If Da Vinci had succeeded in developing a working aircraft in the 15th century.....(He probably would have been burned at the stake for practicing witchcraft),.....Christopher Columbus would have used a Douglas DC-3 instead of a sailing vessel,...Cabeza De Vaca and his explorer's would have traveled in First class on a Lockheed Constellation,....The Pligrim's at Plymouth Rock would have flown across the Atlantic in a Douglas A-20-A, in comfort,...General George Washington would have sent his high altitude bomber's to harass the British in Yorktown,...Who know's?.....