Elements of Aeronautics

Department of Aeronautical Engineering Subject Name : Elements of Aeronautics Subject Code : 07A306 Semester : Third semester Prepared By : U. Selvakumar, Lecturer, Dept. of Aero, BIT, Sathy Unit – I Historical Evolution Refer the “Introduction to flight” by J.D. Anderson. Unit – II Aircraft Configurations Components of an Airplane and their Functions An airplane contains the following important component sections, 1. Fuselage 2. Wings 3. Empennage 4. Landing gear 5. Propulsion system The following figures shows the isometric and extended view of basic components of an airplane. 1. Fuselage: Fuselage is the main body of an airplane which contains cabin /cockpit which provides space for crew members and flight controls for aircraft. Fuselage also provides space for passengers and payloads. It gives attachment points for some other aircraft components like wing. There are three kinds of fuselage structure. They are ,  Truss structure  Monocoque structure  Semi – monocoque structure Truss: Truss – A fuselage design made up of supporting members longerons, diagonal members and vertical members that resist deformation by applied loads. Monocoque structure: Monocoque – A shell-like fuselage design in which most of the imposed stresses are taken by the outside stressed skin. Here bulkheads and formers are used to give the shape to the fuselage. Stringers are not used. Semi – monocoque structure: Semi – monocoque structure – A fuselage design which contains a substructure of bulkheads and/or formers, along with stringers, that support flight loads and stresses imposed on fuselage. 2. Wings: The wings are lifting devices in which series of airfoils attached. It is placed in each side of the fuselage and are the main lifting surfaces that support the airplane in flight. The cross section of the wing is called as airfoil. An airfoil is a shape designed to produce lift. Besides the wing, propellers and the tail surfaces are also airfoils. An airfoil has a leading edge and a trailing edge. A chord and a camber also characterize an airfoil. The chord is an imaginary straight line connecting the leading edge with the trailing edge. The chord is used for determining the geometric angle of attack and for determining the area of a wing. The mean camber line is the line an equal distance from the upper and lower surfaces of the wing. The camber is the curvature of the mean camber line. A wing that has an airfoil with a great deal of curvature in its mean camber line is said to be a highly cambered wing. A symmetric airfoil has no camber .An airfoil with lift also has an angle of attack. The relative wind is the direction of the wind at some distance from the wing. It is parallel to and opposite to the direction of motion of the wing. The velocity of the relative wind is equal to the speed of the wing. The geometric angle of attack is defined as the angle between the mean chord of the airfoil and the direction of the relative wind. There are numerous wing designs, sizes, and shapes used by the various manufacturers. Each fulfills a certain need with respect to the expected performance for the particular airplane. Wings may be attached at the top, middle, or lower portion of the fuselage. These designs are referred to as high-, mid-, and low-wing, respectively. The number of wings can also vary. Airplanes with a single set of wings are referred to as monoplanes, while those with two sets are called biplanes. Many high-wing airplanes have external braces, or wing struts, which transmit the flight and landing loads through the struts to the main fuselage structure. Since the wing struts are usually attached approximately halfway out on the wing, this type of wing structure is called semi-cantilever. A few high-wing and most low-wing airplanes have a full cantilever wing designed to carry the loads without external struts. The principal structural parts of the wing are spars, ribs, and stringers. trusses, I-beams, tubing, or other devices, including the skin. The wing ribs determine the shape and thickness of the wing (airfoil). Wing flaps are the trailing edge control devices attached to the trailing edge of the inboard wing. They may be fixed or retractable. When deflected downward they will increase lift by increasing the camber during takeoffs and landings. Slats are the leading edge devices which are used to delay flow seperation. Slot is the space between the slat and leading edge. It is used to increases the drag. In most modern airplanes, the fuel tanks either are an integral part of the wing’s structure, Ailerons extend from about the midpoint of each wing outward toward the tip and move in opposite directions to create aerodynamic forces that cause the airplane to roll. Flaps extend outward from the fuselage to near the midpoint of each wing. 3. Empennage: The correct name for the tail section of an airplane is empennage. The empennage includes the entire tail group, consisting of fixed surfaces such as the vertical stabilizer and the horizontal stabilizer. The movable surfaces include the rudder, the elevator, and one or more trim tabs. A second type of empennage design does not require an elevator. Instead, it incorporates a one-piece horizontal stabilizer that pivots from a central hinge point. This type of design is called a stabilator, and is moved using the control wheel, just as you would the elevator. For example, when you pull back on the control wheel, the stabilator pivots so the trailing edge moves up. This increases the aerodynamic tail load and causes the nose of the airplane to move up. Stabilators have an antiservo tab extending across their trailing edge. The antiservo tab moves in the same direction as the trailing edge of the stabilator. The antiservo tab also functions as a trim tab to relieve control pressures and helps maintain the stabilator in the desired position. The rudder is attached to the back of the vertical stabilizer. During flight, it is used to move the airplane’s nose left and right. The rudder is used in combination with the ailerons for turns during flight. The elevator, which is attached to the back of the horizontal stabilizer, is used to move the nose of the airplane up and down during flight. Trim tabs are small, movable portions of the trailing edge of the control surface. These movable trim tabs, which are controlled from the cockpit, reduce control pressures. Trim tabs may be installed on the ailerons, the rudder, and/or the elevator. 