RAF Museum Cosford isn't that far from Rugby, it's free, and possibly has one of the best collections in the country. It just tends to be a bit busy at weekends.
Otherwise, Midlands Air Museum near Coventry airport is even closer to Rugby. It seems to have a reasonable collection but I haven't been there. Mostly outside exhibits.
I can't really recommend the Science Museum in London unless you _really_ want to see one or two of the few interesting things there. Much better looking at dinosaurs in the Natural History Museum next door. The Imperial War Museum in London has a bigger and more interesting collection (I wouldn't recommend IWM-Manchester unless it's _dramatically_ improved in the last few years)