Check out this article on the Bendix Model J Four Place Helicopter:



This co-axial, counter-rotating type helicopter was proposed to the US Navy Bureau of Aeronautics in 1946, which elected to pass on the design. The image gallery reproduces the original proposal document and features numerous rare, high resolution photos of the Model J under construction. Also a featured are two photos of the single place Bendix Model K. Worth checking out if you are a fan of rare helicopter designs!

-Jared