Aerodynamics

Traditional aircraft maneuvering is accomplished by altering the flow of air passing over the control surfaces of the aircraft—the ailerons, elevators, flaps, air brakes and rudder. Some of these control surfaces can be combined—such as in the "ruddervators" of a V-tail configuration—but the basic properties are unaffected. When a control surface is moved to present an angle to the oncoming airflow, it alters the airflow around the surface, changing its pressure distribution, and thus applying a pitching, rolling, or yawing moment to the aircraft.

The angle of control surface deflection and resulting directional force on the aircraft are controlled both by the pilot and the aircraft's inbuilt control systems to maintain the desired attitude, such as pitch, roll and heading, and also to perform aerobatic maneuvers that rapidly change the aircraft's attitude. For traditional maneuvering control to be maintained, the aircraft must maintain sufficient forward velocity and a sufficiently low angle of attack to provide airflow over the wings (maintaining lift) and also over its control surfaces.

As airflow decreases so does effectiveness of the control surfaces and thus the maneuverability. If the angle of attack exceeds its critical value, the airplane will stall. Pilots are trained to avoid stalls during aerobatic maneuvering and especially in combat, as a stall can permit an opponent to gain an advantageous position while the stalled aircraft's pilot attempts to recover.

The speed at which an aircraft is capable of its maximum aerodynamic maneuverability is known as the corner airspeed; at any greater speed the control surfaces cannot operate at maximum effect due to either airframe stresses or induced instability from turbulent airflow over the control surface. At lower speeds the redirection of air over control surfaces, and thus the force applied to maneuver the aircraft, is reduced below the airframe's maximum capacity and thus the aircraft will not turn at its maximum rate. It is therefore desirable in aerobatic maneuvering to maintain corner velocity.

In a supermaneuverable aircraft, the pilot can maintain a high degree of maneuverability below corner velocity, and at least limited altitude control without altitude loss below stall speed. Such an aircraft is capable of maneuvers that are impossible with a purely aerodynamic design. More recently, increased use of jet-powered, instrumented unmanned vehicles ("research drones") has increased the potential flyable angle of attack beyond 90 degrees and well into the post-stall safe flight domains, and has also replaced some of the traditional uses of wind tunnels.[2]