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The 3 Ring: What It Is, And How It Works

Posted Tuesday, October 8, 1996

By Jump Shack

Over the past several years our sport has witnessed an excessive number of difficult cutaways. In order to solve this problem we must better understand the 3-Ring system and its limitations.

The 3-Ring Release was designed by Bill Booth in the mid 1970’s. It was designed using what is now known as the “large set of rings.” This large set was touted as having a more than a 200 to 1 mechanical advantage. We will look at how the system achieves this ratio, later. The introduction of a fourth ring, which was smaller than the smallest ring of the original set, propagated the mini ring set in common use today. The mini ring set employs the “original middle” ring size as the base ring, and the “original small” ring as the middle ring. This mini ring set has a mechanical advantage of approximately 30 to 1.

Both the large and the small sets are sensitive to manufacturing tolerances, and the mechanical advantage produced by either set can vary. The tolerances of the small set are critical, whereas the large set has capacity to spare. A change of as little as 0.03” in the relationship of the rings to each other can reduce the ratio by 50% on the small set.

So why is this important? Let us say you are in a high speed, spinning malfunction and you have to cutaway. You have a mini ring set on your risers and they are manufactured poorly, and only have a mechanical advantage of 12 to 1. You weigh 200 lb. with gear, and are spinning so fast that you are pulling about 3 G’s, which results in a load of 600 lb. on your risers. The load on your yellow cable at the loop is fifty pounds. The yellow cable will pull through the grommet at sixty pounds. Unless your cable is well oiled and you are very strong, you won’t be able to cut away. Believe me, I have been there.

How do you know if your risers are made correctly? You don’t unless you have a dynamometer on which to test them or you have a method of measuring the ring relationship under load. The dyno test is simple. Load the riser to a level of say 600 pounds, then with a spring balance or accurate fish scale, measure the force necessary to move the top of the top ring by pulling on the loop where the yellow cable goes through. Simply divide the load applied by the dynamometer, by the force on the fish scale and you have the mechanical advantage, i.e. 600/50 = 12.

The three ring system is a series of three mechanical actions which progressively reduce the force. The first is a second class lever. It occurs when the middle ring loops under the harness ring and is returned to a parallel relationship with the riser. The middle ring becomes the lever and the base or first ring where it contacts the middle ring is the fulcrum. The pass through and return of the 2 ring through the first creates only a force direction change.

The reduction ratio of this step is simply the differential distance from the force load to the top and bottom of the ring. This ratio should be about 5 to 1 on the small set.

The seccond step is the same as the first. It is a class 2 lever, and the force is applied to the lower portion (again hopefully) of the ring, with its retainer webbing acting as the fulcrum. The resultant force is again measured at the top of the ring. This step on a mini ring set should provide a 3 to 1 advantage.

The third reduction is the retainer loop that holds the top of the ring. This is a simple pulley and always reduces the load by 50% or 2 to 1.

By beginning at the first reduction and multiplying each subsequent reduction to the product of the previous reduction we determine the total capability of the system. i.e. the 1st reduction is 5 to 1, the 2nd reduction is 3 to 1, the resultant advantage = 15 to 1. This 15 is then multiplied by the 3rd or next reduction which is 2 to 1. 2 x 15 = 30.

The large ring set, because the rings are larger in diameter, can attain a higher ratio in the first and second step. The first is about 8 to 1, and the second is 5 to 1.

If the ring relationship in the small set varies to less than the 5 to 1 of the middle ring, and the 3 to 1 of the small ring, as described above, then the total system ability is greatly reduced. For example, 3 to 1 instead of 5 to 1 on the first to second ring relationship, and 2 to 1 on the relationship of the second to the third ring, reduces the total system to 12 to 1.

The above, to many, is gibberish and therefore must be boiled down to a simple inspection procedure which can be performed on the unassembled risers. The U.S. Air Force jumped into the breach in 1987 by issuing a document to the field mandating inspection of all risers. This document is paraphrased here. The inspection is performed by observing the relationship of the small ring to the middle ring, and then to the grommet. This method of a non-dimensional- relationship inspection seems to be applicable to any 3 Ring system no matter what size ring set is used.

3ring1

This is a small set assembled to ideal relationships yielding a 30 to 1 ratio.

3ring2

When we tumble the rings to their unassembled position and remove the harness ring they look like this. Note the overlap of the rings. They must overlap metal over metal.

3ring3

The top ring is then turned up and related to the grommet. The top ring should be aligned with the hole of the grommet as shown.


The Jump Shack
Reprinted with permission




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