Canopy collision

[billvon 2,406]

>This statement is ONLY true if the L/D for both canopies is the same.

Agreed.

>>The faster canopy will reduce how much that footprint moves with wind.

>Not true.

True, if you accept the first part. Think of it this way - a smaller canopy is in the air for a shorter period of time, on average. In that shorter time the wind has less of an effect.

>Downrange distance = (Vhc + W) * (Dv/Vvc)
>Uprange distance = (Vhc - W) * (Dv/Vvc)
>Footprint = uprange distance - downrange distance

Or footprint = (Vhc + 2W) * (Dv/Vvc)

Thus, footprint sensitivity to wind is reduced when Vvc is increased.

>I jump a smaller canopy at a higher WL than I really want to
>because I do not want the people from the plane after me to buzz
>me at landing.

One can always construct scenarios in which one's choice is the correct one. I once heard a jumper explain to me that a small canopy was safer because then he could pass other canopies in the pattern; he felt that passing them was safer than having them 'sneak up' on him.

I have no problem with people making any (informed) decisions they want about canopies. But I don't buy that in general smaller canopies give one an edge in safety.

[MakeItHappen 15]

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Or footprint = (Vhc + 2W) * (Dv/Vvc)

Thus, footprint sensitivity to wind is reduced when Vvc is increased.

No, Bill, that's not right.

I just want to clarify something here.

Footprint:
There are two components to 'footprint'.

1. the distance between the maximum possible upwind and downwind distances.
The distance between these two points is equal to 2 Vhc (Dv/Vvc)
[In skydiver-speak: twice horizontal speed times hang time]
It is independent of wind.
The upwind and downwind points get shifted by the same amount whenever there is wind.

2. the distance this 'window' of possible landing sites shifts with respect to the wind.
That 'shift' distance is equal to W(Dv/Vvc)
[In skydiver speak: wind speed times hang time]
The shift is downwind.
The greater the wind speed the greater the shift.
For a given wind speed, the shift decreases as canopy descent rate increases.
The distance between the uprange point and the downrange point with wind is the same as the distance between those points with no wind.

From a practical standpoint, if you had a bad spot and there was an open space below you and slightly downwind, you'd spiral down to make the open area. It would not be a good idea to hang high, get pushed back by the wind and land downwind of the open area.

Or you could hang high (minimize descent rate and increase the time being pushed by the wind) to reach an open area further downwind.

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DiveMaker

[billvon 2,406]

I said:

>>Thus, footprint sensitivity to wind is reduced when Vvc is increased.

You said:

>For a given wind speed, the shift decreases as canopy descent rate increases.

I think we agree here. The faster the canopy descends, the less the footprint moves in a given wind. Its size does not change; the size depends on the L/D of the canopy.

[freakydiver 0]

Well hell - I'm going to go out and buy me a katana 80 since it gets me where i need to go faster. That after all is a "pro" no?

-- (N.DG) "If all else fails – at least try and look under control." --

[kallend 1,635]

I think something is being lost here. The post that started this speed discussion implicitly assumed that my Spectre was slower than the other guy's Stiletto. That is clearly an unjustified assumption since WL was never mentioned. Given our respective canopy sizes and our masses, I suspect the speeds in straight unaccelerated flight were actually very similar.

I would like to emphasize that I am really glad I had my Spectre in my rig, and not my Stiletto, when spun around into line twists with both end cells collapsed at around 100', maybe lower. The canopy reinflated right away and kept flying straight.

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The only sure way to survive a canopy collision is not to have one.

[mjosparky 3]

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It is safer for me to jump a higher WL and to land with people from my airplane than to have the people from the next load under pocket rockets buzz me at 50 ft.

Why is it safer to buzzed by someone on your own plane then it is to get buzzed by someone from another plane? You jump mostly big ways and it is possible to buzzed by more than one for any direction. jmo

My idea of a fair fight is clubbing baby seals

[rehmwa 2]

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It is safer for me to jump a higher WL and to land with people from my airplane than to have the people from the next load under pocket rockets buzz me at 50 ft.

