Forum: F-35 Design & Construction

I was going over the latest edition of "The Radar Game" and noticed two passages that appear to be an inconsistent and not caught by the editors..

"For example, the radar range equation can be used to demonstrate logarithmically that a 40 percent reduction in RCS causes only a 10 percent reduction in the detection range."

"An aircraft that reduces its front?aspect signature by a factor of 10 cuts the notional detection range by 44 percent."

The first passage is the correct one, right?

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Last edited by indochina on Feb 10, 2013 - 04:28 PM; edited 12 times in total

Well It just makes a controversial information and insufficient basis, we can not use this type of information to calculate the distance from the radar to the target.

I realize this is a private websitesx , they deliberately made ??confusing term for those who are not professionals in the field of rada

I guess this is a site lobbying for a certain organization, they deliberately made ??confusing term for those who are not specialized in the field of radar can trust

Well It just makes a controversial information and insufficient basis, we can not use this type of information to calculate the distance from the radar to the target.

I realize this is a private websitesx , they deliberately made ??confusing term for those who are not professionals in the field of rada

popcorn wrote:

I was going over the latest edition of "The Radar Game" and noticed two passages that appear to be an inconsistent and not caught by the editors..

"For example, the radar range equation can be used to demonstrate
logarithmically that a 40 percent reduction in
RCS causes only a 10 percent reduction in the detection
range."

"An aircraft that reduces its front?aspect signature by a factor of 10 cuts the notional detection range by 44 percent."

Thge first passage is the correct one, right?

Theoretically it's correct. The radar power equation is proportional to 1/range^4 and only linearly proportional to RCS. However at very low RCS it becomes difficult to distinguish a signature from noise.

But yes in theory, to half detection range you have to cut RCS to 1/16.

mcraptor wrote:

popcorn wrote:

I was going over the latest edition of "The Radar Game" and noticed two passages that appear to be an inconsistent and not caught by the editors..

"For example, the radar range equation can be used to demonstrate
logarithmically that a 40 percent reduction in
RCS causes only a 10 percent reduction in the detection
range."

"An aircraft that reduces its front?aspect signature by a factor of 10 cuts the notional detection range by 44 percent."

Thge first passage is the correct one, right?

Theoretically it's correct. The radar power equation is proportional to 1/range^4 and only linearly proportional to RCS. However at very low RCS it becomes difficult to distinguish a signature from noise.

But yes in theory, to half detection range you have to cut RCS to 1/16.

So I can work out:

F-35 RCS = 0.001 m2 (20000 times smaller than 20m2) => distance mig-31 can detect the F-35 is: 400 * (0.56 ^ 4) = 39.3 km !

Repeat my words

It is correct? I found that high technology can not be calculated in such a simple formula

Last edited by count_to_10 on Feb 10, 2013 - 09:46 PM; edited 1 time in total

What is "400 * (0.56 ^ 4) = 39.3 km"?
The fourth root of 20000 is about 14, so you are looking at 1/14 times the detection range for the 20m2 object, before you consider issues of clutter, which should reduce the fraction further.

Edit: oops, I used the square root of 2 instead of the fourth root. I don't have a calculator handy at the moment, so all I can say is that it should be less than 14, but more than 11.

indochina wrote:

mcraptor wrote:

popcorn wrote:

I was going over the latest edition of "The Radar Game" and noticed two passages that appear to be an inconsistent and not caught by the editors..

"For example, the radar range equation can be used to demonstrate
logarithmically that a 40 percent reduction in
RCS causes only a 10 percent reduction in the detection
range."

"An aircraft that reduces its front?aspect signature by a factor of 10 cuts the notional detection range by 44 percent."

Thge first passage is the correct one, right?

Theoretically it's correct. The radar power equation is proportional to 1/range^4 and only linearly proportional to RCS. However at very low RCS it becomes difficult to distinguish a signature from noise.

But yes in theory, to half detection range you have to cut RCS to 1/16.

So I can work out:

F-35 RCS = 0.001 m2 (20000 times smaller than 20m2) => distance mig-31 can detect the F-35 is: 400 * (0.56 ^ 4) = 39.3 km !

Repeat my words

It is correct? I found that high technology can not be calculated in such a simple formula

It's not that simple. Irbis-E and CAESAR claim to be able to detect 0.01m^2 at 90-100km, so in theory that implies detecting 0.005m^2 (F-35) at about 75-80km.

Your calculation is wrong anyway. The 4th root of 20000 is 11.89, so that comes out at 33.6km BUT it isn't that simple.

popcorn wrote:

Thge first passage is the correct one, right?

They are both approximately correct without taking losses into account.

For case 1 where it claims 40% RCS reduction = 10% max detection range reduction

percentage reduction = (1-(1-0.4)^(1/4))*100 = ~12%

For case 2 where 1/10th the RCS = 44% reduction in detection range

percentage reduction = (1-(1/10)^(1/4))*100 = ~44%

mcraptor wrote:

indochina wrote:

mcraptor wrote:

popcorn wrote:

I was going over the latest edition of "The Radar Game" and noticed two passages that appear to be an inconsistent and not caught by the editors..

"For example, the radar range equation can be used to demonstrate
logarithmically that a 40 percent reduction in
RCS causes only a 10 percent reduction in the detection
range."

"An aircraft that reduces its front?aspect signature by a factor of 10 cuts the notional detection range by 44 percent."

Thge first passage is the correct one, right?

Theoretically it's correct. The radar power equation is proportional to 1/range^4 and only linearly proportional to RCS. However at very low RCS it becomes difficult to distinguish a signature from noise.

But yes in theory, to half detection range you have to cut RCS to 1/16.

So I can work out:

F-35 RCS = 0.001 m2 (20000 times smaller than 20m2) => distance mig-31 can detect the F-35 is: 400 * (0.56 ^ 4) = 39.3 km !

