For questions about experimental aircraft that have not been granted a type certificate by a regulatory agency.
An "experimental" aircraft is one that does not have a type certificate issued by the FAA or another regulator, i.e. it is considered a 'one-off' aircraft, rather than a standard type.
Experimental aircraft include homebuilt aircraft and aircraft used for special purposes (e.g. research, air racing), but they do not not usually include military aircraft.