I am affraid I disagree with Dean about getting away with 300mm a couple of years ago I used a Canon 500mm and still could of done with a bit more
not saying you wont get some shots that you will like... but Longer the better for duxford, plus its not helping if the sun shines !!!
but looking at the forecast I doubt that the sun will be the problem
still a really good day out for the family, enjoy and dont for get to post your pics here
cheers Chris