Perche Vmax Large, Xlarge, Owner'S Manual

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7
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7. Behaviour during the Flight
7.1 Combination of True Air Speed and Ground Speed
Normally, the glider flies at the speed of 25-40 km/h. This true air speed is
the speed which the glider needs to create its lift. No matter whether you fly
with head wind or tail wind it remains the same. It is the ground speed that
changes.
As a general rule it can be said that the true air speed decreases quickly
when you apply more than 70% of the brake. In this case even the best
glider does not fly any more.
Forces which act during the flight:
lift
drag
pressure air flow
gravity