Danny Dunn, Invisible Boy, by Jay Williams and Raymond Abrashkin (epub/Kindle)
A mistake by Danny leads to one of the Professor's most startling inventions—ISIT, the Invisibility Simulator with Intromittent Transmission—a dragonfly-like probe which could be piloted with a telepresence helmet and gauntlet gloves. They all get to try it out. Irene uses it for bird watching. Joe investigates a bee hive. And Danny discovers a bully plans to cheat in a spelling bee. But none of them realizes the ISIT has military possibilities—until a general tries to seize it!