Many of you are familiar with the catapult launched profile fuselage gliders that are sold in hobby stores. Since these tend to rather fragile, I am designing gliders with better durability out of card, and also with a full fuselage. These will have a 20 cm wingspan typically. Given that low drag and a thin wing are required, how do I maximize the range and / or flight duration of these gliders? Specifically, what is the science behind the way these operate : they fly using the kinetic energy imparted in the launch, this can be made high as possible, however once launched they begin to slow down due to air resistance. A heavier glider will have greater inertia and slow down less. A heavier glider will also cause higher induced drag towards the later potions of flight where the nose will be pitching up slowly to maintain height. What are the equations I should look at to maximize distance flown or duration ?