I was looking at older planes, specifically the Cessna 180. It is discontinued, but people love them, so they fetch premiums. I saw St. Just Aviation has a kit Cessna 180. There are only 25ish planes in existence.
I'm curious if it would still take a large amount of testing to certify their replicated design - since the Cessna 180 already went through all that years ago?
The FAA requires all aircraft above a certain weight (>ultralight) to be certified. You can certify the design and production process so that everything that comes out of the factory has a guaranteed level of safety, or you can certify the result. The former gets a standard certificate, the latter gets a special airworthiness certificate. Other jurisdictions make similar distinctions, with minor variations.
Kit planes, such as your 180 replica, get a special airworthiness - amateur built certificate. FAA AC 20-27G outlines the process for satisfying this requirement. It is sixty pages of instructions, limitations and forms. The two most commonly mentioned requirements are for majority construction by the amateur and for flight testing.
It is important to document the entire fabrication and assembly process from the beginning to the end, in a continuous and sequential manner. This is because, at the time of certification, the FAA is required to ascertain whether the amateur builder(s) fabricated and assembled the major portion of the aircraft. Making this finding requires adequate, sufficient, and credible documentation.
For flight testing
It does not matter to the FAA whether or not it was based on some production certified aircraft.
We do not certify amateur-built aircraft designs or require that you modify the design before airworthiness certification. However, we may deny airworthiness certification when we inspect your aircraft if we find it does not meet the requirements for the certification you request or is not in a condition for safe operation.
This is far less stringent that the requirements for a standard certificate. You will have to decide whether you consider this "a large amount of testing".
As I understand it (I am not a pilot) kits basically do an end-run around the normal certification process.
Type certification is a very arduous process, but in some countries (including the US and Canada) Amateur-Built aircraft can receive a special airworthiness certificate under much lighter rules (the US considers this a sub-type of "experimental"). By selling the aircraft as a kit and having the end user do a sufficient proportion of the work the aircraft counts as Amateur-Built and the costs of type-certification are avoided.
The downside of those rules though is that they come with operating limitations that prevent or severely restrict commerical use. So if you want the aircraft for fun then a kit clone is fine, but if you want it for work then you will need to splash out for a type-certified original.
