In aviation, slow flight is the region of flight below the maximum

lift to drag ratio In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under give ...

, where

induced drag In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, 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 a combination of form drag and skin friction drag. It affects all objects regardless of ...

. 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. Among the common conventions for qualifying airspeed are: * Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system; * Calibrated a ...

s. A very high

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

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

flight control surfaces Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude. Development of an effective set of flight control surfaces was a critical advance in the development of aircraft. Ea ...

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 around ...

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 Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

. In many modern aircraft,

flight envelope protection Flight envelope protection is a human machine interface extension of an aircraft's control system that prevents the pilot of an aircraft from making control commands that would force the aircraft to exceed its structural and aerodynamic operatin ...

in the

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

prevents this from happening. The

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...

remains effective in slow flight, and yaw provided by it can be used to control the

bank angle A banked turn (or banking turn) is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. For a road or railroad this is usually due to the roadbed having a transverse down-slope towards the ...

and direction of the aircraft.

References

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