How much can two heavy duty helicopters in tandem lift off the gound? A lot!
(No offense, ma'am.)
HeliGraphix is club of radio controlled helicopter hobbyists that puts videos of its amazing stunts online. Their latest project is HULC: Heavy Ultra Lifter Crane. HeliGraphix claims that it has completed the first successful human flight by an RC aircraft. In fact, they did several, some of which were over 40 seconds long.