(Note: these are some of the few without some glaring music in the background, other one using
Where Eagles Dare theme in the background while also showing other helicopter designs)
The Fl-282 'Hummingbird' intermeshing rotor helicopter. The world's first
serial production helicopter. From what I understood, it is also one of the
easiest to fly. As in 'a grandmother with some basic sub-100 hour training can do it' easy.
The US had its own designs but they were fraught with mechanical and reliability issues... at least until they managed to nick a few surviving Fl-282 and had one of the designers help them out, which eventually led to the HH-43 Husky:
It also has a grandson in the K-MAX.
It must be noted that using intermeshing rotors is
more efficient than pretty much every other design I've seen, at least from what I've gleaned. Then again, the K-MAX can
literally haul itself in external cargo weight.