Flytec 5030 v2.24 * - Manual (Page 43)

Flytec
5030 GPS
correct polar curve and calm air, the netto vario would have to show a value of 0 at all
speeds. Or, the other way around, we are in the position to check our polar curve when we
are certain that the air is absolutely still. If the netto vario here in the upper speed range
indicates air which is continuously rising by 0.3 to 0.5 m/sec, then we know that our wing is
better than the stored polar curve and sinks less than the 0.4 m/sec that the polar curve
states. This can be corrected. ( Basic Settings / Polardata)
What else is the netto vario used for?
Another example from common practice:
A pilot crosses a valley rapidly. Suddenly he/she notices a sharp decrease in sink rate and
turns in instinctively. This was a mistake because the desired climb turns out to be nothing
more than zero lift. A quick glance at the netto vario, which in our case shows 1m/sec rising
air, would have kept him/her from losing time and altitude. The netto vario display only
makes sense during longer descending glides. While climbing in a thermal it is better to
activate the integrated vario, which indicates the average climb over a chosen integration
time period.
If you chose Brutto, Netto Sink the following time apply:
Ascent -> Integration time chosen in the Basic Settings
Netto Sink -> Integration time always 1s
5.3 True or Indicated Airspeed; TAS or lAS
In general aviation it is custom to measure the airspeed with the help of a pitot tube as a
dynamic pressure speed (= IAS) and also to display it as such. The advantage of this
method is that at any altitude level the maximum allowable speed or the stall is marked
(flight safety) at the same position on the scale. This is also the case for the speed of the
best glide (flight performance) at preferred altitudes which have a fixed position on the speed
scale. However, the disadvantage of this system is that the indicated speed is correct only
at a certain altitude (usually at sea level). The glider will fly increasingly faster the higher one
climbs due to air getting thinner, without the indicator picking this up. At approx. 6,500m the
air weighs only half of that at sea level, and the air speed will therefore increase 1.41 times
that ( as a radix of 2). You could picture the physics of it as follows:
In order to create a certain lift, a certain number of air particles have to hit the surface
bearing the weight (wing). Because at an altitude of 6’500m there are now only half as many
particles present per cubic metre, the surface has to fly faster, but not twice as fast because
each particle possesses a higher striking energy, around 41% faster.
However, in calculating wind, arrival altitudes, or arrival times you always require true air
speeds. The wing wheel sensor (propeller sensor) shows the true air speed (=TAS)
because it runs practically without friction.
Thanks to modern processor technology, our Flytec 5030 GPS will always use both speeds
side by side, regardless of which speed input is used or which type of speed is displayed.
The pilot can set the speed he/she would like to see in the display. However, the pilot
shouldn't be surprised if he/she sets the display as IAS, for example, that, at high altitudes
and with calm air, the difference between groundspeed and airspeed will correctly show
zero, although the groundspeed provided by the GPS will be much higher than the indicated
airspeed.
5.4 Polar Curve and Required Speed
The polar curve of a wing is represented as a diagram. It shows the connection between
flying speed and the associated sink rate directly. It provides information about an aircraft's
ability to perform. From the polar curve the minimum sink rate and the associated speed
can be read immediately. If one plots a tangent from zero on the diagram to the polar curve,
it shows the best glide speed in calm air where the points meet. If one divides the speed by
the associated sink rate, the result would yield the best possible glide ratio. (Both values
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