Any fuel injected or turbine chopper (a carborator would cut out at a really bad time due to excess negative g's) can do flips/loops/rolls as long as the cyclic allows a negative pitch on the blades. Most civilian chopppers can't unless modified, although it isn't a difficult modification, mainly modifying the control linkages length, any civilian chopper pilot would be risking his life and certification doing this. An aircraft has to be certified to do aerobatic maneuvers. Most fixed wing civilian aircraft are just as capable uncertified at doing these maneuvers, but, due to insurance companies mainly, are simply not certified.
