Flight Training in an Experimental
I can offer flight instruction in an experimental. However, the aircraft itself can't be a commercial endeavor. In other words, we can use your RV, and my charge involves only my instructional time. What I can't do is use my aircraft and charge you a higher rate for my instruction and zero for the plane - the FAA would consider that fraudulent. You are probably aware that there are some instructors offering transition training in their RV's. In order to do this, they must get a "Letter of Deviation" from their FSDO to be legal. This letter involves presenting a syllabus (description of scope of training) to the FAA which, if they accept, reclassifies the aircraft as a commercial endeavor. This results in a requirement for 100 hour inspections as well as an increase in the operators insurance. To my knowledge, these letters so far allow only for transition training - I don't believe a student can solo under these conditions or the plane can be rented out. Don't know if that's been tried.
Also, regarding flight testing, I can have another person on board as long as that person is essential crew. Think of the Airbus A380. Pretty tough to fly, much less test, with just one on board. At the same time, don't bring your buddy along and claim that he's there to record data. Won't work. In my case, I did have my brother join me on about half of my missions. This was OK with the FAA as his qualifications (CFI, CFII, MEI, ATP) exceeded mine and offered meaningful input and assistance during the test phase. One thing to keep in mind during the test phase is that some insurance policies don't begin to offer full coverage until you're finished testing.
Finally, there is nothing to prevent you from building a plane, having someone else flight test it for you (ALWAYS a good idea for pilots with low experience), and then do your flight training in it. The only downside to this approach is that the plane is likely to be subject to some abuse as you're learning to fly it properly. Personally, I'd learn to fly in someone else's, while I was building a RV-9. Good luck
Terry, CFI
RV-9A N323TP