How would you rule?

[NCASAUmp]

At one of our local parks, there's some knucklehead who flies his model airplane. A lot. While it's his right to fly the model plane in a public park, he quite often flies a little too close to the field, sometimes as low as 40-50 feet above the outfielders' heads. We can't see whoever it is, and I don't think it's malicious in intent.

However, my question becomes: what if a pop-fly ball to the outfield hits that plane? How would you rule? Would it be different from, say, hitting a bird?

And how many of you have visions of Randy Johnson's pitch hitting the dove in mid-flight?