Collapsed canopy

[Fullonmother 0]

I have heard numerous stories about end cells closing close to the ground and have stumbled across references to 3 types of turbulence - is it advisable to land well away from buildings and airstrips - (I realise that buildings and planes hurt if you hit them - but I am enquiring with regards to the sudden closure of the canopy at 90 feet odd.) We are a quiet DZ and I have landed 30 odd feet from the runway and a similar distance from the buildings. Maybe I am way off mark and this closure is caused by something else. Any advise would be helpful.

[phoenixlpr 0]

You may start with filling your skydiving profile.

[damion75 0]

Quote

I have landed 30 odd feet from the runway and a similar distance from the buildings

What kind of canopy were your flying?
What was your wingloading?
What kind of approach were you doing?
What were the prevailing weather conditions?
Did the wind come over the building?
Was it hot or cold?

What is your actual question here? If your canopy 'collapsed completely' at about 90ft I would be impressed that you were typing here...

***************

Not one shred of evidence supports the theory that life is serious - look at the platypus.

[tombuch 0]

You may have experienced turbulence from the buildings or the runway. You are correct that you should stay away from these things.

A general rule is that turbulence can occur as far downwind as 10-20 times the the height of the object. There is a brief overview of this in the USPA Skydivers Information Manual (SIM) in section 4, category "C" on pages 48-49 (2006 version, the pages may be slightly different in the 2007 edition). The SIM is available on line at http://www.uspa.org/publications/SIM/2007SIM/Section4CatC.htm. One way to think of this kind of turbulence is to visualize a small stream or river, and think about how water moves over and around rocks. There will generally be an area of disturbed water below and to the sides of the rocks, extending further downstream when the water is moving faster. Sometimes there will even be swirls below objects. Air turbulence acts in very much the same way when wind moves over ground obstructions.

Runways are a special issue. They will heat up in the sun and create a thermal, that is rising air over the runway. If air is rising and moving vertically away from the runway, then colder air will sink and move to replace the rising air. So, on a hot or sunny day you can expect rising air over the runway, and sinking air to the sides, with a sheer between the two moving air masses. If there is wind you can expect these air masses to be off-set to the downwind side.

Rising air is sometimes a good thing for us, and jumpers will sometimes use thermals to extend their canopy time to get back from a long spot, but we should know that wherever there is rising air, there is also going to be associated sink and dangerous downdrafts. If you are crossing a runway you may experience the lift and smile at the extra "hang time," but be aware that you may soon hit a powerful downdraft.

In desert areas there can also be dust devils. These are swirling masses of rising and descending air. Folks from Southern California or Arizona are probably more experienced with these than I am, but basically they tend to pop up when the ground is heated and the air starts to rise. It will sometimes appear as a boiling mess of sand and dirt over a specific piece of ground, but there will sometimes be no indication at all. As the heated air moves up and cooler air moves down, the air masses will clash and a tiny lateral movement will happen. From that point the airmass can rapidly spin like a mini tornado and then move across the landing area just like a big tornado you sometimes see on TV. It's a pretty cool thing to witness, but ominous because it can happen so suddenly, and because dust devils are so are so dangerous. The uncovered and rapidly heating dirt in a desert like environment tends to spawn dust devils, and they are easy to see once they blow-up because the loose dirt swirls in the funnel and gives them shape.

If you are jumping in a desert area, ask for a briefing about dust devils. Local jumpers will be able to tell you when and where they tend to form, and indications that conditions are right for their formation. The same phenomenon can also happen in non-desert areas, but these movements are harder to see, and tend not to be as pronounced. They will usually form on hot sunny days with no wind, or light and variable wind, and will tend to form over conflicted surfaces, such as a driveway, plowed field, or even a pea gravel pit.

Most jumpers don't worry too much about all the ways air moves, or about the specifics of how turbulence forms, but this is a fascinating topic called micro-meteorology . We tend to avoid conditions that create turbulence, but glider pilots and hang glider pilots actively seek out rising air, and have a much better understanding of how air masses work.

If this is something you are interested in, talk with local jumpers about their specific experiences at your drop zone. Turbulence isn't magic. It happens in very predictable ways, and once you identify the usual causes at your DZ, and the wind conditions that favor turbulence, you will be better able to avoid it. And, if you understand the micro-meteorology of your drop zone, you will have a better sense of when to stay on the ground.

Tom Buchanan
Instructor Emeritus
Comm Pilot MSEL,G
Author: JUMP! Skydiving Made Fun and Easy

[SpecialKaye 0]

nice job Tom!

[DocJames 0]

thats good stuff i must say

canopy collisions are bad

[drae 0]

Thank you for this information. It was given in an explanation that I understand. This has been a question of mine and, although people have tried to explain it, prior to reading your description, I just didn't get it!
Thanks again.

[Stumpy 284]

Quote

A general rule is that turbulence can occur as far downwind as 10-20 times the the height of the object.

Worth noting also that you can get turbulence 3 times the height UPWIND of the object.
I know kitesurfers who have been badly hurt for this reason.

Never try to eat more than you can lift

[mnealtx 0]

A fair distance overhead, as well... 3x , if I recall correctly...

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[Fullonmother 0]

Just to say thank you for this composite reply Tom - I appreciate your help greatly,


FullonMother