Can amateur-built aircraft or helicopters be awarded Airworthiness Certificate?

According to the FAA regulation if the majority of an aircraft has been fabricated and assembled by an individual or group of individuals for educational or recreational purpose, a Special Airworthiness Certificate (SAC) may be awarded.  This SAC regulation is also commonly known as the 51% rule.

Reference to the FAA AC No. 20-27F, dated 9/26/2003, for "CERTIFICATION AND OPERATION OF AMATEUR-BUILT AIRCRAFT" below:

AC No. 20-27F gives you information and guidance on how to:
(1) Fabricate and assemble an amateur-built aircraft,
(2) Register your aircraft,
(3) Identify and mark your aircraft,
(4) Get your aircraft inspected and certificated,
(5) Flight test your aircraft,
(6) Operate your aircraft,
(7) Receive certification of an amateur-built aircraft purchased outside the United States, and
(8) Become a repairman for your amateur-built aircraft.

FAA states that ".....amateur builders are free to develop their own designs...... as it would be impractical (for the FAA) to develop design standards for the wide variety of design configurations created by designers, kit manufacturers, and amateur builders."