Once upon a time, I went to a technical school to study helicopter maintenance. The school had an awesome turbine engines instructor. The next 7-8 years I tightened bolts on helicopters. 20 years later, I'd not touched a helicopter for years and am now a freelance artist. One of my current regular clients is that helicopter turbine engines instructor who's become a self-published science fiction author.
(Huh! I just checked there's a gallery of my covers on his website's front page: http://davidleyman.com/