claims that the real MiG's gyro gunsight is indeed locked to 300m, and that best results are obtained between 250m and 350m firing range."

From the page linked above:

227. In attacking the target with gun firing in a maneuvering air combat, it is recommended to take aim with the optical sight in the GYRO mode, the 300-m fixed (constant) range being introduced into the sight.

When using the sight in this mode, set the AUTO - MAN, switch to MAN. and rotate the throttle lever handgrip all the way backward (the BREAKOFF light should come on in this case).

[i.e. you are within 300 m - : BREAKOFF!]

On detecting the target and recognizing its type, set the appropriate span on the sight outer scale; at a range of 400 to 500 m superimpose the central dot of the sight reticle on the target; the moment the target is framed by the range-finding ring, start firing, keeping the central pip on the target during the burst.

In that mode, aiming at a target maneuvering at a g-load of up to 3 g presents no particular difficulties (aiming is possible also under g-loads of up to 5 - 6 g, the (next page unavailable)

Fishbreath wrote: "claims that the real MiG's gyro gunsight is indeed locked to 300m"

Actually that is NOT what it says. It says you want to reset its range to close as possible using the Throttle rotator which should be 300m not 400m like it has in the game, the BREAKOFF light comes on (no sh** you are within 300m!) and THEN frame the target with the pipper and it should "presents no particular difficulties" even "aiming at a target maneuvering at a g-load of up to 3 g" from half a kilometer away.

This just proves my point.

It's difficult being a savant because everyone always shoots me down. If I were more aggressive and assertive in what I say, perhaps people would listen, but it's not my fault people only respond to aggression. They are f***ing mammals. God.

Also when it references a 'fixed' sight, it could be referring to the 'fixed net,' and not the pipper itself. The 'fixed net' is locked and has basic scales for engaging targets also.

Art-J wrote: "Your posts above are a bit confusing."

I sincerely apologise for confusing you.

Art-J wrote: "Which of the things You mentioned are wrong and You can back it up and which You THINK are wrong?"

Let me try and clarify, perhaps using your own references.

Art-J wrote: "As Fish mentioned above, when working in Aerial+Gun+Gyro mode ASP sight did have a fixed 300 m distance dialed in automatically."

Wrong.

As I clearly showed above, from that page he linked to, he either didn't bother to read it or his English isn't quite up to par. It in fact says exactly what I was saying. --That you can engage targets beyond 300m, that 300m is the BREAKOFF i.e. minimum safe firing range and that it should be 'easy' to engage moving targets beyond 450m.

Art-J wrote: "It's not because of minimum safe firing distance"

Wrong.

As the 'MiG-21bis RL operating manual' states, the BREAKOFF light lights up at 300m. The 300m safety-distance is most likely RF AF SOP.

Art-J wrote: "[it's] rather the only realistic distance you can hit any maneuvering thing with a cannon."

Wrong.

As the 'MiG-21bis RL operating manual' states, "Aiming at a target maneuvering at a g-load of up to 3 g presents no particular difficulties at a range of 400 to 500 m."

Art-J wrote: "The altitude, at which ground clutter becomes an issue is quoted to be in the 2000-3000 m range"

Most likely the pilot who 'quoted' that simply banked and a mountain entered the side of the emission cone reflecting a strong signal.

Art-J wrote: "Another source posted of MiG development stated that RP-22 radar had an 0 to 500 m "dead zone" "

I uploaded a visual representative of the emission-cone from different perspectives and you can clearly see at close-range it is quite narrow but not quite a dead-zone. Once you are familiar with it it ceases to be a mysterious 'dead-zone.'

The real 'dead-zone' is below the aircraft. Regardless it should be easy to use the radar for getting range information. The original ASPs were designed for use with ranging radar. This whole 300m limit idea is just asinine. It's wrong, a mistake and hopefully will be rectified soon.

Also when you bank in the MiG-21 the 'ground clutter' might return at medium altitude from the side but that's if it hits a hill or mountain, depending on the slope of the terrain.

Either way, banking to the right the return ground clutter shouldn't show consistent at the bottom of the display and should instead show on the right/lower-right depending on altitude. --I base this on the way it behaves with aircraft return signals.

If it knew exactly what was ground-return, and it appears to since ground-return behaves differently (than aircraft), it would be easy for the designers of the radar to have a filter to switch it off. This is not the case and it is just a quirk of how it was programmed. The ground clutter return is sync'd to the horizon, much as the radar-returns displayed on the FC3 MiG-29 & Su-27 rotate with the horizon.

