Question about speed

Discussion in 'ELR, Ballistics & Bullets Board' started by freebird63, Sep 26, 2018.

  1. freebird63

    freebird63

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    I see some refer to a couple different speeds.
    TranSonic
    SuperSonic
    SubSonic

    What are these speeds in FPS??

    Thank you
    Chuck
     
  2. chkunz

    chkunz Gold $$ Contributor

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    Transonic is Mach 0.8 to 1.2
    Supersonic is above Mach 1.0
    Subsonic is below Mach 1.0

    Mach number is dependent on the local speed of sound which is dependent on the properties of the gas, in air it is 49.02 times the square root of the absolute temperature.

    So at sea level conditions and 70 Deg F Mach 1 is about 1100 feet per second and Mach 2 would be two times the fps, etc. If you are going to do the calculation convert the temperature in Deg F to the Absolute temperature scale.
     
    Last edited: Sep 26, 2018
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  3. Eternal Student

    Eternal Student

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    Most people don't know what the mach are:

    1339 fps and down to about 1126 fps is transsonic (the speed of sound changes a lil on temp, elevation, etc....)
    1339 and up is supper sonic
    below 1126 fps is subsonic .
    the 1126 fps will change.
     
  4. chkunz

    chkunz Gold $$ Contributor

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    Eternal Student, please see my reply above. I have rounded off things a little and I kept the answer at a level where "most people" will understand well enough. Your definition of transonic should be Mach 0.8 to 1.2, the velocities you quote are close to Mach 1.0 to 1.2 at 70 deg F in air. Yes, the speed of sound changes with the temperature of the gas, in air it is 49.02 times the square root of the absolute temperature.
    Best wishes
    Clyde
     
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  5. Eternal Student

    Eternal Student

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  6. damoncali

    damoncali Gold $$ Contributor

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    Subsonic is anything below the speed of sound.
    Supersonic is anything above the speed of sound.
    Transonic is used to describe the transitional area right around mach 1, where aerodynamics are known to do weird things.

    Mach 1 is roughly 1100 feet per second but depends mainly on temperature, and varries significantly from, say, 20 degrees F to 100 degrees F.

    If you look at a chart of drag coefficient vs mach number for a bullet you see that it's very well behaved over mach 1.1 or so, and below mach 0.9. In between, all hell breaks loose. That hell is the transsonic region. Notice the HUGE jump between 1000 fps until about 1200 fps. Before and after it's basically simple, easy to predict curve. In between all bets are off. (That's an oversimplification, but you get my drift).

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    Bullet speeds are often in mach numbers (that is, multiples of the speed of sound) because aerodynamic effects are generally based on the speed of sound, which is the point at which a shock wave forms (more or less). That's why you don't see engineers using fps when discussing aerodynamics - it's the sound barrier that's important, and that moves around with temperature. It's a lot simpler to think in terms of mach numbers that are anchored to the speed of sound.
     
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  7. Mozella

    Mozella

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    Actually, the speed of sound in air depends on temperature. It's that simple.
     
  8. rammac

    rammac

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    The exact speeds related to mach values have to be calculated when the shooter is firing, there are no universal values in Feet Per Second. Trans-sonic speeds are not universally agreed upon either, at least for shooters. Some shooters feel that trans-sonic speeds are a range of mach 0.8 to as high as 1.4.

    Here is a link to an online calculator that will provide you with the speed of sound based on temperature.
     

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