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Reefing Rings

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edwardw

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I was outside on a nice windy (10-15 mph) Colorado day and was testing out what I call a reefing ring. I'm sure other people have tried it but here it is. I wanted to know what you all think - if you have done it before and if it's worth a shot.

I took a 32" parachute and found that a 3/8 ring fit all the lines inside nicely. I pulled all the lines through and put them within 1/2" of the attachement to the chute. I folded the chute and wrapped the lines around it. I attached a 8 ounce weight the the chute.

When throwing it in the air the chute opened a lot more stable - it inflated then the ring went down the lines allowing a nice profile with little or no wobble.

When tried w/out the ring the chute snapped harder and wobbled on the way down.

I think sky divers use this concept with the square of fabric on their lines to keep from hard openings.

What do you all think? Comments, suggestions, snide remarks :p ?

Edward
 

Zippy

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If you ever flight test that post the results. I'm thinking it might be a good way to use a really long delay for a shorter recovery without stripping the 'chute. I'll let you try it first though. :D
 

edwardw

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Keyrings work, I'm using plastic rings from the KNITTING SECTION of Wal-Mart. They had about 10 different sizes. They were cheap too.

Edward
 

Steward

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Originally posted by edwardw
I'm using plastic rings from the KNITTING SECTION of Wal-Mart. They had about 10 different sizes. They were cheap too.

Edward


I'm also considering the use of one on my next project...
Am I right..??? It just slides up and down the shroud lines... (not attached anywhere...???)
My thinking is that it would certainly help... say...if you were to have a late delay, or faster than normal deployment...???
 

edwardw

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I have tried these - they work great. I have been trying them more extensively by deploying out of my car. The let the chute open a lot slower - which is good if your coming in fast.

Yes, your right, they just slide right over the shroud lines, not attached to anything.


Edward
 

polaris

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I have been using an annular slider on 24” circular parasheets (10% vent) for about a year. So far I have been very happy with it. I have found they work better when I lengthen the suspension lines to 1.5 Do. It increases the Cd. It gives more room for the slider to work.

I have had some problems with line-overs without sliders. Sliders slow down inflation rates so I don’t seem to get explosive filling (popping open). It looks like a fix to the line-over problem. (I understand that adding a skirt will effectively eliminate the problem. They also slow down filling. I just didn’t want to turn it into a big sewing project.)

While I can’t prove it, it also seems to give the nose cone and body a chance to fall away before parachute open. I feel there is less shock to the rocket.
 

dr wogz

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I've seen this on spinnakers as well, to help stop the dreaded 'hourglass' effect. Also helps to close the spinnaker, as you 'round the mark'. Of course, it is on a string to pull down on the spinnaker..

Interesting idea..

(Spinnakers are those large 'balloony' colourful sails on sail boats)
 

polaris

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I didn’t know about spinnakers. That’s very interesting.

I did some drop tests off of a parking garage. As the parachute opens, it pushes the slider down the suspension lines. When I used too light a load the chute didn’t fall fast enough to maintain inflation. It looked like the slider moved back up the lines. This reefed the chute, increasing the fall rate. When the rate picked back up, the chute filled forcing the slider back down the lines.

I think the slider acted like a valve. It controlled the effective chute diameter and thereby the fall rate. It makes you wonder, if it doesn’t create optimal drag.
 

wwattles

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I found some nylon spacers at the local home warehouse store, and I was wondering if they would work for this application. The ones I picked up are 1/2" long, 3/8" ID. They came 2/pack, and look to be fairly durable. Certainly enough to take the impact of a moderate-speed opening.

Any thoughts?

WW
 

polaris

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Well, I am not sure. I think the idea is to get orderly deployment. To me that means two big things. First the suspension lines are fully deployed before the canopy begins to inflate. Second the canopy doesn’t pop open.

A slider is a little parachute. So it helps deploy the suspension lines. If I understand the ring you found, I don’t see how it helps deploy the suspension lines. If something else were stretching the parachute, the ring sounds like it will work.

Since the ring restricts the opening at the bottom of the parachute, it reefs the parachute. To me, this means it will take longer to inflate. So it shouldn’t pop open.

While I don’t entirely understand the physics, I am lead to believe sliders can dynamically adjust the parachute opening during descent. This means they can keep the parachute optimally inflated – maximizing drag while minimizing lift.

Conceptually, it appears to work something like this. A loss of airflow results in the canopy deflating, reducing the force pushing the suspension lines apart. Because the slider is always being pushed up along the suspension lines, the reduction in outward forces lets it move up the lines. This maintains the tension on the parachute opening and reduces the apparent size of the parachute. So the drag goes down, the speed picks up – along with it airflow into the parachute. Thus the parachute returns to a condition resembling the deployment phase.

I don’t understand how the ring can provide any of this kind of behavior.

It appears sliders will not help with parasheets that over inflate from say a heavy updraft. Because the parasheet is flat; it will attempt to expand until it is fully flat. The resulting spill means that the oscillating motion will amplify itself until the parsheet slips sideways through the air. At that time there are no inflating forces to maintain shape or tension on the line. Since the slider is located further from the apparent center of the oscillation, it experiences the effect earlier. It cannot help reef the parasheet because there is no apparent upward force. I believe this why parachutes, especially skirted parachutes, are preferred.

I don’t think the ring will help in this situation either.

What do you think?
 
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