Read this and find out (hint, over 100 years ago) https://dspace.ist.utl.pt/bitstream/2295/574042/1/Tese_de_Mestrado.pdf
Great info! I'll have to throw a summary of it into the next editing of the book! For those who don't want to read as much, here are some mentioned: http://www.aviastar.org/helicopters_eng/oemichen.php http://www.aviastar.org/helicopters_eng/convertawings.php
The history shows you how difficult these craft are to make or fly! It looks like it was the 1950's before they were able to actually make something work in a similar way to quads.