4. Landing gear: The landing gear is the principle support of the airplane when parked, taxiing, taking off, or when landing. The most common type of landing gear consists of wheels, but airplanes can also be equipped with floats for water operations, or skis for landing on snow. The landing gear consists of three wheels—two main wheels and a third wheel positioned either at the front or rear of the airplane. Landing gear employing a rear mounted wheel is called conventional landing gear. Airplanes with conventional landing gear are sometimes referred to as tail wheel airplanes. When the third wheel is located on the nose, it is called a nose wheel, and the design is referred to as a tricycle gear. A steerable nose wheel or tail wheel permits the airplane to be controlled throughout all operations while on the ground. 5. Propulsion system: The powerplant usually includes both the engine and the propeller or simply the engine (Turbojet, ramjet and scramjet). The primary function of the engine is to provide the power to turn the propeller. It also generates electrical power, provides a vacuum source for some flight instruments, and in most single-engine airplanes, provides a source of heat for the pilot and passengers. The engine is covered by a cowling, or in the case of some airplanes, surrounded by a nacelle. The purpose of the cowling or nacelle is to streamline the flow of air around the engine and to help cool the engine by ducting air around the cylinders. The propeller, mounted on the front of the engine, translates the rotating force of the engine into a forward - acting force called thrust that helps move the airplane through the air. Conventional Flight Control Aircraft flight control systems are classified as primary and secondary. The primary control systems consist of those that are required to safely control an airplane during flight. These include the ailerons, elevator (or stabilator), and rudder. Secondary control systems improve the performance characteristics of the airplane, or relieve the pilot of excessive control forces. Examples of secondary control systems are wing flaps and trim systems. The axis system has been given below. An airplane moves in three dimensions called roll, pitch, and yaw. Roll is rotation about the longitudinal axis that goes down the center of the fuselage. The ailerons control rotation about the roll axis. Pitch is rotation about the lateral axis of rotation, which is an axis parallel to the long dimension of the wings. The elevators control the pitch of the airplane. By controlling the pitch of the airplane, the elevators also control the angle of attack of the wing. To increase the angle of attack, the entire airplane is rotated up. As we will see, this control or the angle of attack is key in the adjustment of the lift of the wings. Finally, yaw, which is controlled by the rudder, is rotation about the vertical axis, which is a line that goes vertically through the center of the wing. It is important to note that all three axes go through the center of gravity (often abbreviated c.g.) of the airplane. The center of gravity is the balance point of the airplane. Or, equivalently, all of the weight of the airplane can be considered to be at that one point. Primary Control Surfaces: Ailerons: Ailerons control roll about the longitudinal axis. The ailerons are attached to the outboard trailing edge of each wing and move in the opposite direction from each other. Ailerons are connected by cables, bellcranks, pulleys or push-pull tubes to each other and to the control wheel. Moving the control wheel to the right causes the right aileron to deflect upward and the left aileron to deflect downward. The upward deflection of the right aileron decreases the camber resulting in decreased lift on the right wing. The corresponding downward deflection of the left aileron increases the camber resulting in increased lift on the left wing. Thus, the increased lift on the left wing and the decreased lift on the right wing causes the airplane to roll to the right. Elevator: The elevator controls pitch about the lateral axis. Like the ailerons on small airplanes, the elevator is connected to the control column in the cockpit by a series of mechanical linkages. Aft movement of the control column deflects the trailing edge of the elevator surface up. This is usually referred to as up elevator. Moving the control column forward has the opposite effect. In this case, elevator camber increases, creating more lift (less tail-down force) on the horizontal stabilizer/elevator. This moves the tail upward and pitches the nose down. Rudder: The Rudder controls movement of the airplane about its vertical axis. This motion is called yaw. Like the other primary control surfaces, the rudder is a movable surface hinged to a fixed surface, in this case, to the vertical stabilizer, or fin. Moving the left or right rudder pedal controls the rudder. When the rudder is deflected into the airflow, a horizontal force is exerted in the opposite direction. Secondary control surfaces: Flaps: Flaps are the most common high-lift devices used on practically all airplanes. These surfaces, which are attached to the trailing edge of the wing, increase both lift and induced drag for any given angle of attack. Flaps allow a compromise between high cruising speed and low landing speed, because they may be extended when needed, and retracted into the wing’s structure when not needed. Leading edge flaps, like trailing edge flaps, are used to increase both Cl and the camber of the wings. There are four common types of flaps: plain, split, slotted, and Fowler flaps. Slats and Slots: High-lift devices also can be applied to the leading edge of the airfoil. The most common types are fixed slots, movable slats, and leading edge flaps. Fixed slots direct airflow to the upper wing surface and delay airflow separation at higher angles of attack. Movable slats consist of leading edge segments, which move on tracks. Opening a slat allows the air below the wing to flow over the wing’s upper surface, delaying