What are you planning? Where shall we go?
Yes, they accept aircraft / helicopters during the trials. See the 'Aircraft' section of this page.

When you see the queues on the roads around Badminton during the event, you know that there is only one sensible way to arrive and depart :D. There is a PPR form on the link and entrance tickets / landing fees are all dealt with at the aircraft on arrival.

A very civilised day out.

Iceman 8)