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  1. #1
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    since we got the airplane on the treadmill figured out...helicopter in a train?

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    Can a mod move this to the proper forum please?

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    Probably a combination of both. Without any control inputs, the chopper will remain stationary relative to the tracks at first, but then the air resistance will cause it to accelerate with the train. Without more details, it cannot be determined if it will become stationary relative to the train before it hits the wall.

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    Depends on how far from the back wall the helicopter is hovering, and how long the train accelerates for. Air has inertia like everything else (and it's compressible), so there would be a lag time before the air pressure resists the force of the back wall, and it's velocity catches up with the train.

    In any case, the helicopter would not remain stationary relative to the train. It would certainly move towards the back wall; whether it smacks agains it depends on the initial distance and how long the train accelerates until it reaches constant velocity.

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    since we got the airplane on the treadmill figured out...helicopter in a train?

    Quote Originally Posted by Robojerry View Post
    Depends on how far from the back wall the helicopter is hovering, and how long the train accelerates for. Air has inertia like everything else (and it's compressible), so there would be a lag time before the air pressure resists the force of the back wall, and it's velocity catches up with the train.

    In any case, the helicopter would not remain stationary relative to the train. It would certainly move towards the back wall; whether it smacks agains it depends on the initial distance and how long the train accelerates until it reaches constant velocity.
    Wouldn't the rate it is moved also be dependent on the drag force of the helicopter??

    So the variables are acceleration and air drag of the heli?

  6. #6
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    What good is a helicopter without a peak to land on for slaying pow ?

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    Quote Originally Posted by steepconcrete View Post
    Wouldn't the rate it is moved also be dependent on the drag force of the helicopter??

    So the variables are acceleration and air drag of the heli?
    Yeah, word. While we're at it, temperature would be a factor too right, as air resistance is density-dependent?

  8. #8
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    Quote Originally Posted by steepconcrete View Post
    Wouldn't the rate it is moved also be dependent on the drag force of the helicopter??

    So the variables are acceleration and air drag of the heli?
    Is it an African or European helicopter?
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    Quote Originally Posted by PNWbrit View Post
    Is it an African or European helicopter?
    I thought African helicopters were non-migratory?

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    Quote Originally Posted by fatnslow View Post
    What good is a helicopter without a peak to land on for slaying pow ?
    This is all that needs to be said! All other responses are pointless. Save your key strokes.

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    Quote Originally Posted by PNWbrit View Post
    Is it an African or European helicopter?
    How do know so much about helicopters?

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    And no one asks if the train is going at the speed of light? Fucking dentists.
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    Put a helium balloon in your car if you want to see the result of this, although the helium balloon will move forwards in the car when you accelerate.
    Quote Originally Posted by jlboyell View Post
    Climate change deniers should be in the same boat as the flat earthers, ridiculed for stupidity.

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    Quote Originally Posted by jlboyell View Post
    Climate change deniers should be in the same boat as the flat earthers, ridiculed for stupidity.

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    Quote Originally Posted by PNWbrit View Post
    Is it an African or European helicopter?
    What? I don't know! Aaaahhhh!
    "fuck off you asshat gaper shit for brains fucktard wanker." - Jesus Christ
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    Pretty much stationary.

    Since the train car is enclosed the air inside would also basically stay stationary.

    If the train car was open like a flatbed freight train it would slam into the next car.

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    Quote Originally Posted by deepsouthmafia View Post
    Can a mod move this to the proper forum please?
    Why is this posted in the Ski/ Snowboard forum?
    Its an intersting topic, but I feel like it should of been posted in Padded Room, no?

  18. #18
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    Quote Originally Posted by Soups View Post
    Pretty much stationary.

    Since the train car is enclosed the air inside would also basically stay stationary.

    If the train car was open like a flatbed freight train it would slam into the next car.
    Inertia. Helicopters has it.

  19. #19
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    Helicopter will move forwards as the train accelerates and air moves backward. See the balloon video.

    Slightly lower air pressure on the front edge of the rotor will have less lift than the back edge of the rotor. Heli will pitch forward to achieve pressure equilibrium with the pressure gradient of the sloped air and move.

