ON QUICK RELEASES, ROPES, CARABINERS AND THINGS YOU HOOK THEM TO.................

04/20/2004

 

A recent fatality has prompted quite a bit of discussion on the balloon reflector as to the "ideal" release mechanism for balloons, as well as the parts that make it up.  While all of the contributions have been helpful, they have necessarily been brief due to the nature of the reflector.  If you take the time to read this discourse, I hope it will help to pull all the bits and pieces together and see that the sum of the parts involved as well as the procedure for using them is what will contribute to or detract from pilot, crew and spectator safety.

BACKGROUND

I've been building and selling Quik-Releases for just about fifteen years.  During the mid-eighties, I stumbled through a number of mechanisms that different people recommended.  None of them worked very well.  All were various types of parachute or cargo release hardware.  The main problem seemed to be that they really were not meant to release under the amounts of tension that even a small balloon can generate with a moderate wind pushing on it.  It must have been around this time that a couple of balloons dragged into crowds at events and organizers began to require use of restraint systems.  I use the term "restraint system" because all of the parts interact to determine success or failure (the "weakest link" concept).  This is true whether you buy a package such as I offer or put together your own parts.

As an adjunct to building the restraint system, I felt it was important to be able to test various parts and designs and to demonstrate the product.  I tested my first design by attaching it to my 1952 Ford 8N tractor and a stout silver maple tree.  The system held just fine, even when impact loaded by driving to the end of the rope, and released under as much tension as I could keep on it by setting the brakes.  The problem was that I didn't know exactly how much force I was putting on it.  I also demonstrated the system to the pilots at a local balloon rally by putting it between two pickup trucks and pulling one with the other (with the brakes set).  Releasing it under tension resulted in no "springback" at all; the down rope just dropped to the ground. 

The amount of tension that I felt I needed to plan for was the amount it would take to pull a full size pickup.  I didn't plan for shock loading, because if used properly, it isn't a factor.  More on that later.  I finally settled on a design strength of 3500 to 4000 pounds, although I'll admit that it's only an educated guess.

To be able to demonstrate the product at trade shows, I built a test fixture using an Enerpac hydraulic cylinder activated by a hand pump.  This unit can develop a pull of 5000 pounds.  By mounting a pressure gauge in the line and calculating the pressure with the cylinder size, I can read out the pull as it is applied.  In addition to testing each Quik-Release as it is assembled, the test fixture is used to tension the ropes for application of the "whipping" that holds it together when it's not under tension.

CRITERIA

 A restraint system only needs to do two things: 1) keep the balloon in place and 2) release when the pilot wants it to. 

Additionally, it should not cause damage to the balloon it is attached to, be safe, look good (professional), be easy to use, last a long time and be inexpensive.

 

CHOOSING THE COMPONENTS

A half dozen really strong (and motivated) crew people can form a perfectly good restraint system and in fact I've utilized such a system many times with good results.

As far as satisfying item #1 with a mechanical device, it's not too difficult.  A piece of webbing, rope, cable or even a piece of chain would do the trick, as long as it is the proper size and attached to something appropriate.  In fact, 1/2" or 5/8" nylon rope is ideal for tether operations.  Of the common ropes, nylon is the strongest for a given size.  It will also stretch nearly 20%, which is what you want for tethering, so that when the occasional wind gust (false lift) takes you to the end of the ropes, your stop is gradual rather than sudden.  It is also resistant to molds and other nasties it may pick up while being dragged around on the ground.  It's "stretchiness" however is something that is not good in terms of safety for persons in it's vicinity if it does break or if it is  released under tension. 

I don't know if anyone would seriously consider using wire rope or chain; with chain, weight would be prohibitive.  Abrasion from normal use would likely cause strand breakage on wire rope, with resulting sharp ends sticking out.  Both of these products would rust after exposure to damp conditions.

Webbing gets pretty big and stiff in the sizes that will develop the strengths needed.  The other critical thing about webbing is the size and sewing on the "turnbacks" that form the eyes.  If I was going to use webbing, I would want to either buy a rated sling or have it custom made by a sling manufacturer expert in design and fabrication.

Kevlar (Kexlon) rope has some neat features.  As one contributor to the reflector pointed out, it does not stretch.  This makes it a good choice for avoiding the "rubber band" effect upon release.  There are two things to consider, however.  One is that Kevlar rope is not all Kevlar.  It is a Kevlar inner braid covered by a polyethylene outer braid, which protects the Kevlar from ultraviolet deterioration.  Over time the outer braid may shrink causing some stretch and attendant "springback" at release. The second is that the Kevlar fibers are abrasive to each other as they flex.  In the area where the release portion of the restraint system is passed through the eye of the "down" rope, tension is applied and removed each time the system is used, it's tensile strength could degrade quickly.  I'd at least want to do some testing before choosing this material.

