J-20 canopy coating speculation

Discussion in 'Air Force' started by Max Demian, Jun 12, 2019.

  1. Max Demian
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    Max Demian Junior Member
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    This thread is to discuss J-20 canopy coating material for RCS reduction purposes.

    The photos of the 2017 prototype showed a canopy with a coating quite reminiscent of that seen on the F-35.
    j-20.jpg


    F-35:
    f-35 pink.png

    However, all subsequent units featured a very different coating of the canopy. Here is a good photo of the color and the interference pattern:
    j-20 tint.jpg


    The color and the interference pattern appear almost identical to what can be found on modern airliners, like the Airbuses. This material is known as indium tin oxide and is commonly used in the opto-electronic industry.
    a321.jpg

    The Boeing 787 uses a gold thin film in the composite structure of its windshields:
    787.jpg
    Observe how similar this hue is to the EODAS windows on the J-20. According to this article from the manufacturer: https://www.aerospacemanufacturinga...pace-manufacturing-design-boeing-ppg-787-amd/
    one of the purposes of the thin gold film is to reflect IR radiation and prevent excessive heat build up in the windshield.

    Can we claim with some confidence that the J-20 canopy coating is indeed indium tin oxide? How would this material compare to thin gold film in the F-22 and F-35? Both are conductors and offer a Faraday cage protection to the interior of the cockpit. However, they will reflect incoming RF energy.

    Whay are the EODAS windows coated with a different material, likely gold thin film?
     
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  2. Max Demian
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    Max Demian Junior Member
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    Correction: the gold thin film in the 787 windshield is used to reduce the heat buildup inside the cockpit, not the windshield.

    The fact that the material is IR reflective means that it will also reduce the IR signature as seen by thermal sensors and could have stealth application for the military.
     
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  3. Biscuits
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    Biscuits Junior Member
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    To me it looks like a bit different hue compared to the indium tin oxide, but obviously closer to it than to gold film.

    It’s possible a more stealth efficient coating was developed that’s related to indium tin oxide, either through playing with the layer thickness, the material structure, or through adding a layer of something else under/over it.
     
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  4. taxiya
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    taxiya Major
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    You have two questions:
    1. Why choose ITO over gold film.
    2. Why is J-20's EODAS window coated a different material.

    My thought:
    1. I don't think (in my limited knowledge) ITO and gold film are fundamentally different in doing the job. They are all conductors which is the only reason that makes them an RF cage but also equally RF reflecting. Gold film does not absorb incoming RF energy because it is conductor like metal skin. One thing set ITO different (preferable) from gold is its better transparency. Probably the reason of choosing ITO.
    2. From the limited photos of the EODAS window being exposed without a cover, it is hard to tell if it is of different material from the canopy.
    Interestingly I found this on internet https://aviation.stackexchange.com/...canopy-of-the-f-22-raptor-have-a-golden-tinge

    ITO in its thin form is colourless, but in bulk (therefor thicker form) yellowish, so the gold colour. F-22's canopy may well be just thicker film of ITO.
     
    #4 taxiya, Jun 12, 2019
    Last edited: Jun 12, 2019
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  5. Max Demian
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    Max Demian Junior Member
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    That's a good observation. Although, I don't follow where from the yellowish tint would arise from a transparent material. I suspect rather that the tint comes from whatever additional layers are used in the composite structure of the canopy. There could very well be a gold thin film in addition to ITO. Something on the lines of that is mentioned in the article I posted about the 787 windshield design.

    In this photo the contrasting colors of the F-22 and F-35 canopies are quite apparent:
    tumblr_inline_plll14RFZE1tiokib_540.jpg

    This discussion, where I took the above photo from, suggests the possibility that the F-22 canopy has an additional layer of gold film: https://www.tumblr.com/search/indium tin oxide

    I agree that ITO and gold thin film play a similar role, both being conductors and gold being one of the best, after silver and copper. I am curious to know how they deal with the reflected RF. Can they introduce some structure to the film to deflect RF away from the incidence angle, or are the canopies themselves already shaped to achieve that effect?

    The tumblr discussion and the 787 article seem to suggest that gold thin film brings the benefit of IR reflectivity, therefore greatly reducing the IR signature of the canopy.
     
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  6. Max Demian
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    Max Demian Junior Member
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    You're thinking of the FLIR? I meant the small windows distributed around the fuselage. Take a look at the EODAS side windows on the nose in these photos: article_5c6f34a2e235f6_05452256.jpg
    RTS24O7Y.jpg
     
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  7. Max Demian
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    Max Demian Junior Member
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    The tumblr discussion had an interesting point about the IR reflectivity. The F-22 flies very high and is exposed to proportionally larger amounts of heat radiation, so rejecting IR from passing into the canopy would improve pilot comfort as well.
     
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  8. Air Force Brat
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    Air Force Brat Brigadier

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    As well as damaging UV rays...
     
  9. FriedRiceNSpice
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    FriedRiceNSpice Senior Member

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    What if the pilot wants to get a nice tan going?
     
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  10. Josh Luo
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    Josh Luo Junior Member
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    I didn't know that J-20 has a side-scan radar like the one on the Sukhoi Su-57.
     
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