SU-75 Checkmate

Sorry, we've seen nothing to suggest the Checkmate (Su-75) is VLO.........

Yes we did.

1. planform alignment
2. weapon bays
3. stealth nozzle
4. S duct with dsi bump which hide engine

Making something VLO takes a lot of investment into not only development, but also production technology and maintenance. Just having a model doesn't make it VLO. Everything can look kind of stealthy with a model.

Just take a look at Su-57. Once Russia has to start getting it into prototype, there is all sort of stuff on there which are obviously bad for stealth. And once you go into mass production, being able to consistently produce high quality production is a huge challenge. And then there is also the work involved in maintaining the stealth properties of aircraft surface. None of this is easy. And more importantly, the Russians have not shown willingness to go the extra miles for any of it.

You don't get a really VLO aircraft by being cheap. You can take a look at how much money China has spent on J-20 and still have not really achieved it.

VLO: 0.0001 or less
LO: 0.1 or less

Also an important fact about S-duct.
Partially curved is not the same of true s-duct. Super hornet is an example of that, also the erocanards.

If the renders of checkmate presentation are accurate, in some angles is possible to see the engine.

And better not taltk about the spheric IRST and the canopy coatings....

VLO: 0.0001 or less
LO: 0.1 or less

Also an important fact about S-duct.
Partially curved is not the same of true s-duct. Super hornet is an example of that, also the erocanards.

If the renders of checkmate presentation are accurate, in some angles is possible to see the engine.

And better not taltk about the spheric IRST and the canopy coatings....

Well there isn't really define RCS level which is consider stealth. For example what you wrote would mean F-117 isn't stealth at all!

In case of F-117 we can real life scenario in which it was lock-on by SNR-125 radar (X band radar) at least 15km, SNR-125 is able to lock 20m2 for 100km, so at 15km target would be ~0.02m2 which is similar to mentioned RCS of F-117 (~0.01m2).

S-duct and exposed engine? Really? Anyone took photo of engine face like this in case of YF-23:


I don't think. What someone on forum did was draw straight line from intake to engine and said look it isn't stealth because we can see engine from quite narrow angle, which is nonsense YF-23 is example where you can see lot more of engine even in case of F-23 which had bump you still would be able to see engine from not so common angles. It is all compromise, NG go with shorter S-duct to reduce weight and get space for fuel, LM go with long and wide S-duct to hide engine as best as possible.

But in case of Su-75 intake duct isn't simple forum member thought it is.

It is quite strange S-duct as seen in presentation. Behind intake mouth (after short S-duct curve) you have two quite separated narrow and tall ducts which then merge in one not that bended duct.

That solution hide engine excellent without need to use long and wide S-duct.

OLS isn't that problem becuase when it isn't in used backside with thick RAM would be at front and when it is in use as manufacturer of stealth coatings for russian fighters said they applied RAM inside OLS and on safire sphere too. Btw there is EOTS sensor in development for which Rostec UAC already paid to optic company.

Canopy coatings? They already apply them on Su-57 and I think Tu-22/160 also get them. So what you wanted to say by that?

We can argue will Russians make Su-75 in tight tolerances or will they apply advanced RAM on dirt cheap variant but saying it isn't stealth design is really strange.

Well there isn't really define RCS level which is consider stealth. For example what you wrote would mean F-117 isn't stealth at all!

In case of F-117 we can real life scenario in which it was lock-on by SNR-125 radar (X band radar) at least 15km, SNR-125 is able to lock 20m2 for 100km, so at 15km target would be ~0.02m2 which is similar to mentioned RCS of F-117 (~0.01m2).

0.01 and 0.02 are smaller than 0.1...therefore yes, F-117 is LO.

Why is important YF-23 important for you? because "was stealthier than YF-22"????
I remember saw a image (front) of yf-22 prototype where engine was vissible.

You are grossly mistaken in thinking that if the F-22A has a VLO, the YF-22 does too.

Sorry but Americans and Russians does not play in same league of stealth.
Please, stop this joke.

Canopy coatings? They already apply them on Su-57 and I think Tu-22/160 also get them. So what you wanted to say by that?

Well thats will be funny...
As all knows the american coatings in canopy are reflectant, thats make the radar waves reflected up and side (but never front).
In russia is different.. they have absorbent coatings, they claimed that coatings downgrade the radar signal by 50%. That means in a 2 way travell the radar signal become in 25%.

The fact is simple 25% rcs of a human head, helmet, hud and metalic arc is much bigger than the rcs of F-22/35.

In fact,in anechoic chamber test of SU-57 they used a manikin with helmet.


Edit: i found a pic of not soo good YF-22 sduct:

I didn't wrote YF-23 is more stealthier then YF-22, read again. I said NG select such intake as compromise, does it make YF-23 less stealthy from some angle of course, does NG thought it is big problem. No.

But it is really pointless debate about S-duct because in case of Su-75 you don't see engine at all based on 3d X-ray pic from presentation.

Btw can you provide some interesting reading about US canopy coatings which don't allow radar waves to enter cockpit at all?

