Bartram "Bart" Kelley (1909-1998) was a pioneering helicopter
engineer who worked for Bell Helicopter company.
He narrates this remarkable video consisting entirely of archival footage
that chronicles the development by Arthur Young and his team
of what will become the Bell Helicopter, starting with Arthur working on his
own with tethered experimental models in the 1930's through many
iterations and experiments to the eventual evolution to the familiar
bubble-domed Bell Helicopter of the 1950's.
A testimony to engineering perseverance, dedication and ingenuity :-
https://youtu.be/k562IriqnlA