Orbiting Pilotchutes

**david** · February 4th, 2001, 05:43 AM

While watching some of MY OWN Bridge Day video I was noticing that my pilotchute was orbiting real bad. My openings were fine, but a little off heading. I had a Fox 285 with a 42" PC slider up and about a 3.5 second delay on both jumps. Looking back on some old BD videos I noticed that some PC's would orbit and some would not.Why is this? I know Space mentioned this on a post months ago but I didn't understand what he meant.

Dave O

**space** · February 4th, 2001, 06:42 AM

Hi David,
Asymmetricalness is the cause, one part of the skirt is venting more air than the other parts, Then the old observation of "Every action has a reaction" comes into play and this thrusts the PC laterally. There are 4 ways I know of how to acheive this,
1. One that is built that way.
2. Installing it that way.
3. Installing it symmetrical but not tightening the larkshead knot.
4. Older well used PC with stretched materials.
Hope this helps,
space

**Mike** · February 5th, 2001, 10:51 PM

[font size="1" color="#FF0000"]LAST EDITED ON Feb-05-01 AT 11:53 PM (PST)[/font][p]Lots of things cause this. The biggest contributer to orbiting pc's is deployment bags. The bagged canopy, as opposed to a free-packed canopy, has more inertia and exerts a greater impulse on the pilot chute. If this impulse is exerted on the pc in an asymmetric manner (and it usually is), it could cause the pc to oscillate either back and forth or in a circular motion. An asymmetric condition could be achieved by attaching the pc crooked, not evenly distributing the bulk of the canopy in the bag, or by over-zelously throwing the pc to your side in freefall.

With freepacked canopies this is rare since the freepacked canopy exerts a lesser impulse on the pc. The only way to increase the impulse is to use a pc that is too big, or a delay that is too long. Freepacked canopies are also vulnerable to the same kinds of asymmetric loading as bagged canopies. Poor pack jobs can leave more canopy bulk on one side of the bridle attachment. Poorly manufactured pc's or pc's not properly attached to the bridle have the same effect.

Note that velcro rigs will help absorb some of the impulse generated when the bridle tightens. The shrivel flap acts as a sort of shock absorber, straightening out some of the asymmetry in the direction of the load.

Keep in mind this is mostly theoretical speculation. What cannot be speculated is the actual effect an oscillating pc will have. In the bridge day videos it can be associated with anything from a perfect on-heading opening to severe line twists. Based on that, I would conclude that it causes inconsistency and is therefore worth avoiding.

I think it was a couple years ago that someone put some data together after studying the bridge day videos with regard to opening consistency and so forth. Anybody else know about this...?