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Wind Socks - General Introduction
Wind socks are used in airports, on farms, in marine applications, and for general decorative purposes. The major feature of a windsock is a conical textile tube with the tapered sleeve open at the both ends. Its primary purpose is to indicate wind speed and direction. It is designed in such a manner that a metal frame holds the wider end open, and air flows in the wider end and exits in the smaller end. Hence the orientation of the sock will help to identify the direction of the wind, and the shape of the tube will help to give an estimate of the wind speed. ICAO and FAA specifications provide information such as wind sock height and sock material and configuration.
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Proper Wind Sock Functioning
Based on Federal Aviation Administration (FAA) standards, a properly functioning wind sock should fully extend in a 15-knot (28 km/h; 17 mph) wind . Also, a wind sock should orient itself according to the wind direction due to a 3-knot (5.6 km/h; 3.5 mph) wind speed. In general, the wind sock side seams should be at the 9 and 3 o'clock positions.
Any wind sock will perform at its best without any wind shear influence from buildings, roof angles, trees, or orographic influences, so it is good to consider placing the wind sock at a distance greater than 25 m from any other standing object. If this is not possible or practical, the height of the support should be raised as much as possible.
Image credit: Flicker.com
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ICAO and FAA Specifications for Wind Socks
The U.S. Federal Aviation Administration (FAA) (AC 150/5345-27D) and the International Civil Aviation Organization (ICAO) (Annex 14) provide three different wind sock height specifications as follows:
- FAA type L-806 support - those mounted on low mass supporting structures - maximum of 10 ft (3.0 m) mast height
- FAA type L-807 support - those mounted on rigid supporting structures - Maximum of 16 ft (4.8 m) height to wind sock
- ICAO/CAA standard - 20 ft (6.0 m) mast height
FAA and ICAO standards for wind sock sizes are as follows
- FAA, Size 1 - Eight feet (2.5 m) in length and 18 inches (0.45 m) throat diameter at large end
- FAA, Size 2 - Twelve feet (3.60 m) in length and 36 inches (0.9 m) throat diameter at large end
- ICAO/CAA standard - Twelve feet (3.60 m) in length and 36 inches (0.9 m) throat diameter at large end
The taper of the fabric wind sock from the throat to the trailing end must be designed to cause the wind sock to fully extend when exposed to a wind of 15 knots (28 km/hr or 17 mph). FAA Advisory Circular 150/5345-27D also provides specifications for externally lighted, internally lighted, and unlighted wind socks.
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Wind Sock Specifications Vary based on Type of Use
Wind socks render an invaluable aid in moving persons from an area of danger to an area of safety, especially when hazardous materials are involved. The size, shapes, and styles of wind sock vary based on the type of use like airports, marine areas, farm fields, etc.
Airport wind sock heights above ground level are as specified above. Wind socks in farm fields help in targeting the spray drift for crop dusters. These wind socks should be more sensitive and designed with an aim to reduce off- target spray drift of agricultural products to other crops. They are calibrated to indicate wind speeds from a range of 2 to 12 miles per hour.
Marine wind socks are designed from the ground up for salt water surroundings, and their standard size is 18" diameter by 72" long.
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When considering the location for a wind sock, the differences between a "visual only" location and the “true wind” occurrence is very important. Evacuation lanes and their routes must be taken into consideration in industrial and agricultural areas, as improper placement could lead to an unsafe evacuation of personnel to a safe assembly area. Wind sock classifications for airport and marine operating areas are well defined, and simply meeting the regulations for wind sock height and size should result in a satisfactory installation.