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A Case for Compatibility with Functional Integrity

Published by PLI on

First we must acknowledge that there are bad rigs in the field and that most of the problems occur with the main closed. A MARD won’t help if the main is closed. .

The purpose of this effort is to surgically and methodically weed out those rigs and to develop a certification and testing procedure to prevent future occurrence.

For the purpose of this discussion let us think about a horizontal plane with the wearer lying face down along that plane. Think of a protractor on the back of the jumper with zero degrees at the head, which is to the right, and one eighty at the feet, which are to the left. We can see that the first 20 degrees and the last 20 degrees are, for all intents and purposes, unusable. For clarity we acknowledge 90 degrees as straight up and perpendicular to the jumpers back.

The field correction portion of this procedure must include a test for bag extraction. This test must be simple and indicative of the overall extraction effort and should be done when the rigger first opens the container by pulling the ripcord. It must also be made with the main container packed and fully closed. It might be recommended that the owner don the rig and lay on their stomach for the test. They should pull the ripcord and the rigger could then, after pilot chute launch, test the extraction force with a fish scale or similar instrument.

The direction of the pull on the bridle for the extraction test should be 45 degrees up toward the head from the perpendicular or at 45 degrees on the protractor. Assuming the bridle is located at the top of the bag, which is at the top of the container, a pull in this direction would cause the top of the bag to lift and begin rotation as it is extracted. Selecting this direction avoids the airing of the issue of a difficult 20-degree pull or the seemingly impossible 160-degree pull direction. I have seen extremely difficult pulls in both directions but I believe the 45-degree direction will be the lowest extraction force we could expect to encounter while still being indicative of the overall requirements. It is the direction most commonly seen during actual deployments.

The force extraction limits must have a maximum base line force, prescribed by rule. I would begin by recommending the weight of the bag and canopy plus ten (10%) percent. This percent overage is negotiable from my perspective and could go up quite a bit depending upon what others want. Certainly something must be added to allow for some friction. I could handle whatever number as long as it didn’t go over two times (200%).

Rules about what to do as a result of the test: The rigger is there to re-certify the rig. If their initial extraction test exceeds the maximum base line limit, described above, then the rigger must consult the manufacturers instructions to see what limit the manufacturer has allowed on this container which was based upon the drag capability of the pilot chute.

If the test results fall within the recommendations of the manufacturer then the rigger may proceed. If the initial inspection test procedure results fall within the base line requirements then the after pack job test may be waived. If the manufacturers’ specification allow a greater than base line force then the rigger must, after closing the rig and before sealing it, pull the ripcord and repeat the initial test to assure the pack job is good enough to meet the manufacturers extraction requirements. If within compliance, the rig may then be re-closed with minimum disturbance or relocation of the bag and canopy. All other requirements being met the rig may be sealed.

Certification and testing: The manufacturer must develop and publish the allowable extraction force for their container, as above. They must also publish the pilot chute requirements for that container. The pilot chute requirement would be specified as “Effective size” or physical size times the drag coefficient (Cd*So). This information would be published in the owners’ manual. It would appear as “Allowable Extraction force = xx“ and “Pilot chute effective size requirement = xx inches/feet”. Even if the containers extraction force doesn’t exceed the base line a minimum effective size of pilot chute must be specified. I really don’t think it matters how the manufacturer derives the maximum allowable extraction force. What really matters is the drag capability of the pilot chute. Here I believe is the difficult swallow for the manufacturers. All pilot chutes must be placarded with “Effective Size” (Cd*So) or they could be placarded with physical size and Drag coefficient, whatever. This identification of the capability of the pilot chute is necessary as they are components that could potentially be interchanged from rig to rig. With the containers marked with Max effort and pilot chute size requirements and the pilot chute marked with capability the assembling rigger may choose within those numbers.

Lets face it, the manufacturers are going to have to test their pilot chutes and develop the numbers so as to placard them. I believe that the PIA could set up a deal with some school like Embry Riddle to test pilot chutes in the wind tunnel for a fee. I don’t care how they test them but the FAA ACO might… or not!

Initially, in the field, only the extraction test may be made, as our pilot chutes aren’t identified with the “Effective Size”. As a policy I believe the PIA could require its members to publish the required data for their pilot chutes within an agreed upon time frame. “I know, how can they publish the allowable extraction force before they know the drag of their pilot chute”? They can’t, but I won’t tell.  

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