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F-35 avionics system

Discussion in 'Air Force & Aviation' started by moon_light, Aug 12, 2016.

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  1. moon_light

    moon_light New Member

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  2. John Fedup

    John Fedup Active Member

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    Western airforces must be cursing the day the Internet came into being. Sure seems like a lot of free technical information is available. I guess spies already found this stuff long before it got posted on websites.:confused:
     
  3. moon_light

    moon_light New Member

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    Personally , i dont think spies care about these information , these knowledge may seem complex to us but to them it probably like the basics 1+1=2
     
  4. John Fedup

    John Fedup Active Member

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    IIRC, a scientific paper by a Russian scientist was the basis for conceiving the F-117. Basic scientific knowledge is important and so is the talent to apply it.
     
  5. r3mu511

    r3mu511 New Member

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  6. moon_light

    moon_light New Member

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    Didnt the German created a stealth aircraft even before that ?. If i remember correctly , it the Ho229 or something
    http://www.luft46.com/ggart/ggho9-2.jpg
     
  7. swerve

    swerve Super Moderator

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    IIRC Gerhard Löbert, the head of the German Lampyridae 1980s stealth project, said after it was made public, & someone questioned whether it was really independent of US work, given that it had adopted faceting like the F-117 that "Maxwell's equations have been public for over 100 years".
     
  8. r3mu511

    r3mu511 New Member

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    ^maybe the question they should've asked instead was whether it was independent of Ufimtsev's work, hehe :D
     
  9. swerve

    swerve Super Moderator

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    It would be interesting to know if the Lampyridae team knew of Ufimtsev's work.

    Ufimtsev showed a way to calculate RCS before building a model. That method wasn't useful until computers could be thrown at it, which is why the USSR wasn't interested in it to start with. It was a step, which built on earlier work by people in other countries (e.g. the UK & Germany), as others later built on it. Low RCS aircraft could be designed & built without his work, but given his papers & significant computing power, it was much easier.

    Good stuff, & useful for more than designing low RCS aircraft, but not absolutely essential.
     
  10. gf0012-aust

    gf0012-aust Grumpy Old Man Staff Member Verified Defense Pro

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    I've snapshotted the history of all the major players and timelines in the stealth primer elsewhere.....
     
  11. gf0012-aust

    gf0012-aust Grumpy Old Man Staff Member Verified Defense Pro

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    the east germans were regarded as probably the greatest tech harvesters of all time - and yet a fat lot of good it did them as they reached the tipping point where the knowledge they were securing was beyond their capacity to utilise even when handed on to the soviets

    after the downfall of the wall it was apparent that they struggled and never were in a position to maximise what they had gathered.
     
  12. r3mu511

    r3mu511 New Member

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    Fwiw, the technical content of Ufimtsev's paper (link to paper was in my first post above) is actually at a much lower level, as it was focused on a method of computation for the electric and magnetic fields produced by wave diffraction on simple geometric shapes (triangular wedge, disk, cylinder, cone, and other rotated paraboloids).

    What he provided was a numerically computable approximation for the diffracted EM field strengths for these simple shapes which, though not as rigorous as those produced by the mathematical theory of diffraction, did not have as large a variation/error in values (when compared to experimental results) as those produced from the diffraction theory based on geometrical optics (he presents both in his paper as well).

    Ufimtsev achieved the better results compared to geometrical optics because his work included focus on the currents induced on the surface of those simple shapes near the discontinuities/edges of the surface (what he termed as "non-uniform induced currents", as opposed to the "uniform induced currents", ie. current away from the edges, which was the focus of the geometrical optic approach).

    As for the Germans, Ufimtsev does prominently cite Karl Schwarzschild several times in his paper as one of the early innovators in using the same computational method (what he terms the "physical theory of diffraction") in the computation of the wave diffraction of a slit. So this should make the German Lampyridae team happy as Ufimtsev credits a German physicist as an innovator of this computational approach, lol.

    ---

    After that, it was then up to Denys Overholser (the mathematician at Lockheed) to actually take Ufimtsev's computation approximation method for triangular wedges and marry that with decompositioning a body into an aggregate of such simple shapes, computing the field strengths for each shape, and via the principle of superposition summing up the individual fields to give a resultant EM diffracted field value which when compared to the incident EM field strength would allow him to compute the RCS of the body he was studying.

    In Rebecca Grant's book "B-2 Spirit of Innovation", that's exactly what she described about how Northrop went about in designing their XST aircraft (ie. the competition that led up to the F-117).

    Since they didn't use Ufimtsev's paper and didn't have an equivalent to Overholser's "Echo-1" software being used at Lockheed, they instead relied on their historical experience in experimental testing/evaluation of RCS of actual USAF aircraft, with their XST design work progressing by bulding models and using actual range testing to validate their design.
     
  13. swerve

    swerve Super Moderator

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    OK, so Ufimtsev provided a base on which a good method of predicting RCS could be built.

    I've read that Northrop had its own software for predicting RCS, which predated the translation of Ufimtsev's main paper & was therefore written without reference to it, & gave a much looser approximation, therefore needing much more application of the old methods of models & range testing.
     
  14. gf0012-aust

    gf0012-aust Grumpy Old Man Staff Member Verified Defense Pro

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  15. r3mu511

    r3mu511 New Member

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    Do you happen to have any more info on this? Maybe the name of the person who worked on this software for Northrop? I'ld really like to read up on more papers which were used in the past by other manufacturers similar to the 1970's relationship of Lockheed to Overholser/Ufimstev's work.

    Yup thanks, I read that article of yours right after I joined the forum. I'll admit though my tech interest is less on LO as a whole, and more on just RF scattering.
     
  16. gf0012-aust

    gf0012-aust Grumpy Old Man Staff Member Verified Defense Pro

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    rf scattering is only part of the sig management set though....
     
  17. r3mu511

    r3mu511 New Member

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    Yup, it's a limited scope for me - just a personal preference of what I like to study :)
     
  18. swerve

    swerve Super Moderator

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    I'll have a look for it, & see if I can find the place I read about it again. IIRC it named the software, but I don't recall any mention of whose work it was.
     
  19. r3mu511

    r3mu511 New Member

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    Ok thanks, much appreciated.
     
  20. r3mu511

    r3mu511 New Member

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    Was reading up on diffraction (and hunting for some info on Northrop's work) and came across the textbook "Fundamentals of the Physical Theory of Diffraction" by Ufimtsev, which had a foreword by Kenneth Mitzner (who worked on the B-2 for Northrop), in which he said (in the quote "PTD" refers to Ufimtsev's physical theory of diffraction):

    So it seems at least for the B-2, Northrop shifted to using Ufimtsev's methods to numerically approximate RF scattering.

    There are alternative methods for numerical approximation of RF diffraction which like PTD account for the contributions from edges/discontinuities, but have more limitations than PTD. One method was devised by Joseph Keller around the early 1950s, called the "geometrical theory of diffraction" (GTD, and it's extension the "method of equivalent currents", MEC), but I haven't found any traces of a possible link of Keller's work to Northrop during their pre-B-2 development (ie. XST project).

    For the timeline in question (1950s-1970s) published numerical solutions to RF scattering (which included edge/discontinuity effects) were either PTD or GTD based, so I'm really curious as to what Northrop might have been using for their pre-B-2 XST development.