Competition Cobalt 95 = Neck Breaker

[Hooknswoop 19]

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i am saying that i have video and sensor data logged showing a 29g's at line stretch with canopy completely in the bag.

After watching the clip, the large jump in the graph occurs after the canopy leaves the bag. Looks like an awefully large PC too. Looks large enough to be considered a drogue.

Edited to add the pic.

Hook

[skygod7777 0]

lets make it clicky

http://www.extremefly.com/aerospace/press/index.html#


later

[billvon 2,476]

A 4 millisecond impulse of 29G's will move an object .08 inches, and change his speed by about 2 mph. In other words, it will not be perceived as a hard opening. If you run a car with no bumpers into a concrete wall at 2mph you can easily get 50G's of deceleration for a millisecond or two, but due to the low speed change it is not perceived as a serious shock to an occupant. In other words, the poor coupling between his skeleton and the car frame prevents him from reacting much to that 50G's.

In the case you mention, it sounds like the 6.4 G's is the big deal, since it lasts a lot longer.

[ramon 0]

Makes sense. I guess for this example the brief 29 Gs would be experieneced by part of the riser or links while a skiydiver body is merely coaxed to begin pivoting upright.
Any long term G's experienced would involve the skydiver no longer having pivot romm and would be felt directly on the decelerating body.

"Revolution is an abrupt change in the form of misgovernment.", Ambrose Bierce.

[listo 0]

ok, lets use some common sense here guys. Sure it might have been possible to have 29 g's, but how long was that load sustained. Then, how long was the 6 g's sustained. You can experience 29 g's for a 1/4 of a second and then experience 6 g's for 5 seconds and you will feel the 6 g load a lot more. The 1/4 second 29 g load will feel like a slight jerk compared to the sustained 6 g load. Lets get back to using common sense here guys. PEACE!

Live today as tomorrow may not come

[cobaltdan 0]

btw the 29g was measured at the jumpers chest in line with pivot point of the harness.

as far as what you feel: it is all about force vs time, there are instances where higher peak shocks can be percieved as lower by the jumper, but it is the higher peaks that inflict injuries. do not view a high peak force at a short duration as harmless. the sabre that broke my neck was since jumped twice with a datalogger both times brieflly pegging 50g accelerometers off the scale.

sincerely,

dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[dterrick 0]

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then a completely new peak of 6.4 g's when the canopy exits the bag and catches air (6.4 stage 1, droping to 3.5g's stage 2, width 5 seconds).

VERY interesting, Dan. you have just confirmed my suspicions about a jump that knocked me silly on deployment. I had a big BANG after a sit/stand dive (C 182 DZ, just learning the position). I thought I had enough deceleration but I DO know that I literally didn't have time to resume Box before the slam.



I'm 'physics challenged' but a friend calculated about 6.5G average over 1 sec given 150 to 15 mph deceleration. Your numbers suggest I was sufficiently slowed down and the subject of line dump. The timeline seems correct and it is much more likely than my still being at 150 after 2k of decel (started sit at about 8k).

Anyway, for those still reading, I think the ultimate solution (for me) has been to ONLY use the smallest elestics available, take bigger bights, and to change them frequently. Even with all this I've noticed the litle elastics get tired before they break.


Dave

Life is very short and there's no time for fussing and fighting my friend (Lennon/McCartney)

[Cajun 0]

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Even with all this I've noticed the litle elastics get tired before they break.

If you choose, you can try skybands, they are what I use. last for about 100 jumps and hold the lines very well. Only problems is, these things are so strong that a PC will not break them. If you do not stow your lines correctly you will have a bag lock. I love them and have never had a problem.

[diablopilot 2]

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Only problems is, these things are so strong that a PC will not break them. If you do not stow your lines correctly you will have a bag lock.

I disagree. A SkyBand takes no more force to break than a coventional rubber band. They just do not degrade as fast from repeated strechings. If you have a bag lock with one you would have with a normal rubber band. Either the PC was sub standard or a packing error happened.

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I love them and have never had a problem.

Me too!

----------------------------------------------
You're not as good as you think you are. Seriously.

[Hooknswoop 19]

Dan-

Could you reply to my post, the one w/ the pic attached?,

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=314679;page=2;sb=post_latest_reply;so=ASC;mh=25;

Thanks

Hook

[cobaltdan 0]

hi hook,

i did respond. go back in the thread and you will notice i said it was a military tandem drop.

1000# exit weight, 350 sq' main, vector tandem rig, 184mph speed at deployment. scrunchie failed to collapse drogue, line stretch generated 29g's, canopy upon exiting bag generated a max of 6.4 g's stage 1, about 3.5 g's stage 2.

sincerely,
dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[Hooknswoop 19]

I mean the post with the pic. The pic clearly shows the canopy out of the bag and the "G" graph hasn't hit a peak. You said:

Quote

i am saying that i have video and sensor data logged showing a 29g's at line stretch with canopy completely in the bag. the peak width is 4 miliseconds. then a completely new peak of 6.4 g's when the canopy exits the bag and catches air (6.4 stage 1, droping to 3.5g's stage 2, width 5 seconds).

But this isn't consistant with the video. Just looking for clarification. Is the graph not quite in synch with the video?

Hook

[cobaltdan 0]

hook,

it has hit a peak. it is just a very fine line (peak rise time is 2 miliseconds) and doesn't show well on the compressed mini format video posted. you can distinctly view the peak on the original dv or by comparing time code to data logged.

sincerely,

dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[Hooknswoop 19]

OK, that explains it, thanks.

Hook

[Beppo 0]

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6 g's for 5 seconds and you will feel the 6 g load a lot more. The 1/4 second 29 g load will feel )]

6 g's for 5 seconds reduces 658 mph - wow ;-)
29 g's for 1/4 second reduces 159 mph....

[cobaltdan 0]

an opening that peaks at 6 gs and takes 5 seconds, is not at 6 g's for the entire 5 seconds.

sincerely,
dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)