Parks College Parachute Research Group
High Performance Canopy Shoulder-Down Deployment Study
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:
- Shoulder down deployments of the Stiletto cause quicker that normal openings and
tend to cause turning openings.
- Having the shoulders unlevel does not seem to be the only factor involved in
hard, fast, on heading, openings
- Hard, fast, on heading openings do not seem to be reproducable only by having the
shoulders unlevel at deployment
Further research to be done:
- Attempt to note the exact conditions present when hard, fast, on heading openings occur
- Instrument hard, fast, on heading openings once they become reproducible
- Video hard, fast, on heading openings once they become reproducible
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