From what I saw, US engineers aren't at all transparent as Russians are so I really doubt you can find anything about US canopy coatings or at least as detailed as Russian official info about thiers.

I didn't wrote YF-23 is more stealthier then YF-22, read again. I said NG select such intake as compromise, does it make YF-23 less stealthy from some angle of course, does NG thought it is big problem. No.

They lost, maybe they thought bad.

But it is really pointless debate about S-duct because in case of Su-75 you don't see engine at all based on 3d X-ray pic from presentation.

Is not a pointless debate if your claim is false therefore.
I post this on august:

This video of the presentation is interesting because at 3:40 you can see an image of the duct from behind the cockpit to the engine, and at 6:27 from the intake to the same point behind the cockpit as before.

In Paint i did this:





Not the most accurate render, but the official. The duct is better than SU-57(very easy...), but worse than F-22/35

YF-22 and YF-23 meet stealth requirements so no YF-23 didn't lose because it had exposed engine from some angles.

In case of you analyze second picture show what is problem. You need to take in account curving of intake in horizontal plane too and also shape of intake itself.

It is more like two smaller curved in both planes intakes which merge in duct then one classic S-duct.

So it is very complex without 3d model and info about intake and duct geometry to do analise. Btw even your analyze show how easy it would be to counter adding bump to counter problematic angle

Is F-35 better? For sure but calling Su-75 non stealth because you think it could have exposed engine from some very narrow angle is nonsense. We can argue about build quality and RAM but design, design is fine.

You are confused with one thing.

It is not that from one angle it is seen but not from another. The idea is that the more labyrinthine a conduit is, the greater the number of rebounds and therefore the lower the RCS. Even if you can't see the Super Horner's engine from the front, there are few bounces that make it impossible to stealth.
It's not binary, there are various types of curves that can be built, and thus various degrees of stealth, even orders of magnitude.
Clearly far fewer bounces are needed on the Russian plane.

In case of F-117 we can real life scenario in which it was lock-on by SNR-125 radar (X band radar) at least 15km, SNR-125 is able to lock 20m2 for 100km, so at 15km target would be ~0.02m2 which is similar to mentioned RCS of F-117 (~0.01m2).

According to the following chart:


And in the following thread:
viewtopic.php?p=399432

The SNR-125 is able to lock a 10 square meter target at a range of 80 nautical miles or 148 km.
This means that at 15km (14.8 to be more precise) would be the maximum range that this radar would detect a 0.001 square meter target (and not 0.01).
According to that scenario (F-117 shot down by SA-3) the F-117 RCS would around 0.002 square meters (and not 0.02).

So yes, the F-117 would be VLO.

It is Pechora 2M which is latest upgrade. We have original Pechora which is lot less capable system I don't have time but I will try to find info for it later.

Btw Ancics book about F117 downing create confusion. If you talk with crew it isn't like Zoltan or Ancic say. Both added drama.

Only thing which os same is 15km stable lock. Some mentioned they lock target earlier which wasnt Zelkos F117 but another (4 fly in formation if I remember right) but didn't continue tracking becuase it was already outside on engement zone for S125. Zelko plane was first locked from more then 15km but because of poor tracking capability of Pechora they lost the lock.

Yes, the F-117 was shot down by the 'original' SNR-125 and not by Pechora 2M (which only entered in service after 2000) so my point about the F-117 RCS still stands.

Moreover the above concurs with the stated RCS for the F-117 which is roughly the "size of a golf ball" which again is around or close to 0.001 square meteres (and not 0.01).

When it comes to F-117 shootdown, you have to take into account the engagement geometry. The F-117 was at about 8000 m altitude at the time or something like that. That would present much more of the aircraft at less ideal angle at that distance. The SNR-125 was looking at the belly of the aircraft with very likely higher RCS than frontal view RCS.

YF-23 lost to YF-22 more than 30 years ago. Both PAVs were designed and manufactured in the 1980s, when Ronald Reagan was the POTUS and the USSR was still a thing! F-117 was based on the 1970s tech. The last F-117 was delivered in 1990. The shotdown event was more than 20 years ago. It is amazing in 2022 people are still bringing such things into the argument about some Russian fighter not yet flying.

When it comes to F-117 shootdown, you have to take into account the engagement geometry. The F-117 was at about 8000 m altitude at the time or something like that. That would present much more of the aircraft at less ideal angle at that distance. The SNR-125 was looking at the belly of the aircraft with very likely higher RCS than frontal view RCS.

Indeed!
And just to add to what you said, when the F-117 was shot down it was going away from the SAM site or more precisely it had its rear (together with the belly that you mentioned) faced to the radar emitter. And the rear aspect RCS of a stealth aircraft should be somehow bigger than the front.

It is amazing in 2022 people are still bringing such things into the argument about some Russian fighter not yet flying.

Well, yes and no.
I would say that it's not that amazing because the Russians still need to reach the "levels of stealthiness" (RCS) of the F-117 and it seems that they are still very far from it.
And the same applies to the Chinese (although they should be closer).