(because idiotic radar can't find the target)

It sounds funny, because in reality that radar was even worse than in the game. :)

If I were head of a Russian design team and someone came up with the system working in this way... I'd have them shot for treason. ;-) The MiG-21 is designed for A-2-A combat.

:D

In real life a MiG-21 depended on a ground controlled interception unit (GCI) because of a very weak radar and little quantity of fuel. After you take off you start to receive commands from a GCI or an AWACS. Searching a target on your own is almost pointless thing. This plane is a pure interceptor.

It's interesting that tipping the nose up slightly will lose radar contact with a target (correct) but for some magical reason the radar returns show ground clutter even with the nose pointed up or with it not pointing at the ground at all (wrong)... And the magical invisible A-10s don't seem to show up even with their clunky, sub-sonic architecture.

The ground clutter when pitching up being still visible seems to be correct, as the radar is self levelling within the following roll and pitch angles:

Scan zone stabilization, bank angles: ±70°

Scan zone stabilization, pitch angles: +8° climb -25° dive

Once you have locked the target, it should be able to track the target in ±30° into all directions, even below the weapon axis.

However, anything below the weapon axis will create problems with ground clutter, possibly breaking the lock.

EDIT: Also talking about the minimum range of the radar of 500m, this probably has to do less with any sort of cone width, but more with the time it takes for the radar waves to travel from the radar to the potential target and back. They have to have some sort of intended (you have to filter out the reflections that the nose-cone itself creates) and possibly also unintended (response time of electronics) minimum range on that, which is probably the main factor for the minimum range of the radar.

First off, cut the attitude crap. Nobody likes a smart-aleck.

On detecting the target and recognizing its type, set the appropriate span on the sight outer scale; at a range of 400 to 500 m superimpose the central dot of the sight reticle on the target; the moment the target is framed by the range-finding ring, start firing, keeping the central pip on the target during the burst.

This is entirely consistent with using the sight as recommended. As you're closing in, align the target with the pipper. As soon as the pipper frames the target—that is, the target is 300m distant—begin firing.

In that mode, aiming at a target maneuvering at a g-load of up to 3 g presents no particular difficulties (aiming is possible also under g-loads of up to 5 - 6 g, the (next page unavailable)

The next page is available for me. It goes on to say:

"[...] reticule still remains in the field of view); the best precision in firing is achieved within the range of 250-350m."

It further goes on to describe the process for attacking a target with the fixed net sight.

It's difficult being a savant because everyone always shoots me down. If I were more aggressive and assertive in what I say, perhaps people would listen, but it's not my fault people only respond to aggression. They are f***ing mammals. God.

The way people respond to 'aggression' is by thinking you're a bit of a dick. Your arguments are based on a reading of the operating instructions document. (I don't know its provenance exactly; I do seem to recall hearing that it was provided to NATO pilots as an insight into the -21bis' capabilities.) There are some cases where I'm more than willing to allow that Leatherneck may have gotten something wrong, but they're MiG-21 experts and you aren't, and in this case, there is no evidence in your favor beyond 'things should work this way'. I've had enough experience with simulated Russian military hardware to understand that you just can't say that about it.

Mode wrote: "It sounds funny, because in reality that radar was even worse than in the game. In real life a MiG-21 depended on a ground controlled interception unit (GCI) because of a very weak radar and little quantity of fuel."

Thank you for your input, Mode. The radar is quite limited, I agree but some things in the game are IMO not quite up-to-par with the realism espoused in Digital Combat Simulator games.

Mode wrote: "Searching a target on your own is almost pointless thing. This plane is a pure interceptor."

I agree, but when you are within visual range and you are pointing the nose-cone right at the target and not getting anything, even though the target should be painted bright... I do not believe the radar was quite that useless.

xxJohnxx wrote: "The ground clutter when pitching up being still visible seems to be correct, as the radar is self levelling within the following roll and pitch angles:

Scan zone stabilization, bank angles: ±70°

Scan zone stabilization, pitch angles: +8° climb -25° dive"

That is fascinating, xxJohnxx, I didn't realize it was gyro-stabilized, but I think you may be confusing gyro-stabilization with manually directing the radar, please let me explain what I mean.

DCS: MiG-21bis manual, page 137:

"The Sapphire's antennae can't be manually moved up-down or left-right like in modern fighters. Instead, it will scan ±30° in azimuth, and -1.5° and +17° in elevation, searching for any targets at a maximum of 30 km distance."

