Parks College Parachute Research Group

High Performance Canopy Shoulder-Down Deployment Study

last update September 2005
Investigator: Gary Peek

Goals:

This study was undertaken to try to understand why a Performance Designs Stiletto 150 canopy, which normally opens with a comfortable snivel and in a normally controlled manner, should open hard and fast with no sniveling when deployed with the shoulders not level.

Note: My previous high performance canopy was the Performance Designs Sabre 150, which I never noticed to exhibit this type of opening under these conditions.

Background:

Before I began jumping high performance canopies I had gotten used to looking over my right shoulder to observe my pilot chute deployment, and have often seen my deployment bag leave my back also. Although I have retrained myself to avoid doing this when jumping high performance canopies, I still revert to looking back occasionally. Therefore, my first experience with the effects of doing this probably came on my first two jumps on my Stiletto 150. I had jumped Stiletto's of various sizes before and had experienced typical openings, but when jumping my new Stiletto for the first few times I was probably apprehensive about the opening as one might expect after connecting a new canopy, and I probably looked back during deployment.

The first two openings were very fast and somewhat uncomfortable, however they occurred so quicky that the opening was on heading. I was confused as to why this was happening on a normally well behaved canopy, but I continued jumping it that day, and the openings were more as I expected. Since that time and after over 300 jumps on this canopy, I have occasionally still experienced a fast and hard opening, always on heading.

The most puzzling part of these occasional hard openings is that they are on heading. One would expect a shoulder low opening to cause a turn on opening.

Test jumps performed

To begin research on shoulder down deployments, I made several instrumented jumps with the Stiletto 150 connected to the standard PRG riser load instrumentation, which contains load cells attached to all 4 risers and a portable data logging system. The freefall speeds at deployment were in the normal range of skydiving, and the sample rate from the load cells was 1000 times a second to enable reading any short load peaks.

I was not, however, able to produce the hard, fast, on heading openings that I have experienced in the past with shoulder down deployments. All of the jumps produced at least a short period of sniveling before the canopy spreading, which was faster than normal, but not particularly hard or uncomfortable, and resulted in a 180 degree turn after canopy spreading. On one of the jumps my shoulder was low enough that I even observed the point of bag launch.

Here is an annotated graph of riser forces during a typical deliberate left shoulder down deployment of a Stiletto 150 with a 1.7 wing loading.

This graphics file was constructed from multiple screens of the plotting program where different periods of the opening were displayed on the different screens. In addition to the opening forces, which are displayed on a scale to the right of the plotting screen, several other interesting events are annotated. From the graph, one can tell, among other things, 1. when the snatch force occurs, 2. when the canopy is in the sniveling portion of the opening, and 3. when the canopy begins flying after canopy spreading, and 4. the direction of the turn on opening.

Conclusions:

Further research to be done:





Notice/Disclaimer: This study is not intended to provide advice on manipulating the deployment of a canopy, 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 canopy and its performance, always begin by contacting the manufacturer.





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

log file