Nick,
The "A" model Chinook had a "sharp" tail fin.....and the subsequent models have all had the "square" butt design. I have been led to believe that simple change equalled the effect adding 37 feet of aft vertical fin to the aircraft. I know the stability increase betweent he "A" model and the others is tremendous thus the change was most effective. Did ya'll at Sikorsky ever play with that concept on any of your machines.....squaring off the fin to enhance stability in forward flight?