aerodyne vs aerostat

aerodyne

noun
  • A heavier-than-air aircraft, deriving its lift from motion. 

aerostat

noun
  • An aircraft, such as a dirigible or balloon, that derives its lift from buoyancy rather than from wings or rotors. 

  • A moored balloon flown in a semi-permanent manner, such as a border patrol monitoring balloon affixed at 18,000 feet (~6 km). 

How often have the words aerodyne and aerostat occurred in a corpus of books? (source: Google Ngram Viewer )