Speed ​​polar

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Speed ​​polar

The speed polar is the graph that arises when the rate of descent of a gliding aircraft ( e.g. paraglider , glider ) is plotted as a function of airspeed . The speed polar plays an important role in speed-to- fly theory .

The shape and position of the polar depends on the wing shape ( extension , profile ) and the wing loading .

In addition to the speed polar, the flight performance can also be described by the glide polar or the resistance polar.

Slightest sinking

Min Sink indicates the flight condition, in which a plane the least vertical - speed has. You can fly the longest with the slightest sink. The horizontal speed in this flight condition is also low.

Approximation function

For mathematical calculations, the polar is usually approximated by a quadratic function :

This equation describes the polar in the speed range relevant for gliding with sufficient accuracy. The following table shows examples of the coefficients for some known gliders .

Airplane type a b c
LS 4 −0.000178 0.0276 −1.66
ASW 19 −0.000150 0.0218 −1.39
Astir −0.000172 0.0269 −1.70
Discus CS −0.000156 0.0234 −1.47
Duo discus −0.000155 0.0298 −2.14

The parameters a, b and c in the table above are selected so that the flight speed appears in km / h and the descent speed in m / s. The polar is of course only valid for the permissible speed range of the glider in question.

Best glide ratio

The glide ratio can be determined for each speed using the speed polar . For the example above, however, it should be noted that the units of measurement for flight speed and sink rate are not the same. Therefore: . It should also be noted that the origin of the horizontal travel in the illustration is not in the zero point.

The speed of the best glide can be determined graphically. Put a tangent of the corresponding horizontal and vertical wind speed (starting from the zero point) on the curve. The horizontal speed can be read on the X-axis above the point of contact.

See also