AILERON (AERONAUTICAL ENGINEERING)

AILERON
FLAPERON
SPOILERON
TRAILING EDGE
FLAP

INTRODUCTION

Immediately above, a view of the left wing of a typical commercial jet airplane. Four types of aerodynamic surfaces can be seen. There are two closer to the fuselage: a flap forming the trailing edge of the wing and a spoiler, which is an aerodynamic brake. Further out, there is another flap (or, in some models, a flaperon) forming another part of the wing's trailing edge, accompanied by a spoileron, on the upper surface (extrados) of the wing. And finally, closer to the wingtip, the left aileron, one of the main components responsible for making the airplane change trajectory. Immediately below, the Cessna 172 Skyhawk, a typical example of an aircraft equipped with a simple wing, with a simple aileron.

Ailerons are movable sections of the trailing edges of fixed-wing aircraft wings, used to control the aircraft's rolling motion around its longitudinal axis. They are moved by the pilot through lateral action on the yokes, control sticks, and, in more sophisticated aircraft models with fly-by-wire controls, on sidesticks, similar to the joysticks used in video games.

Ailerons are control aerodynamic surfaces widely used in fixed-wing aircraft. They are components made of metal (generally aluminum and/or metal alloys) or composite material (generally carbon fiber or fiberglass and epoxy resin) used extensively in aviation as important movable control surfaces that allow the aircraft to bank laterally in relation to its longitudinal axis.

Ailerons are generally interconnected, so that one on one side of the aircraft moves down while the other on the opposite side moves up, and vice versa. The aileron that moves down increases lift on the wing it is connected to, while the aileron on the opposite wing causes the opposite effect, a reduction in lift, producing a rolling motion about the aircraft's longitudinal axis. Ailerons are usually located near the wingtips. The word aileron comes from the French language and means small wing.

Ailerons are part of the wing of fixed-wing aircraft and are just as important as other aerodynamic control surfaces, such as the elevators, which are attached to the horizontal stabilizer, and the rudder, which are generally located in the tail and form part of the aircraft's empennage.

Always attached to the trailing edges of the fixed part of the wings, that is, the rear part of the fixed wing, ailerons are also called lateral inclination rudders, although this expression is little known and used in the aeronautical community.

LIMITATIONS

Immediately above, a schematic image of the aerodynamic forces or quantities acting on a wing when air flows over its upper surface (extrados) and lower surface (intrados), i.e., when the aircraft has speed. Immediately below, a simplified video that illustrates didactically how the left and right ailerons on an airplane's wings move and how the airplane itself reacts to these movements, around its longitudinal axis.

An undesired side effect of aileron operation is adverse yaw, a yaw moment in the opposite direction of the roll. Abrupt and excessive use of the ailerons to roll the airplane to the right, for example, can eventually produce a yaw to the left.

As the aircraft rolls, adverse yaw is primarily caused by the change in drag on the left and right wings.The rising wing has an increase in lift, which causes an increase in induced drag. The descending wing has reduced lift, which reduces induced drag. The difference in drag between the wings can eventually produce adverse yaw. The difference in drag between the ailerons can also be a cause of adverse yaw.

To supplement or complete the turning maneuver, the pilot also uses the rudder in the same direction as the turn.

During the turn, with the ailerons in a neutral position, the wing on the outside of the turn develops more lift than the opposite wing, due to the variation in airflow speed along the wing's span, which causes the aircraft to continue to roll. Once the desired angle of rotation about the longitudinal axis is reached, the pilot uses the opposite aileron to prevent the angle of rotation from increasing due to the variation in lift along the wingspan.

TRAILING EDGE

The trailing edge is the rear part of the wing, which has a more tapered shape, and from which the air that has traveled over its surface flows off. The function of the aileron, which is part of the trailing edge, is to move up or down, alternately on each side of the wing, in order to alter this airflow, respectively decreasing or increasing lift on that side of the aircraft, making it rotate around its longitudinal axis, which is called the rolling motion.

When the ailerons are actuated with a movement of the control stick or sidestick to the right or left, the ailerons act inversely on each side of the wing: when the pilot wants to turn or bank the airplane to the right, the aileron on the left wing lowers and the aileron on the right wing raises. This decreases the lift of the right wing by changing its angle of attack to a lower angle, and the opposite happens on the left wing, causing the airplane to roll or rotate upward on the longitudinal axis.

SPOILERON AND FLAPERON

Immediately above, with a closer look, one can see the downward inclination of almost the entire trailing edge of the wings of the Beechcraft Beechjet 400A, also known as the Beechcraft Hawker 400, an American-made airplane. This is the flap, an aerodynamic surface that improves the ratio of aerodynamic lift and speed and makes landings and takeoffs smoother compared to other models of swept-wing jets. Immediately below, the Denney Kitfox model, a light experimental aircraft, equipped with a flaperon, which is an aerodynamic control surface that combines the functions of a flap and an aileron.

