User manual

Discus Glider X
Aerosoft GmbH 2009
44
While the calculation to provide the netto value is complex, the
reading of the gauge is the most simple of all: if the needle goes up it
means the air outside the glider is rising, and similarly for sink. For
ridge flying the gauge comes into its own, continuously indicating the
nuances of the vertical air movement as the wind passes over the hilly
terrain, allowing you to optimize your flight relative to the landscape.
Speed-to-fly variometer
The main ‚petal lcd‘ gauge of the SDI C4
displays the total energy climb reading by
default (see above). However, the „VARIO/
SOLLF.“ switch lower down on the panel allows
you to switch the gauge into the most advanced
mode of all, i.e. „speed-to-fly“.
As mentioned earlier, the pilot learns to speed
up when the total energy variometer is indica-
ting sink (to fly quickly out of the sink) and to slow down when lift is
indicated (to loiter in the lift to take the most advantage of it). But
with a total energy or netto variometer the pilot does not necessarily
know how much to speed up or slow down. Indeed you will learn that
speeding up causes the sink reading on a TE vario to increase, as the
glider is less efficient at higher speeds, making it even more difficult to
decide whether to speed up or slow down.
The „speed-to-fly“ variometer takes the burden of this complex
calculation away from the pilot, and although the needle looks like it is
behaving in a similar way to a TE or netto vario it is actually perfor-
ming the triple compensation calculations so the needle UP simply
means SLOW DOWN, and the needle DOWN means SPEED UP. This is
consistent with the direction the needle would move if it were
indicating underlying lift or sink, but the pilot no longer needs to
consider how much to accelerate or decelerate - the needle reads zero
when the optimal airspeed is reached.