Sorry couldn't resist!
All good points Nik and very valuable at this time of year as we come out of winter hibernation...
Kirsty x
From: "kirsty2@talk21.com" <kirsty2@talk21.com>
To: "tvhgc_members@googlegroups.com" <tvhgc_members@googlegroups.com>
Sent: Tuesday, 1 March 2016, 15:29
Subject: Re: [TVHGC Members] Flying sites when the wind is significantly off the hill
Nik. Could you not just move the hill to be more in to wind?
Thanks in advance.
Kirsty x
From: Nik Valiris <nik.valiris@hotmail.co.uk>
To: "tvhgc_members@googlegroups.com" <tvhgc_members@googlegroups.com>
Sent: Tuesday, 1 March 2016, 15:27
Subject: [TVHGC Members] Flying sites when the wind is significantly off the hill
We've all been there on hills on days that the wind has been significantly off the hill and I hear it a lot from pilots "if we could only just move the hill to be more into wind".
There have been a number of serious incidents over the years on both on Thames Valley sites and other sites in the UK and across the world where the wind which wasn't directly flowing up the face played one important factor in all those incidents. Even on light days we have seen issues. So this information is just to reiterate the caution to help avoid these incidents.
Most site guides are built up over years of experience by pilots and clubs and all the learning and mistakes are included for the benefit of all. Those guides tend to explain which range of directions sites can usually take.
-- There have been a number of serious incidents over the years on both on Thames Valley sites and other sites in the UK and across the world where the wind which wasn't directly flowing up the face played one important factor in all those incidents. Even on light days we have seen issues. So this information is just to reiterate the caution to help avoid these incidents.
When the air flow isn't flowing up the face of a hill directly and is off to one side it creates turbulence caused by the obstacles and surface of the hill itself. Similar to water in a river and eddies seen at the side of the banks as the water flows. The more 'off the hill' the more turbulence is caused and this is compounded with wind strength. This causes hazards when flying in close proximity to the hill where deflation's of Paragliders caused by the turbulence may occur. There is an increase in risk when the wind is off either direction however it also depends on the terrain of the hill.
On thermic days the wind can be deflected by thermals flowing up the face of a hill. There is a chance however that between cycles the actual wind direction can change suddenly increasing the risk to pilots. Where the wind is significantly off the face of a hill and its a thermic day expect considerable turbulence close to a hill. Some pilots will have no issues but they've taken and accepted the risk and it just takes one pilot to be in the wrong place in the invisible turbulence and a deflation and rotation can happen very quickly. Gliders just don't fall out of the sky, its the pink fleshy interface underneath that is the cause of most problems.
Also be aware of the changing conditions during flight. If the wind is due to change over the course of a day then be aware of that in flight. Look for the signs of wind direction, gliders launching etc.
With hills that have bowls always remember that the bowl means air will flow up all sides but the true direction of the wing might be completely different so there is a risk of rotor or turbulent air if caught out. e.g. Pilots have flown Milk Hill (NW) incorrectly when its been a SE'ly wind direction.
Most site guides are built up over years of experience by pilots and clubs and all the learning and mistakes are included for the benefit of all. Those guides tend to explain which range of directions sites can usually take.
There is always more than one factor in all incidents however this one factor is part of most of our club's worst ones.
Fly safe.
--
Nik Valiris
Mob: 07549 527301
Email: nik.valiris@hotmail.co.uk | nik.valiris@gmail.com
Nik Valiris
Chief Coach
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