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Construction-wise, what makes a canopy less prone to an off-heading deployment, symmetry of the packjob, the pilot chute, and body position a given?

Is it valid to say that some (BASE-specific) designs are more likely to open on-heading than others?

i do belive that modern BASE canopyes ALL are good at headding preformance,its all about religion if you jump one or another brand..(headding vise).

The above said as i only has jumped fox´s,Flik and a round meaning i cant compare to other brands.BUT from what i see all the canopyes will open on headding once in a while

An unmodified round (no steering vents) would meet all criteria that you stated.
Hope this helps,
take care,
space

I would have to say that the only thing that would make a difference in heading performance when it comes to different canopies would be the canopy size, and aspect ratio. The lower the aspect ratio, the better the heading performance, the higher the wing loading, or smaller the canopy size. (and/or the canopy weight, due to the effectivness of the pilot chute, the speed it extracts the canopy) (in slider down/off), the better the heading performance. This is all considering the canopy is a base specific 7 cell.

Without commenting on the actual question (on which I do have some opinions, but insufficient time to express them adequately);

Remember that BASE canopies are assembled by humans. My experience has been that you can have 2 canopies of exactly the same size and model that greatly differ in their opening and inflation characteristics. It's possible that the variation between 2 different examples of the same model and size can actually be so great that they are nearly as important as the underlying design differences.

In other words, if I say that my Unit opens like crap, and you say that your Unit opens great, we may both be right.

very rarely do i disagree with tom, but i guess i do now.
I would guess that what you are writing there is much more opinion than actual fact, canopies are made by humans, and they do inevitably differ from canopy to canopy. but the actual differences between two same size/model/color canopies are probably so small for a human to notice, i would guess it would take some pretty exact measuring equipment to even tell the difference in the canopies. I bet the only thing that might matter at all would be spanwise fabric stretch discrepancies and porosity.

I have 3 Assemetrical color canopies, none of wich seem to have any heading problems at all, the only problem i hve had is a dagger that likes to turn to the left

I took what ta said to mean more like assembling the rig, as in connecting PC to bridle, bridle to canopy, canopy to risers, etc.

these days I think the small variations in the building of canopies shows only neglegible differences in performance, although I would certainly expect a hand-cut canopy to be more inconsistent than a laser cut canopy...
pope

well...
Icarus came out with the Crossfire II to quell customer dissatisfaction. they originally used 3 factories, and claimed to have serious quality issues from one. I even heard one trustworthy source claim the sewing was off by inches.

several incidents were reportably caused by poor quality control. many users complained their canopies flew poorly. Icarus issued bulletins, etc.

mine continues to fly fine, a friend claims the same. ours were manufactured in Spain.

so, when Tom says different examples of the same make/model can differ, I'd agree. humans HAVE noticed it. I also expect most manufaturers pay closer attention to quality control since this occured.

(oh, and don't forget how the trim changes as lines age...)

Whenever you chuck a bunch of nylon in the sky at varying airspeeds it might do all kinds of things... it's not worth the mental masturbation. Roll the dice and take what you get.

Ah, there's the spirit that's done so much to push the safety of this sport forward. "It's complicated. And I'm sleepy."

People have already commented on aspect ratio and various factors that I think boil down to "speed of opening" (the longer the canopy spends bunched up tight, the more likely it is to interpret minor body english as "Quick! Turn left!"). Body position, conditions and packing aside (and really, I think these are the most important factors), those two might be next on the list...

That said, I'd also like to point out the importance of colour, and the general "brightness" and finish of the fabric. Brighter colours reflect more light, with blue fabrics reflecting photons with the highest momentum. Failure to properly coordinate canopy colours can result in a canopy which opens preferentially sunward or antisunward. In extreme cases, a poorly-chosen colour scheme can even promote tail inversion and line-overs.

So, every BASE jumper knows (hopefully) that a lower aspect ratio helps onheading performance, but where's the point of diminishing returns?

Has a parachute manufacturer ever experimented with an actual square canopy (chord length equals span length)? Or how about a canopy with a longer chord than span? What would happen with those?

A little purple does miracles for heading performance

There were, as I recall, a few 5-cell canopies in skydiving that were near 1:1. My understanding is that a lot of other characteristics go to hell long before heading performance turns downard -- which is to say, while I've never heard anybody say anything about the heading performance of these canopies, I've heard plenty about other performance aspects (such as the ability to turn and flare). Which makes some sense... As the canopy gets narrower, the lever arm that each rear corner has on the thing gets smaller, and the trailing edge becomes shorter.

Of course, those characteristics might have been related to the fact that these were thick 5-cell canopies, too.

Low drive and poor lift with 5 cells despite on heading openings. The nose inlets are so large to keep the cells inflated that they provide significant drag on the canopy, preventing significant forward speed. The aspect ratio near 2 seems to give the best overall performance.

man as soon as i read that i was just about to razz your fury but you beat me to it.
late,
RJ$$

Yo!

A recent study by physicists at Moscow Institute of Physics and Technology showed that Coriolis force greatly affects the heading performance.

