Is a Cobalt safer for big way jumps?

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Its possible for a hard opening to cause internal damage or just render the jumper unconsious for some time. Being knocked out under a spinning canopy can quickly lead to impact. Lets not go into the results of something like a torn aorta or a ruptured lung while under canopy.

Opeing in a track induces a lot more velocity into the mix. Force is'nt scaled linear, its a progressive curve. I'm not sure of the exact figures but if even 5 mph faster results in a 1% harder opening, then a 7 mph could be 3%. Figure in that you are able to track at 35-50 mph away from a formation that could be a lot harder opening then you want. Hitting the brakes right before you dump will lower your speed and decrease the opening force that is applies to your body. Materials like Dacron can also help in this type of issue.

A good flat track has far less vertical velocity than "hugging the ball". Even when you add in the horizontal component (vector addition) you come up with less speed overall. The trouble is that a lot of people can't do a "good" flat track.

Right in line with what I was going to say. The track of a skydiver has a greater forward speed than a BASE jumper. The impact of a head-down preemie at 150 vs. a head-up preemie at 150 (or even greater) is quite obvious. The energy transmitted down through the spine, instead of snatching or perpendicular is much less painful. This' especially important with regards to the neck. The human head is rather heavy (especially when you add in a camera helmet) for our necks. When our head is directly above our neck - no problem - we can hold it up for hours and hours. Try to hold your head up for a long timelaying flat, with your head unsupported. The whiplash effect is what knocks people out during a hard opening. This effect would be magnified during a hard track.

I'm not going into the math here. Those of you who were in some of my camera seminars were bored with it during the power-point section. Suffice to say it hurts more when you are moving forward/head down.

The answer I have taught for many years is the tracking "flare." Converting the forward speed of a hard track into a bit of lift. Birdmen can convert the speed of a dive into enough lift to gain altitude tracking out of the dive (not more than they lost in the dive, of course). The object is not just to decrease your vertical speed, though. The additional benefit is in body position. The track is done normally (flat, fast, and away), with knee brakes and pulling the head high, with a last look around, during the wave-off. This sets you upright just a little, and slows the forward speed very quickly. Pitching in this head-high position reduces the impact on your neck.

Cajones has it and described the whole thing very eloquently...

http://www.zct.co.uk/skydivemag/pages/articles/jun96/controlyourdeployment.htm

This link also has pictures for those of you who skipped the good words posted above.

Cya
Dave

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A good flat track has far less vertical velocity than "hugging the ball". Even when you add in the horizontal component (vector addition) you come up with less speed overall. The trouble is that a lot of people can't do a "good" flat track.

I gotta agree with Kallend. In my experience, dumping out of a track makes for a slightly *softer* opening. As a big boy, my comfortable fall rate on my belly is somewhere between 125 and 130 mph. My fall rate in max track is around or slightly below 95 mph, and I'm sure I'm not hitting the perfect 1:1 glide ratio, so my horizontal velocity is considerably less than 95 mph. I believe if Paul does the math with a lower fall rate than 100 mph (100 mph would be a pretty poor track for most folks) and a more likely glide ratio, say 1 foot horizontal for every 2 feet vertical, he'll find that the total speed is a lot lower than the stated 140 mph.

Blues,
Dave

According to my Pro-Track, my fall rate in a track is in the 70-85 mph range. My softest openings are when I pull in a track. If your canopy opens harder if you pull in a track, you need to work on your flat tracking skills.

Hook

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The track of a skydiver has a greater forward speed than a BASE jumper.

Cajones, can you elaborate on this? I don't see how the track speed is going to be different at opening. Once you've hit terminal, how long does it take to reach maximum speed?

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I think that a lot of it is packing and body position

i'm in TOTAL agreement with this statement. it does kind of take the mystery out of it though!

All,

Thanks much for the great discussion. I always believed it was the relative wind your deploying canopy saw vice strictly the vertical component of it that would cause a hard opening. To me this was supported by the one time I remember dumping in a track and had a knot jerked in my butt. It was the hardest opening I can remember other than a nasty Sabre 190 incident that tore the canopy.

