MiG-21bis and fixed beam radar

Im a bit curious about the fixed beam radar mode on the Mig-21bis.

From the information we have, Kh-66 "Grom" and RS-2us missiles are beamriders,

not really compatible with the RP-22 radar we have in sim (those missiles are for gameplay purpose or for simulating/roleplaying cheaper export Mig-21bis with RP-21 radar).

There has been several threads over the years about the ASP sight, what is working and what is not functioning like it should. Trying to filter those threads it seems like the real life MiG-21bis does not actually have a "ccip" mode for rockets and bombs (like we have now)

If that is the case. What is the purpose of the MiG-21bis fixed beam mode in real life operation? It is not used for guiding missiles, so I guess it has something to do with getting the range of targets. Maybe only used for A-A radar rangeing with the 23mm cannon or for IR missiles without radar lock?

Anyone that has more information about the fixed beam usage on the MiG-21bis?

From old manuals I have read: It's an old school analog to a boresight/gunnery radar.

It appears for firing at ground targets:

Flight for Launching Rockets at Ground Targets

Flight for Gun Firing at Ground Targets

Oddly it's not mentioned in the Bombing Mission section where one assumes it would be most useful for slant range determination which is so critical to release timing. On the other hand the rocket aiming angle is almost exactly this 1.5 degree fixed beam depression where it is significantly different for bombs. In this case perhaps the barometric slant range unit is more reliable or the fixed beam being not along the aiming direction is deemed not acceptable.

I don't see any reference to using the fixed beam in any capacity in the air to air attack.

Use of fixed beam mode for RP-21 does make mention of air to air attack use including failure to switch to auto tracking mode (interference, low height, cloud reflections). Partial failure of RP-21 (direction finding channel). Group target engagement where auto tracking cannot resolve individual targets due to their spacing.

The fixed beam of the RP-21 makes a very large 10° footprint because it is nutating the 5° primary beam in a circle. The RP-22 on the other hand may or may not be capable of a much smaller beam area despite having a similarly large beam (3-4°) because it effectively has four channels of reception and can only concern itself with the region of overlap which can be much smaller than the size of the beam itself. If the radar is optimized for the air to ground attack it may have only a small angle in which the distance is measured.

Thanks for info Frederf!

In that case, using fixed beam for A-G rockets and cannon seems like the procedure used in the real MiG-21bis. Strange about not use radar for bombing, since, for example, the F-86F had radar-assisted bombing already in the 1950's, and the MiG-21bis entered service in 1972.

On the other hand, 1970's/1980's F-5E Tiger II does not use radar for bombing, so it might be correct that the MiG21 does not use it either..

One other thing about the fixed beam mode. I have been trying to use it with the RS-2US missile. but it seems like it only works in auto tracking mode, very strange for a beam rider. I know it is made for the RP-21, but from what I remember - in DCS you could fire it in fixed beam without "locking" the target? In theory we should be able to fire it at ground targets too, but I don't think that was ever implemented in DCS.

Maybe RP-22SMA can use radar for ranging. I don't really know what happens when you try or when you set ASP switches for auto and bombing. Manual is made to tell you what to do, not what is possible. I'm guessing it's because LOS to target and fixed beam direction were different so avoided use.

RS-2US used to work fine on fixed beam but some update inhibited missile firing unless locked so now RS-2US can't be fired on the beam as per reality. I'm not sure if RP-21 could support RS-2US in auto tracking mode in addition to fixed beam. Presumably yes if the autotracking mode was a spin-scan beam the same as fixed beam (but following target). Missile wouldn't know the difference.

I tried to use tracking to get firing and then switch over to fixed beam... no joy. It's clearly the case that in DCS module both missiles are using SARH logic and not beam riding logic. Both missiles do impossible and incorrect maneuvers compared to beam-riding behavior.

I read somewhere that RS-2US was modified over the years, either by attaching IR seeker (making it into the R-55) or modified with semi active seeker. But I have not found more information about this supposed semi active modification :noexpression:

Here is a detalied description about the RS-2US produced under license in Romania 1984, no semi active, but very informative in how the missile works.

https://www.rumaniamilitary.ro/armament-de-aviatie-produs-in-romania

also for R-3S/R-60

https://www.rumaniamilitary.ro/racheta-aer-aer-autodirijata-in-infrarosu-a-91

https://www.rumaniamilitary.ro/rav-rs-racheta-romaneasca-de-top-ir

There has been several threads over the years about the ASP sight, what is working and what is not functioning like it should. Trying to filter those threads it seems like the real life MiG-21bis does not actually have a "ccip" mode for rockets and bombs (like we have now)

 

If that is the case. What is the purpose of the MiG-21bis fixed beam mode in real life operation? It is not used for guiding missiles, so I guess it has something to do with getting the range of targets. Maybe only used for A-A radar rangeing with the 23mm cannon or for IR missiles without radar lock?

 

Anyone that has more information about the fixed beam usage on the MiG-21bis?

There is a limited "CCIP" mode for gun and rockets, just not for the bombs. You can turn off CCIP for bombs in DCS options.

The radar can be used for ranging in both ground and air attacks. I read the real manuals some time ago and don't remember right now but I think you would get CCIP for ground attacks only with radar in "fixed beam".

You can turn off CCIP for bombs in DCS options.

Where? I can only find an option for the IR arcade mode, but not for unrealstic bombing.

IIRC this option also turns off the bombsight

Unfortunately not

There is a limited "CCIP" mode for gun and rockets, just not for the bombs. You can turn off CCIP for bombs in DCS options.

