airliner vs hot-air balloon

airliner

noun
  • A passenger-carrying aircraft, especially one of a fleet operated by an airline. 

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 airliner and hot-air balloon occurred in a corpus of books? (source: Google Ngram Viewer )