Aircraft Motion and Control Know aircraft motion and how it is controlled. 1. Identify the axes of rotation. 2. Identify the effects of flaps on flight. 3. Identify the effect of slats on flight. 4. Identify the effects of spoilers on flight. 5. Identify the effects of drag on flight. 6. Describe the elements of controlled flight. Lesson Objective: Know aircraft motion and how it is controlled. Samples of Behavior/Main Points 1. Identify the axes of rotation. 2. Identify the effects of flaps on flight. 3. Identify the effect of slats on flight. 4. Identify the effects of spoilers on flight. 5. Identify the effects of drag on flight. 6. Describe the elements of controlled flight.

Overview 1. The Axes of Rotation 2. Flaps 3. Slats 4. Spoilers 5. Drag Devices 6. Controlled Flight In this lesson we will discuss: 1. The Axes of Rotation 2. Flaps 3. Slats 4. Spoilers 5. Drag Devices 6. Controlled Flight

The Axes of Rotation The fuselage of the conventional airplane is the basic structure to which all the other parts are attached. The wings, which are the primary source of lift, have ailerons attached to them. The tail, or empennage, consists of the horizontal stabilizer, with attached elevators and the vertical stabilizer, with attached rudder. The Axes of Rotation The fuselage of the conventional airplane is the basic structure to which all the other parts are attached. The wings, which are the primary source of lift, have ailerons attached to them. The tail, or empennage, consists of the horizontal stabilizer, with attached elevators and the vertical stabilizer, with attached rudder.

The Axes of Rotation Longitudinal Axis Running from the tip of the nose to the tip of the tail. This axis can be thought of as a skewer which turns either right or left and causes everything attached to it to turn. Longitudinal Axis Running from the tip of the nose to the tip of the tail is the longitudinal axis of an airplane. This axis can be thought of as a skewer which turns either right or left and causes everything attached to it to turn. The wings, tail, and landing gear all move about the longitudinal axis when movement is initiated.

The Axes of Rotation Longitudinal Axis The cause of movement or roll about this axis (or roll axis) is the action of the ailerons. Ailerons are attached to the wing and to the control column in a manner that ensures one aileron will deflect downward when the other is deflected upward. The cause of movement or roll about this axis (or roll axis) is the action of the ailerons. Ailerons are attached to the wing and to the control column in a manner that ensures one aileron will deflect downward when the other is deflected upward.

The Axes of Rotation Longitudinal Axis When an aileron is not perfectly aligned with the total wing, it changes the wing’s lift characteristics. To make a wing move upward, the aileron on that wing must move downward. The pilot can cause a wing to lift very slightly, or by very positive movement on the controls, the wing can be made to rise very quickly. When an aileron is not perfectly aligned with the total wing, it changes the wing's lift characteristics. To make a wing move upward, the aileron on that wing must move downward. When this happens, the total lift being produced by the wing is increased according to the amount of aileron movement that takes place. The pilot can cause a wing to lift very slightly, or by very positive movement on the controls, the wing can be made to rise very quickly.

The Axes of Rotation Longitudinal Axis While the one wing is moving upward the other wing is moving downward due to the deflection of its aileron. The reason again is a change in the amount of the wing airfoil’s lift. The “up” aileron’s deflection is greater than that of the “down” aileron. The “up” aileron must be deflected to a greater degree in order for it to affect the airflow and change the lift characteristic of the wing. While the one wing is moving upward the other wing is moving downward due to the deflection of its aileron. The reason again is a change in the amount of the wing airfoil's lift. The "up" aileron's deflection is greater than that of the "down" aileron. The "up" aileron must be deflected to a greater degree in order for it to affect the airflow and change the lift characteristic of the wing.

The Axes of Rotation NOTE: This slide shows how the aircraft will react when the aileron’s are moved up and down.

The Axes of Rotation Lateral Axis An imaginary rod, running from one wing tip through the fuselage and exiting the other wing tip, forms an airplane’s lateral axis. Another name for the lateral axis is the pitch axis. The elevator can be deflected up or down as the pilot moves the control column backward or forward. The Axes of Rotation Lateral Axis Another imaginary rod, running from one wing tip through the fuselage and exiting the other wing tip, forms an airplane's lateral axis. The lateral axis theoretically allows the airplane to spin around and around its wings. This cannot happen because the wings would not produce enough lift. Another name for the lateral axis is the pitch axis. The airplane is actually caused to pitch its nose upward or downward about the lateral axis. The elevator can be deflected up or down as the pilot moves the control column backward or forward. Movement backward on the control column (or stick) moves the elevator upward. This changes the shape of the stabilizer airfoil so that the direction of lift on the tail surface is down. This pulls everything aft of the airplane's lateral axis down with it and causes everything forward of the lateral axis to pitch upward. This movement increases the wings' angle of attack, which in turn creates more lift, and the airplane climbs. Deflection of the elevator downward creates a high lift condition on the stabilizer-elevator airfoil and the tail is raised. This pitches the portion forward of the lateral axis downward and the airplane dives.

