Subject: Would a helicopter rotor work in a 'ducted fan' type of configuration?

I would like to know if helicopter rotor would work if enclosed horizontally, 
similar to how a propellor can be enclosed in a ducted fan type of set-up.  
I've read another article on here which talked about the perils of flying a 
helicopter in a tight tunnel, but I'm wondering if the setup was such that it 
was completely open above and below the rotors, if this would work.  The 
simplest way to describe this is to imagine two pie tins, with one turned 
upside down.  Place them on top of each other, remove a portion of the center, 
connect those inside edges and place the rotor inside of that hole, where the 
ends of the rotor blades are very close to the sides.  Would a setup like that 
work, or would this be too inherently unstable and hard to control to be safe?

Thanks,
Dean

Re: Would a helicopter rotor work in a 'ducted fan' type of configuration?