Check this out:
Which isn't much, but is pretty impressive when it's only in the air because the pilot is managing, from pure muscle strength, to push enough air downwards to levitate himself and the contraption he's sitting in.
Gamera II looks like a total fake in that video, because they didn't get the whole enormous thing in shot, in this indoor testing area. (This helicopter is, of course, not likely to react well to outdoor breezes.)
Here's another test with a wide shot:
Now Gamera II barely looks as if it's getting off the ground at all. This is part of the secret of its success: Even when the helicopter's more than two metres off the ground, the four gigantic rotors are still in deep ground effect, making more lift than they would if they were even half of their 13-metre diameter off the ground.
Among Gamera II's numerous weight-saving cheats is the drive system for the rotors. You'd expect a shaft or belt, but instead there's just a cord wrapped around each rotor's drive wheel like the string around a yo-yo. The cord is wound in by the little wiry dude in the middle cranking away with both hands and feet. When the cord runs out, after only about sixty seconds, the flight is over.
Sixty seconds is enough to win the Sikorsky Prize for human-powered helicopters, though. To win fame and a quarter of a million dollars, your helicopter must have a flight duration of 60 seconds, and reach an altitude of three metres (9.8 feet), which Gamera II has now very nearly achieved.
Thanks to the yo-yo-string drive and various other ingenious tricks, the whole Gamera II weighs 71 pounds - a little more than 32 kilograms.
The little bubble-canopied Bell 47 helicopter...
...famous for its countless appearances on M*A*S*H, had a maximum takeoff weight of 2950 pounds (1340 kilograms).
With its sixty-kilogram little-wiry-dude pilot on board, Gamera II's takeoff weight is 203 pounds - about 92.2 kilograms. So, about 14.5 Gamera IIs to the Bell 47.
(The Bell 47 is also the only helicopter that actually makes that distinctive "chiew-chiew-chiew..." noise that's become the stock sound effect for any movie or TV helicopter being shut down.)
Gamera II, like numerous other human-powered or otherwise-required-to-run-from-not-many-horsepower aircraft, really is huge. The Sikorsky Prize requires the helicopter to remain in a ten-metre (32.8 ft) square during its flight, but I presume that only applies to the middle of the helicopter, since the whole of Gamera II does not even come close to fitting in a ten-metre square. From the outer edge of one rotor disk to the outer edge of the disk opposite it, Gamera II is 105 feet, 32 metres, in diameter.
The Gamera II info-handout PDF has this handy little table in it:
Forget that, though. This thing's even bigger than the sadly unpopular Fairy Rotodyne:
(The Rotodyne was a compound gyroplane that drove its rotor for takeoff and landing, but cruised with the rotor spinning freely, like an autogyro. The rotor was also driven by tip-jets, not a shaft, so the Rotodyne didn't need a tail rotor. The deafening noise of the tip-jets on takeoff and landing is usually cited as a major factor in the commercial failure of the Rotodyne.)
(I just finished watching the two-part documentary Jet! When Britain Ruled the Skies; the Rotodyne scores a mention toward the end. My favourite part of Jet! was when the narrator, who has only played the Queen once, said "Not only did Capital Airlines fly the Viscount, but they also admired its virtues, in that warming, homespun way that only Americans can fake.")
The Rotodyne's rotor had a diameter of ninety feet - 27.4 metres. That's 15 feet (4.6 metres) smaller than the Gamera II's diagonal.
If you want really big helicopters, you need to go to the Soviets.
The Mi-24 "Hind" is still flying today...
...(probably because all the service manual says is "oil main rotor bearing every three years"). The Hind's rotor diameter is a mere 17.3 metres, though. Four-thirds as big as a single Gamera II rotor, but only 54% of the Gamera II's total maximum diameter.
OK, what about the Mil Mi-26 "Halo"?
Forty metres long, 11,400 horsepower... rotor diameter 32 metres.
The Gamera II would fit neatly on the Halo rotor footprint, sort of like the Vitruvian Man.
And how about the defunct Mil Mi-6 "Hook"?
Rotor diameter 35 metres. Conclusively bigger than the Gamera II.
And, finally, the staggering Mil V-12 "Homer"...
...of which only two prototypes were built. Two slightly overlapping rotors (out of sync with each other, of course), each of which was 35 metres (115 feet) across.
OK, that one wins.
(For comparison, the Boeing Chinook, with its less-bizarre tandem rotor design, only has 18-metre, 59-foot, rotors.)
These comparisons are of course ridiculous; it's like comparing a dandelion seed head with different sizes of musket ball. I only did it to have an excuse to post a bunch of giant-helicopter videos.
(Some Wikipedia-helicopter-data-table writer must have enjoyed filling in the names of the three "powerplants" the Gamera II's used, and its cruise speed of "0 kn; 0 km/h (0 mph)".)