By Nate Theriault,Tripp Middle School

Flaps: The flaps are found on the trailing edge of the wing. They are usually the surface inboard in relation to the ailerons. Unlike the ailerons, they move collectively rather than inversely. When extended, their trailing edge is moved downward in relation to the fulcrum near their leading edge. Depending on the aircraft, they may be manipulated manually or with electric actuators/hydraulics. Though flaps are very common and most modem aircraft have them, they are not essential. When the flaps are deployed in low increments, they mostly increase lift, but also increase drag slightly. The effects of flaps on lift listed above are long term effects if the airspeed is maintained. At a given engine power setting, when the flaps are extended they increase lift for a short period of time, then the drag they produce will decrease the airspeed enough to make the long term effect on lift a decrease. The flaps also decrease the stall speed, when they are deployed in high increments, they mostly increase drag, but also increase lift. The most common types of controls for the flaps are (a) a small lab, often part of or beside the throttle quadrant (the throttle quadrant is also called “the pedestal)” on the side farthest from the pilot, that can be moved down to extend the flaps and up to refract the flaps, usually via electric actuators/hydraulic; (b) a handle on the floor of the cabin in approximately the same location as an emergency/parking brake on some cars (between the two front seats) that is pulled up to extend the flaps and let down to retract them. The handle/tab that controls the flaps is often made to fall into notches at the recommended increments. There are different types of flaps.

• Plain flaps are the simplest of the types of flaps that I will list. They are surfaces that make up the trailing edges of the wings. To extend, they angle downward from the axis near their leading edges.

• Split flaps are not used much on modem aircraft. They are somewhat similar to plain flaps with one difference. Part of the wing in the same apparent location (if the point of view is from above the wing) as a fixed part of the trailing edge is movable. This means that when the flaps deploy, the trailing edge of the wing will split and the lower of the parts will extend downward in the same way as a plain flap.

• Slotted flaps are an aerodynamic improvement to plain flaps. When slotted flaps are deployed, not only are the trailing edges of the surfaces extended downward, but a gap is formed between the leading edge of the flaps and the wings, If you recall from the previous document, the attack angle of the wing causes the air to pull apart on the upper surface and compress together on the lower surface. This is basically just another way of saying that the air near the upper surface is low pressure and the air near the lower surface is high pressure. When a slot forms between the wings and the flaps, air from the high pressure area under the wings is pushed into the low pressure area above the wings. This forms jets of high speed air moving over the flaps. According to the Bernoulli Equatsion, the total energy that a fluid has must remain the same. This means that as the kinetic energy (speed) of the fluid increases, the potential energy (pressure) of the fluid roust decrease, Because this high speed jet of air near the trailing edge is also lower pressure, the atmosphere pushes the air over the surface of the wing in whole faster. This creates better deflection over the wing and a greater increase of lift than plain flaps produce.

• Fowler flaps are meant to increase the wing area when extended. Their location in relation to the wing when retracted is similar to that of retracted split flaps. Rather than extending straight down. however, they move back so that rather than the trailing edge of the wing and the trailing edge of the flap being in the same general location, the trailing edge of the wing and the leading edge of the flap are in the same general location. When extended, fowler flaps may also form a slot between wing and flap for the same benefits mentioned above. Some aircraft even double or even triple-slotted fowler flaps (this can be found on some large jet aircraft.)

Spoilers: The spoilers usually deploy from the upper surface of the wing. Their purpose when deployed is to destroy the aerodynamics on the upper surface of the wing. essentially creating an artificial stall and creating a significant reduction in lift. These are not found on most small general aviation aircraft. They are often found on commercial/corporate jet aircraft. The spoilers have many uses. By causing a reduction in lift, the pilot can raise the nose slightly without even temporarily gaining altitude. By raising the nose, the pilot presents a larger surface of the wing to the oncoming airstream, increasing drag (drag is also increased significantly by simply causing an aerodynamically disruptive surface to protrude from the wing.) On many aircraft equipped with this surface, the spoilers deploy differentially to assist the ailerons when making roll adjustments. When spoilers are set up to do this, they are called “spoilerons.” This also helps counter the effects of adverse yaw, a condition when rolling into a turn in which the aircraft yaws away from the direction of turn because of the lowered aileron creating more drag. They can correct this by increasing the drag on the side of the raised aileron. The spoilers, on an aircraft where they can be manually controlled, are usually operated by a lever in the throttle quadrant to the left of the thrust levers. When the lever is pulled back. the spoilers deploy. When the lever is in the forward position, the spoilers are retracted. The spoiler controls sometimes have an “arm” position. Sensors on the landing gear detect when the tires rotate, when the landing gear is holding up weight, or both. When the spoilers are armed, they are set to deploy when these sensors signal. The purpose of this is to prevent the aircraft from bouncing on landing, to place more weight on the main landing gear to allow more effective braking, and to allow the pilot to engage the thrust reverses earlier (many aircraft are not certified to deploy/engage the thrust reverses if airborne.) Please be advised that the latter of these may have less importance than the other reasons, seems how many pilots only deploy the thrust reverses only when the nose gear is on or near the ground.

Leading Edge Slats: Slats are surfaces that can extend from the leading edges of the wings. Like spoilers, they are not found on most small general aviation aircraft. They are often found on large commercial jet aircraft and military fighters. They extend forward and angle to extend the curvature of the wing. Slats are a measure used to prevent stalls. When flying at extreme attach, angles, the air is barely able to follow the Coanda Effect and adhere to the wing. This is because it has to sharply change direction downward to do this- According to Newton’s Laws, it does not have a tendency to change velocity easily. When the curvature of the wing is extended forward and downward by the slats, the air is deflected the same amount, but undergoes a more gradual change in direction-. Another feature of slats is the fact that they also form a slot between themselves and the wing. The same effect occurs when a slot is formed between the wing and the slat as when a slot is formed between the flap and the wing and the jet of low’ pressure high-speed air allows the atmosphere to move the air over the slat faster. The slats are deployed by the same control as the flaps when the slats are controlled by the pilot. In some cases, the slats are deployed aerodynamically without the pilot’s command. This is achieved by setting up the slats so that when a certain attack angle is reached, the air will get under and extend them.

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