# Polar curve (aviation)

Under the polar curve is defined as the graph which arises when the settling velocity of a moving aircraft (for example: Paraglider, Glider ) is a function of airspeed. The polar curve plays an important role in the speed to fly theory.

The form and position of the polar depends on the wing shape ( stretching, profile) and the surface load.

In addition to the polar curve can describe the flight performance by the Gleitzahlpolare or the Polar resistance.

## Min Sink

Min Sink called the flight condition in which an aircraft has the least vertical speed. With the slightest fall can be the longest fly. The horizontal speed at this flight condition is also low.

## Approximate function

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

This equation describes the polar sufficiently accurate in the relevant to the gliding speed range. The following table shows the coefficients for some known gliders are some example.

The parameters a, b and c in the above table are selected such that the air speed in km / h and the rate of descent will appear in m / s. The Polar naturally applies only for the permitted speed range of the relevant glider.

## Best glide ratio

With the polar curve can be determined for each speed the glide. For the above example, however, to note that the units of measurement of flight and descent are not the same. Therefore:

The best glide speed can be determined graphically. You put a tangent of the corresponding horizontal and vertical wind speed at the curve. Can be read from the touch point on the x- axis the horizontal velocity.