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 Post subject: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 5:40 pm 
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... or wind that has passed over nearby land making it excessively erratic. Land induced turbulence or rotor can have major gusts, extended lulls making flying a full sized traction kite a lot of work to downright dangerous.

Try to use launches with no upwind land mass, trees, buildings, etc. to disturb the wind. If the wind is close to sideshore and is uneven as a result, be extra careful. If it is too uneven, move to a better launch or go some other day when the wind improves. How close is too close? Can be many miles in some cases, depends on the height and nature of the land mass upwind.

Image
The rolling or rotoring wind disturbed by vertical structures (buildings, dunes, mountains, trees, etc.), can mess kiters up, powered aircraft too in some cases. The velocity of the wind and direction can change too much for safe, stable flight. You kite can stall suddenly fall like a rock and then yard you at light speed into the center of the power zone in the following gust and into whatever hard stuff is in the way. Try not to let wind shadow, "Shadow Blast" you.
From: http://www.atsb.gov.au/


Last edited by RickI on Wed Dec 08, 2010 7:17 pm, edited 3 times in total.

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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 5:40 pm 
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To some degree it is what you are skilled in and used to within limits. In extreme cases it can be a bear for almost anyone. Recently, there have been some fatalities and near fatal accidents caused by rotor. Some were well experienced kiters and all were using flat kites with substantial depowering capacity.

It all comes down to LOCATION. If the wind is passing over nearby land before it reaches you, there can be problems. The kite may surge up in gusts, stall and fall like a rock in lulls and you might get yarded in a successive gust. It happens, all too often over the years. If you can move to an area free of rotor, do it. If not, maybe it is a good day to pass on riding. Riders choice, know what to look for and choose well.

Some examples ...

Image
Winds around and to the left or west of the line are frequently rotored. They can have substantial gusts and lulls. The land and cover are fairly low, residential housing. Still, they are high enough to significantly disturb the wind. Kiters have been severely injured here as a result, one within the last month.


Image
This was the scene of a particularly severe lofting. With the land mass to the south rising a few hundred feet off the water and land in most other directions, rotor is common here from most directions. Just a 1/4 mile to the west, there is an area without rotor from some wind directions at least. For kiting, for most winds, this launch is a poor choice.


Image
This is the scene of a recent severe lofting. The land rises dozens of feet above the water and with low houses creates enough rotor to dangerously disturb the wind.


Image
Not aware of any recent accidents at this location, historically, maybe. This is a more obvious cause of rotor, large buildings upwind. They could just as easily be a set of dunes, hills, mountains or even a high tree line.


Beyond that, there are some famous cases of rotor winds like Mistrals in the Med. A number of messed up kiters in those winds as well, often enough in riders lacking sufficient experience.

So, avoid offshore or side off winds with turbulent conditions. Pick a good location for conditions. If it is close to side shore but still turbulent be extra cautious, i.e. avoid flying your kite over head on land it may be better to keep it arched towards/over the water, be ready to sheet out and deal with stalls, etc.. Here's a good point, rotored areas may LACK significant waves making it easier to kite, do tricks, etc.. The wind on the other hand can be too unstable despite the wave conditions.

Pick good locations.

FKA, Inc.

transcribed by:
Rick Iossi


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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 6:45 pm 
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Great info! I wanted to add that thermals can travel across the water lacking the trigger to send it skyward and the first obstacle it hits releases from the water, I think just like the eric eckman flight or lofting. Some of those rotor examples could also be thermal triggers. Bad places to hang out with your kite overhead! The youtube video "terrible kitesurf crash" Is the result of a thermal waterspout / gust that we watched go all the way across the lake, maybe 15 yards wide. This is just my opinion and any clarification would be
great. waynepjh


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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 8:14 pm 
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site is acting up


Last edited by RickI on Tue Feb 17, 2009 8:29 pm, edited 2 times in total.

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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 8:30 pm 
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Kiters severely lofted by thermals can be rare as far as I know unlike what gliders routinely seek out and experience. Extreme ridge lift lofting similar to what happened to Erik Eck virturally unique. That is with the possible exception of Malek's lofting snowkiteboarding in Morocco. Rare are stuff in other words.

Wind shadow induced rotor is extremely common as are gust/lull related problems. Wind will be offshore or side off at most launches at some time or other. It has killed or come close to it about five times in around a month, that I have heard about. Erik's singular ridge lift lofting happened seven years ago.

Do you have the complete footage of the accident including the impact or is that all of it? Without the complete footage it might be easy to conclude the imagery has been altered. Where did this take place, (Utah or Nevada?) and how wide was the lake upwind. What is in the upwind direction, mountains, if so how far away?



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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 8:53 pm 
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I like that first diagram, it removes the notion of "wind holes" caused by obstacles and replaces it with "terrible wind" :)
It's a mistake to think that if it's windy, then an upwind obstacle is "far enough away".

