IIRC the biggest problem with the cheyanne wasn't the technical aspects and cost over runs, rather it was its tactical employment. Apparently it was to fly high and fast and attack in a steep dive, which put it right into the perfect engagement zone for the new SA6 SAM, which was launched at a low slant and then zoomed up. Sorting out the other stuff wouldn't reduce the basic vulnerability, so the AAH project designed helicopters that were slower and flew at low levels.