To construct a usable polar curve for a paraglider, or a hang glider, is not necessarily an easy task. The first prerequisite is absolutely calm air – not a common occurrence anywhere. Second is a good memory, or simply a Dictaphone, a vario and a speed probe. Early mornings offer the best chances of recording an accurate polar curve. I won‘t even begin to list all the possible errors that may adversely influence the final result. It is important to know how the polar curve looks in principle. That is useful for optimising our gliding in different situations – it doesn‘t matter so much if the actual polar is dead accurate or not.
🛠️ How a polar curve is acquired
In order to get a sufficient number of coordinates in our coordinate system to draw the polar we simply fly at all the speeds our wing is capable of (for example in 2km/h increments), all the time recording the descent rate corresponding to the different speeds. Once we have all the values (speed/descent) we plot them into the coordinate system. Illustration 10.2 shows a table where the values for a modern sports-class wing have been entered. Notice that both axis‘ are in m/s, so we‘ll have to convert our speed measurements into m/s before entering them into the table. With these numbers we can also calculate our L/D ratio, often referred to as our glide ratio, by dividing A (speed) with B (descent rate).
