d&b J-Series - Manual (Page 30)

5. Wind loads
When loudspeaker arrays are flown in an open air environment,
possible wind effects should be taken into account. Wind load will
produce additional dynamic forces to the rigging components and the
suspension, which may lead to a dangerous situation.
WARNING! Generally flying loudspeakers overhead at wind forces
higher than 6 bft is not recommended.
When planning an open air event it is essential to get current weather
and wind information.
The following wind speed scale according to Beaufort gives an
impression of the effects of the different wind forces (bft).
bft knots km/h mph Description Effects on land
0 0-1 0-1 0-1 Calm Smoke rises vertically.
1 1-3 1-5 1-3 Light Air Direction of wind shown by smoke drift, but not by wind vanes.
2 4-6 6-11 4-7 Light breeze Wind felt on face; leaves rustle; ordinary vanes moved by wind.
3 7-10 12-19 8-12 Gentle breeze
Leaves and small twigs in constant motion; wind extends light
flag.
4 11-16 20-28 13-18 Moderate breeze Raises dust and loose paper; small branches are moved.
5 17-21 29-38 19-24 Fresh breeze
Small trees in leaf begin to sway; crested wavelets form on
inland waters.
6 22-27 39-49 25-31 Strong breeze
Large branches in motion; whistling heard in telegraph wires;
umbrellas used with difficulty.
7 28-33 50-61 32-38 Near gale
Whole trees in motion; inconvenience felt when walking against
the wind.
8 34-40 62-74 39-46 Gale Breaks twigs off trees; generally impedes progress.
9 41-47 75-88 47-54 Severe gale
Slight structural damage occurs (chimney-pots and slates
removed).
10 48-55 89-102 55-63 Storm Trees uprooted; considerable structural damage occurs.
11 56-63 102-117 64-72 Violent storm Accompanied by wide-spread damage.
12 > 64 > 117,0 > 72 Hurricane Heaviest damage and destruction.
Tab. 1: Wind force and its effects on land
WARNING! If according to the forecast wind forces higher than 5 bft
are possible the following actions have to be taken:
•••• The actual on site wind speed has to be monitored
permanently. Be aware that wind speed typically
increases with height above ground.
•••• Suspension and securing points of the array should be
designed to accommodate double the static load in
order to withstand any additional dynamic forces.
WARNING! If the wind force exceeds 8 bft there is a risk of
mechanical damage to the components which may lead
to a dangerous situation for persons in the vicinity of the
flown array.
Stop the event and make sure that no one is left within
the vicinity of the array.
Lower down and secure the array.
J-Series Rigging manual (1.3 EN) Page 30 of 34