Su-35 Irbis

[TorwaK]

Su-35's PESA radar.

 

[Kusch]

Another:

 

http://www.youtube.com/watch?v=yELuKJFDM80&

 

And pics (down on site):

 

http://maks.sukhoi.ru/maks2007_3.htm

[VMFA117_Poko]

Im a noob. Can You explain me what profit comes from rotating the plate when it's centered?

[TorwaK]

it's about attain to radar signal to wide angles stable.

[VMFA117_Poko]

No. I mean why it rotates in straight, centered position.

[TorwaK]

IMHO it returns to starting position. I mean like a circle... starts from 1.....10 and again return to 1.

[EvilBivol-1]

Im a noob. Can You explain me what profit comes from rotating the plate when it's centered?

On the contrary, it has to do with being poor. I'm not expert and could be wrong, but as I understand it, what a "normal" (Western) radar does with software (adjust for aircraft roll), Russian radars do with hardware (actually roll the antenna). This is why there are limits on aircraft roll in certain radar modes.

[Weta43]

I'd have thought that unlikely with a PESA radar, given the fact that the beam is synthetic & electronically steered anyway... I think it's more likely that (& I have a vague memory of actually reading this) it allows the following : if the radar has a "natural" scan capability of say for arguments sake +/- 50 degrees either side of center (100 degrees total) with the antenna pointing straight ahead, and you can mechanically turn the antenna horizontally at right angles, you can now track (& keep locked) something that is 50 degrees "behind" you (40 degrees off your tail - allowing you to fire, turn & retreat, while still guiding either a SARH or an ARH missile that has yet to go 'active'), and if you turn it downwards you can still be locked on something with your multimode radar that you've actually overflown...

 

The end result being something not much inferior in coverage to that given by mounting a backwards facing radar in the tail (something the Russians have shown an interest in for a while), but only needing one radar, & allowing a full size, full feature antenna to be used...

 

 

(Interesting thing I just noticed - according to the symbol below left, I'm actually offline as I write this !)

[EvilBivol-1]

I think we are talking about different things. What you are describing is slewing the antenna to either side of the nose. I believe Poko was asking why the radar also rotates (rolls) around the aircraft's horizontal axis. The answer, I think, because it is the only way it can compensate for aircraft roll.

 

AFAIK, the MiG-31's fixed PESA radar forces severe roll restrictions on the aircraft. Even though the beam is electronically steered, it's so strictly in the vertical and horizontal axes. When rolling the aircraft, software is required to process the signal to compensate for the roll. Russian radars lack this. What we are seeing in the Irbis is that the problem still hasn't been solved and the only solution the designers could come up with is to roll the entire antenna. Should we add a link to the thread about the state of Russian aviation? ;)

[Weta43]

I believe Poko was asking why the radar also rotates (rolls) around the aircraft's horizontal axis.

 

From watching the vid it looked to me that they'd just mounted the dish to swivel on a single axis ,then rotated that axis to get movement in the other plane ...

 

What I assumed was that they would already have had experience with similar gimbal system from previous radars & the most obvious solution for mechanically augmenting the scan limits was to adapt existing systems

 

AFAIK, the MiG-31's fixed PESA radar forces severe roll restrictions on the aircraft. Even though the beam is electronically steered, it's so strictly in the vertical and horizontal axes. When rolling the aircraft, software is required to process the signal to compensate for the roll. Russian radars lack this.

 

- In the 70's (and think back to the state of computers & coding at that time), when the Russian's were writing the software for what was the first electronically scanned radar deployed in a fighter, they perhaps lacked the processing power and expertise to code in an ability to compensate for roll (or maybe they decided to keep processing requirements down in a plane that wasn't designed to be engaging in dogfights anyway).

 

I seriously doubt that given the advances in both computer hardware and programming that have happened between the 1970's and now, Russia has been unable to find a team that could write some code to compensate for roll :-)

 

In this day & age does that really seem likely to you ?

 

Even if you couldn't find anyone in Russia up to doing the job - which I seriously doubt, how many man-years of software genius could you hire from developing nations for the cost of a single fighter ?

 

If you have software to compensate for the plane's roll, it will also compensate for the dish's roll, & so the method of acheiving the movement is neither here nor there, and given the obvious advantages of coupling mechanical steering with electronic scanning, I think a more likely scenario is that they've simply applied existing & proven mechanical steering designs to the problem of moving the dish (especially given your comments about being cash strapped - why re-tool when you already have something that will do the job).

[Pilotasso]

YEah, if Russian cant write code to compensate roll for a PESA antenna, then I wonder what else is lacking?

[mvsgas]

I don't know nothing about RADAR and RADAR systems but why does the radar rotating makes it less capable. It looks like to me it does that to keep a target( ground or air) lock while the aircraft maneuvers, I don't know about the RADAR looking 40 or 50 degrees behind the aircraft, would that give radio radiation to the pilot? I know RADAR can literary cook you from the inside out if your hit with it from to close. Sorry just wandering

[Trident]

If they really need mechanical roll compensation that would certainly indicate something is seriously amiss. I tend to agree with Weta, most likely the intention is to have only one gimbal for slewing around the vertical and horizontal axes. The further aft you can mount the radar inside the radome, the bigger you can make the antenna. Does the Bars antenna roll?

[Excelsior]

My thoughts.

 

Rotation as seen in the second vid would be needed if you roll your craft while tracking anything off angle.

Rotation like in the first vid (rotation in straight, centered position), is this used while in flight? Could be used as a visual thing just to wow the crowds and for demo purposes.

[EvilBivol-1]

I seriously doubt that given the advances in both computer hardware and programming that have happened between the 1970's and now, Russia has been unable to find a team that could write some code to compensate for roll :-)

 

In this day & age does that really seem likely to you ?

