Parks College Parachute Research Group

Hard-Opening Ram-Air Parachute Research


Investigator: Gary Peek

First of all: Read the Manual!

Make sure that you have gathered the latest information that the manufacturer and the industry is providing on how to properly pack your parachute.

Some years ago the advent of zero porosity canopies and suspension lines that stretch very little, e.g., Spectra, created many opportunities for variations and errors in packing to cause hard openings on these canopies. It has taken a while for information about how to prevent errors in packing to reach everyone, but now, there is no reason to be making obvious packing errors when so much is known about these problems.


Personal Experiences and Research

Strong Enterprises Z-PO 150:

I purchased a Z-PO 150 when the design was quite new and had rather hard openings from the beginning. Stong Enterprises had no particular advice on how to slow down the openings, only that they had not yet gotten much feedback about hard openings. I suggested to Bill Morrissey of Strong Enterprises that we try a larger slider, a solution which has "traditionally" been assumed to make canopies open slower. (This may or may not be the case any more, as I will explain below.) He sent me a slider designed for a Strong Tandem 425 canopy. It is quite large of course, but on the Strong Z-Po canopy it made very little difference. (The Strong Z-PO was not constructed with a tuck in the nose as are many canopies.) Since that time, Strong Enterprises has found the solution of using a "pocket slider" on this canopy as well as other canopies that they make.

Performance Designs Sabre 150:

I purchased a new PD Sabre 150 (original Sabre, not the Sabre 2) that nearly always opened quite hard, as many Sabres seem to do. It seemed that many people had no problems whatsoever with hard openings on this particular canopy model (not particularly related to size) but occasionally someone would get one that opened unacceptably hard on most jumps, and eveything that they tried would not slow down the opening. This seemed to be the case with the Sabre 150 that I got. I discussed the problem with John LeBlanc of PD and even had him pack this canopy for me at the World Freefall Convention when we were both there, but even this pack job changed the opening very little.

Around this time, many people were purchasing Sabres and some were having hard openings no matter what they tried. This was also around the time that John LeBlanc published the document about hard openings, because it was believed that many of the problems people were having were due to errors in packing. I knew that this was not the case with my packing, so after dealing with two different zero-porosity canopies that opened much faster than I wanted, I decided to try to find another solution.

John LeBlanc suggested that a slightly larger slider might help in this particular case but that he was hesitant to suggest this solution to very many people. He thought that eventually someone would eventually solve their packing problems that were causing their fast openings, and then have a Sabre with a big slider that snivels for a long time, another undesirable type of opening.

I began measuring the slider sizes of many Sabres in order to find one that I could use that was bigger, but found that all of the sliders from canopies sizes ranging from 135 to 210 were within an inch of each other. The size I measured was about 30 inches by 19 inches. (Discussion about why different size canopies have the same slider size is a lengthy topic in itself.)

Experiments

So, I tried a "radical" experiment: I put the Strong Tandem 425 slider on the Sabre 150. I opened high on the test jump in case it sniveled severely, however, the opening was very good, and continued to be good no matter what packing technique was used. I eventually sold this canopy, but the person I sold it to jumped it the way it was for a long time, and until having it relined, kept the Tandem slider on it.

After observing my success in getting my Sabre openings slowed down, people that I know began asking me to make them larger sliders for their Sabres, so I made several different sizes as "demo" sliders to see what size is really neccessary to work well without being too large.

Conclusions

What seems to slow down Sabre openings reasonably well is a slider that is 2 inches wider and 10 inches bigger from front to back: (32" wide by 29") (This assumes that Sabre sliders are still 30" by 19".) Note: All of the sliders that I built used number 8 grommets even though many canopies with small lines have stock sliders with smaller grommets.

I made larger sliders for about 6 people that had hard opening Sabres and they were all very pleased with the results. I have not made any in several years because many people are choosing Stiletto canopies over Sabres, and the need has been reduced.

I do not have time to be in the business of making custom sliders, but you should be able to talk a rigger into making one for you. Be advised that they will find it difficult to believe that such a large slider is necessary, but it is.


About the Pilot Chute

Larger pilot chutes in and of themselves do not cause hard openings! However, combined with some particular packing errors, such as having very loose line stows, a larger pilot chute can perhaps cause a problem that a smaller pilot chute might not.

In order to debunk this persistant myth, I have been using a 34 inch (finished size) zero porosity pilot chute to deploy my Stiletto 150, for well over 500 jumps, with no hard openings.


Update November 2004

Performance Designs Stiletto 150:

A while back I made and installed a 34" by 29" slider on my Stiletto 150 to see if this would provide even slower openings than a stock slider. It did indeed make them slightly slower and a good bit "softer", (although describing it as such is a bit subjective of course). I have made approximately 200 jumps on this configuration.

Note: Stiletto canopies usually open quite nicely with stock sliders. I did not make this modification because I thought the openings were bad, but to try to make them even better.

Update September 2005

A few people are still purchasing new Sabre canopies and finding that they open harder than they like, and people are still purchasing used Sabre canopies that open hard, but whose previous owner did not mind or accepted. Therefore, I had made larger sliders for 2 more people that had hard opening Sabres and they were very pleased with the results.

Added September 2005

This graph of Sabre 150 inflations from PIMS, the Parachute Inflation Modeling Suite, shows simulations of the opening forces from using larger sliders on the canopies compared to the actual force data collected during the test jumps on these canopies.

Added January 2006

This is a video of a Sabre 230 opening with such a slider installed, and with Dacron lines, which not only absorb much of the opening shock, but also create more friction on the slider grommets, slowing the opening even more.


Added October 2008- Another Model Parachute

From winston [morepower@ozemail.com.au]

Thanks for your article you wrote about bigger sliders for Sabres. I just picked up a Monarch that opens like a mongrel. I just ordered a bigger slider for it with the similar size you recommended for the early Sabres.

I brought the (Precision Parachute) Monarch zp canopy which is a 215 square foot 1993 model. It had done 80 jumps and the first time it opened it nearly killed me. It was extremely painfull and not fun at all. I had tried different packing methods like rolling the nose numerous ways. I had 4 different people pack it their own different way and do different things with the slider. Nothing worked. After reading about early model Sabre canopies doing a similar thing I decided to get a bigger slider made up. The original one was 610 x 710 mm (24 x 28 inches). The new one measures 750 x 850 mm (29.5 x 33.5 inches) which was 47% bigger. The first time it opened I waited for the snatch to happen but it never did. It now opens great. I am only a beginner jumper so I haven't really experienced a modern canopy open so I can't really compare it to one. All I know is that I am no longer in a lot of pain after opening and now my skydives are 100% fun, fun, fun. Thanks again. guys



Notice/Disclaimer: This study is not intended to provide a definitive solution for the problem of a hard opening ram-air canopy, but is intended only to provide information which we believe to be useful and informative to the skydiving community. If you have questions regarding a particular canopy and its performance, always begin by contacting the manufacturer.





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

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