Hop Harrigan Serial Cliffhanger Description:

Hop Harrigan (1946) is a Columbia film serial, based on the Hop Harrigan comic books. Hop Harrigan (Bakewell) and his pal "Tank" Tinker (Getchell) operate a small airport and flying service where they are hired by J. Westly Arnold (Vogan) to fly scientist, Dr. Tabor (Merton), to his secret laboratory where he has a revolutionary new power unit. But an unknown character known as The Chief Pilot (Oakman) is interested in the invention and uses a destructive ray to cripple Hop's airplane and kidnap Tabor. Hop and "Tank", aided by Gail Nolan (Jennifer Holt) and her younger brother, Jackie (Robert 'Buzz' Henry), finally overcome the criminals only find a bigger threat to them all within their group...

text from wikipedia

Believed to have entered the public domain on January 1, 1971