The Axes of Rotation NOTE: This slide shows how the aircraft will react when the elevators are moved up and down.

The Axes of Rotation Vertical Axis An imaginary rod or axis which passes through the meeting point of the longitudinal and lateral axes. It is also referred to as the “yaw” axis. The airplane turns about this axis in a side-to-side direction. The airplane’s rudder is responsible for the movement about this axis. The Axes of Rotation Vertical Axis An imaginary rod or axis which passes through the meeting point of the longitudinal and lateral axes. It is also referred to as the "yaw" axis. The airplane turns about this axis in a side-to-side direction. The airplane's nose is made to point in a different direction when the airplane turns about this particular axis. The airplane's rudder is responsible for the movement about this axis. The cause of this movement is the change in the direction of lift generated by an airfoil. When a pilot presses on the rudder pedals, the rudder is deflected from a neutral or streamline position with the vertical stabilizer. The deflected rudder forms a curved or cambered airfoil surface, which on one side generates induced lift while on the other side dynamic lift. Rudder controls are rigged so that the rudder moves toward the direction of the rudder pedal that is pressed. This causes the airplane's nose to point toward the direction of the rudder pedal being pressed.

The Axes of Rotation NOTE: This slide shows how the aircraft will react when the rudder is moved.

Flaps The flaps are attached to the trailing edge of the wing. In cruising flight, the flaps simply continue the streamline shape of the wing’s airfoil. When flaps are lowered either partially or fully, lift and drag are increased. Flaps The flaps are attached to the trailing edge of the wing. In cruising flight, the flaps simply continue the streamline shape of the wing's airfoil. On small airplanes, the flaps can be "lowered" as much as 40o to the cord. When flaps are lowered either partially or fully, lift and drag are increased. Pilots use the flaps during certain takeoff conditions and during most landing situations.

Flaps Flaps increase the camber of the wing airfoil for the portion of the wing that it is attached. This causes the air to speed up over the wing section where the most lift is created. On the underside of the wing, dynamic lift is increased. When landing, flaps permit the steep descent that may be necessary to land on a short runway. Using flaps when taking off helps the airplane get off the ground in a shorter distance. Flaps increase the camber of the wing airfoil for the portion of the wing that it is attached. It does not affect the remainder of the wing. When the flaps are lowered air flowing over the top of the wing has to travel farther. This causes the air to speed up, particularly over the wing section where the most lift is created. On the underside of the wing, dynamic lift is increased because there is now more surface area exposed to the impact of the relative wind. On the negative side of this situation is the drag produced by the flap (or flaps). Anything that obstructs the airflow certainly increases drag. The net effect of the increased lift and drag when the flaps are lowered is without an increase in power to compensate for the additional drag, an airplane will descend much more steeply than possible without flaps, and the increased lift allows slower flight because the stall speed is decreased. When landing, flaps permit the steep descent that may be necessary to land on a short runway that has an obstruction along the landing path. The flaps also lower the stall speed. This allows a pilot to touch down at a slower groundspeed upon landing that leads to less wear and tear on all parts of the airplane. Using flaps when taking off helps the airplane get off the ground in a shorter distance. This might be desired when the runway is short or a shorter distance takeoff is necessary. It also helps when taking off from a soft or muddy field as it gets the airplane's weight off the landing gear as quickly as possible to reduce "mud drag" on its wheels.

Flaps In addition to the simple hinge flap there are much more complicated ones. When an extended flap leaves a space between the wing and flap, it is known as a slotted flap. This happens because the high-speed relative wind going through the slot adds energy to the upper wing airflow. In addition to the simple hinge flap there are much more complicated ones. Jet airliners use flaps that actually extend below the wings' trailing edges and some of the short-takeoff-and-landing types of aircraft have even more involved flap systems. When an extended flap leaves a space between the wing and flap, it is known as a slotted flap. The slot between the wing and the flap permits the relative wind to flow through the slot and thereby increase the wing's induced lift. This happens because the high-speed relative wind going through the slot adds energy to the upper wing airflow.

Flaps and Slats NOTE: This slide shows how the aircraft will react when the flaps and slats are moved.

