The Codex on the Flight of Birds, which examines a certain behavior of birds to propose this behavior's mechanisms by machines, states that If the back of the machine is to the wind, then the tail must be above the wind, on the other hand, if the back of the machine is below the wind, then the tail must be below the wind.
Under the wind (debatable, according to Leonardo) Tailwind How birds fly depending on wind direction, based on Leonardo's On the Flight of Birds 
