Stall strips
Encyclopedia
A stall strip is a fixed aerodynamic
device employed on fixed-wing aircraft
to modify the airfoil
used. They are usually factory-installed or, on rarer occasion, an after-market modification. Stall strips are almost always employed in pairs, symmetrically on both wings. In rare installations they are employed as a single strip on one wing to correct aberrant stall behaviour.
characteristics and ensures that the wing root
stalls before the wing tips. This is usually as a result of initial aircraft flight testing which shows that the existing stall characteristics are unacceptable for certification.
In some cases, such as the American Aviation AA-1 Yankee
, stall strips are planned to be used on the wing from the start. In the case of the AA-1 the left and right wings were identical, interchangeable and built on a single wing jig, thus the more traditional use of washout
in the wing design was not possible.
Stall strips can be an alternative to washout in aircraft design or they can be used as well as washout to improve stall performance.
Stall strips typically consist of a small piece of material, usually aluminium, triangular in cross section and often 6-12 inches (15-30 cm) in length. It is riveted
or bonded
on the point of the wing’s leading edge, usually at the wing root. Here it acts to trip the boundary layer
air flow at higher angles of attack
, causing turbulent flow and air flow separation. This has the effect of causing the wing root to stall before the outer portions of the wing, ensuring a progressive outward stall, minimizing the risk of spinning
and giving maximum aileron control throughout the stall.
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
device employed on fixed-wing aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
to modify the airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
used. They are usually factory-installed or, on rarer occasion, an after-market modification. Stall strips are almost always employed in pairs, symmetrically on both wings. In rare installations they are employed as a single strip on one wing to correct aberrant stall behaviour.
Operation
A stall strip alters the wing’s stallStall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
characteristics and ensures that the wing root
Wing root
The wing root is the part of the wing on a fixed-wing aircraft that is closest to the fuselage. On a simple monoplane configuration, this is usually easy to identify...
stalls before the wing tips. This is usually as a result of initial aircraft flight testing which shows that the existing stall characteristics are unacceptable for certification.
In some cases, such as the American Aviation AA-1 Yankee
Grumman American AA-1
The Grumman American AA-1 series is a family of light, 2-seat aircraft. The family includes the original American Aviation AA-1 Yankee Clipper and AA-1A Trainer, the Grumman American AA-1B Trainer and TR-2 and the Gulfstream American AA-1C Lynx and T-Cat.-Development history:The Yankee was...
, stall strips are planned to be used on the wing from the start. In the case of the AA-1 the left and right wings were identical, interchangeable and built on a single wing jig, thus the more traditional use of washout
Washout (aviation)
Washout refers to a feature of wing design to deliberately reduce the lift distribution across the span of the wing of an aircraft. The wing is designed so that angle of incidence is higher at the wing roots and decreases across the span, becoming lowest at the wing tip...
in the wing design was not possible.
Stall strips can be an alternative to washout in aircraft design or they can be used as well as washout to improve stall performance.
Stall strips typically consist of a small piece of material, usually aluminium, triangular in cross section and often 6-12 inches (15-30 cm) in length. It is riveted
Rivet
A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole, and the tail is upset, or bucked A rivet...
or bonded
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
on the point of the wing’s leading edge, usually at the wing root. Here it acts to trip the boundary layer
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
air flow at higher angles of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, causing turbulent flow and air flow separation. This has the effect of causing the wing root to stall before the outer portions of the wing, ensuring a progressive outward stall, minimizing the risk of spinning
Spin (flight)
In aviation, a spin is an aggravated stall resulting in autorotation about the spin axis wherein the aircraft follows a corkscrew downward path. Spins can be entered intentionally or unintentionally, from any flight attitude and from practically any airspeed—all that is required is sufficient yaw...
and giving maximum aileron control throughout the stall.