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4.4 POLAR (WITH OPTIONAL PITOT TUBE)

A polar curve (see figure below) is the graph of your glider’s
sink rate over its speed range.

S is the glider’s stall speed (on the left) and T is the glider’s
max speed (on the right).

On the graph, you can also see three pairs of relative speed
readings and sink rates. The graph shows at point A, the
lowest sink rate achieved at the top of the curve; therefore,
Sink A is the minimum sink rate and VA is the speed at
which this is achieved.

The glide ratio is the ratio between the glider’s horizontal speed and its sink rate. To find the best glide rate on
the graph, it is necessary to draw a straight line from the origin of the graph (point O) tangent to the curve.

The intersection of the tangent with the curve (point B) shows the speed to fly (VB) to achieve the best glide,
where you are in B sink; so, your best glide ratio is VB / Sink B.

On your Digifly AIR you can insert three different polar curves using the parameters in ADVANCED SETUP \ n. 11
- 19 PxA / PxB / PxC where Px is the polar 1, 2 or 3 and A, B and C are the ka-kb-kc specific values used by the
Digifly AIR to define the polar curve. They must be calculated with the “Curve Editor” a special function within
the AirTools program:
o
Open the AirTools program on your computer, go to the “Configurations” tab, then to “Advanced Setup” and on
the P1, P2 or P3 parameters line, next to the factory polar values, you will see a small box with two dots.
o
Click on the box to open the Polar Curve Editor. Use your polar curve, input the speed and sink values.
o
Click on the “calculate” button to obtain the ka, kb and kc values that you will then manually set in your AIR.
Note that
if you want to upload these values to the AIR using the AirTools on your computer, you should first
download your parameters, calculate the polar values ka, kb and kc and then upload the entire parameters file.
You cannot upload one separate parameter.

To choose which polar to use, go to (ADVANCED SETUP \ n. 10 POLA).

If this parameter (ADVANCED SETUP \ n. 10 POLA) is set to “OFF”, all the information relating to McCready,
McCready Equivalent, and Net Vario are not displayed on the instrument.
 On the instrument, there are three preloaded polar curves, (2 for hang gliders and 1 for paragliders); using the
Digifly AirTools software, you can see the values of the three default polar curves and set your own.

We suggest that you insert your own polar curve data which best reflects the actual performance of your glider.

If one of the polar curves is active, it will be displayed on the top of Standard PAGE 11 AHRS. Its layout is:
o
ka, kb, kc coefficients (calculated with the AirTools Calculator)
o
Best efficiency value (L/D max eff)
o
Airspeed in km/h at max. efficiency
o
Descending rate at max. efficiency (m/s max eff)
o
Minimum sink rate and its corresponding airspeed