Why triple parachute works?

  1. How are parachutes like this made work:

    [​IMG]

    Why do the parachutes remain on the sides nicely instead of colliding in the middle?
     
  2. jcsd
  3. Ranger Mike

    Ranger Mike 1,617
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    it is all in the D bags..deployment bag each chute is pack into. these bags use a static line attached to the airplane/ helicopter and a A piece of parachute line ( string) is tied to the opening loop at the apex of the canopy(top of the parachute). the weight of the pallet ( object to be dropped) pulls the shroud line out and then the folded chute from the D bag and once fully deployed but not opened , the tie is broken from the D bag. ( the jump master has to haul in the static line and D-bag before the plane can land or he has to cut it away) Anyway, each canopy begins to open simulataneoulsy. Notice the shroud lines running up to the panels prevent entry of the deploying chutes. All three caponies are fully deployed and air starts to fill each chute..no one chute is under the other thus preventing the possibility of one chute tangling into another.
    parachute riggers are highly trained people who rig the pallet for the air drop...
     
  4. I understood nearly nothing of that explanation.

    I wasn't speaking about possibility of one chute to get tangled with other ones ropes, but about the possibility of one chute colliding with other chutes.

    Could it be that the chutes are not symmetrical in weight distribution, but instead have the outer sides heavier than the inner sides?
     
  5. Ranger Mike

    Ranger Mike 1,617
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    you asked how they work and some times they do smack into each other. they are identical in construction. it is in the rigging, amigo!
     
  6. FredGarvin

    FredGarvin 5,087
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    Not sure if it really answers the overall question, but I didn't see anything in particular in the Apollo system report on special rigging. The one thing I thought was neat was that the three chutes were ejected 90 degrees from the vertical. I would think that by doing this simultaneously that the parachutes would reach equillibrium in the 120 degrees configuration before they could run into each other perfectly vertical.

    http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730062665_1973062665.pdf
     
  7. nvn

    nvn 2,124
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    jostpuur: I have an answer, but is this question a school assignment?
     
  8. Let me restate the original question. Why are the chutes forced apart?

    They are free to spin on their axis, as they are only supported by cord. Thus, there is nothing in asymmetrical rigging that would help keep them separated while each is free to rotate around its point of suspension. Any I wrong about this?

    Why aren't they colliding?
     
  9. I don't know how to prove this to you with certainty, but I can promise that I've already got my master's degree in mathematics, and I'm not attending lectures or classrooms about stuff like this anymore. :cool:
     
  10. DaveC426913

    DaveC426913 16,362
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    I can't be sure but I'll bet there are vents in the chutes that cause spillage. The spillage acts as a propulsive force, pushing the chute the direction opposite the vent.

    The only thing I can't be sure is how they would keep the chutes from spinning on their own axis, bringing the vents to the outside, causing the propulsive force to act inward.
     
  11. nvn

    nvn 2,124
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    jostpuur: I think the parachute cords on the outer perimeter of the three-parachute configuration are slightly shorter than the inner parachute cords. This causes more of the trapped air to escape underneath the inner edge of each parachute. This radially inward net air flow creates a horizontal, radially outward propulsive force on each parachute. The parachute therefore moves radially outward until the outward propulsive force is balanced by slightly higher tension on the inner cords than on the outer cords.

    I'm currently not sure what guarantees one of the three parachutes will not spin. Perhaps there is a cord linking the three inner cords of each parachute, which would prevent spinning.
     
    Last edited: Oct 25, 2009
  12. Ranger Mike

    Ranger Mike 1,617
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    cargo chutes do not have gores or open panels in them. a steerable parachute like a square or a MC1-1 steerable troop chute has a gore located at the rear of the canopy. this gore can provide significant forward thrust...SF teams exit at 25000 feet AGL and can land 25 miles from the jump point. A jumper must steer the chute into the wind to stall it out before landing..if he did not do this the forward motion would add to the wind speed and he would get busted up on landing. Ref: cargo chutes- you can not have a 40 ton vehicle wandering around in the air all over the Drop Zone. you want the pak to exit the rear of the airplane and land where the DZ officer wants it to. This is why so there is no steerable gores or forward motion for these cargo chutes..they are all the same length and dimensions and they do not spin..spin is bad for chutes and yes they do smack in to each other but the air fills each canopy to the maximum expansion and this pressure is increased the closer to ground level the pak descends...
     
