Forums: Skydiving: Safety and Training:
Re: [Martini] Opening High for Bad Spots

 1 2 3 4 5 6 7 8 9 10  View All Thread Options

mnischalke  (D 26290)

Feb 20, 2004, 9:06 PM
Post #226 of 246 (844 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
I do things the hard way, I guess. I used the 990 you gave me minus the 440 from the 11 seconds x 40 fps. Oh well

Btw, you certainly are the professor, with all that distracting bs mixed in there.

I guess, I could have pared it down further, but this is what I used:
Quote:
at 2500ft agl. an easterly wind is 40ft/sec.

at altitude the winds are westerlies 50ft/sec

A team leaves the Otter. open at 2500ft.

a second team leave after 11 seconds.

How far from (the center of the first group) is the center of the second group, and is there a risk of collision between groups?

Thanks for the fun!

kallend  (D 23151)

Feb 20, 2004, 9:18 PM
Post #227 of 246 (840 views)
Shortcut
 Re: [eames] Opening High for Bad Spots [In reply to] Can't Post
50 x 11 = 550ft.

Don't you have to subtract the 40 x 11 = 440 ft that group one drifts while under canopy since the uppers and the lowers are heading in opposite directions?

-Jason

How can they drift when there's no wind (remember the cigar smoke).

eames  (D 23844)

Feb 20, 2004, 9:41 PM
Post #228 of 246 (833 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
How can they drift when there's no wind (remember the cigar smoke).

They are the wind. Uppers and lowers are pointing in opposite directions.

11 sec in the door at 50 ft/sec in one direction, then 11 sec under canopy at 40 ft/sec in the other direction.

I guess I'll have to think about it more.

-Jason

mnischalke  (D 26290)

Feb 20, 2004, 9:47 PM
Post #229 of 246 (831 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
Methinks kallend is fucking with us...

On another note: Don't we got a freshly-painted otter to play with tomorrow? hehe

velo90

Feb 20, 2004, 11:37 PM
Post #230 of 246 (816 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
Excellent quiz Kallend
You tell a nice stroy as well, I really liked the guy messing with his booties.
It's rather sad that 550 ft did not pop into peoples head straight away. But there again, unless you forget about the ground you will let all the references to the ground in your story affect how you answer. What's more, unless you ignore the ground, you never see all the other useful hints in your story.

eames  (D 23844)

Feb 21, 2004, 12:13 AM
Post #231 of 246 (813 views)
Shortcut
 Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post
It's rather sad that 550 ft did not pop into peoples head straight away. But there again, unless you forget about the ground you will let all the references to the ground in your story affect how you answer.

I don't think I'm considering the ground at all. In fact, if the guy in the balloon saw another balloon in the upper winds, and used his handy laser rangefinder, he would see it moving 90 ft/sec. He would still see the Otter moving at 50 ft/sec in the other direction. The Otter and the upper balloon would be moving away from each other at (90 + 50) 140 ft/sec.

So the groups gain 550 ft of separtion from the upper winds and the plane, then lose 440 ft due the first group reversing direction in the lower winds for the 11 seconds before the second group opens.

Would you explain to me why I'm wrong?

-Jason

eames  (D 23844)

Feb 21, 2004, 12:13 AM
Post #232 of 246 (812 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
Can you explain to me why I'm wrong?

eames  (D 23844)

Feb 21, 2004, 4:18 AM
Post #233 of 246 (804 views)
Shortcut
 Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post
I hear bells ringing....

Now that I think of it, who cares about 50 ft/sec x 11 sec? That's not how fast the plane is flying through the upper airmass.

140 ft/sec x 11 sec = 1540 ft in the upper airmass.

-90 ft/sec x 11 sec = -990 ft (because of the difference in speeds of the air at exit altitude and opening altitude).

1540 ft + (-990 ft) = 550 ft

Ding, ding, ding. Man, if I had only plugged the numbers in according to how I've been preaching the whole time! Sorry for being slow.

Yay, we all agree!

-Jason

(This post was edited by eames on Feb 21, 2004, 4:39 AM)

eames  (D 23844)

Feb 21, 2004, 4:38 AM
Post #234 of 246 (801 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
All you need to know is that the plane is going 50ft/sec faster than the balloon, and multiply that by the exit delay 50 x 11 = 550ft.

This is (of course) a better way to do it. But it took doing it with the real numbers to understand why.

Now I really have it down... conceptually and practically. Thanks for the quiz.

-Jason

diverdriver  (D 19012)

Feb 21, 2004, 7:05 AM
Post #235 of 246 (794 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
Quote:
And real circumstances exist where blindly relying on groundspeed might kill you.

