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Elevator (aircraft)
Encyclopedia
Elevators are flight control surfaces, usually at the rear of an aircraft
, which control the aircraft's orientation by changing the pitch
of the aircraft, and so also the angle of attack
of the wing. In simplified terms, they make the aircraft nose-up or nose-down. (Ascending and descending are more a function of the wing—aircraft typically land nose up.) An increased wing angle of attack will cause a greater lift
to be produced by the profile of the wing
, and a slowing of the aircraft speed. A decrease in angle of attack will produce an increase in speed. The elevators may be the only pitch control surface present (and are then called a slab elevator or stabilator
), or may be hinged to a fixed or adjustable surface called a tailplane
or horizontal stabilizer
.
The rear wing to which elevators are attached have the opposite effect to a wing. They usually create a downward pressure which counters the unbalanced moment
due to the airplane's center of gravity
not being located exactly on the resulting centre of pressure, which in addition to the lift generated by the main wing includes the effects of drag
and engine thrust
. An elevator decreases or increases the downward force created by the rear wing. An increased downward force, produced by up elevator, forces the tail down and the nose up so the aircraft speed is reduced (i.e. the wing will operate at a higher angle of attack, which produces a greater lift coefficient
, so that the required lift is produced by a lower speed). A decreased downward force at the tail, produced by down elevator, allows the tail to rise and the nose to lower. The resulting lower wing angle of attack provides a lower lift coefficient, so the craft must move faster (either by adding power or going into a descent) to produce the required lift. The setting of the elevator thus determines the airplane's trim speed - a given elevator position has only one speed at which the aircraft will maintain a constant (unaccelerated) condition.
In some aircraft pitch-control surfaces are in the front, ahead of the wing; this type of configuration is called a canard
, the French
word for duck
. The Wright Brothers
' early aircraft were of this type. The canard type is more efficient, since the forward surface usually is required to produce upward lift (instead of downward force as with the usual empennage) to balance the net pitching moment. The main wing is also less likely to stall
, as the forward control surface is configured to stall before the wing, causing a pitch down and reducing the angle of attack of the wing.
Supersonic
aircraft have stabilator
s, because early supersonic flight research revealed that shock waves generated on the trailing edge of tailplane
s rendered hinged elevators ineffective. Delta wing
ed aircraft combine aileron
s and elevators, and their respective control inputs, into one control surface, called an elevon
.
s, elevators, elevon
s, flap
s and flaperon
s into wings to perform the aerodynamic purpose with the advantages of less: mass, cost, drag, inertia
(for faster, stronger control response), complexity (mechanically simpler, fewer moving parts or surfaces, less maintenance), and radar cross section
for stealth
. These may be used in many unmanned aerial vehicle
s (UAVs) and 6th generation fighter aircraft
. Two promising approaches are flexible wings, and fluidics.
In flexible wings, much or all of a wing surface can change shape in flight to deflect air flow. The X-53 Active Aeroelastic Wing is a NASA
effort. The Adaptive Compliant Wing
is a military and commercial effort.
In fluidics
, forces in vehicles occur via circulation control, in which larger more complex mechanical parts are replaced by smaller simpler fluidic systems (slots which emit air flows) where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles. In this use, fluidics promises lower mass, costs (up to 50% less), and very low inertia
and response times, and simplicity.
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...
, which control the aircraft's orientation by changing the pitch
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...
of the aircraft, and so also the 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...
of the wing. In simplified terms, they make the aircraft nose-up or nose-down. (Ascending and descending are more a function of the wing—aircraft typically land nose up.) An increased wing angle of attack will cause a greater lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
to be produced by the profile of the 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...
, and a slowing of the aircraft speed. A decrease in angle of attack will produce an increase in speed. The elevators may be the only pitch control surface present (and are then called a slab elevator or stabilator
Stabilator
A stabilator is an aircraft control surface that combines the functions of an elevator and a horizontal stabilizer...
), or may be hinged to a fixed or adjustable surface called a tailplane
Tailplane
A tailplane, also known as horizontal stabilizer , is a small lifting surface located on the tail behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed wing aircraft such as helicopters and gyroplanes...
or horizontal stabilizer
Stabilizer (aircraft)
In aviation, a stabilizer provides stability when the aircraft is flying straight, and the airfoil of the horizontal stabilizer balances the forces acting on the aircraft....
.
