Vee-tail-1:
And some of them are very small. The Black Widow is 15gms and flies for 20 mins. I believe that the biggest UAV is 26,000 Kgs and can fly for 22 hours (don't quote me though, I heard this second hand).
But the UAVs are no problem, most often, for GA provided you call PPR before departure. So I was told by both John in the tower and by a regular who was visiting and had never had a problem.