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# Flight Basics

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The basics of "Physics of flying" and related data

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### Flight Basics

1. 1. The Physics of Flight <ul><li>T here are four basic forces at work when an aircraft is in flight: </li></ul><ul><li>Lift </li></ul><ul><li>Thrust </li></ul><ul><li>Gravity </li></ul><ul><li>Drag </li></ul><ul><li>Of these four forces, only gravity is constant (unchanging), the remaining three forces can be altered or affected by the pilot.When an aircraft is flying level at a constant speed, all four of these forces are in balance or equilibrium. </li></ul><ul><li>  </li></ul>Lift Lift is achieved through the cross-sectional shape (airfoil design) of the wing. As the wing moves through the air, the airfoil's shape causes the air moving over the wing to travel faster than the air moving under the wing. The slower airflow beneath the wing generates more pressure, while the faster airflow above generates less. This difference in pressure results in lift . Lift will vary dynamically depending on the speed an aircraft is traveling at.
2. 2. Angle of Attack <ul><li>The angle at which the airfoil meets the airflow also greatly affects the amount of lift generated. This angle is known as the Angle of Attack (AoA). It is commonly thought that AoA is the angle of the aircraft relative to the ground - this is incorrect . The AoA is the angle of the wing relative to airflow , which can be a very different angle, depending on the attitude of the aircraft. </li></ul><ul><li>For example, if you are flying at 300 mph on a level course, your AoA is normally close to zero (actually about 5°) since your wing is pointed in the same direction as your mass is traveling. Picture an aircraft on a landing glide. The pilot maintains a nose-up attitude to help slow the aircraft, while the actual direction the aircraft is traveling is in a slope down toward the runway. </li></ul><ul><li>Thus AoA is the angle between where the wing is pointed and the glide slope the plane is on. </li></ul><ul><li>Why is AoA important? Angle of Attack is critical to all planes because the AoA greatly effects the flow of air across the wings. Since planes have different wings, planes also have different AoA limits that they must fly within. If you exceed your maximum AoA, you interrupt the flow of air over one or both wings and you induce a stall. This is NOT just at low speeds. The Focke-Wulf Fw 190 series were well known to be susceptible to high speed stalls if the AoA was exceeded. Despite flying at 300 mph, you can pull the aircraft into a turn which interrupts airflow and will quickly cause a dangerous stall. </li></ul>
3. 3. Thrust When the propeller on the aircraft engine rotates, it pulls in air from in front of the aircraft and pushes it back towards the tail. The force generated by this is thrust . Thrust gives the aircraft forward momentum, and in turn, creates lift on the lifting surfaces (mainly the wings). Generally, the greater the thrust, the greater the airspeed. Thrust is controlled by raising or lowering the revolutions-per-minute (rpm) of the engine by using the throttle. Drag As an aircraft is propelled forward by thrust, an undesirable effect is also created: resistance. When the aircraft travels through the air, its frontal area pushes against the air in front of it, and air flowing over the aircraft causes friction. This is known as drag . For any given aircraft, drag can be increased and decreased depending on the conditions. For example, a more streamlined aircraft will reduce drag, while other factors may increase drag. These include increased AoA, lowering flaps and/or landing gear, and carrying external stores, such as bombs and rockets Altitude Air density varies with altitude; at lower altitudes, it is thicker, while higher up, the air is thinner. The density of the air directly affects drag and thrust. For example, at lower altitudes the thicker air increases thrust by supplying the propeller with more mass to move. However, that mass also increases drag. The lesser amount of oxygen associated with the thinner atmosphere of higher altitudes reduces the power output of the engine, thereby reducing thrust. However one benefit of thinner atmosphere is that it creates less drag. G-Forces Gravity effects all objects within the Earth's gravitational field - G-force . When a person is standing still on the earth, they are experiencing One G (one times the force of gravity). When a pilot in an airplane changes its orientation rapidly (tight turns, loops, etc.), the aircraft will undergo additional G-forces. These may be positive or negative G-forces.