  13. DaveC426913

    DaveC426913 16,362
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    Well correct me if I'm wrong but even round chutes sometimes have slots in them. This may not be the case for personal chutes, but that's not the same as multiplie chutes for cargo.

    Of course there's no forward motion, that's not what the OP is asking about.

    None of this answers the question as to why the chutes are, in fact, staying (for the most part) separated from each other. You can see it in the pics and in videos.
     
  14. Mike, perhaps you can answer this one. I think the answer may lay in the rigging. Do all cargo shoots used in multiples have the extra long rigging? The lines are about 4 chute diameters in length. In personnel chutes they seem to be about twice the chute diameter.
     
  15. Ranger Mike

    Ranger Mike 1,617
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    ok I really did not want to get into this but inquiring minds insist. Parachute are application specific. if you want to concentrate a force in a small area you do not want wide dispersment via steerable chutes so no open gores should be used. Typical cargo chute come in 34, 64 and 100 ft. diameters. depending upon the requirement.. they may be single door bundle or rigged in clusters up to 8 chutes for platform delivery system.
    Now the wrinkle..the military has developed a steerable cargo chute delivery system that can exit the Ac at 25,000 ft AGL and land 22 kilometers away..it has been done and it does work...and the chute is steerable. This is not the typical cargo delivery system used in airborne resupply operations..back to the round canopies. I am most familiar with the 64 foot model that has 64 gores and no openings. I understand improvements have been made since my jumpmaster days and there may in fact be cargo chutes with open side gores but if this is the case...most certainly these are spaced in such a way as to not to provide forward thrust. Regarding cargo chutes that are bundled..they do bump into each other if excess wind is present other wise they descend in a separated manner..now my turn..why would you think they would all want to share the same space???
     
  16. Ranger Mike

    Ranger Mike 1,617
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    i will give you another couple of hints...
    hint number 1...think garden hose and a stream of water..what happens when you stick your palm into the stream???
    hint number 2.
    the air fills each canopy to the maximum expansion and this pressure is increased the closer to ground level the pak descends...
    Hint number 3 . they do bump into each other if excess wind is present other wise they descend in a separated manner..

    think of the chute as a giant air brake....
    what is happening while the pak descends?
     
    Last edited: Oct 26, 2009
  17. MacLaddy

    MacLaddy 226
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    So the air being released from each chute on the sides is forcing them apart? Sort of a spill-over effect.

    Probably didn't even remotely describe that correctly, but hey, I'm new at this.

    Sorry for just jumping in here.
     
  18. mheslep

    mheslep 3,531
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    Yes indeed there are vents, per a NASA documentary I viewed on the Mar's rover landings. Calculating the optimum vent size and shape is a difficult problem, involving iterative wind tunnel tests.
     
  19. Ranger Mike

    Ranger Mike 1,617
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    Trapped air inside the canopy is low speed high pressure and spills out around the periphery of the canopy where it meets high speed low pressure airstream moving over the outside canopy. Now you got a boundary layer of flowing air.
    If wind speed at altitude us high enuff to overcome this, the chutes will smack. Newer cargo chutes for very high speed deployment have four open gores at 12,3,6 and 9 o'clock to prevent panel blow out due to the very high exit speed
    a C130 aircraft used to slow to 120 knots before dropping
    this made one big slow target over the DZ
    so the new chutes permit higher drop speeds
     
  20. mheslep

    mheslep 3,531
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    http://marsrover.nasa.gov/spotlight/20040826.html

     
  21. Perusing the images from a google search on 'cargo parachutes', it appears that the rigging from chutes to common tie point tend to get progressively longer with the number of chutes deployed.

    The large arrays of 4 or more don't appear to be in any general order, but appear free to find their own position in the group.

    It appears that only aerodynamic forces push the parachutes apart without the aid of any special asymmetrical rigging or vents, and are capable of pushing each parachute about 10 degrees from vertical under static conditions.

    The more parachutes deployed in a group, the longer the rigging must be with respect to the parachute diameter to meet the ~10 degree value.
     
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