Slats Slats are protrusions from the leading edge of a wing. The secret of the slat is the slot it produces. In normal flight the relative wind struck the leading edge of the slat, passed over the slot, and continued around the airfoil. Modern airplanes have retractable slats. Slats Slats are protrusions from the leading edge of a wing. They also add to the induced lift of a wing and the more sophisticated flap systems will most likely have slats. The secret of the slat is the slot it produces. At high angles of attack, the relative wind passing through the slot is speeded up and this additional velocity adds energy. The slat causes energy to be added at the front while the flap causes energy to be added at the back and the combined actions of these devices result in a significant increase in lift. The earliest forms of slats were fixed in the "open" position. In normal flight the relative wind struck the leading edge of the slat, passes over the slot, and continued around the airfoil. This arrangement would only work at those times the airplane was in a high angle of attack attitude. Modern airplanes have retractable slats. The slats, on some models, automatically extend at certain airspeed, or the pilot can manually control them.

Spoilers Spoilers work to destroy lift. Spoilers are found on various aircraft from the jet airliner to the sailplane. On the jet airliners, spoilers are hinged so that their aft portion is tilted upward into the smooth airflow. Spoilers Spoilers work to destroy lift. This is the origin of the name spoiler; a spoiler spoils lift. Spoilers are found on various aircraft from the jet airliner to the sailplane. It is found somewhere along the top of the wing and it will be located along a line on the airfoil where its deployment will be most effective. They fit into, or flush with; the upper cambered surface of the airfoil, and located along a line from wing root to wing tip (the exact placement will depend on the airfoil design). The size will vary according to how much lift is to be "spoiled." On the jet airliners, spoilers are hinged so that their aft portion is tilted upward into the smooth airflow. Many of the sailplane types are designed to thrust straight up from the wing's surface. Both arrangements of spoilers destroy flow of air for a portion of the wing and thereby reduce a certain amount of induced lift. An airplane, such as an airliner, can thus fly at a safe airspeed while reducing some of the induced lift. The result is a steep descent for landing.

Spoilers A favorable feature about spoilers is that they can be deployed or retracted quickly. The use of flaps lowers the stalling speed. A favorable feature about spoilers is that they can be deployed or retracted quickly. If an airplane has them deployed and is descending toward a runway but suddenly has to "go around,” the spoilers can be retracted and lift is restored. The use of flaps lowers the stalling speed, so an airplane may fly again if it bounces upon landing. When it is equipped with spoilers, the pilot can keep this from happening.

Spoilers NOTE: This slide shows how the aircraft will react when the spoiler’s are moved up and down.

Drag Devices These devices may be located at the trailing edges of the wings, or they may protrude from the aircraft’s fuselage upon activation by the pilot. These devices may be called dive brakes, air brakes, dive flaps, or drag parachutes. Their purpose is to produce a significant amount of drag without affecting the airfoil’s lift. Drag Devices Some airplanes are equipped with special devices that produce drag only. These devices may be located at the trailing edges of the wings, or they may protrude from the aircraft's fuselage upon activation by the pilot. These devices may be called dive brakes, air brakes, dive flaps, or drag parachutes. Their purpose is to produce a significant amount of drag without affecting the airfoil's lift. They allow very steep descents, which can be stopped almost instantaneously by retracting the devices.

Controlled Flight Takeoff and Climb After taxiing to the runway, a pre-takeoff checklist is accomplished. As take off airspeed is approached, gentle back pressure on the control wheel raises the elevator which causes the nose to pitch upward. Once the nosewheel is off the runway, right rudder is applied to counteract the left-turning tendency, which is present under low airspeed, high-power flight conditions. Controlled Flight Takeoff and Climb After taxiing to the runway, a pre-takeoff checklist is accomplished. This check is to ensure that all systems are working normally. When this is completed the airplane is taxied to the center of the runway and aligned with it. The throttle is opened fully to start the takeoff run. The control wheel, or stick, is usually held in the neutral position, but the rudder pedals are used to keep the airplane on the runway's centerline. As takeoff airspeed is approached, gentle back pressure on the control wheel raises the elevator which causes the nose to pitch upward. This lifts the nosewheel off the runway. Using the control wheel to keep the airplane in this attitude allows the airplane to fly itself off the runway. Once the nosewheel is off the runway, right rudder is applied to counteract the left-turning tendency, which is present under low airspeed, high-power flight conditions. As the airplane lifts clear of the runway, the pilot varies pressure on the control wheel.

