Boeing Unveils New Stealthy F-15

[Crusader2000]

Sorry if i misunderstood your question. but do you imply that size does not matter, because it does.

So, are you saying that the F-35 and F-117. Have a smaller RCS that the vastly bigger B-2 Bomber????

 

[LS1 Miata]

Sorry if i misunderstood your question. but do you imply that size does not matter, because it does.

No, size does not matter at all.

If you were to take a model of the F-117 and scale it up to the size of an aircraft carrier, then compare it to that of a normal sized F-117, the two aircraft would have a similar RCS. There would be small differences, but not large enough to really affect anything.

 

[LS1 Miata]

"He [Kelly Johnson] told me later that he was surprised to learn that with flat surfaces the amount of radar energy returning to the sender is independent to the target's size. A small airplane, a bomber, an aircraft carrier, all with the same shape, will have identical radar cross sections."

"Skunk Works", page 33, Ben R. Rich




As I said before, size is NOT dependent on it's RCS. Ben Rich, Kelly Johnson, and Denys Overholser would agree with me.

 

[gf0012-aust]

Sorry if i misunderstood your question. but do you imply that size does not matter, because it does.

It certainly does. A B1 has a lower RCS than a rafale and a gripen.

its not about size, its about signal management. the same issues actually apply to submarines (fluid mechanics and aerodynamics are kissing cousins)

some much larger nukes actually have a lower sig profile than smaller conventionals.

that's the common misconception that people have - ie that larger assets means larger footprint at an RCS level.

 

[PhysicsMan]

"He [Kelly Johnson] told me later that he was surprised to learn that with flat surfaces the amount of radar energy returning to the sender is independent to the target's size. A small airplane, a bomber, an aircraft carrier, all with the same shape, will have identical radar cross sections."

"Skunk Works", page 33, Ben R. Rich




As I said before, size is NOT dependent on it's RCS. Ben Rich, Kelly Johnson, and Denys Overholser would agree with me.

You don't really understand what you're stating here. What you said is only somewhat true for exactly flat surfaces, so it would apply to F-117 to a large degree, but for all other aircraft currently out there (not with flat surfaces) it does not apply. Would you say a bigger sphere has the same RCS as a smaller one? It doesn't, and neither do aircraft.

 

[PhysicsMan]

So, are you saying that the F-35 and F-117. Have a smaller RCS that the vastly bigger B-2 Bomber????

Actually, F-117 probably does have a smaller RCS...

 

[Bonza]

You don't really understand what you're stating here. What you said is only somewhat true for exactly flat surfaces, so it would apply to F-117 to a large degree, but for all other aircraft currently out there (not with flat surfaces) it does not apply. Would you say a bigger sphere has the same RCS as a smaller one? It doesn't, and neither do aircraft.

Why then does GF state that a B-1 has a lower RCS than something like Rafale/Gripen? They're not exactly "flat" aircraft.

He's shown himself to be an extremely reliable source in the past so I'm curious as to your response.

Edit: Your response followed a moment after my post, disregard.

 

[PhysicsMan]

It certainly does. A B1 has a lower RCS than a rafale and a gripen.

its not about size, its about signal management. the same issues actually apply to submarines (fluid mechanics and aerodynamics are kissing cousins)

some much larger nukes actually have a lower sig profile than smaller conventionals.

that's the common misconception that people have - ie that larger assets means larger footprint at an RCS level.

you're right, but when you say it's not about size it can be misleading as well, since the size does matter, it's just not the only variable, or not even the most important variable, as your example shows. scaling B-1 to a larger size will increase its RCS.
and about the nukes... what is it that is done differently with their construction to get a smaller profile?

 

[PhysicsMan]

Why then does GF state that a B-1 has a lower RCS than something like Rafale/Gripen? They're not exactly "flat" aircraft.

He's shown himself to be an extremely reliable source in the past so I'm curious as to your response.

Ok, I'll clarify. If you take the same airframe and blow it up to a larger size it will in general have a larger RCS. This does not in any way logically imply that any larger thing has a larger RCS than any smaller thing.

 

[LS1 Miata]

You don't really understand what you're stating here. What you said is only somewhat true for exactly flat surfaces, so it would apply to F-117 to a large degree, but for all other aircraft currently out there (not with flat surfaces) it does not apply. Would you say a bigger sphere has the same RCS as a smaller one? It doesn't, and neither do aircraft.

The F-117 and F-22 operate off of the same principle - deflecting radar energy away from the radar receiver. The only reason why the B-2, F-22, and F-35 have curves instead of flat surfaces is because computer technology allowed them develop aircraft from a 3 dimensional aspect. The F-117 was designed from a 2 dimensional aspect because the computer technology back then (mid-late 1970's) wasn't as sophisticated. These curves allow for a better flight profile, which is especially a must on the F-22 and F-35. That being said, a large model of an F-22 compared to a small model of an F-22 will largely be the same, because they operate off of the same principle compared to the F-117. There will be small differences, but not enough to really change anything.

