Helicopters are uncommon, even now in the glory days of sp3x. They are relatively simple to make, but unfortunately they can sometimes be hard to control.
Helicopters weren't possible in SP1 due to the lack of controllable joints.
Helicopters didn't really "lift off" then, but people still attempted to make them. They were mounted on hidden cars and were extremely unrealistic to fly.
Helicopters are existent in SP3, but now that thrusters have been added into SketchyPhysics' repertoire, they actually fly.. However, few methods have been devised of keeping one in the air for sustained periods, so they are not in abundance.