I settled on double braided polyethylene rope.  The release portion itself uses several different sizes, depending on the tension the particular area is expected to see in service (more on that later).  The "down" rope is the same material in a 9/16" size.  The rope has a rated tensile strength of 10,500 pounds; the "eyes" woven on the ends reduce the ultimate tensile strength by 10%.  When doing the initial design, I got the help of Mr. Warren Buesing of the John Rauschenberger Company in Milwaukee.  His insight into rope design and fabrication were invaluable.  He also provided the tools and books that helped me learn to make the rope assemblies.

 

RELEASE DESIGN

Satisfying item #2, releasing when the pilot wants it to, is trickier, although it can be pretty straightforward.  One contributor mentioned keeping a sharp knife handy in case he couldn't pull the last knot out of the daisy chain.  In fact, I had one customer who bought twenty-five feet of rope and a knife upon embarking on his ballooning career.  He said he would get a Quik-Release from me when the rope got too short.  As I recall, it lasted most of his first summer.  If anyone is interested in doing things this way, I can tell you where to get the proper knife, designed to be used by rescue personnel specifically for cutting rope.

Snap shackles, such as Cameron supplies, can't be pulled open if loading is very great.  Even under light loads (500 pounds) the eye in the "down" rope will capture the end of the snap shackle that is supposed to slide through it.  One of my early attempts at the Quik-Release used a small brass snap shackle to hold the last loop.  I couldn't get it to work.  In order to have any hope of working, the "down" rope has to have a steel eye woven in for the snap shackle to be passed through.  This introduces a potential flying piece of metal (albeit small) if a stretchy material is chosen for the "down" rope.

The Bonanno release from Cameron is a nice, beefy all aluminum unit which works very well.  It is far from inexpensive however, ($256) and still leaves you to choose and buy the appropriate "down" rope.

"Italian Hitches" appear to offer friction control over the carabiner which is in turn attached to the balloon.  I seem to remember hearing of using climber's "Figure Eights" to the same end.  There are two potential problems I can see with this system as I understand it: 1) getting the correct knot tied each time, and 2) the free end of the rope has to slide through the carabiner or Figure Eight when it is released.  With uninitiated bystanders and even crew who may have their attention diverted by the excitement of a high wind inflation in the area, the idea of a loose rope end whipping around is kind of a scary thought.

The remaining designs are variations on the "3 Ring" release that was designed in 1976 by Bill Booth for the parachute industry.  Some of these releases with the original metal rings have found their way into balloon use, however concerns about the weight of the metal parts rebounding in high tension situations have dictated the creation of releases with interlocking loops of rope.  I haven't had the chance to test any of these small units, but I don't see that they can be very strong, given the amount of stitching holding them together.  I did get to test one of the larger all rope units on my fixture at one point.  It was made of climbing rope and stretched a lot before failing at about 1500 pounds of pull due to stitching breakage.

                              

Stress distribution in a quick release is depicted above.  If an overall pull of 4000 pounds is placed on the unit (point A), it is dispersed as 2000 pounds in the loop and 2000 pounds in the standing part of the unit.  In the second loop (point B), 1000 pounds in the loop and 1000 pounds in the standing part.  At each subsequent loop that is added (points C & D etc.), the pull is again halved.  The last loop is typically captured with a pin, or if you make enough loops, you can hold it with a Velcro strip.

The problem here is that there is also some friction trying to hold each loop together, the effect being that a release that works well under 4000 pounds of pull won't come apart if only 1000 pounds is applied to it.  Conversely, if you don't use enough loops, a large pull (say 3000 to 4000 pounds) will trap the pin & you won't get it to release.

Either situation is intolerable.  If you have to slap the unit with your hand to break the friction and release it, you stand the chance of getting your hand caught.  I had a pilot relate that experience to me a one of the trade shows I attended in the early 1990's.  He said that it just about tore his thumb off and that trying to fly and land the balloon with such an injury was a real treat.  If you can't pull the pin, you may as well revert to your trusty knife.

                                                                  

Stress distribution in the Quik-Release: If 4000 pounds is applied at point A, point B has 2000 and point C (carried by the handle) has 1000 pounds.  The handle provides a 5 to 1 mechanical advantage and the force applied to it is perpendicular to the line of the tension in the unit, so it releases easily even under maximum load.  When in service on a balloon, with the unit stretched out horizontally under minimal load, it will fall apart of it's own weight when the safety strap is unwrapped.

 

PUTTING IT ALL TOGETHER

If what I've laid out here makes sense, you can buy everything you need in one package.  The parts are all sized and the materials chosen with this specific application in mind.  If you have some rope lying around and maybe some old carabiners, maybe they will serve. 

