Launching Windsond by a condom
The team and I launched a sond a few days ago by inflating a condom with helium. Condoms are much lighter than regular balloons but above all they improve the mood of the mission participants considerably. 😉 The helium volume was estimated to 17 liters. This gave an average ascent rate of 1.5 m/s. The ascent rate given the neck lift 15.1g should be 1.0 m/s so the shape of the condom probably helped to improve the speed.
The condom burst a bit prematurely at 2400m AGL, a few hundred meters before the sond was instructed to let go. The temperature had dropped from 0*C on the ground to -12.4*C at this altitude. Although it’s doubtful condoms are designed to “operate” at freezing temperatures, the gas expansion at the altitude is the probable cause of the burst. On the other hand, a ground test showed a condom of the same model could contain over 40 liters of air before popping but maybe there are variations between copies. I considered to write a complaint to the manufacturer over this blatant product failure. 😉
The launch was done in the evening, after dark. While the sond was still falling, I activated the beacon strobe by a button in the GUI. We were still 3-4 km away from the falling payload but the brief flashes of light were clearly visible, like a shooting star. The sond landed 65 m from the location originally predicted at 2400m altitude. In the dark, the blinking was very effective to locate the sond. The whole enclosure lit up and illuminated a meter of the ground around it. In the open landscape, the beeping was faintly audible at 200 m distance.
Another Windsond was also launched to compare the results of two data sources. They coincided very closely. The profiles of wind direction, wind speed, temperature and humidity were found to agree within tight margins. The second sond was launched while the first was still in the air which also demonstrated the ability of the system to handle multiple soundings at the same time. For the second sond I picked a landing location on a field close to a minor road. We picked up the sond 50 meters from the estimated position.