I didn't pull out a ruler but it's about 30ft long which puts the wingspan around 50-60ft. As for staying attached to the ground, there are several foundations with nothing on them. I'll have to dig through old pictures to find out what got away but I know one was a fairly substantal eagle.
I really like that yard. It's the private residence of a local artist type that died in the mid 90's. I think his kids live there now. There's a whole bunch of things like that in the yard and they all balanced so well that they'll move with the slightest breeze. The windmill is just awesome.