What is the designation for an aircraft intended for permanent special tests?

The designation for an aircraft intended for permanent special tests is actually "Special Test, Permanent." This indicates that the aircraft is specifically modified or built to conduct ongoing tests relating to various technical requirements or operational capabilities. This kind of aircraft is used to gather data and evaluate performance in a permanent sense, rather than being used solely for transient or experimental testing.

In contrast, the designation “Experimental” typically refers to aircraft that are undergoing initial testing or evaluation phases and may not be intended for long-term use in a specific testing role. Aircraft classified as "Fighter" and "Cargo" serve distinct operational purposes – with fighters designed for air-to-air combat and cargo aircraft intended for the transport of goods and personnel – and do not apply to the context of aircraft specifically meant for conducting permanent tests.