The new X-Plane concept from the US Department of Defense Advanced Research Projects Agency (DARPA) lacks all elements of the vertical and horizontal tail, such as slats, flaps, elevators and rudders. This is done to reduce aerodynamic drag and improve fuel efficiency.

This project is at odds with more than a century of aviation practice, from the Wright brothers' first aircraft to state-of-the-art fifth-generation fighters. But DARPA says it has a real alternative to classic aircraft fins to control aircraft in the air at high speeds. Aurora Flight Sciences, a subsidiary of Boeing, recently received a design contract from DARPA for the Control of Revolutionary Aircraft with Novel Effectors (CRANE) program, which aims to launch an experimental aircraft without moving control surfaces.

"Aurora Flight Sciences will develop the full-scale X-Plane, an aircraft that will rely solely on airflow changes for in-flight maneuvers," DARPA said. If the concept succeeds, officials added, the project will be "a new milestone in aircraft development." The vertical and horizontal tail surfaces of aircraft have been a necessary inconvenience for more than a century: they create aerodynamic drag, which grows cubed with speed, and increase fuel consumption. However, no alternative has yet been created, so pilots must use flaps, slats, rudders, and elevators to control the aircraft, which have been used and improved over decades.

DARPA is by no means the first to consider removing parts previously considered essential to flight. In 2018, an MIT team flew what they called "the world's first aircraft with no moving parts," but that term referred to the propulsion unit, not the control system. The Massachusetts Institute of Technology used an effect known as "ionic wind" to propel an experimental aircraft, rather than traditional propellers or gas turbines.

However, some aircraft of the past did get rid of one or more of the traditional elements of the plumage. An example is the integration of pitch and roll systems into the wing itself, like the Concorde supersonic liner. True, he still could not do without a rudder. This is the most striking example, and in general, aircraft with a reduced number of control planes were designed and created throughout the 20th century.

Little information is available at this time on the technologies that allow CRANE to remain stable and controllable in flight, but some intriguing details are available in a 2021 presentation by Alexander "Xander" Valan, Program Manager, Tactical Technology Division, DARPA. For example, the active flow control principle from Aurora Flight Sciences uses various methods, such as jets of air or even electrical discharges, to shape the air flow around the aircraft. It is planned to use "modular wing configurations that will allow the integration of advanced technologies in the future." Based on available photos, the X-Plane will use a "co-planar connected wing" type, which includes two forward wings and two rear wings, instead of the traditional V-wing found on most commercial and military aircraft.

The next phase of CRANE development (phase two) will include the design and development of flight controls and software. It will culminate in a thorough testing of the X-Plane design.

At the third stage, DARPA can launch a scale copy of the 3175 kg X-Plane demonstrator aircraft with active flow control technology. No financial details or projected timelines have been released.