Has anyone else heard the "an obstacle has to be 3 times its height in distance away" to avoid turbulance? I knows it's simplified as wind speed has a big influence, I"m not even sure where I heard it, but it seems to make sense. (how you judge that distance/height is a different matter ;) )


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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Tue Feb 17, 2009 9:12 pm 
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I recall something from hang gliding, from Pagen's "Understanding the Sky" perhaps, of distances of 10 to 20 times the height of the obstruction as a rule of thumb. I think higher wind velocities will also stretch this distance out. Horizontal gaps play into this as well. Sometimes they can really boost winds and maintain them and in others make the wind too erratic.

Been a long time since Fluid Mechanics, boundary flow separation just came to mind and from that found some interesting diagrams:

Image
The chaotic separation of blobs of color simulates rotor. Imagine trying to keep a kite flying in one direction and above stall speed in that mess. That block could simulate a tree line or building in near side upwind conditions.
From: https://www.arl.psu.edu/capabilities/fsm_compmech_eddysim.html#images

Rotor can be a bear. In lesser cases it can simply stall your kite in a lull cause it to Hindenberg to the beach, clotheslining anyone standing in the way. How many times have you seen that happen? Pays to keep your kite aloft in clean air, free of much rotor.


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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Wed Feb 18, 2009 5:26 pm 
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Some more examples of terrain that creates dirty air along with clear zones. In some of the following cases the upwind obstructions are fairly low. As such, the normal issue with close to side shore winds flowing over these lower barriers is avoiding kites stalling, falling like rocks and risking wrapping other kites, cutting people with line. In these cases getting your kite up, over the water and getting out promptly is indicated. As a rule, going in side off winds in these areas isn't feasible. You might get offshore with some effort but the lulls nearshore (within a 1/2 mile or so) will usually see your kite on the water and you swimming your stuff back to shore.

In areas with large upwind obstructions, tall buildings, hills, mountains, etc. particularly with strong and direction shifting winds the hazards of kiting in rotor go up substantially and feasibility of kiting drops (vanishes?) dramatically. Depending on local conditions the wind shifts in the "some rotor" area may still be too excessive at times.


Image
The larger the obstruction and the stronger the winds, the more erratic and potentially hazardous the rotor induced lulls and gusts. In this case given the size of the obstruction, it might be more fair to call "some rotor," "lots of rotor."


Image
Here is an example of a low obstruction. It can still easily mess up prospects for staying upwind or easily returning to shore if side off. The quality of wind when it is side shore is lessened as well.


Image
Islands often have irregular shorelines, frequent wind obstructing headlands. Changing launch locations can make a big difference in the quality of wind on islands. As compared to some parts of Florida where you might travel 50 miles with no significant change in wind direction relative to shore.


Image
SE Florida mountains, aka condos. Where you have them there's wind shadow and eddies spinning off the sides downwind. Where there are holes, you can get stronger wind but still uneven, perhaps dramatically so. Where they are bunched together you may have no useable wind. Again, side off in this area generally doesn't work, at least not without a chase boat and a few miles from shore. When it is close to sideshore and shifting over barriers near the water, kite launch, landing and riding can be challenging and even dangerous.


Image
The "some rotor" zone is wide in the case due to the island and notch present to windward. The wind direction can shift quite a lot due to eddy effects around these objects. With the shifting the wind can gust and lull substantially making staying upwind, launching and landing tricky and again potentially dangerous.

If you are new to kiting, to the area or are just back from being away from the sport for a while, avoiding "some rotor" and definitely "rotor" conditions makes good sense, even more so in stronger winds. There have been too many avoidable injuries related to these causes.

FKA, Inc.

transcribed by:
Rick Iossi


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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Wed Feb 18, 2009 5:58 pm 
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if 'rotor' winds concern you you wouldnt like my home spot hahaha.............


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 Post subject: Re: Shadow Blasted ... Flying In Dirty Air
PostPosted: Wed Feb 18, 2009 8:32 pm 
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PKPC08 wrote:
if 'rotor' winds concern you you wouldnt like my home spot hahaha.............


Too funny, thing is, there are probably 20 or 30 people around the world dealing with dead or severely messed up relations right now. All this in only a month or so. Rotor seems to have been a important contributing factor among others.

I did say ... To some degree it is what you are skilled in and used to within limits.

So, where do you ride and what are conditions like there? What causes the rotor and what do you do to manage the effects?

Guys that ride at inland venues may have more regular rotor effects than riders on the coast. Even at inland venues there can be some wind directions so heavily rotored out, that guys don't ride in those conditions. In all the examples I have photographs for, there are options for avoiding rotor by choosing a different time or location. Some people such as yourself, may have rotor all the time, ranging from moderate to nasty.

At least one of these injured riders kited for years in an intensely rotored area. Despite that, it may have been a big factor in a bad outcome. In most cases, it seems like the riders weren't used to the conditions, may have been caught off guard or were simply overwhelmed by extreme rotored conditions. In most perhaps all of these cases, all they had to do was move to another location or at worst blow off that session. There were readily available options in these cases.


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