Actually the "twenty-five feet of rope and a sharp knife" approach has something to recommend it here, since you then don't need to select carabiners.  If you are going to attach with carabiners, there are some considerations.  Some of these have been elucidated on the reflector, but are worth repeating.  I would not use aluminum carabiners, unless the only thing touching them was going to be rope.  I've been told that climbers throw away any aluminum carabiner that falls and hits a rock.  The notch that may have been created makes for a stress riser which can significantly reduce it's strength and makes it unreliable.  While hardened steel carabiners will wear and develop stress risers with time, they generally start out so much stronger that it doesn't become an issue.

Having said that, constant stress eventually causes failure even though it's not nearly to rated strength.  I break the carabiner that I use for building Quik-Releases every couple years.  The ones I supply with units are not real expensive, but they are rated at 23 KN (5750 pounds).  The reason they break is that when applying loads in a steel-to steel contact situation, the load is applied to a point, rather than spread out over the diameter of a rope.  This causes distortion in the carabiner each time the load is applied.

How will you attach to the balloon?  Remember we said we didn't want to damage the balloon?  With that in mind, we have to resolve several things:  On Cameron, Lindstrand, T & C, Aerostar with flexi-rigid uprights, Aerostar Aurora baskets, things are pretty simple.  These envelopes are connected to the baskets with carabiners, so the restraint system can simply be hooked to those.  Aerostars with load block and pin hook up present a little more of a challenge.

                            

Some pilots have purchased an extra pair of blocks and pins, placing them on the lower set of holes, as shown.  Doing this gives the force the restraint produces a large lever arm to work through, possibly damaging the upright tube by twisting.  It also gets pricey, since you have to buy the blocks and pins.

What I have chosen to do on my 140 is to use an eyebolt in the lower hole to attach the carabiners from the Quik-Release.  This reduces the length of the lever arm and I've had no problems with tube damage.  If you do this, the eyebolt must be welded to prevent pulling open.  Pull testing on a 3/8" eyebolt from the hardware store showed that it started to pull open under about 1000 pounds of force.  After welding, I was able to pull it to 4000 pounds with some distortion but without breakage.  If you can find the proper size forged eyebolt, that would be better still.

To completely eliminate twisting on the upright, I've sewed up a 12" loop of four thicknesses of 1" webbing for several customers.  This can be passed around the upright tube above the attachment block and the restraint system carabiners hooked to it.  The force produced is now centered on the tube.

On FireFly (Balloon Works) balloons that are attached with three toggles, the challenge is to accomplish the restraint without putting undue stress on the burner supports or the basket itself.  My approach to this is to use a single point version of the Quik-Release, which is attached by carabiner to a figure eight shaped webbing loop placed over the #1 toggle before the toggle is placed through the eye of the basket suspension rope.  I'm a little apprehensive about putting all the force on one toggle and set of cables, but I haven't heard of any bad effects so far.

Paul Stumpf tells me that some owners have used the standard 2-point Quik-Release on FireFly systems by hooking it to the FireFly tether harness.  I haven't seen this done and the one concern I have would be to make sure the area of attachment is strong enough to withstand the potential forces involved.

 

THE OTHER END

A tree stump can be an effective anchor for the balloon restraint, although mobility does present a small challenge.  More commonly, however pilots will utilize their chase vehicle.  I think pilots are usually pretty savvy about tying off to tow hooks on the front of the vehicle or the trailer hitch.

The dangers of  utilizing eyebolts for anchor points has been well documented recently.  I have seen several other mistakes that are worth pointing out.  One is use of  the small fender support rod ahead of the rear wheel on a Chevy pickup for restraint attachment.  The one good thing about this one is that the sight of the fender bent out six inches is enough to convince the pilot not to repeat the mistake.  The rear of the trailer is also not a good place to count on.  At a rally years ago, I saw a pilot tip his small enclosed trailer on it's side.  I'll have to give this pilot credit for having the presence of mind not to release immediately, but to pick up the trailer a second time and set it back on it's wheels before departing.

My own preference when I am using my trailer is to park about ten feet behind the basket and perpendicular to the centerline of the laid out balloon.  I then take two turns of the "down" rope around the square tubing that form the trailer tongue and finish off with two half hitches around the standing line.  I feel that it would take more force to pull the vehicle to the side than it would to pull it forward or backward.  When my launch field is too wet to get in with the van, I use my tractor for an anchor, again tying to the side.

One more tip on restraint use before I finish up is to tie the "down" rope off snug.  If there is enough wind to move the balloon, it is much better to have it move only about six inches or one foot.  There is a safety issue to bystanders and crew to leave a slack rope lying on the ground which may suddenly pull tight.  It is easier on the crew if the balloon can't move.  Finally if the balloon isn't able to begin moving, there won't be impact loading on the restraint needed to stop it.

Pete Asp

2004