Back in uni we had an ad-hoc competition, throwing paper airplanes out of a 15th storey window, in calm weather. All sorts of designs were tried, flying time measured. Towards the end it occured to me to compare the times against an etalon: an unfolded A4 sheet. Dropped the sheet from the window, and it started the typical erratic descent of a falling leaf, swinging back-and-forth, pulling straight up at the end of the swings. It took twice as long to touch down than the next best airplane, so it pretty much instantly killed the competition.