| Beaufort number | Wind speed | Sideways force | Description | Land conditions | |
|---|---|---|---|---|---|
| km/h | m/s | N | |||
| 0 | 0 | 0 | 0 | Calm | Calm. Smoke rises vertically. |
| 1 | 1-6 | 2 | 10 | Light air | Wind motion visible in smoke. |
| 2 | 7-11 | 5 | 60 | Light breeze | Wind felt on exposed skin. Leaves rustle. |
| 3 | 12-19 | 9 | 200 | Gentle breeze | Leaves and smaller twigs in constant motion. |
| 4 | 20-29 | 13 | 400 | Moderate breeze | Dust and loose paper raised. Small branches begin to move. |
| 5 | 30-39 | 19 | 900 | Fresh breeze | Smaller trees sway. Empty Cabin weighing 100kg blown over |
| 6 | 40-50 | 24 | 1400 | Strong breeze | Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. |
| 7 | 51-62 | 30 | 2200 | Near gale | Whole trees in motion. Effort needed to walk against the wind. Cabin total weight 270kg blown over |
| 8 | 63-75 | 37 | 3300 | Gale | Twigs broken from trees. Cars veer on road. |
| 9 | 76-87 | 44 | 5000 | Severe gale | Light structure damage. |
| 10 | 88-102 | 52 | 7000 | Storm | Trees uprooted. Considerable structural damage. |
| 11 | 103-119 | 60 | 9000 | Violent storm | Widespread structural damage. Cabin with 1000kg load blown over |
| 12 | 120 | 73 | 13000 | Hurricane | Considerable and widespread damage to structures. |
It is unlikely that any PAT system would be designed to keep working in winds stronger than a severe gale. In really violent storms stuff like wooden planks get blown about and one of these end-on at 100 km/hr can do considerable damage. It is unlikely that a Cabin or PAT passenger compartment would provide adequate protection to passengers.
However, if a Cabin or SAC were caught in such a storm then the attachment should be strong enough to keep it attached to whatever is carrying it.
Empty SACs could be quite light in weight, ideally they should be as light as possible consistent with being strong enough for their function. How light is not clear yet but a reasonable guess is somewhere between 100 and 300 kg. In the table below it can be seen that a SAC with this gross weight could be blown over by a not-unusually-strong wind.
This tells us that storing SACs by placing them on a flat surface would only be practical in sheltered conditions. When they are supported by the rails they would need the restraint tongue to prevent them being tipped over in a wind.
This estimate will also be useful as a guide to the torsional forces on guideways.
The sideways profile of a Cabin approximate to a rectangular surface with rounded corners
The force in Newtons on this will be given by
Where
Approximately 4 m2 for a Cabin.
The figures in the table are based on Cd = 1, which is an estimate, believed to be within a factor of two of a measured value, ie, about the same as a rectangular flat plate and less than 2, the value for a smooth brick, and more than 0.5, for a rough sphere.
figures from wikipedia