For that reason, I always did what Cajones recommended;

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The object is not just to decrease your vertical speed, though. The additional benefit is in body position. The track is done normally (flat, fast, and away), with knee brakes and pulling the head high, with a last look around, during the wave-off. This sets you upright just a little, and slows the forward speed very quickly.

I intuitively believed that the speed of the relative wind directly affected the rate of deceleration of the canopy, regardless of the direction. Simply, the body would decelerate in the direction of the wind it felt (since this was the external component operating on the PC initially and the remainder of the canopy ultimately), realizing that over the length of the event, the wind transition from one with a large horizontal component to one with a large vertical one. From Newtonian physics I knew that F=mA where A was acceleration or the time rate of change of velocity; (delta v/delta t). Thus the two ways to reduce the force would be to either have a lower entry velocity (reduce delta v) from which to decelerate (Cajones flare) or extend the time (increase delta t) over which the deceleration occurred (Cobalt's two stage deployment). Empirically, both would result in a smaller F(orce).

Again, I never considered it to be just a vertical deceleration, but rather a combined horizontal/vertical decel, which, over the length of the event, transformed from one with a large horizontal component to one which was almost totally vertical. I imagined it similar to being accelerated horizontally and then decelerated rapidly, similar to a car accident. Crush zones and airbags are all devices used to extend the length of time for the deceleration and considered lifesavers. I still do not totally buy emphasizing the vertical component to the total exclusion of the horizontal, but again, one bad dump in a track may be tainting me.

Again, mahalo to all for the insight. I have found all input thought provoking. Would love to sit down over a beer with all of you to discuss.

Tracking is an accelerative process. Tracking during a skydive is usually initiated when we are already at TV. This gives us a lot of air to deflect, and allows much faster acceleration. With a BASE track/delta, the speeds are lower, and the resulting forward speed is much lower. There are factors of body position and composition that can have great effect, also. I've never seen a BASE jumper with booties, but I've heard that tracking pants have given some very strong BASE tracks. Birdman suits, of course, mote excellent BASE tracks, but not nearly the forward speeds of terminal skydive tracks. These forward speeds are the vectors in the crazy math that hurts much more than the vectors perpendicular that gravity gives us.

As an additional factor I failed to mention, and this may be subconscious, I see BASE jumpers deploying head-high. Especially evident on short delays, just looking over footage from Bridge Day, I see jumpers with far more experience than I have, folding their legs, and pushing their heads up, to deploy. Just a few degrees of getting your head up where your neck can support it better, can reduce impact significantly.

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I always believed it was the relative wind your deploying canopy saw vice strictly the vertical component of it that would cause a hard opening.

Don't change your beliefs about this one! The deploying canopy sees the relative wind and doesn't really care about the direction.
The thing is that the relative wind when you are tracking is slower than the relative wind when you are falling vertically. See Paul Quade's post or mine for suggested values.
Kallend, Livendive and HookAndSwoop are also emphasizing on the total speed, not only the vertical speed.

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Again, I never considered it to be just a vertical deceleration, but rather a combined horizontal/vertical decel

You're absolutely right. the deceleration is in the direction of the airflow. If the airflow has an horizontal component, the deceleration has one as well.

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I still do not totally buy emphasizing the vertical component to the total exclusion of the horizontal, but again, one bad dump in a track may be tainting me.

Don't buy it. I don't think that anyone on this thread emphasizes on the vertical speed only. Most people agree that it's the air speed, whatever the direction.
If you had a hard opening in track, it might be that you were unlucky, or that you were in a bad track position when you did it. As the relative wind in track is slower than in normal belly to earth vertical freefall, openings in track should be softer (and actually they seem to be softer).

bb

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My vertical speed is a bit higher than yours in a track (~90) so my airspeed during a 45 degree track is actually _faster_ than freefall speeds.

How do you know that it is a 45 degree track?

bb