Which letter denotes an Experimental aircraft in the Fixed Wing classification?

The letter that denotes an Experimental aircraft in the Fixed Wing classification is X. In aviation and military terminology, the designation system uses specific letters to categorize types of aircraft based on their design and purpose. The letter X is universally recognized as signifying experimental aircraft, which are typically used to test new technologies, designs, or capabilities before they enter regular operational service.

This classification helps differentiate experimental models from operational ones and aligns with standardized naming conventions across various branches of the military and aviation sectors. Other letters in the classification system correspond to different specific roles or categories: for instance, N is often related to civilian registrations, P denotes airplanes, and R signifies reconnaissance aircraft.