 

The radar can be used for ranging in both ground and air attacks. I read the real manuals some time ago and don't remember right now but I think you would get CCIP for ground attacks only with radar in "fixed beam".

Thanks for further info. I have the Realistic ASP IR A-A Missile Reticle selected in Special Options selected, If that is what you mean?

Fixed beam for rockets works very nicely, just enter A-G mode, flick the fixed beam switch - put reticle over target and wait for launch light.

I read somewhere that the ASP in DCS: Mig21bis is not implemented correctly, so how should I go about bombing without the "ccip" / fixed beam? (for maximum realism?)

Another thing I have found interesting is the three "lock-on" lights on the right side of the ASP. Indicating both R55/RS-2US and R-60 lock.

But I have never seen a picture of a real life R-55+R-60 loadout.

Fixed beam mode have two purposes:

1. In A-G mode, measuring distance to earth surface for rockets and canon use,

2. In A-A mode, measuring distance to air target in heavy jamming conditions, when RP-22 radar functionality is minimized ( all anti-jamming technics not working, most of them not present in module) then pilot switches radar to "fixed beam" mode and points whole aircraft to target in order to get distance readout.

You never saw picture with R-55 because those missiles were never sold outside USSR, and even in USSR were in use mostly on Su-9 interceptor ( the plane for which they were created in the first place ).

Thanks for further info. I have the Realistic ASP IR A-A Missile Reticle selected in Special Options selected, If that is what you mean?

 

Fixed beam for rockets works very nicely, just enter A-G mode, flick the fixed beam switch - put reticle over target and wait for launch light.

 

I read somewhere that the ASP in DCS: Mig21bis is not implemented correctly, so how should I go about bombing without the "ccip" / fixed beam? (for maximum realism?)

 

Another thing I have found interesting is the three "lock-on" lights on the right side of the ASP. Indicating both R55/RS-2US and R-60 lock.

But I have never seen a picture of a real life R-55+R-60 loadout.

In real life you would have bombing tables with various trajectory parameters, set the sight manually for correct depression or use markings on a fixed net, and fly the bombing profile maintaing speed, altitude and dive angle according to the tables. In game we don't have tables, bomb ballistics are probably different and sights are likely not calibrated, so it's pure luck and "feel".

ASP for rockets works mostly like it would in real life, except it gives you wind correction which it wouldn't in real life (no doppler, can't measure drift angle), ignores radar fixed beam setting, ignores CC/Gyro setting, the range dial IIRC is incorrect and allows for mixed payloads, while in real life the ballistic calculator could be set on ground only for one type of rockets. So yeah, it's "mostly" accurate simulation, lol.

The lights for R-55 are there because the rockets didn't generate audio tone when locked on target. The light for R-60 is there next to them not because it was some sort of mixed payload design, but because in analog aircraft like this (relays and switches), it was easier to install another light than to plug R-60 into R-55 launching circuits. :)

Wow. That is really cool info on the R-55 missile. I did not know that the R-55 didn't produce a tone. But why put a light for the R-60?

Trying to figure out some early MiG21bis loadouts and I wonder what usually went with the R-55...

Possibly because R-60 can be dual racked and lights show which on rack is locked? R-60 dual rack is smart to select and fire the missile with the best lock quality so it won't always fire in the same order.

R-55 is essentially RS-2US changed from radar beam to forward looking IR seeker I think directly taken from R-3S. RS-2US does not lock on so there is no point of such an indication. Maybe radar signal can be fed directly into missile while still captive just to prove circuits work (similar to how tone test works for R-3R). Polish manual warns that when R-3S was carried (outboard) of R-55/R-13 that latter missile must be fired first.

ASP-PFD-21 does not do "CCIP" for rocket attacks. Best it can do is set a single preset vertical angle when in automatic mode (e.g. 1.5 degree) but it is not changing based on other parameters so it is only accurate for rated condition. I think different rocket types can have different preset fixed angles for automatic.

ASP does not ignore CC/Gyro lever as it is a physical lock of the reflecting mirror and is also detected in circuitry. AG rockets can be delivered with either, CC being recommended if pilot is not very experienced with the "floating" sight in this type of attack.

On the other hand ASP does do variable vertical angle for AG cannon according to range, similar to AA cannon use.

No manual describes bombing except by manually entering a vertical angle with mirror fixed "CC." The radar or if radar not valid the slant range unit (calculating by attitude gyroscope and baro height) would supply ASP with range information.

 

ASP-PFD-21 does not do "CCIP" for rocket attacks. Best it can do is set a single preset vertical angle when in automatic mode (e.g. 1.5 degree) but it is not changing based on other parameters so it is only accurate for rated condition. I think different rocket types can have different preset fixed angles for automatic.

I think we've had this discussion already :)

There's a lengthy chapter in the manual on how the system works when doing "CCIP" for gun AND rockets. The fixed angles are used only in case of slip/aoa sensor failure or when the pilot locks the moving sight in place by switching it to CC position.

If this was as simple as setting fixed angle all the time, they could just stick with the angles manually entered by the pilot, like on the L-39 or F-5, and get rid of all the complexity.

Wow. That is really cool info on the R-55 missile. I did not know that the R-55 didn't produce a tone. But why put a light for the R-60?

Probably redundancy. Audio signal could get distorted or pilot could have trouble hearing and discerning when the missile locked.

It is a Bore sight , when in that mode and in a fight just get him in front and hit the lockup key and your radar missiles are good to go.

It does work as advertised, I use this frequently with good effect.