"Basically, you don't need to do anything except to fly at an appropriate altitude in order to actually "see" the target with your radar."

So when you say it stabilizes to the horizon this makes perfect sense –otherwise it'd be getting return signals from mountains (within range) every time it banks.

I've created a graphic with the radar emission cone (-1.5° to +17°) and you can see that even with mountains in front and slightly below the aircraft they do not enter the emission cone.

And the gyro-stabilization you described means there should be even less ground returns!

xxJohnxx wrote: "EDIT: Also talking about the minimum range of the radar of 500m, this probably has to do less with any sort of cone width, but more with the time it takes for the radar waves to travel from the radar to the potential target and back. They have to have some sort of intended (you have to filter out the reflections that the nose-cone itself creates) and possibly also unintended (response time of electronics) minimum range on that, which is probably the main factor for the minimum range of the radar."

Thank you again for your input. IMO this is where the 'fixed-beam' mode would solve all these issues. The original ASPs were designed for use with ranging-radar and if I were designing this system I would simply use fixed-beam as ranging radar when in A-2-A gun-mode.

The radar control switches are 3-way switches.

• [RV62] RADAR OFF / STNDBY / ON
  
• [RV64] GROUND FILTER OFF / ON / TILT ANTENNA UP +1.5°
  
• [RV66] FIXED-BEAM OFF / ON
  

I would simply have 2 settings for Fixed-beam mode, A-2-G locked at -1.5° and A-2-A mode which would be a little wider, perhaps -1.5° to +8.5° so I could use the Fixed-net to aim the longitudinal axis (nose-cone) at an aircraft I was approaching and it would input the ranging information to the ASP to make its use more intuitive. --But that's just me.

The signal-returns from the ground should be much weaker than a target, painted bright and reflecting un-refracted signals directly back to the antenna and IMO this would be how the Ground Clutter filter system would work IRL.

It would simply ignore signal returns that are weaker up to a calibrated point. It could be done easily enough by the Russian engineers who created the whole thing back in the 50s.

So the radar's gyro-stabilization should reduce ground return because (as the example I created shows, even with mountains in front and only slightly below the radar does not point at the ground by default! It points up!

PS:

I think your Youtube vids are really great. :-)

Fishbreath wrote: "First off, cut the attitude crap. Nobody likes a smart-aleck."

Am I a "smart-aleck" ? I wasn't aware of any "attitude crap," thank you for politely informing me of your opinion. You have a gift also; for stating the obvious.

Fishbreath wrote: "The next page is available for me. It goes on to say:"

In that mode, aiming at a target maneuvering at a g-load of up to 3 g presents no particular difficulties (aiming is possible also under g-loads of up to 5 - 6 g, the reticle still remains in the field of view); the best precision firing is achieved within the range of 250 to 350 m.

So at high g-loads (5 - 6 g) the reticle still remains visible on the HUD at close range. Obviously. The best precision firing is achieved at 300m ±50m (250 to 350m). Closest possible range --obviously. At high g-loads and longer ranges the pipper leaves the HUD and can't be used as a reference to aim the guns. At close range targets are easier to hit. Obviously. This is all self-explanatory. It does not say anything about 300m being the limit at which you can hit targets. It says it is easier to hit targets which are at that distance (300m ±50m.)

It was describing the use of the ASP in MAN mode and how you use the Throttle rotator to adjust range to frame the target and fire as you will ("a target maneuvering at a g-load of up to 3 g presents no particular difficulties" even at half a kilometer distance).

It does not explain or mention or give a reason as to why the AUTO mode is 'locked' to 300m (in-game). It does NOT say you must wait until the target is at 300m. If I may, that is a stupid interpretation of a description of a tool with varying settings for use in varying environments.

What you say is the same as saying --that person who knows how to use a sniper-rifle says you must close to within arms length of the target before using the rifle because it's 'locked' at arms-length and it's the only distance you're likely to hit the target and I know it has a scope, but that's not to be used because you can see the target right there. And it says 'locked' somewhere, in some sentence from that book that guy wrote, somewhere.

Fishbreath wrote: "The way people respond to 'aggression' is by thinking you're a bit of a dick."

You should follow your own advice.

Fishbreath wrote: "I've had enough experience with simulated Russian military hardware to understand that you just can't say that about it."

A shame your English skills aren't quite up to task.

Fishbreath wrote: "I do seem to recall hearing that it was provided to NATO pilots as an insight into the -21bis' capabilities."

