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Thread: Shooting in the rain

  1. #31
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    From Wikpedia: "Shock waves can travel through any medium, including solids, liquids, gasses, and plasmas."

    https://en.wikipedia.org/wiki/Shock_wave

    Mach waves are cone-shaped, and extend outward from the bullet in all directions, including to the ground. If air couldn't flow through the wave, then the bullet would have to push an increasing mass of air along with it as it traveled from muzzle to target. It would be lucky to go a few feet before it accumulated so much resistance that it fell to the ground.

    The same sort of Mach wave extends from a supersonic aircraft at 10,000 feet all the way to the ground. If planes had to push everything in its path in front of their Mach wave, they couldn't fly.

    When we hear a sonic boom, the Mach wave has passed through our bodies. It does not push us to the ground.

    The cloud of water vapor that many of us have seen when a bullet strikes a raindrop is not pushed by the Mach wave past the target. The Mach wave passes through it.

    Enough examples?

    Cheers,
    Keith

    No need to bring Bernoulli into this.

    Added:

    Here is a better reference for the mathematically-inclined: https://en.wikipedia.org/wiki/Rankin...iot_conditions

    u2 in the first three equations (conservation of mass, momentum and energy) is the speed of air passing through the shock wave. u2 is not zero.
    Last edited by mks; 10-15-2015 at 08:26 PM. Reason: more info

  2. #32
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    At The Nationals in Phoenix several years ago, we had a sudden rain storm come in during my relay. The rain was not blowing under the firing line awning, it was just a steady downpour.

    I had a shot go almost ONE INCH off from my group. This was at 100 yards.

    This is not the first time I have had this happen.

  3. #33
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    How do you post a photo ? I have some interesting pictures

  4. #34
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    Very easy just go to the above third icon from the right (insert image) click on it and do as it says. First click on the below (reply to thread) icon.
    Chet
    Last edited by coyotechet; 10-15-2015 at 09:29 PM.

  5. #35
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    Click image for larger version. 

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    The shock waves are different on H P Versus a pointed bullet, but in my opinion if it is raining hard enough and the distance is "100 Yards" both bullets will be deflected if the raindrop hits it. The weight of the bullet 68 grain should deflect more than a 168 grain

    I M H O
    Last edited by classcat; 10-16-2015 at 12:27 AM.

  6. #36
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    Quote Originally Posted by brickeyee View Post
    Even air does not flow over a Mach wave.

    The Bernoulli equation fails since it assumes a standing pressure wave cannot exist.
    Waay over my head.

  7. #37
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    Quote Originally Posted by mks View Post
    From Wikpedia: "Shock waves can travel through any medium, including solids, liquids, gasses, and plasmas."

    https://en.wikipedia.org/wiki/Shock_wave

    Mach waves are cone-shaped, and extend outward from the bullet in all directions, including to the ground. If air couldn't flow through the wave, then the bullet would have to push an increasing mass of air along with it as it traveled from muzzle to target. It would be lucky to go a few feet before it accumulated so much resistance that it fell to the ground.

    The same sort of Mach wave extends from a supersonic aircraft at 10,000 feet all the way to the ground. If planes had to push everything in its path in front of their Mach wave, they couldn't fly.

    When we hear a sonic boom, the Mach wave has passed through our bodies. It does not push us to the ground.

    The cloud of water vapor that many of us have seen when a bullet strikes a raindrop is not pushed by the Mach wave past the target. The Mach wave passes through it.

    Enough examples?

    Cheers,
    Keith

    No need to bring Bernoulli into this.

    Added:

    Here is a better reference for the mathematically-inclined: https://en.wikipedia.org/wiki/Rankin...iot_conditions

    u2 in the first three equations (conservation of mass, momentum and energy) is the speed of air passing through the shock wave. u2 is not zero.
    If a Mach wave enters a jet engine inlet the engine is instantly choked off from the interruption of air flow.
    The idea that the mach wave extends to infinity and represents an infinite load is grossly wrong in concept.
    Over a limited area it is a standing pressure wave.
    The pressure difference drops across the wave as you move away from the supersonic object.
    Air flows AROUND the roughly cone shaped pressure wave, but not through the wave.

    As velocity increases the Mach waves forms and attaches to the object.
    It IS in front of the object at the front. How far depends on the density of the 'fuid' the object is moving in.
    As velocity continues to increase the Mach angle (opening angle of the Mach wave that face backwards) becomes smaller and actual drag force declines.

