F-22 Rivet and RCS

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arian

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Unread post17 Feb 2016, 02:02

eloise wrote:F-35 has some on the body and wing too


I think the lighter gray material covering those sections on the F-35 is RAM, so those screws aren't being unfastened regularly (or at all in the field)
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Unread post17 Feb 2016, 02:19

count_to_10 wrote:
hornetfinn wrote:The screws seem to go flush with the surface and the socket is so small that they reflect very tiny amounts of radar energy. Of course they could easily also be covered with some RAM substance or tape if they increase RCS too much. I doubt those hatches are opened that often, so it should not be much of a problem.

Well, if they do have a one-time use RAM treatment for those bolt heads, it would go a ways to explain why the F-22 has maintenance cost issues.


http://www.dailytech.com/F35+Stealth+Co ... e21321.htm

"Some of the [low observables] coatings system and gap-fillers that the F-35 had an advantage on, we have incorporated into the Raptor," said Jeff Babione, vice president and general manager of the F-22 program for Lockheed Martin.

Defense News reports that Babione claims that the new coatings don’t change the radar cross section of the F-22. The coatings according to Babione are simply to reduce maintenance costs. He said, "[The F-35 program] had some more robust materials that were more durable and we were able to pull those back on to the F-22. So our system is better, and the life-cycle cost of the F-22 is reduced."

Analyst Dan Goure said, "It's not going to transform the airplane, but what it's going to really do is make it much cheaper to operate the F-22 fleet, which is terribly important given its small size.

Lockheed had to make some changes to the coatings to be used on the F-22 that the F-35 didn’t require. Goure said, "It's [the F-22] operating at a higher altitude typically and [at] faster speeds, and that would put different stresses on the material."

The only F-22 fighters that are using the new coating for now are the most recent Lot 9 aircraft and other new and improved materials are still in the final qualification phase. Lockheed hopes to roll the coatings out to the entire fleet next year. At that point, all existing aircraft will be retrofitted with the new coating.


I guess this was also a one time cost issue as well but in the long run for the better.
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Unread post17 Feb 2016, 08:04

eloise wrote:
garrya wrote:Thanks you, first time i heard about that
However for some reason ( weight or thickness or cost) F-22, F-35 still use gold layer for their biggest piece of glass ( the canopy)

the inner gold layer is to prevent radar radiation from getting inside the cockpit thus reduce RCS, the transparent RAM is at the outer surface ( or between the gold layer and the canopy ) to further reduce the reflection


This. What happens here is that radar energy is absorbed by transparent RAM and the remainder of that energy is then reflected by the gold layer away from radar system and then absorped again while going through that RAM again. End result is that radar energy is greatly reduced in the cockpit glass and then redirected away from the threat radar as much as possible.

Those lights might not need all that and having just transparent RAM might well be enough to reduce the RCS enough to not matter. I doubt nobody has thought about how they affect RCS of the aircraft.
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garrya

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Unread post18 Feb 2016, 08:59

eloise wrote: the inner gold layer is to prevent radar radiation from getting inside the cockpit thus reduce RCS, the transparent RAM is at the outer surface ( or between the gold layer and the canopy ) to further reduce the reflection

How thick are the transparent RAM though ? , the patent doesnt seem to indicate it , absorbing value seem very high for a thin layer http://www.google.com/patents/US5488371
And does anyone know how thick are F-35 , F-22 canopy ?
hornetfinn wrote:
No, layer of gold is not the only solution for the problem and not even the best one. There are optically highly transparent coatings and materials available. For example Indium Tin Oxide or Graphene can be used to create optically highly transparent and good radar absorbing or reflecting features (depending on application).

I cant find the source indicate that Indium Tin Oxide , Graphene has absorbing capability in X band range , can you give me some ?
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Unread post18 Feb 2016, 13:18

garrya wrote:
eloise wrote: the inner gold layer is to prevent radar radiation from getting inside the cockpit thus reduce RCS, the transparent RAM is at the outer surface ( or between the gold layer and the canopy ) to further reduce the reflection

How thick are the transparent RAM though ? , the patent doesnt seem to indicate it , absorbing value seem very high for a thin layer http://www.google.com/patents/US5488371
And does anyone know how thick are F-35 , F-22 canopy ?


For example F-16 canopy is 5/8 inches (about 17 mm) thick according to this:
http://goo.gl/jnTCHR

According to this F-22 canopy is 3/4 inches thick (about 19 mm).
http://www.f22fighter.com/cockpit.htm

garrya wrote:
hornetfinn wrote:No, layer of gold is not the only solution for the problem and not even the best one. There are optically highly transparent coatings and materials available. For example Indium Tin Oxide or Graphene can be used to create optically highly transparent and good radar absorbing or reflecting features (depending on application).

I cant find the source indicate that Indium Tin Oxide , Graphene has absorbing capability in X band range , can you give me some ?