And what do you see me doing on days we have uppers out of the west and lowers out of the east?

I fly south to north or north to south offset along the river (Fox River next to SDC). Seperation.....no problem. (and then I can go back to relying on my groundspeed is god warm blankee )

kallend  (D 23151)

Feb 21, 2004, 7:33 AM
Post #236 of 246 (792 views)
Shortcut
 Re: [diverdriver] Opening High for Bad Spots [In reply to] Can't Post
Quote:
And real circumstances exist where blindly relying on groundspeed might kill you.

And what do you see me doing on days we have uppers out of the west and lowers out of the east?

)

In another thread I said I spent a lot of time watching a master.

Did I ever mention that all but one out-landings I've had were when a certain DZO was spotting?

kallend  (D 23151)

Feb 21, 2004, 7:35 AM
Post #237 of 246 (792 views)
Shortcut
 Re: [eames] Opening High for Bad Spots [In reply to] Can't Post
All you need to know is that the plane is going 50ft/sec faster than the balloon, and multiply that by the exit delay 50 x 11 = 550ft.

This is (of course) a better way to do it. But it took doing it with the real numbers to understand why.

Now I really have it down... conceptually and practically. Thanks for the quiz.

-Jason

Now you're pleased that I didn't tell you, 'cos when you figure it out for yourself you're more likely to believe it.

diverdriver  (D 19012)

Feb 21, 2004, 7:38 AM
Post #238 of 246 (791 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
Did I ever mention that all but one out-landings I've had were when a certain DZO was spotting?

You know, if he couldn't see the ground he was right on! But man, if it was a clear day look out!

LOL...I had him climb out early on me so many times. God Bless him. That sure was funny.

freeflybella  (D 21113)

Feb 21, 2004, 8:14 AM
Post #239 of 246 (787 views)
Shortcut
Sorry for coming into this late - especially when everyone now seems to agree . . .a question from a right-brained thinker.

On a normal jump day (normal conditions, ie, uppers same direction as lowers) what are the 'experts' agreeing to?

That groundspeed should or should not be used to determine time between exits? If not, please explain?

Please explain in a very practical way (look at ground winds, winds aloft, jump run direction, number/size of groups, etc.) instead of numbers and equations.

diverdriver  (D 19012)

Feb 21, 2004, 8:56 AM
Post #240 of 246 (776 views)
Shortcut
 Re: [freeflybella] Opening High for Bad Spots [In reply to] Can't Post
Sorry for coming into this late - especially when everyone now seems to agree . . .a question from a right-brained thinker.

On a normal jump day (normal conditions, ie, uppers same direction as lowers) what are the 'experts' agreeing to?

That groundspeed should or should not be used to determine time between exits? If not, please explain?

Please explain in a very practical way (look at ground winds, winds aloft, jump run direction, number/size of groups, etc.) instead of numbers and equations.

In the true form of talking about exit seperation the ground plays no part. However, the error caused by using groundspeed to reference seperation adds in an error that potentially increases actual seperation at opening altitude. So, that is why even after all this discussion it is still ok to use groundspeed AS LONG AS the upper winds are blowing in the same general direction (not opposite of) as the lower winds.

Does that help?

(This post was edited by diverdriver on Feb 21, 2004, 8:58 AM)

VectorBoy  (F 321)

Feb 21, 2004, 8:16 PM
Post #241 of 246 (756 views)
Shortcut
 Re: [eames] Opening High for Bad Spots [In reply to] Can't Post
If the ground is irrelevant you could never have a bad spot

Of course the ground is relevant for spotting: You're trying to land on a specific "spot" on the ground.

-Jason

But people use the ground as a reference for their separation from the previous group.
What do you do when it apears that you are far from the DZ. Follow the procedure and allow what seems to be ridiculous interval between groups, wait till the previous group reaches the 45 degree point or just come out right on top of the group before you, say 2 seconds of separation? This is why I bring it up.

kallend  (D 23151)

Feb 21, 2004, 8:19 PM
Post #242 of 246 (755 views)
Shortcut
 Re: [VectorBoy] Opening High for Bad Spots [In reply to] Can't Post
If the ground is irrelevant you could never have a bad spot

Of course the ground is relevant for spotting: You're trying to land on a specific "spot" on the ground.

-Jason

But people use the ground as a reference for their separation from the previous group.
What do you do when it apears that you are far from the DZ. Follow the procedure and allow what seems to be ridiculous interval between groups, wait till the previous group reaches the 45 degree point or just come out right on top of the group before you, say 2 seconds of separation? This is why I bring it up.

