I've seen a CH-47 Chinook in a contest, suspended atop its sling-load of a 105mm howitzer in 1/72nd scale before. Instead of the rotors, rotor diameter plexiglass discs were installed and airbrushed to simulate "rotor-motion". The effect was simply breathtaking! the only thing missing was a sound chip,and dust in the rotor-wash.
Another contest model I've seen was a UH-1H suspended over the LZ by the Air-Cav troopers who were exiting both side doors. Not quite as elaborate as the Chinook but still very effective.
Now you've got my "creative Juices" flowing. I think I'll break-out that 1/35th UH-1B kit by "Seminar"and see what I can come up with!!!