Harness induced turn?

[Liemberg 0]

We all know that parachutes sometimes turn without steering input and we say that the canopy has 'a built-in turn'. It is a bummer if you have one such canopy, since it is notoriously hard to find out what causes this: line shrinkage, unevenly built cells, different batch of fabric - I have heard the wildest speculations and so have you (probably - at least when you have jumped a few years... "try placing the family jewels on the opposite side, hehehe...")

However, someone reported back to me that he replaced an elder canopy in his rig with a new one.
The old one was a CD190 (F111 fabric) the new one is a Zero Porosity square 150 (I'm not giving any brand names for now - if it were alone for the fact that I don't know the brand - suffice to say 'sabre2 lookalike'...)
The new canopy had a distinct built-in turn, not only reported by the user, but also by a 'trusted third party' with enough jumps to know what he is talking about.
When this 'trusted third' took the new canopy and jumped it in his own rig, it did not turn.
On examination of the rig they found one discrepancy which is that the distance of the harness ring / canopy attachment point to the buckle in the leg straps when measured showed a difference of 'between a centimeter and half-a-centimeter...'

Can this, in itself create a built in turn that comes to light when you replace the 'old, forgiving F111' with a higher loaded and smaller Zero P parachute?

Anyone out there who has experienced something similar?

next week - weather provided - the 'trusted third' might make a few jumps with the rig and build his own rocket-pocket in it.

For now, I'll wait and see - but I like opinions, especially from people in the harness building industry.

"Whoever in discussion adduces authority uses not intellect but memory." - Leonardo da Vinci
A thousand words...

[riggerrob 643]

yes, it is possible for an assymetric harness to cause turns.
Assymetry becomes a greater problem as you down-size canopies.

[phoenixlpr 0]

I have noticed too that even amount of harness left out from leg strap does not guarantee even load under canopy. I suspected a "built in" turn. I have found if I feel my leg straps tight equally I load my canopy equally.

[beezyshaw 0]

I think it's probably safe to say that I have as much experience as anyone in jumping canopies with built-in turns, and with taking corrective measures with such. My former position with another canopy mfr. was as customer service manager, and that company, being in business for almost 20 years, has had their share of "turners." That being said, harness symmetry can and does matter, but to induce a noticable turn on a 150 main because of a little more than 1/2 cm. difference in lift web is "unlikely". Not impossible, but "unlikely". Of course if it is the lift web the canopy will turn toward the lift web that is the shorter one. Their are many more factors to consider as well; have the main risers been switched from left to right to check that? I have found risers to be the culprit in several situations. As the various things are checked to try to find the problem, remember to only change one thing at a time as you go through the process.
Now, and believe me when I say this, many times the turn is apparent only because has been perceived to exist. In other words, I can take a straight-flying canopy and give it to someone with thousands of jumps and say, "I think this canopy turns to the left, jump it and tell me what you think." It'll come back with the same conclusion most of the time. I can say to someone else that I think it turns to the right, and the same thing will be perceived by others. So, moral of the story is try to have others evaluate the canopy without giving a pre-conceived notion of the problem. Of course if a canopy is a strong turner, there is no doubt about what the problem is.
As to the causes, there are more theories on this subject than you can count. Many such theories are sound, many are just conjecture, none of them usually conclusive. Enough on that, except to say that there isn't anyone in this industry who can say with certainty (even though you'll hear things to the contrary) why some canopies are built with this problem. If it is determined that a canopy does have a problem, if it is a slow drift it is easily correctable by several known methods; of course one that really takes off and requires a lot of toggle to stop the turn should be replaced.

[Liemberg 0]

* bump *

Not that it is of particular interest, but I got an email about recent developments around this rig.

It reads: "Bob made a couple of jumps with my complete rig + parachute and says (without prejudice) that the whole thing turns significantly to the left. Then he put my chute in his own rig and it flew straight. Then he put HIS chute in the rig and it was flying straight...{/} This surprised him..."

Needles to say that Bob's own chute is smaller and more heavily loaded than the parachute in 'the suspicious combination'...

Quote

have others evaluate the canopy without giving a pre-conceived notion of the problem.

Sound advice (and I told him) but apparently kind of impractical to execute...

(Hey - we should play true scientists and go for the 'double blind test' with 2 complete rigs, not telling beforehand which one may have a problem AND a go-between who is left in the dark also... "Put your evaluation papers in the envelope and seal it"

"Whoever in discussion adduces authority uses not intellect but memory." - Leonardo da Vinci
A thousand words...

[CrazyL 0]

Yes assymetry is a cause of 'turn'. Had come across a Harness that when inspected the MLW showed signs of assymetry. Found extra padding under the mudflap on one side between the wearers side and 4 pt by 3 ring, under 3 ring area. Notified customer, he previously jumped and corrected for turn numerous times. Ask jumper about extra padding and assymetrical harness. Took out extra pad, back to straight flight, little bit less comfy due to the cutaway cable housing.