Hi James! The biggest wind tunnel is the NASA Ames National Full-Scale wind tunnel in California. I’ve never actually seen it but I’ve read a lot of papers that have gathered data in that wind tunnel (so I feel like I know it pretty well now!) It’s able to accommodate planes with wing spans of up to 100 feet and nearly all commercial aircraft made in the United States since 1987 have been tested in this tunnel. The tunnel can replicate the wind conditions of flight via six 22,500-horsepower motors with blades as tall as four-story buildings. It’s also used to test flight technology for space, such as parachutes for Mars missions.