A helicopter was an aircraft that used a rotating blade to achieve flight.
History and specifications
In 1986, Hikaru Sulu flew a Huey 204 helicopter owned by Plexicorp in order to deliver sheets of transparent aluminum to the HMS Bounty which was parked and cloaked in Golden Gate Park. As the aluminum was lowered into the ship it seemed to disappear and a person saw it and later reported it to the papers. (TOS movie, novelization & comic adaptation: The Voyage Home, TOS - Strange New Worlds VI short story: "Whales Weep Not")