There windsock it’s rudimentary anemoscopei.e. a device for measuring the presence and direction of an air current. In fact, the tool also allows an indirect measure of its speed. We still find it in use today where it is important to have a visual indication of the wind, its intensity and its direction: airports and heliports are the most popular, but instruments of this type can also be found in sports flying fields or oil platforms , as well as in gas and chemical materials processing and storage plants. Its strong point, unlike a modern measuring instrument, is the ability to provide a visual indication of wind strength and direction instantly.
The difference between anemoscopes and anemometers
Before going into detail, it is good to clarify the difference between anemoscopes And anemometers:
- The anemoscopes allow identification of the presence of air currents, therefore of their direction;
- The anemometers, instead, they allow measurements, even very precise ones (precision varies in relation to the characteristics of the measuring instrument), of the speed or pressure of air currents.
A typical one anemometer it is the so-called a cups, that is, equipped with some cups connected to a central axis that rotates in the presence of air currents. By reading the rotations of the central axis of the anemometer it is possible to trace the speed of the current that generated the movement.
Windsocks are included among anemoscopessince – even if there is a measurement of the wind speed – this occurs in an approximate manner, not sufficiently precise, and also limited by the length of the truncated cone-shaped fabric at reduced current speeds (around 28 km/h, i.e. the maximum 15 knots measurable).
How the windsock works
The windsock is nothing more than a device made of fabricmounted on a pole placed at a height sufficient to be visible and not to be confused. This height is variable but usually between 4-6 meters above ground level. The fabricwhich is able to resist bad weather and the air flows that hit it, is placed on a swivel end and so it can adapt to the flow of currents and to theirs variability. Its form and realization is dictated by some recommendations And international aviation standard: for example, it must be realized using colors that highlight their presence from at least 300 meters in height, or it must have standardized lengths and diameters (3.60 m is a dimension usually used in length, with a minimum diameter of the truncated cone of 0.9 m).
How to read the windsock: wind speed and direction
The windsock allows for a indirect measurement of the speed of currents as this same it “inflates” the more the faster the air flow is! In fact, the fabric has a shape truncated conethen the air is passed through it by creating a channel from the larger to the smaller circumferential part. The air, which enters the cone with greater difficulty as its section tends to narrow with depth, has the ability to “straighten” the fabric thanks to the pressure game which is created between the internal and external part of the cone itself.
The tissueFurthermore, it is made in two-color bands (usually red and white). Each band represents a speed measurement “notch”, expressed in knots (the knot is a unit of measurement of speed, similar to meters per second or km per hour): for each colored band we have a passage of about 3 knotstherefore for each band raised there are 3 knots of speed, which gradually add up. The total number of bands is 5, which means that at most the sleeve is able to give me current speed information up to 15 knots. Obviously there could be winds with greater speeds, but the instrument would not be able to detect the difference as everything would still be tense. To obtain a measurement in a system more suited to our habits, we can then convert the knots into km/h, using the conversion factor 1.852 (1 knot equals 1.852 km/h). This means that the maximum speed detectable with a windsock is approximately 28 km/h.
For determining the direction of the current, the concept is much simpler and more intuitive: if the wind blows predominantly in a given direction, thanks to the rotating base, the sleeve can be positioned to accommodate the direction in which the wind blowsobviously posing itself with a conical shape that tends to close in the same direction in which the wind pushes. In this way, it is possible to easily trace the direction from which the current comes. For example, if the wind blows from the east then the sleeve faces westand vice versa. To facilitate reading the direction of the current, usually in addition to the sleeve, a reference system of cardinal points is also mounted on the rod, so as to have a direct visual reading of the direction sought.
