Slightly off the topic, the great photo links listed above by some of the contributors put me in mind of a spectacular contraption that the Americans put together quite some time ago.
It had the front ends of 4 single-rotor helicopters positioned at the corners of a large square lifting frame.
As I remember (saw a photo of it somewhere) it had four pilots all setting power on command from the chief pilot who was sitting in one of the airframes.
A brave effort to come up with a heavy lift machine, but too many problems to be successful, I think.
Does anyone have links to pictures/information about this machine, whatever it was?
Thanks.