[Former Fetus]

probably took off from a dirt road

Not likely. A Champ is a tail dragger, and it is hard enough for a pilot to keep it going straight down an airstrip. More likely it was some pasture, and the plane got to go around in circles before taking off. Now, that must have been a sight to see! Technically, it is possible for the plane to take off without pilot, although the chances of that happening are about the same as of Bill Clinton joining a monastery and taking a vow of chastity.

[kylaka]

If the trim is set and the power is just right, its gone. It sounds like it was too.

[Big Bunyip]

In Sydney, Australia, about 12 years ago (maybe longer, I'm getting old), a Tiger Moth took off by itself and circled the city for about four hours while the hotshots in the Australian Air Force tried to shoot it down.

It was quite a show.