4. 4. <ul><li>Positive G-Forces </li></ul><ul><ul><li>Positive G's are generated when an aircraft pitches upwards (the nose pulls up). For example, when the aircraft turns quickly or pulls up sharply. A World War II fighter may be capable of generating 7 G's or more. The physical effect of Positive G's on a pilot is a possible blackout , usually preceded by greyout (a less severe effect).This is caused by the increased effort the heart must generate to counter the G-forces and still supply the brain with sufficient blood. When the G-forces are too great, the pilot will slowly lose vision due to this lack of blood supply. When prolonged, the blackout can cause a loss of consciousness. </li></ul></ul><ul><li>Negative G-Forces </li></ul><ul><ul><li>Negative G's are generated when an aircraft pitches downwards (the nose goes down). For example, a sharp dive or similar maneuver that unloads the aircraft of the force of gravity. Excessive Negative G's will cause a pilot to red out .This is the effect of excessive blood being pumped to the pilot's brain, causing distorted vision. Red out is usually preceded by pink out . This signals the onset of excessive negative G's. </li></ul></ul><ul><li>Compressibility </li></ul><ul><li>When an aircraft approaches the speed of sound, the airflow over the wings of the aircraft can actually exceed the speed of sound. This transonic airflow creates a shockwave and a barrier that disrupts the flow of air over the control surfaces. This causes a dramatic loss in control efficiency and is known as compression . Compression usually occurs between Mach 0.7 to 0.9. Mach 1.0 is the speed of sound. The actual speed of sound varies at different altitudes, depending on air density. </li></ul><ul><li>The practical effect of compression on an aircraft is a lack of control. The ailerons and/or elevators seem to lock up, and moving the joystick has little effect on the aircraft. If you experience compression in a dive, you may not be able to recover. </li></ul><ul><li>For a World War II aircraft to attain these speeds, a high-speed dive would be required. To counter compression, speed must be reduced. Increasing drag and decreasing thrust will slow the plane. Once the aircraft slows, control will be regained. </li></ul><ul><li>Note that some aircraft compress at slower speeds, such as the A6M Zero and Messerschmitt Bf 109. These aircraft are lighter than most others, and sustained high speeds in level fight can begin to compress their control surfaces. </li></ul>
5. 5. Aircraft Control Surfaces <ul><li>An aircraft maintains control in flight with its control surfaces (see the illustration below with its color coded control surfaces). These are: </li></ul><ul><li>The Ailerons that control Roll </li></ul><ul><li>The Rudder that controls Yaw </li></ul><ul><li>The Elevators that control Pitch , and to a somewhat lesser degree, </li></ul><ul><li>The Flaps which provide extra Lift and Drag </li></ul><ul><li>We also mention the Landing Gear which changes the airflow around the aircraft when it is lowered. </li></ul><ul><li>Each of these primary control surfaces controls one set of primary aircraft movements (roll, pitch, or yaw). Coordinated use of these control surfaces allows you to perform complex maneuvers. </li></ul>
6. 6. Primary Control Surface Function Ailerons (Roll) The Ailerons , located on the outer part of the trailing edge of the wings, control the roll or bank of the airplane. The two ailerons (one on each wing), work in opposite directions to each other. When the left one is raised, the right one is lowered. The roll/bank of the aircraft is controlled by the side to side movement of the joystick Elevator (Pitch) The pitch , or the up and down movement of the aircraft is controlled by the Elevator . It is located on the trailing edge of the horizontal tail assembly and is controlled by the forward and backward movement of the joystick. Pulling the joystick back will move the elevator up, causing the nose of the aircraft to point up. Similarly, pushing the joystick forward will move the elevator down and pitch the nose down.