It is a well known fact that toilets in the Northern Hemisphere drain counterclockwise, and toilets in the Southern Hemisphere drain clockwise, due to Coriolis effect. Similarly, given perfect body position and packjob, parachutes in Northern Hemisphere tend to turn left, while in Southern Hemisphere they tend to turn right.

A control experiment involved three BASE jumpers - from USA, Australia, and Norway. The american got severe counterclockwise linetwists which he was not able to undo because his fat red neck was pinned by twists. The australian got a clockwise 180 which actually saved him as he was doing a triple gainer with a twist from a 200ft cliff and was facing the cliff as he pulled. The Norway jumper only got a 90 degree left offheading which saved him from hitting the wall on the opposite side of the 2-mile wide fjord he flew over at superterminal speed.

This is consistent with the fact that Coriolis effect is greatest on the equator and zero on the poles. In fact, if you BASE jump at the North Pole, your heading will always be remarkably consistent - the parachute will always open to the south. Also, the winds at the North Pole for at least the last 100 years have been amazingly consistently blowing only from the south. Therefore, your canopy will always open perfectly into the wind, making landing very easy.

A BASE jump at the North Pole is hard to do due to lack of buildings (B), antennas (A), spans (S) and earths (E). South Pole is more BASE-friendly, although it might take a while to find a bridge there.

It is advised that the jumpers in Northern Hemisphere drop their right shoulder at pull time, and jumpers in Southern Hemisphere drop their left shoulder to counteract the Coriolis effect. If you forget the right direction, just drain the toilet before the jump!

Yuri

Ha, and once more out of charity, ha.
Ok, that was actually good.

Thanks everybody for their input, much appreciated.

<<This is consistent with the fact that Coriolis effect is greatest on the equator and zero on the poles. >>

Yuri,

Are you sure about this? I would think it should be the opposite. The equator is neutral and the poles are at the north and south extreme reaches of the planet. The coriolis effect should gradually come to a halt as you reach the equator and reverse as you pass it. Am I missing something?

-Mike

Like Jason said, the 5 cells were pretty damn close to square. I know a 77 year old guy that flies a DC5 and is one of the top accuracy jumpers at the DZ. I'll ask him about heading.

Bring back the strato star 180 sq. ft. of on heading ground thumping joy of a canopy. I think paraflite is missing out on all the fun! Maggot could proably get sponsered. They made a 215 pursuit that was used for base alot in the early 90's If i rember correctly the center cell was larber than all the rest. I have a friend that still jumps a 230 rw pursuit in his backup rig.You should see the video of the sniveling inflation from a 210 ft. cliff. cool stuff.

I bet the BASE specific canopies have a bit more quality control than a skydiveing canopy. for obvious reasons.

 
Ah, there's the spirit that's done so much to push the safety of this sport forward. "It's complicated. And I'm sleepy."

That Spririt has done at least as much as a bunch of on line mental masturbation... :)

maybe so... but doesn't PD manufacture BASE canopies under contract? do you think they have/use special measuring equipment for the BASE models? (and I accept that PD makes a high quality product...)

I'm thinking that the better BASE canopies are designed to be tolerant of imperfect manufacturing. the perfect design means little if it can't be reliably sewn. run enough parachutes through a shop, and there is bound to be measurable differences during the run. they add to the "personality" of the canopy.

BASE canopies can suffer from far more abuse than skydiving canopies. water, tears, hard openings, all beat up a parachute. the fact that they keep functioning well speaks highly of their tolerance to abuse.

of course, a Centimeter off on a rib in a Xaos 69 means a bit more than the same discrepancy in a Blackjack 260. Savvy?

or


huh? I'm missing something...

my point is, manufacturers can choose to minimize inconsistencies during manufacture, make products tolerant to inconsistencies, or a mixture of the two.

the process somehow failed on the original Icarus Crossfire. (and possibly other models...)

inconsitencies between models will lead to different "personalities." (which is what Tom A. stated.)

another example, the Toxic pilot chute looks particularly complicated, and unfriendly to make. the photos I've seen indicate Marty does a fantastic job of overcoming these issues. could anyone in a factory style setting do the same?

Fair enough, my point was that in a small high speed high wing loading high aspect ratio canopy, the same amount of difference between different canopies of the same size/model that would matter noticably would be much greater actual mistakes in sewing.

Maybe i missed the point of something as usual.

wait, what was the point of this forum? i totaly forgot for a few seconds there, i had to look at the title to remember.


---Being that the BASE pilot chute manufacturers are pretty dedicated to quality, I mean that for real, not these factory made shit quality control promises, REAL quality from hand made stuff that you can only see from the people who CARE about what they are doing. I doubt that this kind of manufacturing will ever be able to be done in a factory setting, unless one can build a machine that can do this perfectly without human interaction. and i doubt that it is worth developing a machine that can make a pilotchute/caontainer/canopy. humans do a good job. just, i think we should stick to the small dedicated companies. if it wasnt such a bitch to build a canopy from scratch, i bet the small companies would do that as well. measuring and cutting equipment is pretty spendy.

I have said before, Wwarped, your avatar is the best one i have seen yet.

I bet the only thing that could matter in that is the tension of the leg straps.