Allbore
I also lived in Cheltenham until September, about half a mile from Glos Airport. I phoned up to ask about a visit one Thursday morning, and visited that afternoon! The staff are great - let me sit around watching circuits on the approach radar for an afternoon.
Plus, when you're done you can stop at the fence just east of the runway and see all the planes on finals 50 feet above you!
Something interesting - according to one of the controllers, if the cottages at either end were knocked down, the runway would be OK for 737s. I wonder if Ryanair want to move in? Cheltenham to Dublin for 50p - make for a nice weekend on the lash!