    Chuck Yeager was the first one with enough balls to go above Mach 1.
    The other pilots tried to creep up.
    Control force increased and buffeting occurred as the Mach waves attached.
    The Mach waves had to be moved along with the control surface.

    Even now we fly below Mach 1 or above Mach 1 (with some margin on each) but not AT Mach 1.

  8. #38
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    When flow is choked, it has reached a maximum that cannot be exceeded without changing the upstream conditions. The flow does not suddenly stop.

    https://en.wikipedia.org/wiki/Choked_flow

    The second equation gives the mass flow rate through the shock wave under choked conditions.

    Again fluids, including air, flow through a shock wave, whether it is around a bullet or in a venturi.

  9. #39
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    Quote Originally Posted by mks View Post
    When flow is choked, it has reached a maximum that cannot be exceeded without changing the upstream conditions. The flow does not suddenly stop.

    https://en.wikipedia.org/wiki/Choked_flow

    The second equation gives the mass flow rate through the shock wave under choked conditions.

    Again fluids, including air, flow through a shock wave, whether it is around a bullet or in a venturi.
    Air does not flow over a shock wave.
    That is the very definition of a shock wave in a compressible flow.

    We sepent a lot of effort to keep the Mach wave out of the inlet of the SR71 engines a long time ago.
    They mostly operated as bypassed ram jett.
    The air flow choked instatly if the mach wave entered the inlet.
    It made for spectacular pictures of flames from teh afgterburner.
    they are very common pictures.

    The computer (originally analog) immediately commanded full rudder to counteract the loss of thrust from an 'unstart' from the choked flow.
    A pilot would never react fast enough to maintain control.

    They complained about their heads striking the inside of the canopy the motion was so violent.

    I have denstrated chocked flow for at least the past 20 years in my lab to undergrads.

    I increase the pressure driving a gas though a small tube higher and higher.
    The tube is instrumented with all sorts of mass flow, velocity, and pressure sensors (the purpose of the class is instrumentation).
    As the flow speed increases the tiny perturbations the sensors create allow Mach waves to attach.
    At the critical speed the pressure shows a step over a short distance, the mass flow drops to zero.
    The tube is still open but the silence is deafening.
    No more screaming gas.

    If there is time we repeat it using a nozzle shaped to increase flow speed through a throat.

    Part of the deonstration is to make sure students stay alert to how sensors can disrupt the very target of measurements.
    Last edited by brickeyee; 10-16-2015 at 09:42 PM.

  10. #40
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    I understand that it is difficult to reconsider a long-held belief, but please have a look at this short lesson on choked flow:

    https://www.youtube.com/watch?v=DNURRIJz94k

    At the 3:17 mark, the instructor shows a graph of mass flow rate as a function of back pressure. You see that mass flow rate is maximized when choking occurs at Mach = 1. Later he shows simulations of flow through the shock wave for different back pressures.

    Here is a video in a supersonic wind tunnel of flow through a shock wave:

    https://www.youtube.com/watch?v=BI7R8KiX8HU

    Not only is there flow through a shock wave, flow is necessary for a shock wave to occur. The shock wave occurs where Mach = 1, i.e., where the speed of the air is equal to the speed of sound.

  11. #41
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    Holey Kowww.... this is why I quit arguing with teachers years ago....

    the tiny perturbations the sensors create allow Mach waves to attach.
    At the critical speed the pressure shows a step over a short distance, the mass flow drops to zero.
    The tube is still open but the silence is deafening.
    No more screaming gas.

    OK, let's read it slowly....


    the mass flow drops to zero

    really?

  12. #42
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    If the mass flow dropped to zero, then there would be nothing to maintain the pressure and density differences across the shock wave, and the wave would disappear. You can't have a shock wave without flow.

  13. #43
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    I'm losing track...(I've lost track)

    Not that I don't lose track a lot but.....are y'all saying that a bullet will or will not strike a rain drop?

    If y'all have moved on to something different just ignore this post...please sirs.

  14. #44
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    A bullet may or may not hit a raindrop but i do know when its raining ive seen some good aggs destroyed in a rain relay. I mean 2" flyers. And it does it during the rain.

  15. #45
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    What's the difference between rain drops and insects ,of all dimensions. Not to mention flag tail material. Does rain drops possess some kind of magical protection from high velocity flying objects?




    Glenn

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