This short article is an attempt to consolidate the data we have collected into typical values, and to compare the difference in values from parachutes that open normally and parachutes that open very hard.
The graphs below show the opening forces on test jumps from a Performance Designs Stiletto 150. All of the deployments were done at the same airspeeds and suspended weights. (We chose data from this canopy because of the many instrumented test jumps that we did with it in the past, and because we had already created graphs of much of ths data.)
The first opening shows a peak G force of about 3 G's, which is a fairly gentle opening for a Stiletto. The second opening shows a peak force of about 6 G's, which is a bit hard, but not unusual for a Stiletto. Note that both the snatch force (when the canopy comes out of the bag and is being dragged through the air) and the sniveling (when the slider is up against the canopy) can be easily identified on the graph.
The next graph below shows the opening forces from seven different Stiletto 150 openings superimposed, to highlight the normal variations in opening forces from one jump to the next. The drag in this graph is given in pounds rather than G's.
In order to show opening forces that are extreme, (i.e., in excess of 12 G's), we must use the graph below of a test drop (of an object) using a Para-Flite Stratocloud canopy with no slider. (The deployment of this parachute was actually done at a speed that is lower than a typical skydiver at terminal velocity. If a higher deployment speed had been used, the G forces would have been much higher.)
Before we used electronic data acquisition systems to collect riser force data we used a mechanical G-meter attached to the test jumpers helmet. Some of the test jumps using a Para-Flite Cruislite canopy resulted in G forces of up to 18 Gs. Because of the high G forces we naturally made as few of these jumps as possible.
If you know how long a canopy takes to open, perhaps by using video of the opening sequence, you can use PIFCALC, the Parachute Inflation Calculator, a Windows-based program we have written for the computation of the opening shock of manned parachutes. PIFCalc can be found, along with our other computer programs, in the Computer Programs area of our web site.
See Hard Opening Ram-Air Parachute Research and Slider Drag Cancellation: Another Cause of Hard Parachute Openings for more technical information about hard opening canopies.
To see riser load data in more detail go to Riser loads during canopy maneuvers and Riser loads during shoulder-down deployments of high-performance canopies.
For questions or comments about this article contact
Dr. Jean Potvin or