DragonView.ch test pilot shows how a tandem paraglider responds under severe underloading in calm condition. In my experience a lighter passenger is more difficult to fly in dynamic conditions than heavier passengers. Helico is a manueuver that helps you learn the dynamics of the wing under non-flying conditions and that's a definitely good idea to know before anyone does something like this. The wind was less than 5km/h. The forward speed was about 20km/h, so it is very slow. Sink rate between 0.5 to 1m/s. Canopy is well inflated, solid, and very stable. No issues detected doing Deepstall, Helico and Flyback, in fact much easier to do than with a normal weighted school glider. Take off requires max speed on trim, otherwise it will cause too much drag for starting run with no wind, and in wind, it will drag you backwards. Landing process was very slow and easy on half trim. Of course turbulence and even moderate wind will be a bad combination, so it definitely isn't recommended!
