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Aerospace Two vertical stabilizers on the F-22 Raptor angled

  1. Dec 8, 2009 #1
    two "vertical" stabilizers on the F-22 Raptor angled

    Why are the two "vertical" stabilizers on the F-22 Raptor angled sort of like a V-Tail as opposed to being completely vertical?
     
  2. jcsd
  3. Dec 9, 2009 #2

    FredGarvin

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    Re: F-22

    To my understanding it is a stealth issue. Right angles are a no-no. I would imagine there are also benefits from getting some more horizontal effect instead of pure yaw control as well.
     
    Last edited: Dec 9, 2009
  4. Dec 9, 2009 #3
    Re: F-22

    Thanks! Using it as an elevator was the only thing I could think of as well. Why are right angles a no-no when it comes to stealth?
     
  5. Dec 9, 2009 #4

    mgb_phys

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    Re: F-22

    If you imagine a right angle corner.
    Whatever angle an incoming radar beams hits one surface at it will bounce of that then the other and return along the same direction - directly back to the radar set.
    With an obtuse angle it will be reflected away in another direction.

    It's the same principle as a corner cube - where you want the light to go back the same way.
     
  6. Dec 9, 2009 #5
    Re: F-22

    Cool. That makes sense, thanks!
     
  7. Dec 9, 2009 #6
    Re: F-22

    I do not buy this "stealth" argument. Many aircraft, F-18, etc use angled twin tails and is not for stealth. It probably has more to do with stability. Note: these aircraft were designed well before stealth design methodlogies were discovered.

    f18_schem_01.gif
     
    Last edited: Dec 9, 2009
  8. Dec 9, 2009 #7

    turbo

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    Re: F-22

    Perhaps not fully a stealth issue, but you've got to admit that replacing those two splayed control surfaces with one bigger one mounted vertically, would result in a larger radar signature.
     
  9. Dec 9, 2009 #8
    Re: F-22

    How would it improve stability?
     
  10. Dec 9, 2009 #9
    Re: F-22

    I emailed a good friend who is head of our wind tunnel. I will quote his response in our email:

    So, it's pretty much not for stealth. Note: the F-14, F-15 have straight tails. This was a good observation and interesting question RandomGuy88!
     
    Last edited: Dec 9, 2009
  11. Dec 9, 2009 #10
    Re: F-22

    Very cool, thanks for the response.
     
  12. Dec 9, 2009 #11

    FredGarvin

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    Re: F-22

    I don't doubt your source for a second (because it is repeated in the link below). However the stealth issue is part of the equation. The SR-71 had them loooooooong time ago and Hav Blue was in the mid 70's and Lockheed was working on it prior to that. So stealth has been around as long as say the F-14, just not in the open.

    http://www.aerospaceweb.org/question/planes/q0157.shtml

    http://books.google.com/books?id=fVQRmQo-bfUC&pg=PA17&lpg=PA17&dq=kelly+johnson,+canted+vertical+tails&source=bl&ots=eUPlC_78Qq&sig=WOYbMSciQuyGYzaqH686TVnHObU&hl=en&ei=5C4gS4qtO5XSMo78ucUC&sa=X&oi=book_result&ct=result&resnum=3&ved=0CAsQ6AEwAg#v=onepage&q=kelly%20johnson%2C%20canted%20vertical%20tails&f=false [Broken]

    Note page 8 here:
    http://www.scribd.com/doc/18029452/NASA-SR71-Blackbird-Challenges-and-Lessons-Learned-2009
     
    Last edited by a moderator: May 4, 2017
  13. Dec 9, 2009 #12

    DaveC426913

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    Re: F-22

    The Raptor's vertical surfaces are significantly more oblique than other craft. Yes, this is to reduce radar signature. The fact that more conventional craft have moderately oblique tails does not change that.


    http://www.globalsecurity.org/military/systems/aircraft/f-22-stealth.htm

    "A quick look at the F-22 reveals an adherence to fundamental shaping principles of a stealthy design. The leading and trailing edges of the wing and tail have identical sweep angles (a design technique called planform alignment). The fuselage and canopy have sloping sides. The canopy seam, bay doors, and other surface interfaces are sawtoothed. The vertical tails are canted. The engine face is deeply hidden by a serpentine inlet duct and weapons are carried internally. "
     
    Last edited: Dec 9, 2009
  14. Dec 9, 2009 #13
    Re: F-22

    No Cyrus, it's not stealth only as in F-117 etc, the reduction of the radar cross section has been a worry for decades. The principle of the radar reflector was well known ages ago and and so was the notion that rectangles were the most effect radar reflectors.

