12 Appendix
12.1 Stall Alarm
If a pilot gradually slows down his or her glider, a stall will eventually result. This situation becomes dangerous if
the airflow suddenly separates from the wing when close to the ground. For this reason wings have washout
(twist) so that the wing tips have a lower angle of attack than the root section of the wing. If the airflow stalls in
the root because of a too high an angle of attack, then lift may remain on the swept wing tips, rotating the nose
down and reducing the angle of attack. It is ill-advised to fly at a high angle of attack near the ground, since the
glider may stall when encountering turbulence.
Anyone who has ever watched a hang glider on approach can observe the following: when a good headwind
prevails, less experienced pilots may flare early and the glider may climb, making for a difficult or hard landing.
With no wind, or with a light tail wind, less experienced pilots may wait too long to flare. The result may be only
a belly landing, but it also could result in a whack, or in a ground loop with broken down tubes. Our experience
indicates that about half of the otherwise not-so-well-executed landings could have been saved by flaring when
an appropriately set stall alarm went off.
Stall speeds vary with wing loading/pilot weights. If you wish to set a stall alarm speed value, you will need to
perform a few tests to determine your own stall speed. It is worth noting that close to the ground the stall occurs
at approximately 1 mph (2 km/h) slower than in free air. The stall speed also depends on the specific weight of
the air at different altitudes. In the 6030, the threshold for the stall alarm is automatically raised with increasing
flight altitude, corresponding precisely to the indicated air speed. It makes no difference if the pilot has chosen
true or indicated air speed for the speed display.
The stall alarm is a loud, concise, acoustic signal that tells you that your air speed has fallen below a
predetermined threshold. The difference between stall alarm threshold and the speed for minimum sink can be
very small. Several pilots have noticed that while circling up in weak thermals at minimum sink speed, the stall
alarm sometimes sounds. For this reason there is an altitude limit, adjustable in Menu>Pilot
settings>Speed>Stall speed, above which the stall alarm will be disabled. Your landing areas should then, of
course, be below this limit.
12.2 Netto Vario
In contrast to the normal vario, which displays the vertical speed of the glider, a netto vario displays the vertical
speed of rising or sinking of the surrounding air mass. The prerequisite for this is a correctly entered polar curve
for the glider and, of course, an air speed sensor. Let’s assume that a pilot is flying at 31 mph (50 km/h) through
the air. The 6030 determines from the glider’s polar curve that at this speed there would be a sink rate of 220
ft/min. Let’s say the normal vario shows a sink rate of 100 ft/min. Consequently, the surrounding air must be
rising at about 120 ft/min. If, in our example, the normal vario indicates a sink rate of 400 ft/min, then the
corresponding air would have to be sinking at about 180 ft/min. With the correct polar curve and vertically stable
air, the netto vario should show a value of zero at all speeds. The netto vario, therefore, can be used to check
our polar curve when we are absolutely certain that the air mass is not rising or descending. If the netto vario in
this example indicates that the air is continuously rising by 60–100 ft/min when the pilot is on a fast glide, then
we know that his wing is better than the stored polar curve and sinks approximately 80 ft/min less than the polar
curve states. In this case the polar data should be adjusted in Menu>Pilot settings>Polar data.
Another example of when the netto vario is advantageous: A pilot is crossing a valley at a fast glide speed.
Suddenly he notices a sharp decrease in sink rate, and turns instinctively. As it turns out this was a mistake
because what was thought to be a thermal turns out to be nothing more than zero sink. A quick glance at the
netto vario would have kept the pilot from wasting time and altitude. The netto vario display only makes sense
during descending glides. While climbing, an averaged (integrated) vario, which indicates the average climb
over a chosen time period, is more advantageous. It is possible to set the digital vario to serve as an averaged
vario while climbing, and as an air mass (netto) vario during glide in Menu>Pilot settings>Vario>Digital vario
mode. The integration time for the netto vario is always 1 second.
12.3 True or Indicated Air speed
In general aviation, it is customary to measure air speed with the help of a pitot tube as dynamic pressure speed
– also called indicated air speed (IAS) – and also to display it as such. The advantage of this method is that at
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