aircraft vs hot-air balloon

aircraft

noun
  • A vehicle capable of atmospheric flight due to interaction with the air, such as buoyancy or lift 

hot-air balloon

noun
  • A balloon-shaped aircraft whose bag is inflated with hot air; it carries passengers and crew in a gondola slung underneath. 

How often have the words aircraft and hot-air balloon occurred in a corpus of books? (source: Google Ngram Viewer )