KRONFELD ON GLIDING AND SOARING.pdf - Lakes Gliding Club

196 KRONFELD ON GLIDING & SOARING
behaviour of the upward currents. He no longer drops
into the gaps on the hillside ; he can fly far out behind or
before the hill without losing height ; he no longer feels the
small individual currents thrown up by every tree or fold
of the ground. The region in which he finds himself is a
broad, tranquil one which is less affected by the inequalities
of the slopes than by the general formation of the range.
Over the ridges which are points of junction for several
valleys that are exposed to through-winds, the pilot will
encounter vast columns of rising current, and these are
the principal factors to be reckoned with when he is too
high to distinguish the separate slopes and high enough
to discern the general outline of the mountains.
Equally important is the influence of heat currents.
A day on which the sun pours down hot rays into the valleys
gives us a far stronger upwind than a cool day, and this
upward rush of warm air will often help us to cross gaps
that would be impossible to negotiate at other times.
Such warm up-currents are generally to be found above
houses, cornfields and rocks.
These factors may influence a pilot to make considerable
revisions in his plans, and on hot days we cannot give our
eyes' entire attention to the conformation of the slopes.
We must take careful note of the patches of sunshine and
shadow and keep a constant look-out for places that will be
likely to be warmed by the sun's rays.
By the rules that govern soaring flights we must always
choose a wind with a direction that is as perpendicular as
possible to the general trend of the ridge when undertaking
a long-distance flight. It is impossible and unnecessary
to attain great heights, for the flight is in reality a series of
hops from slope to slope. This is the ideal way of acquiring
an ultra-sensitive air-sense which will enable us to take
the utmost advantage of every light breath of air. It trains
and sharpens our powers of observation, and improves
our flying skill.
On principle precisely the same methods should be
employed for flights over a fixed course on a hillside. As,
however, flights along special courses can only be undertaken
in one direction from a starting point, they are best