Wind Force to the balloon
Windkräfte am Ballon - Les forces du vent sur l'enveloppe
The amount of the wind force to the balloon depends on the wind speed, and the air drag of the balloon. And the air drag depends on the drag coefficient Cd and the cross-section area. The cross-section area of a balloon is nearly constant, but the drag coefficient changes due of the form of the balloon.
Credits: Pavel Hora
Calculated for a balloon with a volume of 3000m³
| Windspeed (m/s) | round balloon cw=0.4 Force (kg) | dented balloon cw=1.6 Force (kg) |
|---|---|---|
| 1 | 7 | |
| 2 | 28 | |
| 3 | 63 | |
| 4 | 112 | |
| 5 | 175 | |
| 6 | 252 | 1008 |
| 7 | 343 | 1372 |
| 8 | 1782 | |
| 9 | 2268 | |
| 10 | 2800 | |
| 15 | 6300 | |
| 20 | 11200 | |
| 25 | 17500 |
If the windspeed doubled from 5 to 10 m/s, the force to the balloon raised 16x.
Flight Practice
The conclusion for the filling of the balloon is, that to raise the balloon, a very temperature difference between the air in the envelope and the ambient temperature is needed. Dependend on the weight and the volume of the envelope, about 10°C to 20°C. At this low temperature there is nearly no pressure in the envelope. So the wind can easily dent the balloon. To avoid this, the air in the envelope should be heated up fast. But to do so, you need weight in the basket. For this the passengers should be ready to enter quickly the basket after the get the order for it.