If you are anything to go by the Russians have nothing to fear. That is reassuring for some reason. I like Russians. :-)

Thank you again for your input. IMO this is where the 'fixed-beam' mode would solve all these issues. The original ASPs were designed for use with ranging-radar and if I were designing this system I would simply use fixed-beam as ranging radar when in A-2-A gun-mode.

 

I would simply have 2 settings for Fixed-beam mode, A-2-G locked at -1.5° and A-2-A mode which would be a little wider, perhaps -1.5° to +8.5° so I could use the Fixed-net to aim the longitudinal axis (nose-cone) at an aircraft I was approaching and it would input the ranging information to the ASP to make its use more intuitive. --But that's just me.

Yes, while this would be more intuitive, for some (probably technical) reason they didn't implement it. One explanation is, that the ideal gun engagement range of 300m is within the 500m blind zone of the radar.

That radar blind zone probably has to do with the minimum time it takes for the radio wave to travel from the radar to the target and back.

If the timespan it takes for the radio waves to do that is lower than what the analogue electronics can process, you just can't use them for ranging.

This is still a problem, even with very fast electronics. Many laser ranging systems (even in military vehicles such as tanks) have minimum ranges of various reasons. On systems that use the time it takes for the light-pulse to be reflected it is often because of the minimum time the electronics can measure. Don't expect a radar from the 1960s to not have such limitations.

The signal-returns from the ground should be much weaker than a target, painted bright and reflecting un-refracted signals directly back to the antenna and IMO this would be how the Ground Clutter filter system would work IRL.

 

It would simply ignore signal returns that are weaker up to a calibrated point. It could be done easily enough by the Russian engineers who created the whole thing back in the 50s.

This is by no means that easy you make it sound, unfortunately. The radar has to be way more sensitive than that. A radar return from an aircraft 30km away, is probably as powerful as a radar return from a house at the same distance. Filtering on signal strength probably would hide both.

Just as a comparison, in the normal operating mode the radar does even detect moisture in the form of clouds. That's a good indicator how sensitive the radar actually is.

Logically, the radar return of an aircraft is very depended on the size of an aircraft. Head on a bomber will be much easier to detect than say an F-4, as the radar return will be much more powerful. Filtering out on return strength therefore can be very dangerous, as you never know if you aren't filtering out potential targets as well.

So the radar's gyro-stabilization should reduce ground return because (as the example I created shows, even with mountains in front and only slightly below the radar does not point at the ground by default! It points up!

Let's take a look at this picture:

Source: http://www.mig-21-online.de/Funkmessvisier/fmv_UEH.htm

This is a photo from an RP-21 radar (the predecessor of the RP-22 (which is the one in the simulation)). In this particular photo you can see all the radar returns when the ground clutter filter is off. Every radar return on the screen is just from ground-clutter reflections. At the bottom of the screen we also have the returns as we often see them in the DCS MiG-21Bis when flying at a low altitude. We will talk about those in a second.

If you look at the top part of the radar screen, you will see a lot of returns as well. We don't normally see them in the MiG-21Bis, and that is for a reason. I will provide a post in a couple of minutes to explain why.

PS:

I think your Youtube vids are really great. :-)

Thanks! ;)

PS: One question about your radar scan zone diagram, why is it not a rectangle but more a circle? All information I could find about the RP-21 and RP-22 radar indicated that the scan zone is rectangular.

Hey, Shark-Bait, I'm just speaking the only language you seem to understand. I'm perfectly happy to have a reasonable conversation, but I'm not the one who called himself a savant and everyone else in the thread morons.

Unfortunately, you're wrong here, and since you seem to react to that sentence like a vampire does to garlic, I predict this conversation isn't going anywhere, and that you belong on my ignore list.

Anyway, one more time:

1) 250-350m is the best range for accuracy on maneuvering targets.

2) The radar has trouble providing lock/ranging information on targets within 500m.

3) Since AUTO mode is the one you'll be in most of the time, and since it gets hard to flip switches once you're in close with a maneuvering target, it makes sense that the fewest switch flips to select the gun gets you a reticule setup which is most useful in close-range dogfights against maneuvering targets.

4) Since you can be much more methodical in your approach to a bomber, if you want to use the gun at longer ranges, you can switch to MAN and follow the more complicated, less dogfight-ready manual ranging procedure.

Okay, as promised, let's talk about the radar and the ground clutter it displays:

Let's first take a look at this screenshot:

In this situation, the aircraft is flying level, 500m above the ground.

If you look at the radar screen you can see ground clutter returns from 0 to 5km.

