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  #1  
Old 09-06-2015, 09:42 PM
Padruig Padruig is offline
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Default Parachute questions

A couple of questions pertaining to parachutes I've been mulling over...

1) Are there recommended lengths of string to be used for the various parachute sizes? If so, what are they? In some of my old stuff I found a number of loose parachutes (no string) that I would like to restring.

2) From what I recall as a kid, on a hexagonal parachute, all the parachute cords were attached side by side, i.e. 3 equal loops. Some of the kits I've bought recently have two loops that are opposite of each other and one loop that spans from one point of the parachute across to the opposite point. What are the pros and cons to either methods?
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Old 09-06-2015, 11:29 PM
Padruig Padruig is offline
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Found the answer to one of my questions: http://archive.rocketreviews.com/to..._patterns.shtml
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Old 09-07-2015, 12:20 AM
Les Les is offline
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Quote:
Originally Posted by Padruig

2) From what I recall as a kid, on a hexagonal parachute, all the parachute cords were attached side by side, i.e. 3 equal loops. Some of the kits I've bought recently have two loops that are opposite of each other and one loop that spans from one point of the parachute across to the opposite point. What are the pros and cons to either methods?



See this article. The across the point help prevents tangles

Apogee article - tangle free parachute lines
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  #4  
Old 09-07-2015, 10:00 AM
Padruig Padruig is offline
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That's a hell of an article! Thanks Les!
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  #5  
Old 09-07-2015, 11:05 PM
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luke strawwalker luke strawwalker is offline
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The general recommendation for shroud line length is 1.5 times the diameter of the chute canopy. Since you usually use a length of string tied to the canopy at both ends and attached to a swivel or the rocket in the middle, each shroud line string you cut should be 3X the width of the canopy... that puts each end tied or taped to the chute canopy and the swivel or rocket tied on in the middle. I consider this as a basic minimum. One can go up to 2X the diameter of the canopy, which means each string would be 4X the canopy diameter when cut, with each end tied or taped to the canopy itself and the swivel or rocket tied on in the middle. There's really no advantage to going longer than that. The shorter the shroud lines, the more "scrunched" the canopy will be when opened (it won't fully inflate) and thus the faster the descent rate will be. In fact, sometimes folks will add a ring of tape to the shroud lines between the swivel or rocket and the canopy edge, taping them all together, to effectively "shorten" the shroud lines, to keep the canopy "reefed" (not allowing the parachute to open all the way to its full diameter, which increases the descent speed of the rocket under parachute).

Having used both methods of tying on shroud lines, (tying them all to two adjacent holes and then gathering them to the center, or 2) tying them all parallel across the canopy, and gathering them at the center) I can tell you that the second method works MUCH better and results in far less tangling and deployment problems. Regardless of the number of shroud lines (depending on if the parachute is hexagonal, octagonal, or round) the best way is to start with two adjacent holes, tie each end of a single line to them, and then tie the next line's ends to the holes immediately next to them, on either side of the first set of holes, and keep working one's way around the chute canopy until the last line is tied on to the last two holes in the edge next to each other opposite where you started... This method puts ALL the shroud lines PARALLEL to each other, which reduces crossed lines and tangling.

Best of luck! OL JR
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Old 10-02-2015, 05:09 PM
UlteriorModem UlteriorModem is offline
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Default Spill hole? or Holze in da Chutze!

Thought I might just add to this thread instead of opening a new one.

I have always cut holes in the center of my chutes. Today I learned they call them "spill holes" of course they increase the rate of descent but I wonder if there is any way to guestimate the rate of descent vs the same chute with no spill hole.

In my meager attempts at research I found this article from Apogee which is quite good but only briefly mentions a spill hole.

https://www.apogeerockets.com/educa...wsletter149.pdf

I was just wondering if other folks cut holes in their chutes and your thoughts, and experiences with doing so.

Thanks!
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Old 10-03-2015, 06:34 AM
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mojo1986 mojo1986 is offline
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I used to cut spill holes to reduce the wobble during descent, but I have no idea (other than using reduced surface area as a starting point) how to calculate the increase in rate of descent. But my observation was always that a small spill hole didn't really change the descent rate very much.

Joe
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Old 10-03-2015, 05:37 PM
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Quote:
Originally Posted by mojo1986
I used to cut spill holes to reduce the wobble during descent, but I have no idea (other than using reduced surface area as a starting point) how to calculate the increase in rate of descent. But my observation was always that a small spill hole didn't really change the descent rate very much.

Joe

It's a really simple scientific law. The nicer your model, the less effect a spill hole will have on decent on a windy day. However, it will have the inverse effect on hard landing surfaces, making decent rates increase with the increase in model quality.
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Old 10-03-2015, 08:23 PM
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Quote:
Originally Posted by tbzep
It's a really simple scientific law. The nicer your model, the less effect a spill hole will have on decent on a windy day. However, it will have the inverse effect on hard landing surfaces, making decent rates increase with the increase in model quality.


Like...

Murphy's Laws of Aerodynamics... LOL Later! OL JR
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