With the right ultralight, you don't need much more than two to three hundred feet, which is plenty doable on a few acres.
You haven't seen my place
In all of 40 acres, we've got one sorta level spot that is about 100x200, which happens to be our riding arena. But then you would have to climb up a side canyon (to the west, into the usual wind) to get above the plateau level. To the east is the creek bottom with some power lines and there are steep cliffs just east of the creek.
So one
might be able to take off OK into a headwind, but then to land you would have to come down the main valley and hook a sharp left at just the right altitude, dance over the power lines, and touch down perfectly. (but the corral/arena/barn is where the strip would have to be!)
There is another mostly flat spot up on top of the hill in the pasture - would have to cut a lot of trees and bulldoze out some stumps. It would be like landing on a (small!) carrier.
