The Collaborative International Dictionary of English v.0.48:

Barnstormer \Barn"storm`er\, n. [Barn + storm, v.]
   1. An itinerant theatrical player who plays in barns when a
      theatre is lacking; hence, an inferior actor, or one who
      plays in the country away from the larger cities. --
      Barn"storm`ing, n. [Theatrical Cant]
      [1913 Webster]

   2. an aviator who flies an airplane from place to place,
      usually at small airports, doing flying stunts or flying
      passengers for sightseeing, for the purpose of earning
      money. It was a practise common in the early days of
      aviation, but by late 20th century was seldom encountered.
      [PJC]