3top I cannot speak for other pilots, or the rules in countries outside of the US. I can only tell you about my own experience.
The first point I will address is that of aircraft. Until the early eighties it was legal to do aerobatics in helicopters in the US as long as there was no "prohibition" or "restriction" from doing so by the manufacturer of the helicopter. The theory was if it was not forbidden or prohibited, you could do it.
Later the FAA took the position that it was not legal do any maneuver that was not included in the certification process and proven safe even if the maneuver or maneuvers were not "prohibited" or "restricted" by the manufacturer of the helicopter. The theory was could only be done if proven safe and approved by certification.
To my knowledge (which may be a bit dated) there is no civil helicopter certificated in the U.S. for which aerobatic maneuvers are allowed by certification.
It is possible to receive a special airworthiness certificate which will allow aerobatic maneuvers. To return the aircraft to a normal certificate requires that the owner prove to the FAA that no damage or reduction of life to componants occured during any aerobatic operation (nearly impossible), or replacement of nearly all the rotating or moving componants (prohibitively expensive). Once an aircraft is used legally for aerobatic flight it almost always stays that way because of the cost of returning it to normal category.
Many manufactuers have actually conducted extensive-but not FAA approved- testing that shows there is no loss of componant life or damage to componants during certain aerobatic type maneuvers. Others have conducted no testing whatsoever so don't have a clue what damage or loss of life has occurred.
Military and public aircraft operate under their own rules and approvals.
In the United States the current rules to obtain a Statement of Airshow Competency card require a practical test before an Aerobatic Competency Evaluator (ACE). These are experienced airshow pilots approved by the International Council of Airshows (ICAS) under authority from the FAA. A new pilot will have to demonstrate knowledge of airshow rules, regulations and safety. They will need to discuss their routine and fly the routine at the altitudes and in the order of the proposed show. If successful they will be allowed a safe, high altitude first and as they get experience and demonstrate competence they are allowed lower and lower floors. It takes a lot of time and demonstrated competence to receive an unrestricted Airshow Competency. Military pilots do not require a Statement of Airshow Competency-only government approval.
The rules, forms and fees are published on the ICAS website. It is not easy for helicopter pilots to become qualified to perform an aerobatic display at airshows in the US. It is, however, relatively easy to fly "agility" demonstrations. These demonstrations can be more dramatic (and dangerous) than aerobatic displays but do not include the set of maneuvers the FAA considers aerobatic in a helicopter. They are loop, roll, hammerhead and split-s. Any other maneuver is almost always okay-even some that are way beyond normal. When an agility show is performed the helicopter can work to low speed show line very close to the crowd (an example of this was the Chinook demo at Farnborough which was not filed as aerobatic so could be closer and lower than the AH-64D).
At the Schofields Airshow I only did one proper loop for validation. When it was not approved for the show I did an offset loop which is a loop (or very large barrell roll), but not exactly a proper loop. Neither Chris nor eye performed classical airplane style aerobatics. We performed agility style maneuvers well within all the limitations of our aircraft. Whenever I have performed aerobatic maneuvers at a public display (over 1,000 to date) it has always been in an approved aircraft and with military or civil authority approval.
This in no way is meant to encourage pilots to do aerobatic flight without training or approval in an aircraft approved for those maneuvers. Many of the concerns in this thread are valid. Some are only emotional and based on ignorance.
Almost any helicopter is capable of some aerobatic flight as defined by the FAA when flown by a competent pilot. Done correctly, smooth control application with positive G within all limitations, the aircraft can fly right side up or up-side down (for brief periods). The real problem is that helicopters are extremely unforgiving of ANY mistake. Allow a helicopter to pitch couple during a low-level roll and you will be lucky to recover with your life and you will damage the aircraft or cause some loss of life.
Also liability is a huge issue in the US and for that reason alone, no manufacturer can condone aerobatic flight. As for the R-22, I am sure that Frank would never, ever condone aerobatic flight.