Repeat my words

It is correct? I found that high technology can not be calculated in such a simple formula

It's not that simple. Irbis-E and CAESAR claim to be able to detect 0.01m^2 at 90-100km, so in theory that implies detecting 0.005m^2 (F-35) at about 75-80km.

Your calculation is wrong anyway. The 4th root of 20000 is 11.89, so that comes out at 33.6km BUT it isn't that simple.

So, please help me with a formula to calculate specific?

Thank Smile

Last edited by indochina on Feb 11, 2013 - 03:31 AM; edited 3 times in total

count_to_10 wrote:

What is "400 * (0.56 ^ 4) = 39.3 km"?
The fourth root of 20000 is about 14, so you are looking at 1/14 times the detection range for the 20m2 object, before you consider issues of clutter, which should reduce the fraction further.

Edit: oops, I used the square root of 2 instead of the fourth root. I don't have a calculator handy at the moment, so all I can say is that it should be less than 14, but more than 11.

My example: temporary I understand that RCS reduced by 10 times the radar range is reduced by 44% ?! (This means that the remaining 56%)

Radar Zaslon-M with detection range of 400 km with a target of RCS = 20 m2, so the F-15 with RCS = 10m2 (Of course this is only the estimated parameters, smaller than 2 cuts the 20 m2)

F-15 will be detected at a distance: 400 * 0.56 = 224 km.

And I for example with F-35

munny wrote:

popcorn wrote:

Thge first passage is the correct one, right?

They are both approximately correct without taking losses into account.

For case 1 where it claims 40% RCS reduction = 10% max detection range reduction

percentage reduction = (1-(1-0.4)^(1/4))*100 = ~12%

For case 2 where 1/10th the RCS = 44% reduction in detection range

percentage reduction = (1-(1/10)^(1/4))*100 = ~44%

Thank

but I do not really understand

Its just an adaption of the radar maximum range formula. It's possible to estimate (I say estimate because losses are not factored in) relative detection ranges based on target RCS.

There's no need to calculate absolute ranges to do this, especially not basing them off manufacturer "claims" (in fact you can't use them as a starting point because the losses have already been factored into these claims).

So for example 1 above, assume you're comparing a detection range of target A with an rcs of 1 vs a target B with 40% reduced rcs (ie rcs of 0.6)

Using the radar max range formula and ignoring all other variables as they are the same for both cases (except losses), target B with its lower RCS will be detected at 0.88011 ( the 4th root of 0.6 ) the range of target A.

So this equals an 11.99% reduction in detection range.

munny wrote:

Its just an adaption of the radar maximum range formula. It's possible to estimate (I say estimate because losses are not factored in) relative detection ranges based on target RCS.

There's no need to calculate absolute ranges to do this, especially not basing them off manufacturer "claims" (in fact you can't use them as a starting point because the losses have already been factored into these claims).

So for example 1 above, assume you're comparing a detection range of target A with an rcs of 1 vs a target B with 40% reduced rcs (ie rcs of 0.6)

Using the radar max range formula and ignoring all other variables as they are the same for both cases (except losses), target B with its lower RCS will be detected at 0.88011 ( the 4th root of 0.6 ) the range of target A.

So this equals an 11.99% reduction in detection range.

Thanks for your help, as I think RCS calculated by the formula more complicated than the way we (civilians) to predict.

As we can see that the Zhuk radar manufacturers claim can detect objects smaller than 5m2 in the range of 282 km, so all my calculations are wrong and we have to infer much about the problem. It was not merely to calculate the distance

I found this forum to mention a few examples of how to calculate the distance RCS (only for our reference)

http://www.indiandefence.com/forums/us- ... is-v4.html

This is formula!

(RCS1/RCS2) = (R1/R2) ^ 4, RCS = radar cross section, R = range.

Eg: 0.1 (RCS) / 400 (km) = (2.5 x 10 ^ -4) ^ 4 = 3.90625 x 10 ^ -15 km? Razz

Or 400/0.1 = 4000^4 = 2.56 x 10^14 km ?

However they do not articulate any quantity divided by the quantity?
I do not know "/" there must be a division in mathematics! In this article author identifiers

(RCS1/RCS2) = (R1/R2) ^ 4

This is the same equation I used pretty much, just a different way around. I was using R1/R2 = (RCS1/RCS2)^(1/4), just using 1 as the reference RCS2 in my example. Its the range difference you want to find.

If you wanted to ignore the losses (the longer the detection range the more innacurate this method is) and calculate the Zhuk's range on targets of various RCS, you'd simplify it to:

Assuming the F-15 = 10msq
Test detection range against 20msq = 400km

R1 = R2 * (RCS1/RCS2)^(1/4)

for your F-15 example, applying this method

Detection Range = 400 * (10/20)^(1/4)
Detection Range (10msq) = 336km

trying it out on the 5Msq target to see what we get based on the 20msq known range (282km quoted for 5msq)

Detection Range = 400 * (5/20)^(1/4)
Detection Range (5msq) = 282km

looks about right to me and I don't think manufacturers have been quoting loss numbers (either purely theoretical or testing their radars in space?) if the 400km and 282km figures came from them Shocked

F-35?

Detection Range = 400 * (0.001/20)^(1/4)
Detection Range (0.001msq) = 33km

F-22?

Detection Range = 400 * (0.000143/20)^(1/4)
Detection Range (0.000143msq) = 20km

Slap it into excel with some pretty formatting, vomit it onto a web page and completely screw up the supporting text, start up a site called ausairpower.com.au and you're good to .... oh wait.

...or based off the Irbis-E stats quoted above, of course max range is out.

Forum: F-35 Design & Construction

Stealth question - Reduction in RCS