http://www.piasecki.com/heavylift_pa97.php I find it more than ironic that on the anniversary of the Lunar Landing, I stumble across that. The Piasecki 97, ostensibly a blimp with a bunch of helicopters welded onto the frame.
I'm honestly not sure what makes my head hurt worse--the fact that someone conceived of the design at all, or that that were mass produced in the 1980's. Just...what? Why would anyone think this was a good idea?! It's like some kind of shop class project gone terribly wrong, and yet someone with no concept of torque, ground resonance or structural thresholds figured if one helicopter worked then surely four would work four times better.
I'm all for trial and error, but this was an error before it even left the drafting table.