In 1947, Howard Hughes' H-4 Hercules took flight. Critics called his aircraft the "Spruce Goose" because it was made out of mostly birch and spruce wood due to wartime restrictions on steel. But the largest aircraft ever built (coming in at a price tag of a cool $23 million) had a successful flight test. That would be the model's only flight, as it never went into production. Check out what the inside of the plane looks like today.