Now let's draw something in paint and do some maths:

Yes, I do have the paint skills of a 5 year old.

If our altitude is h = 500m and the radar scans 1,5° below the horizon (angle a) (stabilised) we can calculate the distance d where the ground clutter should appear on the screen.

 d = h / tan(a) = 500m / tan(1,5°) = 19094m 

This means, that the lowest part of the radar beam intercepts the terrain at an distance of 19km. Therefore the ground clutter indications have to start in that distance and continue to the maximum range of 30km.

But wait, in the screenshot I posted there are no reflections up there. The only reflections we can see are from 0 up to 5km. This is well within the 19km it takes for the lower part of the radar beam to intercept the ground (and therefore we should not be able to see it).

So in theory our radar should not even be able to see that ground clutter at that distance, still it does. Why?

The reason this happens is something that has been a problem with antennas ever since and still is. It does not matter if you build an antenna for a radar or you build an antenna to communicate with satellites, you will always have so called side lobes. Side lobes are electro-magnetic waves that are emitting into another direction than the main part of the antenna it self.

Source: https://earth.esa.int/handbooks/asar/aux-files/ephimg-20188850.gif

When you build a communication antenna, you do all you can to minimize those side lobes, because they don't add to your transmission but still consume power.

When you build a radar, this is also true, but with the additional effects.

The ground clutter that is displayed on the radar at a distance from 0 to 5km is exactly one of those additional effects. While the main lobe is not being reflected from the ground (as it only reaches the ground 19km as calculated previously), the side lobes that are possibly emitted straight down, are. These side lobes, that are reflected from the ground at very steep angles (therefore a lot of the signal returns) create that ground clutter at the bottom of the display. Due to the amount of reflection, the low altitude filter does not do much and the low altitude radar elevation does even less, as the side lobes are just moved a little bit.

The only time you do see ground clutter on the radar screen that is not created by side lobes, is when you are in a very steep dive (> -25°, because the earlier mentioned self levelling of the radar).

This looks like this:

In the screenshot you can see that those reflections seem to appear at a correct distance of 15-30km.

In such a situation both low altitude radar modes (filter and lifting the radar) do have an effect on the radar returns displayed.

I hope this answers the question about the ground clutter displayed on the radar to some extend.

It seems to be fairly well simulated, although it is hard to tell if there should not be more ground clutter all over the screen (not just the bottom) in some situations. For example, when you fly at 100m above ground, the -1,5° depressed radar beam reaches ground just 3km in front of the aircraft, and it therefore should create a high amount of ground clutter all over the display. This would also be the point where the second low altitude mode for the radar would start to come in handy.

Best regards,

John

Thank you for that very informative explanation John, I really appreciate it.

Your explanation is awesome and very easy to understand. :-)

xxJohnxx wrote: "PS: One question about your radar scan zone diagram, why is it not a rectangle but more a circle? All information I could find about the RP-21 and RP-22 radar indicated that the scan zone is rectangular."

It was just meant to be something quick for my own reference with the circular radar display. :-P I should have used rectangles, I guess!

xxJohnxx wrote: "One explanation is, that the ideal gun engagement range of 300m is within the 500m blind zone of the radar."

I did say I am a layman and in-game in A2G mode, the radar ranging seems to work just fine up to 400m (minimum on CU30 scale.)

However I really appreciate your detailed explanation and any other person who is not familiar with these things and also has questions now have your posts to explain why the radar sucks! ;-)

I did say I am a layman and in-game in A2G mode, the radar ranging seems to work just fine up to 400m (minimum on CU30 scale.)

Yes, this is a good point actually. This is also something that confuses me.

This German MiG site has a lot of information about the export version used by Germany. Unfortunately their data is about the RP-21, where it says that the dead zone is from 0-300m and the ranging zone begins at 500m. However, I am not sure how it looks about the RP-22SM simulated. It is very hard to find any information on that online. It appears to be even harder to find any information about the ASP sight. Hard to tell what is correct and what is not.

In such situations knowing Russian would come in handy, because there seem to be quite a lot of knowledgable guys over in the Russian parts of this forum.

Fishbreath wrote: "I'm perfectly happy to have a reasonable conversation, but I'm not the one who called himself a savant and everyone else in the thread morons."

I never called anyone a 'moron,' you liar. Interesting that you are so deluded that, to quote you: "cut the attitude crap", "Nobody likes a smart-aleck." "The way people respond to 'aggression' is by thinking you're a bit of a dick", is being reasonable.

