Shots of the X-80 use footage of a Convair F-102 Delta Dagger, but not always the *same* F-102, as evidenced by the identification number on the side of the aircraft. During re-entry, some footage of a Convair F-106 Delta Dart is used as well, giving the impression that the plane changed from an F-102 to an F-106 and then back again.
When Col. Martin orders the Sergeant to post a guard outside the operating room, the Sergeant salutes. The Colonel is "covered" (wearing a hat); the Sergeant is not. Military protocol specifies hats are not worn indoors and salutes are not rendered indoors nor when "uncovered."
One of the scientists states that "time is unaffected by the laws of gravity". This is untrue as Einstein's theory of relativity predicted and has been proven: the higher the gravity, the slower time passes.
As the X-80 is gaining altitude, there is a shot of the plane supposedly in a steep climb. But the clouds in the background are obviously at the same sharp angle, revealing that the footage of a level flight has just been "tilted" optically.