7. 7. Control Surface Function <ul><li>Rudder (Yaw) </li></ul><ul><li>On the trailing edge of the vertical stabilizer is the Rudder . This controls the yaw or the left/right sliding movements of the aircraft. On a real aircraft, this is controlled by the foot pedals. War birds supports the use of rudder pedals, but for those who don't have pedals, the rudder may be manipulated with the following keys: A will move the rudder left, causing left yaw forces, D will move the rudder right initiating right yaw force, and S will center the rudder </li></ul>Flaps The Flaps are located on the underside of the trailing edge of the wings, inboard of the ailerons. This set of control surfaces, when lowered, changes the cross sectional shape (airfoil) of the wing. By lowering the flaps, more surface area on the wing is created, thus increasing lift. This enables you to lower your stall speed and increase your Angle-of-Attack (AoA). However, the flaps also increase the drag on the aircraft, which reduces speed. Flaps are most commonly used for take off and landing.
8. 8. Un conventional Control surfaces FLAPERON: is a type of control surface that combines aspects of both flaps and ailerons. In addition to controlling the roll or bank of an aircraft like conventional ailerons, both flaperons can be lowered together to function much the same as a dedicated set of flaps would. Both ailerons could also be raised, which would give spoilerons. The pilot has separate controls for ailerons and flaps. A mixer is used to combine the separate pilot input into this single set of control surfaces called flaperons. The use of flaperons instead of separate ailerons and flaps can reduce the weight of an aircraft. The complexity is transferred from having a double set of control surfaces (flaps and ailerons) to the mixer. Certain aircraft use different kinds of surfaces, such as a V-tail/ruddervator, flaperons, or elevons, to avoid pilot confusion the aircraft will still normally be designed so that the yoke or stick controls pitch and roll in the conventional way, as will the rudder pedals for yaw. V-TAIL/RUDDERVATOR: In aircraft, a V-tail (sometimes called a Butterfly tail ) is an unconventional arrangement of the tail control surfaces that replaces the traditional fin and horizontal surfaces with two surfaces set in a V-shaped configuration when viewed from the front or rear of the aircraft. The rear of each surface is hinged, and these movable sections, sometimes called ruddervators, combine the tasks of the elevators and rudder. Advantages: With fewer surfaces than a conventional three-aerofoil tail or a T-tail, the V-tail is lighter, has less wetted surface area, and thus produces less drag (disputed). In modern day light jet general aviation aircraft such as unmanned aerial drone Global Hawk .the power plant is often placed outside the aircraft to protect the passengers and make certification easier. In such cases V-tails are used to avoid placing the vertical stabilizer in the exhaust of the engine Disadvantages: Combining the pitch and yaw controls is difficult and requires a more complex control system. The V-tail arrangement also places greater stress on the rear fuselage when pitching and yawing ELEVONS: On an aeroplane, elevons are a single control surface which combines the function of the elevators and ailerons in one. They are usually seen on delta-wing aircraft
9. 9. In addition to the primary flight controls for roll, pitch, and yaw, there are often secondary controls available to give the pilot finer control over flight or to ease the workload. The most commonly-available control is a wheel or other device to control. A few of the most common Secondary control Surfaces are as follows <ul><li>SLATS: Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a product of angle of attack and speed, so by deploying slats an aircraft can fly more slowly or take off and land in a shorter distance. They are usually used while landing or performing maneuvers which take the aircraft close to the stall, but are usually retracted in normal flight to minimize drag. </li></ul>Secondary control Surfaces SPOILER : (sometimes called a lift dumper ) is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag while making little change to lift, while spoilers greatly reduce lift while making only a moderate increase in drag. Spoilers are sometimes used when descending from cruise altitudes to assist the aircraft in descending to lower altitudes without picking up speed. the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding. Reverse thrust is also often further used to help slow the aircraft on landing. AIR BRAKES: In aeronautics, air brakes are a type of flight control used on an aircraft to reduce speed during landing. Air brakes differ from spoilers in that air brakes are designed to increase drag while making little change to lift, whereas spoilers greatly reduce the lift-to-drag ratio and a higher angle of attack required to maintain lift, resulting in a higher stall speed.