airflow separation. Spoilers: On some airplanes, high-drag devices called spoilers are deployed from the wings to spoil the smooth airflow, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft, one of the advantages being the elimination of adverse yaw. Trim Tabs: The most common installation on small airplanes is a single trim tab attached to the trailing edge of the elevator. Most trim tabs are manually operated by a small, vertically mounted control wheel. However, a trim crank may be found in some airplanes. The cockpit control includes a tab position indicator. Anti servo Tabs: In addition to decreasing the sensitivity of the stabilator, an antiservo tab also functions as a trim device to relieve control pressure and maintain the stabilator in the desired position. The fixed end of the linkage is on the opposite side of the surface from the horn on the tab, and when the trailing edge of the stabilator moves up, the linkage forces the trailing edge of the tab up. When the stabilator moves down, the tab also moves down. This is different than trim tabs on elevators, which move opposite of the control surface. Balance Tabs: The control forces may be excessively high in some airplanes, and in order to decrease them, the manufacturer may use balance tabs. They look like trim tabs and are hinged in approximately the same places as trim tabs. The essential difference between the two is that the balancing tab is coupled to the control surface rod so that when the primary control surface is moved in any direction, the tab automatically moves in the opposite direction. [...]... measures the relative strength of the force of gravity and the force of inertia caused by a turn When the aircraft is flying straight-and-level, there is no inertia acting on the ball, and it remains in the center of the tube between two wires In a turn made with a bank angle that is too steep, the force of gravity is greater than the inertia and the ball rolls down to the inside of the turn If the turn is... called a vertical velocity indicator (VVI), and was formerly known as a rate -of- climb indicator It is a rate -of- pressure change instrument that gives an indication of any deviation from a constant pressure level Inside the instrument case is an aneroid very much like the one in an ASI Both the inside of this aneroid and the inside of the instrument case are vented to the static system, but the case is vented... characteristics of an instrument gyro are great weight for its size, or high density, and rotation at high speed with low friction bearings There are two general types of mountings; the type used depends upon which property of the gyro is utilized A freely or universally mounted gyroscope is free to rotate in any direction about its center of gravity Such a wheel is said to have three planes of freedom... instrument case so it appears to be flying relative to the horizon A knob at the bottom center of the instrument case raises or lowers the aircraft to compensate for pitch trim changes as the airspeed changes The width of the wings of the symbolic aircraft and the dot in the center of the wings represent a pitch change of approximately 2° For an AI to function properly, the gyro must remain vertically upright... Attitude and heading indicators function on the principle of rigidity, but rate instruments such as the turn-and-slip indicator operate on precession Precession is the characteristic of a gyroscope that causes an applied force to produce a movement, not at the point of application, but at a point 90° from the point of application in the direction of rotation 4 Turn-and-Slip Indicator: The first gyroscopic... stabilizer are similar to those of a trim tab End of Lecture Unit – II Aircraft Configurations Lecture - II Basic Flight Instruments for Flying Pitot Static Flight Instruments There are two major parts of the pitot-static system: the impact pressure chamber and lines, and the static pressure chamber and lines They provide the source of ambient air pressure for the operation of the altimeter, vertical speed... gravity and the ball rolls upward to the outside of the turn The inclinometer does not indicate the amount of bank, nor does it indicate slip; it only indicates the relationship between the angle of bank and the rate of yaw Unit – II Aircraft Configurations Typical systems for Control Actuation AIRCRAFT HYDRAULIC SYSTEMS Objective: Identify the components of aircraft hydraulic systems and recognize their... are those mounted so that one of the planes of freedom is held fixed in relation to the base There are two fundamental properties of gyroscopic action—rigidity in space and precession Rigidity in Space: Rigidity in space refers to the principle that a gyroscope remains in a fixed position in the plane in which it is spinning Procession: Precession is the tilting or turning of a gyro in response to a deflective... 1,000 feet Each number represents 100 feet and each mark represents 20 feet A drum, marked in thousands of feet, is geared to the mechanism that drives the pointer To read this type of altimeter, first look at the drum to get the thousands of feet, and then at the pointer to get the feet and hundreds of feet A sensitive altimeter is one with an adjustable barometric scale allowing the pilot to set the... older horizontal card indicators, except that the gyro drives a vertical dial that looks much like the dial of a vertical card magnetic compass The heading of the aircraft is shown against the nose of the symbolic aircraft on the instrument glass, which serves as the lubber line A knob in the front of the instrument may be pushed in and turned to rotate the gyro and dial The knob is spring loaded so it . center of the wing. It is important to note that all three axes go through the center of gravity (often abbreviated c.g.) of the airplane. The center of gravity is the balance point of the. elevators control the pitch of the airplane. By controlling the pitch of the airplane, the elevators also control the angle of attack of the wing. To increase the angle of attack, the entire airplane. direction of the wind at some distance from the wing. It is parallel to and opposite to the direction of motion of the wing. The velocity of the relative wind is equal to the speed of the wing.