In aviation, slow flight is the region of flight below the maximum lift to drag ratio, where

induced drag Lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, in aerodynamics, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or ...

becomes more significant than

parasitic drag Parasitic drag, also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is defined as the combination of '' form drag'' and '' skin friction drag''. It is named a ...

. Slow flight can be as slow as 3-5 knots above stall airspeed. Slow flight is sometimes referred to as the “region of reversed command” or the “back side of the power curve”. This is because in slow flight, more power is required to maintain straight and level flight at lower

airspeed In aviation, airspeed is the speed of an aircraft relative to the air it is flying through (which itself is usually moving relative to the ground due to wind). In contrast, the ground speed is the speed of an aircraft with respect to the sur ...

s. A very high

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...

is required to maintain altitude in slow flight. At these low airspeeds,

flight control surfaces Flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude. The primary function of these is to control the aircraft's movement along the three axes of rotation. Flight control surfaces ...

begin to lose their effectiveness due to the reduction in airflow over them.

Aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement aroun ...

s are the most affected, and roll control is significantly degraded. If ailerons are used in slow flight, there is a possibility that the high wing will stall due to the increased angle of attack, sending the aircraft into a spin. In many modern aircraft, flight envelope protection in the

aircraft flight control system A conventional Fixed-wing aircraft, fixed-wing aircraft flight control system (AFCS) consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's di ...

prevents this from happening. The

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, airship, or other vehicle that moves through a fluid medium (usually air or water). On an airplane, the rudder is used primarily to counter adverse yaw ...

remains effective in slow flight, and yaw provided by it can be used to control the bank angle and direction of the aircraft.

References

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