The vast majority of manufacturers of simpler and less expensive fixed-wing aircraft tend to divide the trailing edge of the aircraft wings between the flaps, which are closer to the fuselage, and the ailerons, which are closer to the wingtips. However, in larger and more sophisticated aircraft models, such as the Boeing 777, for example, manufacturers have opted to include a device or aerodynamic control surface called a flaperon.

Furthermore, in some cases, manufacturers have opted to decrease the length of the ailerons and increase the length of the flaps in aircraft that develop high or medium speeds, such as executive jets, commercial jets, and turboprops for executive use. There are cases where ailerons were and/or are completely eliminated. The Beechcraft Beechjet 400A, also known as the Beechcraft Hawker 400, for example, is an aircraft equipped with spoilerons, which are movable surfaces on the upper surface (extrados) of the wings, responsible for the rolling motion.

To reduce the size of the ailerons or simply improve the aircraft's maneuverability, it is necessary to make aircraft designs more sophisticated, with the addition of new aerodynamic control surfaces, the spoilerons, which contribute to the lateral banking about the aircraft's longitudinal axis and, simultaneously, slightly increase the drag of the lowered wing to assist the elevator and rudder during turns.

Theoretically, the wider and longer the flaps, the lower the speeds required to take off and land an aircraft (also called V1, VR and Vref), therefore the better the fixed-wing aircraft's performance on runways, meaning the shorter the runway length required for landing and takeoff.

For this reason, some manufacturers make a huge effort in high-speed aerodynamics research to increase wing efficiency, with the addition of flaperons and spoilerons, which are aerodynamic control surfaces that combine the functions of flaps and ailerons in a simultaneous action, and, to supplement this, they also include slats on the leading edges of the wings in their designs.

For example, without the appropriate use of flaps, a sophisticated executive jet with swept wings would not be able to take off and land safely, with full tanks and passengers on board, on runways less than 2,000 meters long.

AXES

Illustration in French about the three axes of an aircraft: the red arrow represents the longitudinal axis, the blue arrow represents the lateral or transverse axis, and the green arrow represents the vertical or central axis. Ailerons are responsible for the movement of the aircraft around its longitudinal axis, lowering one wing and raising the other.

In all airplane models, there are three axes of movement:

Longitudinal axis - An imaginary line that crosses the airplane from its tail to its nose. Ailerons, spoilerons, and flaperons are responsible for movement around this axis;
Lateral axis - An imaginary line that crosses the airplane from one wingtip to the other. The horizontal stabilizer, along with the elevator, is responsible for the movement of the aircraft around this axis;
Vertical axis - An imaginary line that crosses the airplane from top to bottom. The vertical stabilizer (fin), along with the rudder, is responsible for the movement of the aircraft around this axis;

The three imaginary lines intersect at the airplane's center of gravity. In practice, almost all of the airplane's weight is over the wing, as it is largely responsible for providing the necessary lift to take off and maintain flight. When the pilot pulls the control stick or sidestick back (tail down and nose up), the angle of attack increases, and consequently, lift also increases.

AILERON COMPONENTS

HORNS AND BALANCE

In larger and faster aircraft, control forces are heavy. During the First World War, it was discovered that extending the area of the control surface or aerodynamic surface called the aileron forward of the hinge line smoothed the forces required for control. Thus, the structure of the ailerons was extended beyond the wingtip to contain a horn forward of the hinge line with the wing, thereby decreasing the force required for the crew or the aircraft's hydraulic system to perform the maneuver.

TRIM TABS

Trim tabs are movable parts, similar to smaller ailerons, located on the trailing edge of the ailerons. In most piston-engine or turboprop aircraft, engine rotation creates a roll opposite to the direction of rotation, according to Newton's Third Law, which states that for every action, there is an equal and opposite reaction. To prevent the pilot from having to maintain continuous pressure in the same direction on the control stick, which causes fatigue, trim tabs are used to adjust the necessary pressure against any unwanted movement.

The trim tab is deflected relative to the aileron, causing the aileron itself to move in the opposite direction. Trim tabs can be of two types: adjustable or fixed. A fixed trim tab is manually controlled to achieve the desired deflection, while adjustable trim tabs are controlled from the cockpit, the aircraft's command cabin, so that different power settings or flight attitudes can be compensated for.

IMAGE GALLERY

CONTROL SURFACES

AILERONS AND ELEVATOR

SWING (LIFT)

FLAPERON (BOEING 777)

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