The Wright brothers studied birds. This proved largely futile until they discovered the principle of the curved airfoil, because birds are inherently unstable and must constantly trim their wings. Aircraft are designed, with a few exceptions, to be inherently stable. That is, once they are “trimmed” (in level, stable flight) air currents acting on their wings and tails tend to keep them flying on a straight line. Birds trim their wings constantly like a type of fighter aircraft which “flies by wire” using computers to vary the controls hundreds of times a second in order to keep it in trim. If the onboard computer and its backups fail, the aircraft crashes.