While working on the editor I started wondering how people would fly their pure sailplanes without engines or slopes. The simplest thing would be to automatically launch them at altitude. I thought towing would be cooler.
Although both the graphics and the physics are very basic, it adds to the fun.
For the implementation I had to adjust the flight recording and playback to include flaps and gear setting as the tow plane is equipped with them. So the tow plane is actually a recorded flight. For the glider to behave like on a rope, an extra step was added to the flightmodel that constrains the maximum distance from the tow plane to the cable length (in this case 10 meter). When further away, the gliders speed will automatically match (or slightly exceed) the tow planes' speed, in the direction of the rope. The effect isn't 100% realistic at extreme maneouvring, but acceptable for two evenings of coding.