    That said, the maximum rate of acceleration for a subway train on level ground is somewhere around 1.3 m/s/s. Japan's N700 series bullet train accelerates closer to 0.42 m/s/s. That whole steel wheels on steel rails low friction platform thing combined with sophisticated traction control technology doesn't allow for sick train burnouts.
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    Quote Originally Posted by zartagen View Post
    Inertia. Helicopters has it.
    Frame of reference. Earth has it too. When a heli lifts off the ground, it doesn't start seeing the planet spinning at 1600 kph. (yes, the earth is moving)
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  21. #21
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    Quote Originally Posted by DJSapp View Post
    Helicopter will move forwards as the train accelerates and air moves backward.
    Forwards relative to what?

    Obviously, once the train reaches constant velocity, it becomes an inertial reference frame so the helicopter will act just like it would when earth is the inertial reference frame (assuming all the air in the train is moving at the same speed as the train, i.e., there are no air leaks — maybe inside a plane would be a better scenario). But while the train/plane is accelerating, I'm pretty sure the chopper will move backwards inside the train but forwards relative to the point at which it starts. Even if it pitches forwards.
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  22. #22
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    Forward being the direction of motion of the train. Watch the balloon video

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    Like I said, it certainly will pitch forward. The question of whether it moves forwards or backwards depends on the force generated by the rotor vs the inertial and drag forces on the helicopter. Assuming there isn't a controller that will increase the rotor speed to maintain position, I would suspect most scenarios would result in it moving backwards. Especially because acceleration causes gas (air) to become more viscous so the propeller will spin slower and not generate as much force as it does during normal operation and simultaneously there body of the copter will have more drag than usual.

    The helium balloon has almost no mass, so it will obviously move forward. How is that relevant here?
    "Alpine rock and steep, deep powder are what I seek, and I will always find solace there." - Bean Bowers

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  24. #24
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    Quote Originally Posted by DJSapp View Post
    Frame of reference. Earth has it too. When a heli lifts off the ground, it doesn't start seeing the planet spinning at 1600 kph. (yes, the earth is moving)
    The train wouldn't count as an inertial reference frame because it's accelerating, unlike earth which moves and spins at constant velocity.

    Quote Originally Posted by DJSapp View Post
    Helicopter will move forwards as the train accelerates and air moves backward. See the balloon video.

    Slightly lower air pressure on the front edge of the rotor will have less lift than the back edge of the rotor. Heli will pitch forward to achieve pressure equilibrium with the pressure gradient of the sloped air and move.
    I think the helicopter would still move backwards unless the train accelerated slowly. The balloon moves forward because the denser air has more inertia, and displaces the less dense helium. I'm with you that a hovering helicopter behaves sort of like a helium balloon, but it's so much denser and would quickly overcome the air pressure if the train accelerated quickly enough.

  25. #25
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    Robojerry, please stop.

    Basic Newtonian physics:

    1. Speed is a scalar
    2. Velocity is speed with a direction
    3. Acceleration is the rate of change of velocity.

    To move in a circle means you are undergoing an acceleration, as your direction is constantly changing. The Earth is spinning on it's axis, and orbiting the sun, and orbiting the center of the milky way. Keep that in mind as we move to this.

    We are all accelerating with respect to a fixed point in the universe. That said, you can change reference points to suit your situation. This feels natural as the motion of the planet and stars are too large to perceive.

    So going to a helicopter. Heli's hover because they make themselves buoyant in air with the lift from the rotors. The even lift a heli needs to hover is based upon the assumption of constant air pressure providing a constant reaction for the rotors to push against.

    Now take our train. Fill the car halfway with water. What happens when the train accelerates? The water sloshes backwards because as the train under it moves forward, nothing is reacting against the water to make it move with the train until it hits the back of the car. Once the train reaches a constant velocity, the water will level out.

    Now take our heli. It is floating in the air because it is pushing against a constant gradient of air pressure. Like humans can't feel the universe moving, the heli cannot perceive the motion of the train, so it is irrelevant.

    When the train accelerates, the air moves like the water within the train car, pooling toward the back and creating a surface of air that is not perpendicular to force of gravity. This creates an uneven reaction force on the heli's lift on the air and the force of gravity and causes it to pitch forward. This uneven set of forces creates motion in the direction of the accelerating train.
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