Flytec 5030 v2.24 * - Manual (Page 42)

Flytec
5030 GPS
5 Appendix
5.1 Stall alarm
If a pilot gradually slows down his/her glider, he/she will cause a stall when falling below a
certain speed, which has different consequences depending on the type of aircraft. If the air
current is suddenly cut off from the entire surface, then a completely unforeseeable crash is
inevitable. For this reason manufacturers are building a so-called cross-setting (washout)
into the support areas of the wings; this means during flight that the wing tips, will always
have a smaller angle of incidence than the middle of the wing. If the air flow stalls in the
middle area of the surface when falling below a minimum speed, then lift still remains on the
wing tips. The aircraft does not enter a deep stall or incipient spin. Because the wing tips are
situated behind the aircraft's centre of gravity, the wing will drop nose downwards and will try
to recover by gaining speed. It is not advisable to stay long in this flight situation, as the
glider will react very sensitively to even small air turbulence. A stall can be dangerous,
especially during the landing approach. The consequence could be a stall or an incipient
spin. The stall alarm is a loud, concise, acoustic signal that tells the pilot to fly faster. It
assists, first and foremost, hang gliders and paragliders but the latter to a lesser extent.
Anyone who has ever watched a hang glider come in during an approach can observe the
following: when a good headwind prevails, many pilots will pull out their steering bar too
early; the glider climbs a few more meters so that, in a favourable case, it ends up with the
keel stuck in the ground. With no wind or with a light tail wind most pilots wait too long to
pull out the bar. With luck the result is only a belly landing, but the result can also be ground-
loop with broken base side tubes, or the glider's nose absorbs the impact, causing the pilot
to swing like a pendulum, hitting his helmet on the front keel tube.
Different stall speeds apply for varying wing loads and pilot weights. Several tests to
determine your own speed are necessary for setting your correct stall alarm limit in the
Setup menu. It is worth noting that close to the ground, because of the air cushion under the
wings, the stall occurs at approximately 2 km/h lower speeds than in free air. On our own
gliders the correct setting has always been between 30 and 34 km/h. The stall speed also
depends on the specific weight of the air at different altitudes. In the Flytec 5030 GPS the
level for the stall alarm is automatically raised with increasing flight altitude, corresponding
precisely to the indicated airspeed. It makes no difference if the pilot has chosen true or
indicated airspeed for the speed display.
The distance to stall speed is easy to control now.
The limit between stall alarm and the speed for minimal sink is very small. Several pilots
have complained about the fact that while circling up in weak thermals at the speed of
minimal sink, the stall alarm sometimes turns on. For this there is an altitude limit the pilot
can adjust in the Basic Settings / Stallspeed , above which the stall alarm will not be initiated.
The landing areas should then, of course, lie below this limit.
Experience has shown that about half of the otherwise not so wonderfully executed landings
could have been saved by pushing the steer bar upright when the stall alarm turns on.
5.2 Netto vario
In contrast to the normal vario, on which the vertical speed of the glider is shown, a netto
vario indicates the rising and sinking of the surrounding air mass. The prerequisite for this is
a correctly entered polar curve and, of course, a speed sensor. Let's assume that a pilot is
flying at 50 km/h through the air. The Flytec 5030 GPS determines from the polar curve that
at 50 km/h there would be a sink rate of 1.1m/sec expected. In our example, the normal
vario could only show 0.5m/sec. Therefore, the surrounding air has to rise by 0.6m/sec to
reach this pair of values. However, if in our example the normal vario indicates a 2m/sec
sink, then the corresponding air would have to sink by 0.9 m/sec. This means, with the
42/53