Why is it safer to buzzed by someone on your own plane then it is to get buzzed by someone from another plane? You jump mostly big ways and it is possible to buzzed by more than one for any direction. jmo

Your point that either way "buzz jobs" happen, just the position of her being the buzzer instead of the buzzeeee.

Like most of us, I'd assume she trusts her own abilities more than the strangers in the following plane. I like that, she's making an active choice based on her confidence rather than some blanket statement about how everyone should fit some mold.

as long as everyone doesn't do that, then we just see a bunch of people under specs (eventually). Less collisions, since half the population hooks themselves into the turf.

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Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[MakeItHappen 15]

To continue hijacking John's thread…..

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Why is it safer to buzzed by someone on your own plane then it is to get buzzed by someone from another plane? You jump mostly big ways and it is possible to buzzed by more than one for any direction. jmo

People from the same plane I jump from do not usually buzz me. The high WLs land before me. The high WLs from the next plane may catch up to me if their exit is 'soon' after mine. Likewise, I may catch up tandems from a previous load, if my exit is 'soon' after their exit. I stay well clear of tandems.

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Your point that either way "buzz jobs" happen, just the position of her being the buzzer instead of the buzzeeee.

ha, ha, ha That's funny - me as a buzzer ;)

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Like most of us, I'd assume she trusts her own abilities more than the strangers in the following plane. I like that, she's making an active choice based on her confidence rather than some blanket statement about how everyone should fit some mold.

as long as everyone doesn't do that, then we just see a bunch of people under specs (eventually). Less collisions, since half the population hooks themselves into the turf.

Actually, I know the people in the following plane too.
What I do is help stack the landing order. When I was jumping a WL of 1.0 the newer jumpers with WL of 1.5 or more would buzz me under 100 ft. They were from the next load. They had tunnel vision on the ground and never looked around. If it was Luigi or Clint behind me, I wasn't worried. It was the newer jumpers with only a few hundred jumps, high WL and sometimes out of towners from small DZs that posed the greatest danger. I have no influence on changing that. What I could do is land sooner. That's when I went to the whopping 1.1 WL I have today. I generally hang high and let everyone, except tandems and students, get below me, whether it's one otter load, two parallel loads, or a big way load. It's also easier to work into the pattern to land by the gate too. I only do that if traffic permits it. I'll take the dirt landings when I have to.

Another advantage is that you get more photo ops ;)

Of course, if you jump with a photographer that cuts into the pattern abruptly, you might get attacked as John did.

Now we are back to John's thread topic, unless you want to ask me about my regular pilot chute, uncollapsed slider, no booties, no helmet and why I don’t put my hands through the toggles.

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DiveMaker

[mirage62 0]

Now we are back to John's thread topic, unless you want to ask me about my regular pilot chute, uncollapsed slider, no booties, no helmet and why I don’t put my hands through the toggles.
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Okay I'll bite on this one but ahy would you not put your hand through the toggles. (I know you'll have a good answer I just can't come up with one)

Besides who cares if with screw with Johns thread

Kevin Keenan is my hero, a double FUP, he does so much with so little

[mjosparky 3]

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Your point that either way "buzz jobs" happen, just the position of her being the buzzer instead of the buzzeeee.

No, that was not my point at all. And the question I asked way answered by the person I asked thank you.

My idea of a fair fight is clubbing baby seals

[MakeItHappen 15]

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Now we are back to John's thread topic, unless you want to ask me about my regular pilot chute, uncollapsed slider, no booties, no helmet and why I don’t put my hands through the toggles.
***

Okay I'll bite on this one but ahy would you not put your hand through the toggles. (I know you'll have a good answer I just can't come up with one)

Besides who cares if with screw with Johns thread

Deja Vu


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DiveMaker

[Trae 1]

in reply to "I think something is being lost here. The post that started this speed discussion implicitly assumed that my Spectre was slower than the other guy's Stiletto. That is clearly an unjustified assumption since WL was never mentioned. Given our respective canopy sizes and our masses, I suspect the speeds in straight unaccelerated flight were actually very similar.

