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LeeroyJenkins

Dust devils are sketchy...

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I'm not even sure that was a dust devil. It looked to benign.

Dust devils can pick you up and throw you to the ground multiple times. And can kill. Not from just a bad first landing but when they decide to pound the ground with you again.

None of the dust devil landings on youtube are as bad as the one I witnessed, except the Russian one under a round.
https://www.youtube.com/watch?v=WHrTWih0rnE&t=14s

And one I witnessed slamming a friend into the ground three or four times was in Michigan, on a small dropzone on grass next to a tree line surrounded by fields and other woods. No wide open spaces or bare ground.
I'm old for my age.
Terry Urban
D-8631
FAA DPRE

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>I hit a dust devil back in March, just had the video supplied to me. It was fun.

That looks more like a little rotor or something than a dust devil. A dust devil has a powerful circulating core that wreaks havoc when encountered at ground level; even at >1000 feet it can collapse canopies. It doesn't just tweak your canopy a bit.

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The dust devil I ran into caught me 10 ft off the ground, took us up to 40 ft or so going backwards. Collapsed the canopy, dropped us to 5 ft above the ground. Re-inflated the canopy, snapped us back up to 25 ft or so, horizontal and then dropped us to the ground. After all that fun we got drug 100 ft across the ground until I could disconnect the rsl and cutaway.
That was a tandem in PA.


Sometimes you're the windshield, sometimes you're the bug.
Pelt Head #3

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It was a small dust devil, I clipped the edge of it. The guy filming was telling that girl in the video that there were dust devils out and why they were dangerous (and there were) a few huge ones, couple thousand feet tall further off the DZ. DZ shut down after that load because it was getting dangerous.

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I witnessed a dustdevil "grab" a high-performance landing at 20 ft AGL and literally turn and swung him so he was now above the canopy and the canopy started to collapse but then it pulsed and reinflated. The turbulance and airmass had pushed him high enough that as he pendulum swung underneath he gained control at the last second before he slammed in just a few feet above AGL then slid it in across a soft sand/pond.

Amazing to watch. I wish I had video. The jumper walked!!! back and basically said he was done with skydiving as it scared the poop out of him. I was speechless and humbled by the spectacle.

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>I saw a dust devil take out a small two seater (side-by-side) experimental
>airplane in Colorado one day.

Yep. Dust devils at Perris have caused two airplane crashes within the past two years. We were very fortunate that there were no serious injuries (both happened on landing.)

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For what it's worth...

Dust devils occur with high adiabatic lapse rates...meaning the temperature decreases with increasing rise in altitude.

The dust devil starts life as a bubble of heated air attached to the ground with surface tension similar to a bubble on the bottom of a pan of boiling water only much bigger called a "thermal". These bubbles will continue to grow until the surface tension is overcome by its buoyancy or until its surface tension is disturbed by a gust of wind, someone walking into it, a rabbit hopping into it or say a parachute on short final.

Only after breaking free of the ground will it start to spin...normally counter clockwise as it is a low pressure area as the air rushes in to replace the rising thermal but can spin either direction. I have witnessed some huge dust devils with the center having numerous counter spinning cores.

This landing looks like the right edge of the canopy caught the edge of a thermal as the thermal was lifting off the ground. It's pretty hard to tell from the video where the turbulence originated.

Thermals and dust devils with no debris or dust I call "blue devils"
these are the most dangerous because they are invisible. On days with a high lapse rate these blue devils cannot be seen and can bite you!

eta: As pointed out in the above posts, dust devils are nothing to fuck around with while in the air flying anything low to the ground!

hangdiver

"Mans got to know his limitations"
Harry Callahan

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lyosha


That's was not likely caused by a dust devil. Were there solid objects upwind from you? Was there weather moving in?



I don't understand why you and billvon think this was a rotor not a dust devil. The conditions for each to form are very different, one is no-wind to light surface winds, the other requires strong surface winds.

From the way the canopy drops after landing winds are light. Not all dust devils have to be huge, and clipping the side of one seems reasonable.
It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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hangdiver

For what it's worth...

Dust devils occur with high adiabatic lapse rates...meaning the temperature decreases with increasing rise in altitude.

