Turbulence and low wingloading on high performance canopies

[peek 21]

The spring winds here in the Midwest, and the early summer winds, along with the turbulence caused by heat, has caused me to revisit some canopy issues.

So I have a comment/suggestion for some readers, and a questions for others.


Over the years I have seen a number of canopies, when either flown in thermal turbulence, or accidently flown in the burble of an obstacle, partially collapse for a very short time and then reinflate.

Often this is an end cell rolling under somewhat and then quickly snapping back, and in the process, making a very noticable sound.

Canopies that are lightly loaded seem more susceptable to this, and it is not hard to imagine why. Lighter wing loadings usually mean less speed and the cells not being rammed with air as hard.

To me it seems that non-zero-porosity canopies do not exhibit this unless the wingloading is _extremely_ low or the cells are very short. For example, back when Strong Tandem Master 520 (square feet) tandem canopies were common, I saw a number of end cell rollunders and snap-backs, simply when there were thermals, and not downwind of obstacles.


My suggestion for the less experienced jumpers (bear with me, it doesn't hurt to reiterate this):

If you have a low wingloading you need to be particularly aware of where you are landing in relation to obstacles, and how much thermal activity there is when you jump. (Also how close you are landing in time and distance, behind another canopy.)

Please be careful, and study up on where to expect turbulence. It can't be seen, and usually we can't even see the effects of it unless something happens to us.


And for the more experience jumpers and instructors:

Suggesting to less experienced jumpers that they keep their wingloading low is a very good idea, to reduce the rate of descent in general and to be more forgiving of slight canopy control errors.

However, in doing so we might be giving them another set of problems, since most are going to have _high performance zero-porosity_ canopies. We should remember to tell them about the disadvantages of light wingloading too.


Leading up to the question:

My first few jumps on a Sabre 230 were spooky. I am about 230 pounds and there were some thermals that day. It did not feel very firmly inflated at times.

Today an experienced instructor told me that he though the original Sabre canopy, when lightly loaded, had a tendency to not be firmly inflated, and that this was considered common knowldge in his area.

The question is:

Do any of you experienced jumpers know of any other canopies that you have heard of from _a number of sources_ that exhibit this.

Note! Note! Note!
We already know about the Nova! No need to rehash that. And this is not intended to be a Sabre bashing event. Although some of them open hard, they also fly well, so quite a few novice skydivers will be obtaining them for quite some time to come, since more experienced jumpers will be going to even higher performance canopies.

[dmbale 0]

I experienced this on Sunday. I jump a lightly loaded Spectre and had my left end cells collapse for a second and then snap and reinflate, I was on my downwind leg. Density altitude was above 8K, I was near a taxi way and winds were around 18. Scared the crap out of me.

I decided to maintain a light wingloading because I was a slow learner on canopy control and I jump at a DZ with a field elevation of 5,500 MSL.

I am going to be more careful when it comes to turbulence and thermals. I am thinking of downsizing a little sooner than I had previously thought. I was going to go to a 170 in Sept/Oct because of the altitude issues.