What is Thermal and Ridge lift?
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Thermals |
On
a summer's day, you can see birds circle upwards
without flapping their wings. They are 'thermalling'.
A thermal is a volume of air that has been heated
by the sun more than the surrounding air - imagine
if you were standing on sunlit concrete, you
would feel warm! As you know, hot air rises
and it is circling within this air that allows
birds and gliders to go upwards. Next you may
ask "so how do you know where the thermals
are?" Well, sometimes this is educated
guess work, based on how you imagine ground
features below are warming up. However, often
cumulus (cotton-wool type) clouds form at the
top of the thermal, marking where the thermals
are. |
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Occasionally,
you may be joined in the thermal by a bird -
from a Swift to an Eagle. You can never do it
as well as they can, but it's great fun trying!
Thermals are used in cross-country flying -
you climb in a thermal to gain the height to
move forwards to the next thermal on track (or
thereabouts). The largest flight in the UK was
done like this. Just over 1000 kilometers were
covered in the flight which took about 12 hours.
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Ridge Lift |
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Another
way of staying airborne requires a hill (ridge),
and the wind to blow against the face of it. Try
to imagine this scenario: When the wind hits the
hill, it gets forced upwards. Again, it is this
upward movement of air that allows gliders to
stay airborne. With a long ridge, it's possible
to travel considerable distances without turning,
generally flying fast and low to stay in the best
'lift' close to the ridge.
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