RCS for dummies

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swiss

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Unread post24 May 2019, 14:16

sprstdlyscottsmn wrote:Good thing the F-35 knows this and has multiple display options to help the pilot avoid detection zones.


Absolutely. This is indeed an amazing feature of the Lightning II.

eloise wrote:When it is written like that, the RCS value is calculated in dBsm instead of m2
If you see the ring as 0-> 1-> 100 then the RCS value is in m2
If you see the ring as -10 -> 0 -> 10 ->20 then the RCS value is in dBsm


Thanks to enlighten me eloise. I was always thinking this diagram is in m2.
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ricnunes

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Unread post24 May 2019, 14:52

garrya wrote:
eloise wrote:There is one simulation from Hellenic airforce with rather different result

The differences came from the way they made the model
Zikidis's study doesn't simulate air intake and they use a transparent radar cone, the pitch angle is also different


Absolutely.

IMO, I believe that the only thing we can accurately conclude from what F-35 model/study is that the aircraft's RCS will increase in some angles, namely on the sides but this I believe we all already knew, no? (since this would be "common sense")

What I mean is that we cannot use the RCS values that we observe in that same F-35 model/study diagram as being actual F-35 RCS values, they are not.
For example, doesn't that same study admit that RAM material coating is not taken into account for that same F-35 model?

So doing a gross oversimplification and if we consider that 30% to 40% of the F-35 RCS reduction comes from RAM (while 60% to 70% from the shape) than all those values on that same diagram would be 30% to 40% shorter which means that instead of having a highest peak/spike of 15 dBsm that same highest peak/spike would be something close to 0 dBsm or perhaps even lower.

Moreover, is the F-35 model used for that study 100% accurate? From what I've been learning about this subject is that small diferences in angle in some small or even very small surfaces can have a big diference on RCS values.
So if that F-35 model has some small inaccuracies then this could translate in a quite big diference between the RCS results observed on that diagram and the actual/real F-35 RCS values.
A 4th/4.5th gen fighter aircraft stands about as much chance against a F-35 as a guns-only Sabre has against a Viper.
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sprstdlyscottsmn

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Unread post24 May 2019, 15:46

We don;t need to speculate much. We already know the spikes of the real plane as seen from a SAM site.

Threat Blossom.png


From the direct front (bottom of the blossom) we see a roughly 12nm detection range, edging out to ~17nm. What is interesting is that just a bit further to the side and the range drops to 10 or less, and from the rear it looks much less than 5nm. So we can see how the ingress plan could be to go in at that front quarter angle, drop munitions, rapidly put your a$$ to the target and egress only spending a few seconds in the detectable zone.
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garrya

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Unread post25 May 2019, 03:31

ricnunes wrote:What I mean is that we cannot use the RCS values that we observe in that same F-35 model/study diagram as being actual F-35 RCS values, they are not.
For example, doesn't that same study admit that RAM material coating is not taken into account for that same F-35 model?

Of course, neither simulation take into account RAM and RAS, because unlike shape, it is actually impossible to correctly predict the performance of RAM and RAS on an airplane if you don't know what they are.
Inlet cavity reflection is especially hard to model and simulate
Inlet RCS simulation.PNG

With that said, the simulation give a good idea about the location of the spikes
Here are some common software used for RCS simulation
https://www.shipjournal.co/index.php/ss ... iew/72/250
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garrya

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Unread post25 May 2019, 04:42

More radar scaterring charts
AV-8B radar scattering.PNG

AH-64 RCS.PNG

ship RCS.PNG

F-15.PNG

aircraft configuration.PNG

plot.PNG
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ricnunes

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Unread post26 May 2019, 19:10

garrya wrote:Of course, neither simulation take into account RAM and RAS, because unlike shape, it is actually impossible to correctly predict the performance of RAM and RAS on an airplane if you don't know what they are.


Absolutely!
But we have to take into account that the RAM coating on the F-35 (as well as on the F-117) is much, much more extensive when compared to any of the other aircraft that we previously observed on RCS diagrams.
So what I mean with my previous post was that the RCS diagrams of other aircraft should be much closer to the real aircraft's RCS (due to the very limited usage of RAM in these aircraft, if any) compared to the F-35 RCS diagram and the real F-35 RCS (and the same also applies to the F-117, I believe).
A 4th/4.5th gen fighter aircraft stands about as much chance against a F-35 as a guns-only Sabre has against a Viper.
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