Controlled Flight Takeoff and Climb As airspeed increases to the best rate-of-climb airspeed, back pressure on the control wheel is adjusted to maintain that airspeed until the first desired altitude is reached. Upon reaching cruising altitude, the airplane’s pitch attitude is reduced and the airplane accelerates to cruising speed. Pressure is relaxed slightly to gain airspeed while still in ground effect (additional lift provided by compression of air between the airplane's wings and the ground). As airspeed increases to the best rate-of-climb airspeed, back pressure on the control wheel is adjusted to maintain that airspeed until the first desired altitude is reached. Upon reaching cruising altitude, the airplane's pitch attitude is reduced and the airplane accelerates to cruising speed. The power is reduced and adjusted to maintain the selected cruising speed. Almost simultaneously the pilot adjusts the elevator and, possibly, the rudder to keep the airplane at the desired altitude and heading.

Controlled Flight Basic Flight Maneuvers Basic flight maneuvers are started from “straight and level” flight. Power setting is maintained at 55 to 75 percent of available power. A series of slight adjustments or corrections in pitch, yaw, and roll are made to keep the wings level and heading and altitude constant. Basic flight maneuvers include climbs, descents, turns, and a combination of these. Controlled Flight Basic Flight Maneuvers Basic flight maneuvers are started from "straight and level" flight: a condition where the wings are kept level and the altitude and heading constant. Power setting is maintained at 55 to 75 percent of available power, using a higher setting within this range if speed is desired and a lower setting if fuel economy is desired. A series of slight adjustments or corrections in pitch, yaw, and roll are made to keep the wings level and heading and altitude constant. Basic flight maneuvers include climbs, descents, turns, and a combination of these.

Controlled Flight Climbs are a combination of power and “up elevator.” Best angle-of-climb. The climb angle is steep and all available power is used. Used when the pilot must rise quickly after take-off to avoid objects at or near the end of a runway. Other than best-rate and best-angle climbs, most climbs are very gentle at low angles of attack. Climbs are a combination of power and "up elevator.” The amount of power used determines whether the climb is steep or shallow. Best angle-of-climb The climb angle is steep and all available power is used. This is a short-term climb that can overheat the engine if sustained because there is too little cooling air flowing around the engine's cylinders. Used when the pilot must rise quickly after take-off to avoid objects at or near the end of a runway. Other than best-rate and best-angle climbs, most climbs are very gentle at low angles of attack. A great deal of distance is covered if high power and a relatively low angle of attack are used. The airplane will get to the desired altitude, but not so quickly as with a steep climb.

Controlled Flight Descent A combination of reducing power and adjusting to maintain the desired airspeed. Airspeed is maintained by varying pressure on the control wheel. This varies the angle of attack and airspeed. The rate of descent, measured in feet per minute, is controlled by applying or reducing power as needed. Controlled Flight Descent A combination of reducing power and adjusting to maintain the desired airspeed. Airspeed is maintained by varying pressure on the control wheel. This varies the angle of attack and airspeed. The rate of descent, measured in feet per minute, is controlled by applying or reducing power as needed.

Controlled Flight Turns Turns are either gentle, medium, or steep, and they may be made when climbing, descending, or while not gaining or losing altitude. Causing the airplane to turn requires smooth coordination of aileron, rudder and elevator controls, pressure on the control wheel and rudder pedal should be applied simultaneously. Controlled Flight Turns Turns are either gentle, medium, or steep, and they may be made when climbing, descending, or while not gaining or losing altitude. Causing the airplane to turn requires smooth coordination of aileron, rudder and elevator controls, pressure on the control wheel and rudder pedal should be applied simultaneously.

Controlled Flight Turns The moment a wing begins to rise in a banked turn, it experiences more drag because of the lowered aileron and its higher angle of attack. Once the coordinated turn is established, ailerons and rudder usually are neutralized. Controlled Flight The moment a wing begins to rise in a banked turn, it experiences more drag because of the lowered aileron and its higher angle of attack. A simultaneous application of rudder compensates for this additional drag by making the airplane also rotate about its vertical axis. Once the coordinated turn is established, ailerons and rudder usually are neutralized. If the turn is of medium bank, the airplane will hold the amount of bank established, but it will not hold its altitude. The reason for the descent is that, in a bank, the direction of lift is not exactly opposite to the direction of gravity (weight). The pilot increases lift by holding back pressure on the control wheel, which raises the elevator and increases the wing's angle of attack.

