Flying Balsa Wood Model Kits
Before plastic model kits hit hobby stores during the late 1940s and early 1950s, you could build and fly balsa airplane models with either rubber band power or a glow/gas/diesel engine. Rubber band power was typically free flight, often indoors to prevent strong winds and other elements from interfering. Powered engines were flown using a control line before the advent of radio control.
It isn't unusual to find large stashes of these kits at estate sales and other venues. Because of the labor involved in completing a model, the enthusiast may have enjoyed buying new kits more than assembling the growing stockpile of unbuilt purchases. Be sure to go through every kit before making a bulk purchase. It isn't unusual for someone to have started cutting out parts before giving up on the project, and started kits are worth considerably less than untouched examples.