Stranger things have happened... Personally, I'm convinced.

Even if you couldn't find anyone in Russia up to doing the job - which I seriously doubt, how many man-years of software genius could you hire from developing nations for the cost of a single fighter ?

 

If you have software to compensate for the plane's roll, it will also compensate for the dish's roll, & so the method of acheiving the movement is neither here nor there, and given the obvious advantages of coupling mechanical steering with electronic scanning, I think a more likely scenario is that they've simply applied existing & proven mechanical steering designs to the problem of moving the dish (especially given your comments about being cash strapped - why re-tool when you already have something that will do the job).

All Russian 4th generation fighters were limited in roll. This limitation has apparently survived into today's Irbis. Whether due to a lack of technological capacity, linear design evolution or questionable design choice, I don't know.

It looks like to me it does that to keep a target( ground or air) lock while the aircraft maneuvers

Exactly right, except Western radars are able to do this without having to physically roll the antenna. This "feature" adds weight and complexity to the design and demonstrates a technological gap.

Does the Bars antenna roll?

Yes, as does the N-001 and N-019... all of them presumably for the same reason... :)

Rotation as seen in the second vid would be needed if you roll your craft while tracking anything off angle.

Rotation like in the first vid (rotation in straight, centered position), is this used while in flight? Could be used as a visual thing just to wow the crowds and for demo purposes.

In a modern radar, rotation should not be necessary at all (see Western examples).

 

Let me just say that this whole thing is an opinion forwarded by a number of people on the Russian forums over the last year +. Given my teenage-level of knowledge in this area, I won't argue the point any further myself, but I'm absolutely confident in the correctness of their thinking.

[Trident]

Yes, as does the N-001 and N-019... all of them presumably for the same reason... :)

 

Why is it credited with additional mechanical scan in the horizontal plane only (unlike Irbis) then? Wouldn't Bars be capable of mechanically slewing the antenna in the vertical plane as well if it was able to roll, similar to what the Irbis demonstrates in that video?

 

I suppose your sources are better than mine though.

[tflash]

I simply do not even start to understand this argument. Something essential about radar must be escaping me if this reasoning were true.

 

Would you really mean that, If I were to roll around my axis in a Mig-29 several turns, I would lose lock? Because I just cannot imagine the radar can turn unlimited?

 

Would it not rather be to compensate the angular deformation of the beam when you are slewing the antenna sideways? So that the roll is just part of the angular rotation?

[EvilBivol-1]

Would you really mean that, If I were to roll around my axis in a Mig-29 several turns, I would lose lock?

Su-27SK flight manual, page 152:

"To avoid loss of automatic tracking [lock] when radar is SOI, maneuver the aircraft within 90 deg. of bank." I believe ED had actually modeled this in one of the game versions at some point.

Because I just cannot imagine the radar can turn unlimited?

That's correct, I believe it can roll through +/-120 deg.

 

Note, it's quite possible that some kind of contact prolongation kicks in and the attack can continue against the "synthesized" target. Actual contact, however, is lost.

 

Note also, this may differ depending on the specific radar and especially on specific radar modes.

 

Finally, keep in mind the quote from the manual is for an export Su-27 model and may not accurately represent domestic aircraft, although the general issue remains.

Would it not rather be to compensate the angular deformation of the beam when you are slewing the antenna sideways? So that the roll is just part of the angular rotation?

Correct again. Officially, the radar changes polarity (what is normally a vertical scan becomes a horizontal scan) when slewed to the side for air-to-ground operation. Informed observers, however, see this "feature" as a "bug." :) The issue isn't settled and not everyone agrees, but I go with the skeptics and conservatives on this one.

[EvilBivol-1]

Why is it credited with additional mechanical scan in the horizontal plane only (unlike Irbis) then? Wouldn't Bars be capable of mechanically slewing the antenna in the vertical plane as well if it was able to roll, similar to what the Irbis demonstrates in that video?

I dunno, will have to do some searching... :)

[Trident]

Finally, keep in mind the quote from the manual is for an export Su-27 model and may not accurately represent domestic aircraft, although the general issue remains.

Correct again. Officially, the radar changes polarity (what is normally a vertical scan becomes a horizontal scan) when slewed to the side for air-to-ground operation.

 

That's a good point, using mechanical rather than electronical roll compensation is a popular way of downgrading export radar sets. Notional export variants of the British Blue Vixen would have followed that path, IIRC. I certainly doubt even the domestic N001 would have electronic roll compensation, but I'd fully expect most Russian PESA arrays to feature that technology. There are a number of systems with completely fixed arrays, after all (Zaslon, Zaslon-A, -M, -AM, Zhuk-MSF, Kopyo-F, B004 and as mentioned above, I was under the impression that the Bars antenna only moved in azimuth). I find it a bit hard to believe they didn't introduce electronical roll compensation somewhere along the way.

[EvilBivol-1]

Did you find it hard to believe the R-27T would not have a datalink, given its presence on the R-27R? ;)

[Mugatu]

Think you might be underestimated the Ruski engineers :)

 

 

[Vekkinho]

Yeah but that's MiG-35!

[Mugatu]

Yes but no but ...

 

http://forums.eagle.ru/showpost.php?p=462162&postcount=9

http://forums.eagle.ru/showpost.php?p=462266&postcount=11

http://forums.eagle.ru/showpost.php?p=462472&postcount=15

[Trident]

Did you find it hard to believe the R-27T would not have a datalink, given its presence on the R-27R? ;)

 

Surprising, certainly. Hard to believe? Not really, after all it seems to be a deliberate omission because it was not considered useful for the intended role of the missile.