Parks College Parachute Research Group

Using a flexible cable closing pin on an experienced skydiver's rig


Investigator: Gary Peek



Purpose of this study

To determine if a flexible cable closing pin is a practical method of closing the containers of rigs for experienced skydivers.

Background

1. My personal rig, a North American Aerodynamics Centaurus, contains a canopy smaller than it was designed for, and tension on the closing loop when the container was closed is very light even with the shortest loop length possible. (The loop originates at the bottom flap, the first one in the closing sequence, not on a tab between the reserve and main, which would allow for more adjustment.) I was concerned about the security of the curved steel closing pin and had considered ways to increase the security of the pin.

2. A skydiver had mentioned this topic on an Internet newsgroup and had posed the question (to all) as to why harness/container manufacturers did not offer flexible cable closing pins on rigs for experienced skydivers, since this could potentially provide a more secure method of closing rigs.

I responded personally to him that I thought the reason might be that the wear to the closing loop would be excessive and that skydivers sometimes do not replace their closing loops as often as they should as it is.

An Experiment:

I constructed an eight inch flexible cable closing pin from standard yellow LOLON coated cable, which is the cable often used for cutaway handle cables in skydiving rigs, and installed it on the bridle of my Centaurus. This application produced a much more secure closing of the container due to the distance that the cable would need to be moved in order to cause the container to be accidently opened. Deployments were not noticably different from using a curved steel closing pin.

The closing loop used was made from Type IIA suspension line sheathing, a typical closing loop type used on experienced skydiver rigs, and has a strength of approximately 100 pounds. The pilot chute used on this rig is a 34 inch zero porosity collapsible type.

Important installation note:
Since a flexible cable pin of any length must move a great deal further than a curved steel closing pin in order for the container to open, it was imperative that I insure adequate bridle length between the closing cable and the top of the deployment bag, otherwise, a container lock could occur.

Supporting Research:

I contacted Strong Enterprises, who has used flexible cable closing pins on their Dual Hawk Tandem containers and who might have some information on this type of closing pin. Ted Strong told me that the company originally used a 400 pound "sheathing" type loop on Dual Hawk Tandem rigs but had switched to an 1800 pound spectra loop, and that closing loops were lasting much longer since then. He also stated that it was his experience that the flexible cable they were using, (which is the type often used for closing static line containers) is less likely to dent or distort than LOLON coated "cutaway" cable for two reasons. First, the inner steel cable is a larger diameter to begin with, and secondly, the clear plastic coating on that cable is harder. He also mentioned that the force exerted during pin extraction by a fully inflated drouge parachute used on a Strong Dual Hawk Tandem rig was something that was never in doubt.

Conclusions:

I observed that a flexible cable closing pin creates considerably more wear to a Type IIA suspension line sheathing type closing loop compared to a curved steel closing pin. In as few as 10 jumps a closing loop of this type shows wear that most skydivers would feel uncomfortable with, and consider replacing the loop.

The combination of a flexible cable closing pin of sufficient hardness and installed at an appropriate place on the bridle, a closing loop with adequate strength and durability, and a pilot chute with adequate and consistant drag could be a practical system of providing a more securely closed rig than using a curved steel closing pin.

However, as in many mechanical systems, it is easy to overlook the critical relationship between the components used in the system, and changing any one component could have consequences beyond the end user's knowledge of the system.




Update 5/99

At the PIA Symposium '99 I was given several 1800 pound spectra loops by Strong Enterprises for use with their Dual Hawk Tandem rigs. I installed one of these loops on my personal rig configured with a LOLON flexible cable closing pin. Since that time I have made over 20 jumps in that configuration with no noticable wear on the closing loop.

Update 10/04

I now have so many jumps on this configuration that I have lost count. Perhaps 500? I have replaced the loop about 7-8 times if I recall correctly, usually with 1800 pound Spectra. About a year ago I noticed a small amount of wear on one of the closing flaps where the cable attachment point rubs past the flap during container opening, so I enclosed the cable's metal swage with binding tape so that the swage could not come in contact with the flap. Since then I have noticed very little additional wear.




Notice/Disclaimer: This study is not intended to suggest that a flexible cable as a closing pin on an experienced jumper's rig is the solution to any particular container problem, but is intended only to provide information which we believe to be interesting and informative to the skydiving community. If you have questions regarding a particular harness/container system and its method of closing, always begin by contacting the manufacturer.




For questions or comments about this study contact Gary Peek at peek@pcprg.com

log file