Here are commercial radar absorbers with rather good description and drawings about their structure:
https://goo.gl/vcKoia

See page 18. This transparent absorber uses Indium Tin Oxide to both absorb and to reflect radar waves. It just has two sheets with different properties (one absorbs and one reflects). With 9.6 mm total thickness it achieves roughly 10 to 30 dB reflection attenuation and is very transparent (over 70 percent transmissivity for visual rays). This is relatively simple and cheap commercial product but I'm sure canopies use similar idea of attenuating radar waves but exact details likely vary. This is also flat plate where radar waves are basically only absorbed but in cockpit canopies the radar waves are also redirected away by shaping from radar antenna further reducing radar energy the radar receives. You might notice that the canopy is actually twice the thickness of these sheets, so it's very possible they offer possibly even better reflection attenuation properties.

ITO and graphene do definitely work in X-band or almost any other band depending on their exact application. One source of information: http://goo.gl/G7z2zZ
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Unread post18 Feb 2016, 20:35

hornetfinn wrote:Here are commercial radar absorbers with rather good description and drawings about their structure:
https://goo.gl/vcKoia

See page 18. This transparent absorber uses Indium Tin Oxide to both absorb and to reflect radar waves. It just has two sheets with different properties (one absorbs and one reflects). With 9.6 mm total thickness it achieves roughly 10 to 30 dB reflection attenuation and is very transparent (over 70 percent transmissivity for visual rays). This is relatively simple and cheap commercial product but I'm sure canopies use similar idea of attenuating radar waves but exact details likely vary. This is also flat plate where radar waves are basically only absorbed but in cockpit canopies the radar waves are also redirected away by shaping from radar antenna further reducing radar energy the radar receives. You might notice that the canopy is actually twice the thickness of these sheets, so it's very possible they offer possibly even better reflection attenuation properties.

correct me if iam wrong , but isn't the transparent RAM only work from 5 Ghz till 7.5 Ghz?
Image

hornetfinn wrote:ITO and graphene do definitely work in X-band or almost any other band depending on their exact application. One source of information: http://goo.gl/G7z2zZ

It the first time i heard of FSS , certainly seem like a good way to reduce RCS of the nose ( radar)
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Unread post18 Feb 2016, 20:38

hornetfinn wrote:With 9.6 mm total thickness it achieves roughly 10 to 30 dB reflection attenuation and is very transparent (over 70 percent transmissivity for visual rays).

Sorry for unrelated questions but what a 70% transparent glass actually look like?
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Unread post18 Feb 2016, 22:47

eloise wrote:
hornetfinn wrote:With 9.6 mm total thickness it achieves roughly 10 to 30 dB reflection attenuation and is very transparent (over 70 percent transmissivity for visual rays).

Sorry for unrelated questions but what a 70% transparent glass actually look like?

Like this I would assume:

Image
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Unread post19 Feb 2016, 09:38

garrya wrote:correct me if iam wrong , but isn't the transparent RAM only work from 5 Ghz till 7.5 Ghz?


In that exact application it works mostly in that frequency range. However the frequency range can be pretty easily tailored to any frequency range using different types of layers (thickness, resistance for example). You can for example combine two different absorbing layers to handle much wider bandwidth. As said, this is relatively simple and cheap commercial product and stealth fighter canopies can use much more demanding and expensive solutions.

garrya wrote:
hornetfinn wrote:ITO and graphene do definitely work in X-band or almost any other band depending on their exact application. One source of information: http://goo.gl/G7z2zZ

It the first time i heard of FSS , certainly seem like a good way to reduce RCS of the nose ( radar)


FSS is not that new idea (at least 30 years old) and I'm sure for example B-2, F-22 and F-35 use some form of FSS.
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Unread post19 Feb 2016, 10:19

eloise wrote:
hornetfinn wrote:With 9.6 mm total thickness it achieves roughly 10 to 30 dB reflection attenuation and is very transparent (over 70 percent transmissivity for visual rays).

Sorry for unrelated questions but what a 70% transparent glass actually look like?


Normal window glass has visible light transmittance of about 80 to 90 percent. Clear heat absorbing window glass and solar control window glasses have about 60 to 75 percent transmittance. That 70% transmittance is about equal to light tinted sunglasses like sporting sunglasses. I think the picture what botsing sent is pretty much realistic.

Some sources seem to indicate that F-22 canopy has about 85 percent visible light transmittance and that might well be correct. The same is probably pretty close to reality for F-35 also.
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Unread post27 Feb 2016, 13:53

garrya wrote:
popcorn wrote:Probably the same reason why they put big windows on your car.

But a car doesn't need to be stealthy, and I think B-2 can totally use a small window instead ( B-747 or B-52 typle window)

Bombers often fly in formation with other bombers or fighters, so you'd want to be able to see the people you're flying with, especially when banking.
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Unread post27 Feb 2016, 15:13

uclass wrote:Bombers often fly in formation with other bombers or fighters, so you'd want to be able to see the people you're flying with, especially when banking.

It may have more to do with lake-off and landing. With no tail to offset flaps, I think the B-2 has to go to a pretty high angle of attack, so the pilot needs a good field of view.
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