The dust devil starts life as a bubble of heated air attached to the ground with surface tension similar to a bubble on the bottom of a pan of boiling water only much bigger called a "thermal". These bubbles will continue to grow until the surface tension is overcome by its buoyancy or until its surface tension is disturbed by a gust of wind, someone walking into it, a rabbit hopping into it or say a parachute on short final.

Only after breaking free of the ground will it start to spin...normally counter clockwise as it is a low pressure area as the air rushes in to replace the rising thermal but can spin either direction. I have witnessed some huge dust devils with the center having numerous counter spinning cores.

This landing looks like the right edge of the canopy caught the edge of a thermal as the thermal was lifting off the ground. It's pretty hard to tell from the video where the turbulence originated.

Thermals and dust devils with no debris or dust I call "blue devils"
these are the most dangerous because they are invisible. On days with a high lapse rate these blue devils cannot be seen and can bite you!

eta: As pointed out in the above posts, dust devils are nothing to fuck around with while in the air flying anything low to the ground!

hangdiver



There's only one problem with that - there's no trigger or source over where he is flying. Yes "bunnies can trigger thermals" in the same way "a meteor might crash into the earth today and wipe out all of humanity" but more realistically that's just not what happens...

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SethInMI

I don't understand why you and billvon think this was a rotor not a dust devil. The conditions for each to form are very different, one is no-wind to light surface winds, the other requires strong surface winds.

From the way the canopy drops after landing winds are light. Not all dust devils have to be huge, and clipping the side of one seems reasonable.



Because a dust devil would not form where he landed. He's not flying over any apparent thermal triggers or thermal generators, and I'd expect the area that he was flying over to actually be the opposite - a source of sink, since there appear to be generators surrounding the grass field (so the air would lower over the grass field and not rise).

For a dust devil to migrate there, it would (by my estimates) have to form elsewhere over dirt then get blown by the wind onto this person's location. This is no longer a weak dust devil but a strong one. One that should have some residual particles floating around and you're not going to "just lightly clip the side" of a dust devil and one that should impact other canopies in the air. I don't see any evidence of any of that. So I'm skeptical that a dust devil is what caused the slight push off course that this person experienced.

There are additional phenomena that can cause turbulence - gust fronts, wind shear. That's why I ask if the weather changed that day. May be a front coming through and the guy landed at an inopportune time and caught some of the shear.

The commentator in the video also states "that's why we're not jumping right now" which makes me think that there were several people that got hit with turbulence on landing.

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The reason the person commented "and thats why we shouldn't be jumping right now" is because there were dust devils everywhere and a few massive ones further off the DZ. When those things move from dirt to grass they become very difficult to see. We followed one that was about 20 feet wide later in the say onto this same field. The only way you could see it was the couple pieces of trash that were in it.

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>I don't understand why you and billvon think this was a rotor not a dust devil.

Due to the intensity of the event.

There are many, many different ways that turbulence can affect your canopy. Rotors can form off the edges of obstructions in wind. You can get rotors and eddies without any obstruction at all. Thermals can lift off under any wind conditions. Plain old differential wind (stronger wind in one location vs. another) can mess with canopies. But none of those are dust devils, which are strong, discrete events that lift dust and debris into the sky, showing a lot of circulation. They are just turbulence, which is common.

Dennis Pagen, in his excellent (and strongly recommended) book "understanding the sky" describes turbulence this way:

============================
If we could make the air visible by adding mist or dye in a large volume, we could actually
see turbulence. What we would see would be swirls, whirls and roils of various sizes turning
this way and that, interacting and breaking apart as they move along with the wind. You can
readily witness a similar thing by watching the eddy action in a fast moving stream. The
swirls or eddies are what we experience as gusts or turbulence when they pass by our body or
wings as shown in figure 94. Here we see a passing eddy from a bird's eye view. A person
standing at point A would first experience a gust from the left, then a lighter headwind, then a
gust from the right and finally a return to the general wind direction as the eddy passes.
We thus can agree to a working definition of turbulence as the random chaotic swirling of
the air. In truth, some forms of turbulence such as rotors and bumps caused by thermals can
be somewhat organized, but randomness of the swirls is what characterizes most turbulence.
=============================

So from that video, the jumper experienced turbulence, not a dust devil. Not all turbulence is due to to dust devils; indeed, turbulence _without_ dust devils is far more common.

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