10. 10. Secondary control Surfaces Elevator trim: The most commonly-available control is a wheel or other device to control elevator trim, so that the pilot does not have to maintain constant backward or forward pressure to hold a specific pitch attitude (other types of trim, for rudder and ailerons, are common on larger aircraft but may also appear on smaller ones) Trim tabs are small surfaces connected to the trailing edge of a larger control surface on aircraft. The angle of the tab relative to the larger surface can be adjusted to null out hydro- or aero-dynamic forces and stabilize the boat or aircraft in a particular desired attitude without the need for the pilot to constantly apply a control force. Many airplanes also have rudder and/or aileron trim systems. When a trim tab is employed, it is moved into the slipstream opposite to the control surface's desired deflection.
11. 11. Major Systems/Parts of Aircraft Fuselage : The fuselage is that portion of the aircraft that usually contains the crew and payload, either passengers, cargo, or weapons. Most fuselages are long, cylindrical tubes or sometimes rectangular box shapes. All of the other major components of the aircraft are attached to the fuselage. Empennage is another term sometimes used to refer to the aft portion of the fuselage plus the horizontal and vertical tails. Landing Gear : The Under Carriage/ landing gear is used during takeoff, landing, and to taxi on the ground. Most planes today use what is called a tricycle landing gear arrangement. This system has two large main gear units located near the middle of the plane and a single smaller nose gear unit near the nose of the aircraft. They are either retractable or fixed .
12. 12. The wing is the most important part of an aircraft since it produces the lift that allows a plane to fly. The wing is made up of two halves, left and right, when viewed from behind. These halves are connected to each other by means of the fuselage. A wing produces lift because of its special shape, a shape called an airfoil. If we were to cut through a wing and look at its cross-section, as illustrated below, we would see that a traditional airfoil has a rounded leading edge and a sharp trailing edge. Top View The top view shows a simple wing geometry, like that found on a light general aviation aircraft. The front of the wing (at the bottom) is called the leading edge ; the back of the wing (at the top) is called the trailing edge . The distance from the leading edge to the trailing edge is called the chord , denoted by the symbol c . The ends of the wing are called the wing tips , and the distance from one wing tip to the other is called the span , given the symbol s . The shape of the wing, when viewed from above looking down onto the wing, is called a plan form . In this figure, the plan form is a rectangle. For a rectangular wing, the chord length at every location along the span is the same. For most other plan form , the chord length varies along the span. The wing area, A, is the projected area of the plan form and is bounded by the leading and trailing edges and the wing tips. Note: The wing area is NOT the total surface area of the wing. The total surface area includes both upper and lower surfaces. The wing area is a projected area and is almost half of the total surface area. Aspect ratio is a measure of how long and slender a wing is from tip to tip. The Aspect Ratio of a wing is defined to be the square of the span divided by the wing area and is given the symbol AR . For a rectangular wing, this reduces to the ratio of the span to the chord length as shown at the upper right of the figure. AR = s^2 / A = s^2 / (s * c) = s / c High aspect ratio wings have long spans (like high performance gliders), while low aspect ratio wings have either short spans (like the F-16 fighter) or thick chords (like the Space Shuttle). There is a component of the drag of an aircraft called induced drag which depends inversely on the aspect ratio. A higher aspect ratio wing has a lower drag and a slightly higher lift than a lower aspect ratio wing. Because the glide angle of a glider depends on the ratio of the lift to the drag, a glider is usually designed with a very high aspect ratio. The Space Shuttle has a low aspect ratio because of high speed effects, and therefore is a very poor glider. The F-14 and F-111 have the best of both worlds. They can change the aspect ratio in flight by pivoting the wings--large span for low speed, small span for high speed. wing Continue
13. 13. Engine : The other key component that makes an airplane go is its engine, or engines. Aircraft use several different kinds of engines, but they can all be classified in two major categories. Early aircraft from the Wright Flyer until World War II used propeller-driven piston engines, and these are still common today on light general aviation planes. But most modern aircraft now use some form of a jet engine. Many aircraft house the engine(s) within the fuselage itself. Most larger planes, however, have their engines mounted in separate pods hanging below the wing or sometimes attached to the fuselage. These pods are called nacelles . PROPULSION The key to making a jet engine work is the compression of the incoming air. If uncompressed, the air-fuel mixture won't burn and the engine can't generate any thrust. Most members of the jet family employ a section of compressors, consisting of rotating blades, that slow the incoming air to create a high pressure. This compressed air is then forced into a combustion section where it is mixed with fuel and burned. As the high-pressure gases are exhausted, they are passed through a turbine section consisting of more rotating blades. In this region, the exhausting gases turn the turbine blades which are connected by a shaft to the compressor blades at the front of the engine. Thus, the exhaust turns the turbines which turn the compressors to bring in more air and keep the engine going. The combustion gases then continue to expand out through the nozzle creating a forward thrust. The above explanation describes a simple turbojet, as illustrated Here Diagram of an axial-flow turbojet The term &quot;jet engine&quot; is often used as a generic name for a variety of engines, including the turbojet, turbofan, turboprop, and ramjet. These engines all operate by the same basic principles, but each has its own distinct advantages and disadvantages. All jet engines operate by forcing incoming air into a tube where the air is compressed, mixed with fuel, burned, and exhausted at high speed to generate thrust.
