Up to 400,000 visitors are expected to attend the Great New England Airshow at the Westover Air Base in Chicopee this weekend.  About 60 aircraft are expected to fly over Westover, the most aircraft in the sky over the show since 1974.  Among the planes at the show will be the B2 stealth bomber, appearing Saturday only.  Organizers say because of the tremendous crowds expected, they recommend arriving to the show early.  They're also offering traffic updates on the event's Facebook page, and website at www.greatnewenglandairshow.com.