Controlled Flight Turns In-flight turns are measured as the number of degrees of bank involved. At 60o of bank the airplane experiences twice the normal force of gravity (2Gs). At 80o of bank a force of almost six times that of normal gravity is felt. The average light airplane has a design limit of approximately 3.8Gs. In steep turns, those of 35o or more of bank, considerable back pressure on the control wheel is required to produce the needed amount of lift. In-flight turns are measured as the number of degrees of bank involved. Measured from straight and level, the wings can be banked up to 90o in turn. Most small aircraft pilots do not exceed 60o of bank. At 60o of bank the airplane experiences twice the normal force of gravity (2Gs). The force continues to increase as the bank is increased. At 80o of bank a force of almost six times that of normal gravity is felt. The average light airplane has a design limit of approximately 3.8Gs. In steep turns, those of 35o or more of bank, considerable back pressure on the control wheel is required to produce the needed amount of lift. Additional power is also necessary because more drag is produced by the wing's high angle of attack. Steep turns produce a tendency for the airplane to roll toward the direction of turn, so opposite aileron pressure is necessary to counteract this tendency.

Controlled Flight Landing A good landing begins with a good approach. Flaps are used to permit a lower approach speed and a steeper angle of descent. The airspeed and rate of descent are stabilized and the airplane is aligned with the runway centerline as the final approach is begun. Controlled Flight Landing A good landing begins with a good approach. Before the final approach is begun, the pilot performs a "Landing checklist" to ensure that critical items such as fuel flow, landing gear down, carburetor heat on, and others are not forgotten. Flaps are used to permit a lower approach speed and a steeper angle of descent. This gives the pilot a better view of the landing area. The airspeed and rate of descent are stabilized and the airplane is aligned with the runway centerline as the final approach is begun.

Controlled Flight Landing When the airplane descends across the approach end (the threshold) of the runway, power is reduced. Continuing back pressure on the control wheel, as the airplane enters ground effects and gets closer and closer to the runway, further slows its forward speed and rate of descent. When the airplane descends across the approach end (the threshold) of the runway, power is reduced. At this time, the pilot slows the rate of descent and airspeed by applying progressively more back pressure to the control wheel. The airplane is kept aligned with the center of the runway mainly by use of the rudder. Continuing back pressure on the control wheel, as the airplane enters ground effects and gets closer and closer to the runway, further slows its forward speed and rate of descent.

Controlled Flight Landing The pilot’s objective is to keep the airplane flying safely just a few inches above the runway until it loses flying speed. With the wheels of the main landing gear firmly on the runway, the pilot applies more back pressure on the control wheel. The pilot's objective is to keep the airplane flying safely just a few inches above the runway until it loses flying speed. In this condition, the airplane's main wheels contact the runway. With the wheels of the main landing gear firmly on the runway, the pilot applies more back pressure on the control wheel. This holds the airplane in a nose-high attitude, which keeps the nosewheel from touching the runway until forward speed is much slower. The purpose is to avoid overstressing and damaging the nose gear when the nosewheel touches down on the runway. The landing is a transition from flying to taxiing. It is the most demanding of all the maneuvers performed while flying.

Controlled Flight Stalls At the critical angle of attack, air going over a wing will separate from the wing or “burble,” causing the wing to lose its lift (stall). This speed will vary with changes in wing configuration (flap position). Most airplanes give adequate warning as the stalling speed is approached. Controlled Flight Stalls At the critical angle of attack, air going over a wing will separate from the wing or "burble," causing the wing to lose its lift (stall). The airspeed at which the wing will not support the airplane without exceeding this critical angle of attack is called the stalling speed. This speed will vary with changes in wing configuration (flap position). Excessive load factors caused by sudden maneuvers, steep banks and gust loads can also cause aircraft to exceed the critical angle of attack and thus stall at any airspeed and any attitude. Most airplanes give adequate warning as the stalling speed is approached. Noticeably less effective controls and buffeting (feel), obviously high-pitch angle for the power setting (sight), and a change in noise level (sound) are the senses that pilots use to recognize the approaching stall.

Controlled Flight Stalls Newer aircraft have stall warning horns and/or lights that activate 5 to 10 knots above the stalling speed. When the wing stalls, the nose of the airplane starts dropping, even though the control wheel may be in the full back position. Newer aircraft have stall warning horns and/or lights that activate 5 to 10 knots above the stalling speed. When the wing stalls, the nose of the airplane starts dropping, even though the control wheel may be in the full back position. The pilot may ensure prompt stall recovery with minimum altitude loss by relaxing pressure on the control wheel, adding power, and recovering in a gentle dive. Rudder and ailerons are used to help keep the wings as near level as possible.

Summary 1. The Axes of Rotation 2. Flaps 3. Slats 4. Spoilers 5. Drag Devices 6. Controlled Flight In this lesson we discussed: 1. The Axes of Rotation 2. Flaps 3. Slats 4. Spoilers 5. Drag Devices 6. Controlled Flight