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Hypersonic Aircraft

  1. May 27, 2010 #1

    Char. Limit

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    http://www.latimes.com/business/la-fi-hypersonic-20100527,0,764506.story

    I found this to be awesome, although I wonder what size of sonic boom a hypersonic passenger jet would make... Nevertheless, imagine flying from Los Angeles to New York in 30 minutes... and we have the technology to go hypersonic, how long could it take to develop a hypersonic passenger jet?

    In a word, awesome.
     
  2. jcsd
  3. May 27, 2010 #2
    The supersonic jet didn't work out so well...
     
  4. May 27, 2010 #3
    They should put a camera on it and fly it by some reference points so we can see just how fast it's going. Like when I run through the hallway in my house, I'm like lightning. But when I get on a football field, I'm the slowest person there. What gives?
     
  5. May 27, 2010 #4

    Astronuc

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    The sonic boom occurs when the aircraft passes through the 'sound barrier'. Once it goes through it's supersonic - actually transonic (~0.7 to 1.2). Supersonic generally applies to M >1.2 to 5. Hypersonic, M > 5.

    http://www.aoe.vt.edu/~mason/Mason_f/ConfigAeroTrans.pdf [Broken]

    Most people apparently define the transonic range M = 0.8 to 1.2.
    http://aero-comlab.stanford.edu/Papers/SympTransIV_DACAJ.pdf
     
    Last edited by a moderator: May 4, 2017
  6. May 29, 2010 #5

    russ_watters

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    No Astronuc. A supersonic plane drags a shock wave behind it as it flies. What you describe is a Hollywood dramatization.

    Also, the strength varies considerably with altitude so a hypersonic plane woulnt necessarily be audible from the ground.
     
  7. May 29, 2010 #6
    That's what they thought back in the day but test showed that even at great altitudes the boom was 'still a problem'.

    The amount of 'boom' is actually more of a function on wing span and the planes weight.
     
  8. Jun 22, 2010 #7
    I have a question.

    What happens if you're traveling faster than the speed of sound... and then you slow down, passing the sound barrier again, back into the "traveling slower than the speed of sound" speeds?

    Do you generate another sonic boom?
     
  9. Jun 22, 2010 #8
    There is no such thing as a sound barrier. However there are shock waves which remain there as long as the aircraft is supersonic or transsonic.
     
  10. Jun 22, 2010 #9
    Can someone clarify the "sonic boom" for me. As I understood it the boom doesn't just happen once. It would be progressing continually along the ground as the displaced air behind the aircraft rushed back together behind the aircraft. The boom wouldn't just happen once the aircraft passed the "barrier". It would be heard by whomever was under the aircraft when it passed overhead. Am I mistaken?
     
  11. Jun 22, 2010 #10
    So you're saying that, the sonic boom noise "turns on" when the object travels faster than sound, and then "turns off" when it slows down to speeds lower than that of the sound..?
     
  12. Jun 22, 2010 #11
    Ah, I think you answered my question as I was typing it.
     
  13. Jun 22, 2010 #12

    russ_watters

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    That is correct. A plane traveling faster than the speed of sound drags a cone-shaped shock wave behind it. The "boom" you hear is this cone shaped shock wave being dragged past you.
     
  14. Jun 22, 2010 #13
    Wow, this is amazing! That thing can travel almost a mile in a single second!
     
  15. Jun 22, 2010 #14

    minger

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    One more point on top of all of this:

    The boom that we hear is associated with a certain type of pressure pulse. We call it in N wave. As the "sonic boom" passes the bystander on the ground, there is a sudden sharp increase in pressure, followed by a sudden sharp decrease (looks kind of like an N). It is this sharp change in pressure that sounds so loud.

    NASA has been doing a lot of work to "smooth" out the N wave as to decrease the intensity of the sonic boom. However, I'm not so sure designs could incorporate both features to decrease the sound while enabling hypersonic flight.
     
  16. Jun 22, 2010 #15

    Char. Limit

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    One thing, just to give a word to your quoted phrase. I believe that speeds slower than the speed of sound are described as "subsonic".

    Although I'm not sure what transsonic is... "beyond" the speed of sound?
     
  17. Jun 22, 2010 #16

    russ_watters

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    Transonic is the speed range right around the speed of sound (around .8-1.2 or .9 to 1.1 mach, depending on the plane), where parts of an airplane are flying through subsonic air and parts of it are flying through supersonic air. In particular, as air travels over the top surface of a wing, it speeds up. At the point on the wing where it speeds-up to Mach 1, a shock wave forms. As the plane accelerates, this shock wave moves backwards on the wing until it reaches the trailing edge when the plane hits Mach 1. The reason this speed region is characterized by unstable flight and high drag is these shock waves are not stable and move around on the plane. For that reason, it is best for planes not to linger in this region, but to accelerate through it relatively quickly.

    See diagrams halfway down this page: http://www.flightlearnings.com/high-speed-flight-shock-waves/480/
     
    Last edited: Jun 22, 2010
  18. Jun 22, 2010 #17

    DaveC426913

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    Spanning the speed of sound, i.e. .8 to 1.2.


    BTW, there are actually multiple booms, all very close together. There's a shock wave from each leading edge of a protrusion on a plane. Usually one can hear, at most, two booms, almost on top of each other - one from the nose, and another from the wing leading edge (or from the tail).

    [PLAIN]http://blogs.discovery.com/news_space/images/2008/11/03/t38.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
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