 

[PhysicsMan]

The F-117 and F-22 operate off of the same principle - deflecting radar energy away from the radar receiver. The only reason why the B-2, F-22, and F-35 have curves instead of flat surfaces is because computer technology allowed them develop aircraft from a 3 dimensional aspect. The F-117 was designed from a 2 dimensional aspect because the computer technology back then (mid-late 1970's) wasn't as sophisticated. These curves allow for a better flight profile, which is especially a must on the F-22 and F-35. That being said, a large model of an F-22 compared to a small model of an F-22 will largely be the same, because they operate off of the same principle compared to the F-117. There will be small differences, but not enough to really change anything.

F-22 body does not minimize radar energy as efficiently as F-117 does, if you discount everything other than the frame shape (and probably overall as well), despite the computer aid. Its design is a compromise between stealth and high maneuverability, unlike that of F-117's. And as long as there are continuous curved surfaces on a plane the signature due to shape will increase with size more or less proportionately. You may have a point in the sense that the shape of F-22 is just one of many contributors to its RCS, with other factors being less or not sensitive to its overall size, so the size is not AS important, but saying that the RCS will be "largely the same" in a bigger frame is just not true.

 

[Marc 1]

I supose it won't truly be revealed for another 50 years, but it would surprise me that a much later design even if it were from curved rather than flat panels would have a larger RCS that something designed 15 years earlier.

 

[PhysicsMan]

I supose it won't truly be revealed for another 50 years, but it would surprise me that a much later design even if it were from curved rather than flat panels would have a larger RCS that something designed 15 years earlier.

well, maybe in 50 years they will be able to get away with an awkward but stealthy shape design like F-117's and still achieve the dynamic requirements, but right now there's just no magic trick to make the shape very stealthy and the aircraft very capable in air. There's just too much F-22 has to be able to do performance-wise to have a very stealthy frame.

 

[gf0012-aust]

Ok, I'll clarify. If you take the same airframe and blow it up to a larger size it will in general have a larger RCS. This does not in any way logically imply that any larger thing has a larger RCS than any smaller thing.

Thats not related to the fact that larger aircraft can have a lower RCS than smaller aircraft.

classic examples are the B1 and B2, - the latter has a "superior" (as in lower) RCS value than the F-117.

similarly the F-22 is a larger aircraft than the F-117 and has a superior signature.

extrapolating RCS transmission re size to signature by upscaling the model does not work.

again, exponential scale is not relevant

 

[gf0012-aust]

what is it that is done differently with their construction to get a smaller profile?

I've got no intention of discussing signature management in detail on an open forum.

I have been involved with sig management for UDT

 

[gf0012-aust]

F-22 body does not minimize radar energy as efficiently as F-117 does

Nope. patently not true. the former has a far superior signature than the latter. USAF has indicated that to some of its allies, and its apparent to those who have cross decked and trained against both types.

A RAF pilot has exchanged on both and been pretty clear on his briefings that the F-22 is the far more discrete platform.

 

[PhysicsMan]

Thats not related to the fact that larger aircraft can have a lower RCS than smaller aircraft.

classic examples are the B1 and B2, - the latter has a "superior" (as in lower) RCS value than the F-117.

similarly the F-22 is a larger aircraft than the F-117 and has a superior signature.

extrapolating RCS transmission re size to signature by upscaling the model does not work.

again, exponential scale is not relevant

Is there any information about how various stealth designs compare in RCS? One source that I've seen puts F-117 RCS lower than F-22's. It's from a paper by Pogosyan, Sukhoi's chief - obviously to a degree a speculative comparison but still...

 

[Bonza]

well, maybe in 50 years they will be able to get away with an awkward but stealthy shape design like F-117's and still achieve the dynamic requirements, but right now there's just no magic trick to make the shape very stealthy and the aircraft very capable in air. There's just too much F-22 has to be able to do performance-wise to have a very stealthy frame.

Bear in mind that the F-22 is the product of more advanced technology and evolved design methods than the F-117 (in addition to the requirements of said design being different), so expecting there to be a necessary "trade-off" between performance and LO for the F-22 on the basis of characteristics inherent to the F-117 could be misleading.

 

[SpudmanWP]

hehe.. that graphic has the F-35 lower than the F-22.

 

[PhysicsMan]

Nope. patently not true. the former has a far superior signature than the latter. USAF has indicated that to some of its allies, and its apparent to those who have cross decked and trained against both types.

A RAF pilot has exchanged on both and been pretty clear on his briefings that the F-22 is the far more discrete platform.

Well, I was talking about the frame shape's RCS impact only - I'm sure it's true that most other aspects of the two designs will favor F-22 in this regard... But in any case, that's interesting info, thanks!