2nd the USAF museum - far more planes than the Smithsonian, even including the Udvar-Hazy annex. Three massive halls, and they're building a 4th. It covers all of military aviation history, literally from the Wright Brothers' hand-built wooden wind tunnel up to today. A must for anyone remotely interested in aviation.That's a horrible, terribly boring drive up I-71. Like, I-90 across NYS boring.
There's also the national USAF museum in Dayton. It's been many years since I went as a kid, but it is typically very well-reviewed. Only an hour drive, depending where around Cincinnati you are.