The rear wing to which elevators are attached have the opposite effect to a wing. They usually create a downward pressure which counters the unbalanced moment
Moment (physics)
In physics, the term moment can refer to many different concepts:*Moment of force is the tendency of a force to twist or rotate an object; see the article torque for details. This is an important, basic concept in engineering and physics. A moment is valued mathematically as the product of the...
due to the airplane's center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
not being located exactly on the resulting centre of pressure, which in addition to the lift generated by the main wing includes the effects of drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
and engine thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
. An elevator decreases or increases the downward force created by the rear wing. An increased downward force, produced by up elevator, forces the tail down and the nose up so the aircraft speed is reduced (i.e. the wing will operate at a higher angle of attack, which produces a greater lift coefficient
Lift coefficient
The lift coefficient is a dimensionless coefficient that relates the lift generated by a lifting body, the dynamic pressure of the fluid flow around the body, and a reference area associated with the body...
, so that the required lift is produced by a lower speed). A decreased downward force at the tail, produced by down elevator, allows the tail to rise and the nose to lower. The resulting lower wing angle of attack provides a lower lift coefficient, so the craft must move faster (either by adding power or going into a descent) to produce the required lift. The setting of the elevator thus determines the airplane's trim speed - a given elevator position has only one speed at which the aircraft will maintain a constant (unaccelerated) condition.
In some aircraft pitch-control surfaces are in the front, ahead of the wing; this type of configuration is called a canard
Canard (aeronautics)
In aeronautics, canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing...
, the French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
word for duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...
. The Wright Brothers
Wright brothers
The Wright brothers, Orville and Wilbur , were two Americans credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight, on December 17, 1903...
' early aircraft were of this type. The canard type is more efficient, since the forward surface usually is required to produce upward lift (instead of downward force as with the usual empennage) to balance the net pitching moment. The main wing is also less likely 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...
, as the forward control surface is configured to stall before the wing, causing a pitch down and reducing the angle of attack of the wing.
Supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
aircraft have stabilator
Stabilator
A stabilator is an aircraft control surface that combines the functions of an elevator and a horizontal stabilizer...
s, because early supersonic flight research revealed that shock waves generated on the trailing edge of tailplane
Tailplane
A tailplane, also known as horizontal stabilizer , is a small lifting surface located on the tail behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed wing aircraft such as helicopters and gyroplanes...
s rendered hinged elevators ineffective. Delta wing
Delta wing
The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...
ed aircraft combine aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s and elevators, and their respective control inputs, into one control surface, called an elevon
Elevon
Elevons are aircraft control surfaces that combine the functions of the elevator and the aileron , hence the name. They are frequently used on tailless aircraft such as flying wings. An elevon that is not part of the main wing, but instead is a separate tail surface, is a stabilator...
.
Research
Several technology research and development efforts exist to integrate the functions of aircraft flight control systems such as aileronAileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s, elevators, elevon
Elevon
Elevons are aircraft control surfaces that combine the functions of the elevator and the aileron , hence the name. They are frequently used on tailless aircraft such as flying wings. An elevon that is not part of the main wing, but instead is a separate tail surface, is a stabilator...
s, flap
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...
s and flaperon
Flaperon
A flaperon is a type of aircraft control surface that combines aspects of both flaps and ailerons. In addition to controlling the roll or bank of an aircraft as do conventional ailerons, both flaperons can be lowered together to function similarly to a dedicated set of flaps...
s into wings to perform the aerodynamic purpose with the advantages of less: mass, cost, drag, inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
(for faster, stronger control response), complexity (mechanically simpler, fewer moving parts or surfaces, less maintenance), and radar cross section
Radar cross section
Radar cross section is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected.An object reflects a limited amount of radar energy...
for stealth
Stealth technology
Stealth technology also termed LO technology is a sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with personnel, aircraft, ships, submarines, and missiles, to make them less visible to radar, infrared, sonar and other detection...
. These may be used in many unmanned aerial vehicle
Unmanned aerial vehicle
An unmanned aerial vehicle , also known as a unmanned aircraft system , remotely piloted aircraft or unmanned aircraft, is a machine which functions either by the remote control of a navigator or pilot or autonomously, that is, as a self-directing entity...
s (UAVs) and 6th generation fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
. Two promising approaches are flexible wings, and fluidics.
In flexible wings, much or all of a wing surface can change shape in flight to deflect air flow. The X-53 Active Aeroelastic Wing is a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
effort. The Adaptive Compliant Wing
Adaptive Compliant Wing
The 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....
is a military and commercial effort.
In fluidics
Fluidics
Fluidics or Fluidic logic is the use of a fluid to perform analog or digital operations similar to those performed with electronics.The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics...
, forces in vehicles occur via circulation control, in which larger more complex mechanical parts are replaced by smaller simpler fluidic systems (slots which emit air flows) where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles. In this use, fluidics promises lower mass, costs (up to 50% less), and very low inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
and response times, and simplicity.
External links
- Aircraft Pitch Motion (elevator function explanation, NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
website)