14. 14. The turbojet (and the turbofan) can also be fitted with an afterburner . An afterburner is simply a long tube placed in between the turbine and the nozzle in which additional fuel is added and burned to provide a significant boost in thrust. However, afterburners greatly increase fuel consumption, so aircraft can only use them for brief periods. Turbofan : A further variation on the turbojet is the turbofan. Although most components remain the same, the turbofan introduces a fan section in front of the compressors. The fan, another rotating series of blades, is also driven by the turbine, but its primary purpose is to force a large volume of air through outer ducts that go around the engine core. Although this &quot;bypassed&quot; air flow travels at much lower speeds, the large mass of air that is accelerated by the fan produces a significant thrust (in addition to that created by the turbojet core) without burning any additional fuel. Thus, the turbofan is much more fuel efficient than the turbojet. In addition, the low-speed air helps to cushion the noise of the jet core making the engine much quieter. Turbofans are typically broken into one of two categories--low-bypass ratio and high-bypass ratio--as illustrated. The bypass ratio refers to the ratio of incoming air that passes through the fan ducts compared to the incoming air passing through the jet core. In a low-bypass turbofan, only a small amount of air passes through the fan ducts and the fan is of very small diameter. The fan in a high-bypass turbofan is much larger to force a large volume of air through the ducts. The low-bypass turbofan is more compact, but the high-bypass turbofan can produce much greater thrust, is more fuel efficient, and is much quieter. Turboprop : A concept similar to the turbofan is the turboprop. However, instead of the turbine driving a ducted fan, it drives a completely external propeller. Turboprops are commonly used on commuter aircraft and long-range planes that require great endurance. The turboprop is attractive in these applications because of its high fuel efficiency, even greater than the turbofan. However, the noise and vibration produced by the propeller is a significant drawback, and the turboprop is limited to subsonic flight only. In a typical turboprop, the jet core produces about 15% of the thrust while the propeller generates the remaining 85%.
15. 15. Ramjet : Another noteworthy variation on the turbojet is the ramjet. The idea behind this type of engine is to remove all the rotary components of the engine (i.e. fans, compressors, and turbines) and allow the motion of the engine itself to compress incoming air for combustion. However, the price of this simplicity is that the ramjet can only produce thrust when it is already in motion. Instead of using a compressor to draw in air and compress it for combustion, the ramjet relies on the motion of the aircraft to ram air into the engine at high enough speed that it is already sufficiently compressed for combustion to occur. Since ramjets typically cannot function until reaching about 300 mph (485 km/h) at sea level, they have been rarely used on manned aircraft. However, the ramjet is more fuel efficient than turbojets or turbofans starting at about Mach 3 making them very attractive for use on missiles. Such missiles are typically launched using rocket motors that accelerate the vehicle to high-subsonic or low-supersonic speeds where the ramjet is engaged. CONCLUSION : ( Interactive) Classification of Aircraft , Discuss What are the control surfaces used for Take off and Landing of an Aircraft ? Sequence of operation ? Discuss