    So, experimenting with design versus radar cross section was done in the early days already. Also, for instance, if you see a bit of a golden hue on a canopy, it's because of generating radar reflection, so that all the rectangles in the cockpit don't act as a radar reflector. But it is still awkward that the F-15 has retangular fins, which are of course easier for structural integrity.
     
  15. Dec 9, 2009 #14
    Re: F-22

    The ability to defeat (thats a loose term) radar was not developted until the early 80s with the F-117. I do not consider this 'ages ago', as this knowledge came much after the existance of many twin tailed fighter jets.

    True, but they were all uncessful up until the 80s. The U-2 was thought to be stealthy, until they flew it and discovered the Russians were tracking it the moment it left the ground.

    Interesting, do you know when (timeline) this golden hue was added?
     
  16. Dec 9, 2009 #15

    FredGarvin

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    Re: F-22

    Nope. The SR-71 used it and that was the late 50's and 60's with the YF-12. I would call that one pretty successful.
     
  17. Dec 9, 2009 #16
    Re: F-22

    The SR-71 was by no means stealthy to Radar. Read the book "Skunk Works" which disproves your claim. While its certainly true that they tried to incorporate some early methods, they were not sucessful as per the theory that lead to the design of the F-117or F-22.
     
  18. Dec 9, 2009 #17

    FredGarvin

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    Re: F-22

    The link above that I gave directly states that they were canted in for reduction in RCS. Whether the aircraft was stealthy or not is a moot point (which I disagree with). They were canted because they were thinking about making the aircraft smaller on radar.

    http://books.google.com/books?id=fVQRmQo-bfUC&pg=PA17&lpg=PA17&dq=kelly+johnson,+canted+vertical+tails&source=bl&ots=eUPlC_78Qq&sig=WOYbMSciQuyGYzaqH686TVnHObU&hl=en&ei=5C4gS4qtO5XSMo78ucUC&sa=X&oi=book_result&ct=result&resnum=3&ved=0CAsQ6AEwAg#v=onepage&q=kelly%20johnson%2C%20canted%20vertical%20tails&f=false [Broken]
     

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    Last edited by a moderator: May 4, 2017
  19. Dec 9, 2009 #18

    mgb_phys

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    Re: F-22

    It's not bad for an airframe that size. IIRC the major issue in practice was that the jet exhaust gave such a huge signature in the cold empty sky at those altitudes.
    Stealth doesn't make the plane invisible (the loss of B2s in serbia proved that) it just gives you an edge. Like any other camouflage it just shifts that few % where they can just see you into the few % where they just can't.
    The dihedral stabilizers are a combination of aerodynamics and radar return. The reflection from a corner cube was very well known before stealth. The same flat angled shape effect can be seen on low visibility ships.

    I went to a lecture by the British radar expert lockheed brought in to perform the tests described in skunk works (don't have my copy here - can't remember his name).

    They found a number of planes that were surprisingly stealthy, The Avro Vulcan was among the best - despite having a delta wing about the size of Iowa it has lots of non-constant radius curves which scatter the radar return, very deep oval engine inlets and a defrosting heating coating which turned out to be just the correct wavelength to absorb radar of the time.
     
  20. Dec 9, 2009 #19
    Re: F-22

    There was a program at AFMDC (Holloman AFB) in the late 50's and early 60's called RAT SCAT (classified at the time) which is now unclassified.

    Google "rat scat" and then (after enjoying all the ads for rodent exterminators), search within results for "radar".

    http://www.stormingmedia.us/57/5744/0574474.html

    Yes, aircraft (and missile) radar cross sections have been an important military concern for a long time.
     
  21. Dec 9, 2009 #20

    turbo

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    Re: F-22

    From Lockheed Martin's Code One, explaining why their F-22 design beat out General Dynamic's design with a single vertical tail and Boeing's similar configuration:
    http://www.codeonemagazine.com/archives/1998/articles/apr_98/apra_98.html
    Note the animation here, demonstrating how the leading and trailing edges of wings and elevators are kept at the same angles to reduce radar signature AND the angles of the engine inlets and the splayed tails are lined up, as well.
    http://www.f-22raptor.com/st_fa22tricks.php#stealthfeatures



    http://www.f-22raptor.com/st_fa22tricks.php#stealthfeatures
     
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