You commented on my profile: "Fortunately, the ED moderators are sufficiently ban-happy that I doubt you'll be around long enough to really get on anybody's nerves."

In other words you were a little itty-bitty bit embarrassed because you were shown to be incapable of reading simple English and you think that because I said politely, that IMO that was a "stupid interpretation" of what you were quoting... That you will have the 'Mods' ban me?

Remember, you started the name-calling. All I did was call you stupid, which is probably a more polite term than you deserve.

I'm a little dyslexic so I've grown up my whole life being called stupid, called a cheater in school for knowing answers without providing how I knew. So to put it bluntly, Fishbreath, your handle fits your personality to a 't', but that doesn't bother me.

What bothers me are threats, which you have made and I hope that any 'Mod' on this forum will agree that threats are not good, for anyone.

This German MiG site has a lot of information about the export version used by Germany. Unfortunately their data is about the RP-21, where it says that the dead zone is from 0-300m and the ranging zone begins at 500m.

If I may, xxJohnxx; it shouldn't be our job to do all this work for the developers. I love the MiG-21bis. Hopefully when all the creases get straightened out it will be even more awesome.

The devs could even have a Bison or similar version with R-77 capable upgraded avionics and radar. :-) That'd be awesome.

In such situations knowing Russian would come in handy, because there seem to be quite a lot of knowledgable guys over in the Russian parts of this forum.

Yeah. :-/ I'll just have to learn Russian. xD Serious.

I posted links to your detailed radar explanations up on that kneeboard radar-cone graphic I made so anyone who views the comments can see the links.

If I may, xxJohnxx; it shouldn't be our job to do all this work for the developers. I love the MiG-21bis. Hopefully when all the creases get straightened out it will be even more awesome.

 

The devs could even have a Bison or similar version with R-77 capable upgraded avionics and radar. :-) That'd be awesome.

 

 

 

Yeah. :-/ I'll just have to learn Russian. xD Serious.

 

I posted links to your detailed radar explanations up on that kneeboard radar-cone graphic I made so anyone who views the comments can see the links.

And what work would that be?

It is troubling to find that some users think they are automatically in the right.

We read everything posted on this forum. Legitimate issues get fixed, non-legitimate, not so much.

No more hostility in this thread, from anyone, please.

And what work would that be?

 

We read everything posted on this forum. Legitimate issues get fixed, non-legitimate, not so much.

I hope my posts in this discussion where not interpreted as such.

It was meant to try and figure out what's going with the radar and see how it works instead of pointing out something that is wrong.

Although I haven't found anything yet that seems wrong anyway.

The signal-returns from the ground should be much weaker than a target, painted bright and reflecting un-refracted signals directly back to the antenna and IMO this would be how the Ground Clutter filter system would work IRL.

 

It would simply ignore signal returns that are weaker up to a calibrated point. It could be done easily enough by the Russian engineers who created the whole thing back in the 50s.

 

QUOTE]

 

Hello Shark, your understanding of the "how it should be" is really great. Could be near engineer Level. But as always this is simply theoretically and in this case not correct. I can't comment on all of the features you brought up but as a former FFG radar operator I can surely tell you that your above theory is wrong.

Using a WM25 2DRadar and the DASA TRS3D ground (or sea) clutter was always a major problem in detecting targets. Don't forget that the ground is no sandbox but has buildings, lighthouses, even big stones that can reflect better than a small fighter. To get deeper into it I would recommend to compare radar cross sections of different airplanes from different aspects. When comparing that to a garage you can imagine which will Show up brighter on your screen :smilewink:

 

In modern systems that will even track the weakest contacts, speedfilters are used most of the time. If the contacts are moving above an specified speed, the system will handle them as contact, otherwise ignore them. I don't think that this technology was available during the 70's.

 

But even with these methods it is no secret that sometimes trains moving on coastlines or even swarms of bird's were interpreted as low flying helicopters or speedboats :music_whistling:. All these things (birds, trains, houses, Stonehenge.....) are treated as clutter so far for my fellow operators.

 

EDIT: The rcs front aspect of a F-4D is around 3,7 sqm, that of a MiG-21 1,3 sqm. My garage has a front aspect rcs of 6,2 sqm :thumbup:

I hope my posts in this discussion where not interpreted as such.

It was meant to try and figure out what's going with the radar and see how it works instead of pointing out something that is wrong.

Although I haven't found anything yet that seems wrong anyway.

Not at all John, was not referring to your posts at all. :)

I really appreciate your posts!