...........................................
implicit assumption.. " Just wondering now if going to a slower canopy is still the idea to reduce risk. ?? ".

Bit clearer now on the issues thanks to previous discussion.
Perhaps smaller faster canopies are relatively more dangerous than larger slower ones.
For now I'm sticking with it 's better to have the range than not .

in reply to " I would like to emphasize that I am really glad I had my Spectre in my rig, and not my Stiletto, when spun around into line twists with both end cells collapsed at around 100', maybe lower. The canopy reinflated right away and kept flying straight. "
....................

That's the best news.
I'm wondering how other similar canopies would respond to such treatment .
Comparison collision test ?
Are some canopies known for stronger pressusisation and self righting qualities?

[DJL 232]

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Are some canopies known for stronger pressusisation and self righting qualities?

Yup. The PD Lightning is the most extreme example of this. Watch some serious CRW vid. You'll be surprised at how many times you thought there would be a wrap and there wasn't.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[Belgian_Skygirl 0]

I am glad both of you are ok. Last summer, I was almost the victim of a canopy collision... a girl with only 3 solo's was talking (under canopy, yelling is a better word) to her friends and she was looking to them, and came in my direction. She was above me... I saw a foot at my right side, so I turned left. Once landed I got very angry, as she wasn't paying attention at all at the canopies around her. I was very lucky.

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No dive, like skydive... wanna bet on it?

[Feeblemind 1]

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There were dozens of eye witnesses on the ground, maybe one of them will comment.

since you asked.
from what i saw you and a good number of others were all facing south and were on final. camera guy (who either pulled lower than he should, spiraled down to land faster, or both - i wasn't paying attention to that part of his descent) was flying WNW slightly higher but with barely enough altitude to be able to turn back into the wind. when he did his turn (toggle - not flat) it put him right in the middle of all the traffic. there was no way you could have seen him before he collided with you. he was, for the most part of his turn, in your blind spot. his comment when he walked back from the field: "the other guy hit me from the back" who? "i don't know. i didn't see him."
even after several of us told him it was his fault he insisted otherwise.
oh yeah, if you think this happened at 100' you must have been measuring it with baby feet or something.
it is true though that after this incident the big way landings became (almost) boring.

I am only a 2 year jumper an I do some video from time to time for 4 to 12 ways. I once made the mistake of being observed as not pulling as the group turned to track. I was "EDUCATED" by the ST & A and advised to not do it again. I also have made the mistake of spiriling down, this again resulted in an "EDUCATIONAL" conversation (actually it was one way).

I would be curious to know:

1) How large was the skydive?

2) What was the break off alt.?

3) Did the camera have the center? (I am assuming so)

4) Has the camera guy seen the photo and relized he was the "high" person"?

I am not going to try and accuse or make a negative statement here, but there is no way to sugar coat my meger opinion. If the camera was to pull in the center, he spirialed down after that, entered in the middle of the pattern (I have jumped at Z-hills, so I know the landing area), collided with a canopy, he disputed the facts from other jumpers that "he" was actually at fault. Well note to self, don't get on a plane with the individual again until he comes to his senses. I would think two fatalities (RIP Tommy and Cliff) in the last month might make make folks more aware, I guess not for some.

Lastly, I am glad your OKAY Prof. and that this had a positive outcome.

In the words of my ST&A:
It's better a long walk back to the packing area rather than a short crawl to an ambulance

Fire Safety Tip: Don't fry bacon while naked

[loudtom 5]

Whoa John I have seen you talk about it and have felt your passion above and beyond our shared trajedy, now I know why...
Thank something you are still here.
tom

tom #90 #54 #08 and now #5 with a Bronze :-)