Wing twist
Encyclopedia
Wing twist is an aerodynamic feature added to aircraft
wing
s to adjust lift distribution along the wing.
Often, the purpose of lift redistribution is to ensure that the wing tip is the last part of the wing surface to stall
, for example when executing a roll
or steep climb; it involves twisting the wingtip a small amount downwards in relation to the rest of the wing. This ensures that the effective angle of attack
is always lower at the wingtip than at the root, meaning the root will stall before the tip. This is desirable because the aircraft's flight control surfaces are often located at the wingtip, and the variable stall characteristics of a twisted wing alert the pilot to the advancing stall while still allowing the control surfaces to remain effective, meaning the pilot can usually prevent the aircraft from stalling fully before control is completely lost.
Twist that decreases the local chord's incidence from root to tip is sometimes referred to as washout
. Twist that increases the local incidence from root to tip is less common and is called wash-in
. The X-29 had strong wash-in to compensate for the additional root-first stalling promoted by the forward sweep.
Wing twist can also, rarely, refer to the deflection of the wing when it is made of insufficiently stiff materials; actuation of the flaps
can, instead of deflecting air as intended, cause the wing itself to be deflected and is related to compressibility effects; this problem has mostly been eradicated however, with modern high-strength alloy
s and composites
.
Wing twist is also observed in insects
.
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...
wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
s to adjust lift distribution along the wing.
Often, the purpose of lift redistribution is to ensure that the wing tip is the last part of the wing surface to stall
Stall (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...
, for example when executing a roll
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...
or steep climb; it involves twisting the wingtip a small amount downwards in relation to the rest of the wing. This ensures that the effective angle 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...
is always lower at the wingtip than at the root, meaning the root will stall before the tip. This is desirable because the aircraft's flight control surfaces are often located at the wingtip, and the variable stall characteristics of a twisted wing alert the pilot to the advancing stall while still allowing the control surfaces to remain effective, meaning the pilot can usually prevent the aircraft from stalling fully before control is completely lost.
Twist that decreases the local chord's incidence from root to tip is sometimes referred to as 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...
. Twist that increases the local incidence from root to tip is less common and is called wash-in
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...
. The X-29 had strong wash-in to compensate for the additional root-first stalling promoted by the forward sweep.
Wing twist can also, rarely, refer to the deflection of the wing when it is made of insufficiently stiff materials; actuation of the flaps
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
can, instead of deflecting air as intended, cause the wing itself to be deflected and is related to compressibility effects; this problem has mostly been eradicated however, with modern high-strength alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s and composites
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
.
Wing twist is also observed in insects
Insect flight
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
.
See also
- Adaptive Compliant WingAdaptive Compliant WingThe Adaptive Compliant Wing is a wing design developed by FlexSys, Inc., which is flexible so that aspects of its shape can be changed in flight....
- Angle of incidenceAngle of incidenceAngle of incidence is a measure of deviation of something from "straight on", for example:* in the approach of a ray to a surface, or* the angle at which the wing or horizontal tail of an airplane is installed on the fuselage, measured relative to the axis of the fuselage.-Optics:In geometric...
- Sail twistSail twistSail twist is a phenomenon in sailing where the head of the sail is at a different angle of incidence from the foot of the sail in order to change the lift distribution with height. Twist is measured by comparing the angle of a straight line between the leading edge and trailing edge with that of...
- Washout (aviation)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...