(This post was edited by kallend on Feb 21, 2004, 8:20 PM)

VectorBoy  (F 321)

Feb 21, 2004, 8:59 PM
Post #243 of 246 (751 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Sometimes you can, sometimes you can't as in the extreme jumprun example that I describe in my first post to this tread relating to Extreme winds aloft.

Try asking for a go around at WFFC or some major boogies. Some places talking to the pilot is verbotten ( to explain why you want a go around ). If the spot is good and the pilot can proove it there may be no go- around, you always have the option to ride down.

bmcd308  (D 27472)

Feb 23, 2004, 9:09 AM
Post #244 of 246 (729 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
>>So you are willing to bet your life on the reliability of the air at exit altitude and on the ground for landing, but at opening altitude you consider it unreliable. Interesting concept. <<

What is worse, an off landing or a collision?

When I "rely" on the wind at exit altitude and on the ground for landing, all I'm doing is making sure that I land on the dz. If the wind dies at exit altitude, I wind up long. If the wind dies at 0 AGL, I might have to run out my landing.

While an off landing might be a contributor to an incident, an off landing is less likely to be an incident than a collision between a jumper in freefall and an open canopy.

I'm not sure the concept of being wary of allowing canopy drift to create separation is all that odd.

I don't advocate basing the entire exit separation decision on groundspeed, blindly assuming that canopy drift will not create problems. I am not even sure that anyone has advocated that position in this thread.

However, I do not advocate planning to have everyone open at the same spot over the ground, blindly assuming that the wind at 3 grand will push the previous group out of the way, either.

The policy implication of my position is that on days when the lower winds are roughly consistent in direction with the uppers, you use groundspeed to maximize separation between the groups, stringing them out along the available jump run. On days where the winds at opening altitude are roughly opposite the winds aloft, you run jump run crosswind or in an arc (like both DD and Mullins do).

Brent

kallend  (D 23151)

Feb 23, 2004, 11:29 AM
Post #245 of 246 (715 views)
Shortcut
 Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post
>>So you are willing to bet your life on the reliability of the air at exit altitude and on the ground for landing, but at opening altitude you consider it unreliable. Interesting concept. <<

What is worse, an off landing or a collision?

When I "rely" on the wind at exit altitude and on the ground for landing, all I'm doing is making sure that I land on the dz. If the wind dies at exit altitude, I wind up long. If the wind dies at 0 AGL, I might have to run out my landing.

While an off landing might be a contributor to an incident, an off landing is less likely to be an incident than a collision between a jumper in freefall and an open canopy.

I'm not sure the concept of being wary of allowing canopy drift to create separation is all that odd.

I don't advocate basing the entire exit separation decision on groundspeed, blindly assuming that canopy drift will not create problems. I am not even sure that anyone has advocated that position in this thread.

However, I do not advocate planning to have everyone open at the same spot over the ground, blindly assuming that the wind at 3 grand will push the previous group out of the way, either.

The policy implication of my position is that on days when the lower winds are roughly consistent in direction with the uppers, you use groundspeed to maximize separation between the groups, stringing them out along the available jump run. On days where the winds at opening altitude are roughly opposite the winds aloft, you run jump run crosswind or in an arc (like both DD and Mullins do).

Brent

Hasn't this discussion left any impression? In the context of separation between skydivers at canopy opening time the ground is irrelevant. A fixed point over the ground is irrelevant. Canopy "drift" relative to the ground is irrelevant. The only thing having any relevance is the behavior of the air between exit altitude and opening altitude, inclusive.

bmcd308  (D 27472)

Feb 23, 2004, 12:26 PM
Post #246 of 246 (706 views)
Shortcut
 Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post
OK. I'll give up trying to explain myself.

 1 2 3 4 5 6 7 8 9 10  View All

Forums : Skydiving : Safety and Training

 General     Announcements     Introductions and Greets Community     Skydivers with Disabilities     Blue Skies - In Memory Of Skydiving     General Skydiving Discussions     Safety and Training     Gear and Rigging     Instructors     Tandem Skydiving     Incidents     Wind Tunnels     Events & Places to Jump     Skydiving History & Trivia Skydiving Disciplines     Swooping and Canopy Control     Relative Work     Freeflying     Canopy Relative Work     Wing Suit Flying     Photography and Video International     En Français     Foro de Salto libre     Stammtisch     Äðîïçîíà.com Dropzone.com     Security and Scam Alerts     Suggestions and Feedback     Error and Bug Reports Archive     2005-2006 USPA BOD Elections     2008-2009 USPA BOD Elections     World Team 2006      2013-2015 USPA BOD Elections     2006-2007 USPA BOD Elections

 Search this forum this category all forums for All words Any words Whole Phrase (options)