I have had my local sheet metal guy make hinge kits in the past, this is not the most economical way but the fans were huge and I felt that was the way to go, I just took the measurements, and he made the kits. It was basically a frame that bolted to the fan and the one that bolted to the duct hinged together. The only problem with this method, is if the eclectric runs under the fan, Then it will have to be unwired so the higed can be put in place and wired back in.