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Thread: Parachute oscillation, off heading.

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  1. #1

    Parachute oscillation, off heading.

    "Since the beginning of parachute making, it was seen that if no spill hole was present in a parachute,it would pitch violently back and forth. In this experiment, the constructed parachute was tested both with and without a spill hole.As was expected, as soon as the spill hole was covered, the oscillations of the parachute were greatly exaggerated. This occurs because excess air pressure builds up at the top of the inside of the parachute and tries to escape out of either side of the bottom of the parachute. This causes it to tip to one side, and as the parachute and payload tip back in the other side of its oscillation, the air pressure escapes out of the other side: therefore reinforcing the oscillations and not allowing it to be damped out as easily. When the spill hole was covered, this was seen immediately. Almost all of the drops without the spill hole simply ended up swinging into the floor directly below the drop floor due to its more pronounced oscillations, which never happened with the spill hole. This phenomena which is seen on full-sized parachutes, was validated by our small-scale testing."

    so on Pc if your using 46,48, go and throw to 1sec. upward toss, the oscillations should be minimal or no factor (not counting the other factor). pass 1 sec. or more you begin to notice oscillations more. time for vent maybe. if you have 50,52PC differently need vent( because of inversion of the pc ).

    oscillations on 42 and smaller PC.factor how you toss,wind angle,the material.
    solid object.

    you toss your pc to your right side(have you try to toss straight up ? hard),
    now if the wind angle is from right to left the wind cross or side will help the center your Pc over your back keeping oscillations and off center opening to minimum.

    if the wind angle is from left to right cross or side will cause the Pc to move away from you than as increase in drag cause to whip back to left causing oscillations and or spinning of the Pc causing off heading and or line twist.

    Have you had a 180 the you know before it happens where you can feel the canopy twisting of your back, I have twice.
    When wind direction Pc throw direction coincide to gather the right way Pc spinning like top, Pc and bridle oscillation causing bridle to twist up, if you read the pc oscillation topic one guy suggest making some thing like a barrel swivel, you have eye on each side the middle work line a swivel, good idea but the wight factor is some thing the think abut, any one have good idea post it.


    If oscillation is keep to minimum there is no problem, if using ZP think abut having vent.

    Using larks head knot on Pc you can't never get it to attach straight, Use a softlink or some thing other to attach the bridle to pc,
    (Manufacture or some rigger can make using 4-500lb specter softlink single loop and tack with e-thred be nice)

    No human is perfect so check you pc for squareness make 12 pie out of the pc and take a measurements make sure vent,cap, and handle is centered to the pc.

    The most important is how you pack,keeping line evenly, when you make figure eight lay the line on top of another with out twisting the line.
    Keep your body symmetrical.
    Watch out for cross wind.
    At pull time pull do not hold on to the pc too long or you will get line twist,
    I did that a yellow ocean had 160 whit2 and ¾ twist and my neck was pin down, I only can look down trying to grab the riser twice to no avail, I bicycle kick out and riser turn away from the cliff.
    A person with phd and ten book to his credit dos not means he is right all the time or some of the time they are all thesis, just like my thought take as you may.

    all bridle is made same way material,pin, length.
    size 42 pc when sew together finish size is 40"

    troll canopy size

    225 = 245 pia or Apex, Asylum
    245 = 264
    265 = 285
    300 = 329
    Last edited by airdog07; June 25th, 2013 at 06:09 PM.

  2. #2

    Re: Parachute oscillation, off heding.


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