The stick is connected by means of wires or hydraulics to the wings’ ailerons. By turning the stick, the pilot can change the positions of the ailerons . When the control wheel is turned to the right, the right aileron goes up and the left aileron goes down, rolling the airplane to the right. When the control wheel is turned to the left, the right aileron goes down and the left aileron goes up, rolling the airplane to the left.
Rudder: The foot pedals are connected by means of wires or hydraulics to the rudder of the tail section. The rudder is the vertical part of the tail that can move from side to side. When the foot pressure on the left rudder pedal moves the rudder to the left, causing the nose of the airplane to move to the left.
The stick (joy stick) is connected by means of wires or hydraulics to the tail section’s elevators. By moving the stick, the pilot can change the position of the elevators. When the control column is pushed in, the elevators move down, pitching the tail of the airplane up an the nose down, rolling the airplane down. When pulling the control column back makes the elevators move up, pitching the tail of the airplane down and the nose up, rolling the airplane upwards. Cars go only left or right, but planes must be steered up or down as well. A plane has parts on its wings and tail called control surfaces to help it. These can be demonstrated by use of folded paper gliders and balsa gliders. Let’s start with an experiment to illustrate how a plane is controlled.
Index of presentationIntroductionThe AtmosphereNewton’s Laws of MotionBernoulli’s PrincipleAirfoilParts of an AirplaneThe Four Forces of FlightThree Axes of MovementStabilityControl
INTRODUCTION It is unnecessary that a mechanic be totally versed onAerodynamics and Theory of Flight. However he mustunderstand the relationships between the atmosphere, theaircraft and the forces acting on it in flight, in order to makeintelligent decisions affecting the flight safety of both airplanesand helicopters.Aerodynamics Aerodynamics is the study of objects in motion throughthe air and the forces that produce or change such motion.
The Atmosphere Air is a mixture of gases composed principally of nitrogenand oxygen. An aircraft operates in the air, therefore, theproperties of air that affect aircraft control and performance mustbe understood.Pressure – Atmospheric pressure varies with altitude. Thehigher an object rises above sea level, the lower the pressure.Density – It varies directly with the pressure and inversely withthe temperature. With the same horse power, an aircraft can flyfaster at high altitude because of less resistance of air at there.Humidity – Humidity is the amount of water vapor in the air. Itvaries directly with temperature.
Newtons First Law of MotionAccording to Newtons first law of motion (inertia), an object atrest will remain at rest, or an object in motion will continue inmotion at the same speed and in the same direction, until anoutside force acts on it. For an aircraft to taxi or fly, a forcemust be applied to it. It would remain at rest without anoutside force. Once the aircraft is moving, another force mustact on it to bring it to a stop. It would continue in motionwithout an outside force. This willingness of an object toremain at rest or to continue in motion is referred to as inertia.
Newtons Second Law of MotionThe second law of motion (force) states that if a object movingwith uniform speed is acted upon by an external force, thechange of motion (acceleration) will be directly proportional tothe amount of force and inversely proportional to the mass ofthe object being moved. The motion will take place in thedirection in which the force acts. Simply stated, this means thatan object being pushed by 10 pounds of force will travel fasterthan it would if it were pushed by 5 pounds of force. A heavierobject will accelerate more slowly than a lighter object when anequal force is applied. F=m×a
Newtons Third Law of MotionThe third law of motion (action and reaction) states that forevery action (force) there is an equal and opposite reaction(force). This law can be demonstrated with a balloon. If youinflate a balloon with air and release it without securing theneck, as the air is expelled the balloon moves in the oppositedirection of the air rushing out of it. Figure shows this law ofmotion. Balloon Reaction Air Action
BERNOULLIS PRINCIPLEBernoullis principle states that when a fluid flowing through a tubereaches a constriction or narrowing of the tube, the speed of thefluid passing through the constriction is increased and its pressureis decreased. Pressure Drop in Venturi Tube
AirfoilAn airfoil is the shape of a wing or blade (of a propeller, rotoror turbine) as seen in cross-section. An aircrafts wings,horizontal, and vertical stabilizers are built with airfoil-shapedcross sections, as are helicopter rotor blades.- The mean camber line is a line drawn midway between the upper and lower surfaces.- The chord line is a straight line connecting the leading and trailing edges of the airfoil, at the ends of the mean camber line. Chord line Mean camber line
Parts of an Airplane Cockpit Empennage Fuselage Stabilizers Wing Rudder Flap Elevator Aileron Engine
The Four Forces of FlightThe forces acting on an airplane in flight are lift, weight, thrust,and drag. These forces are in equilibrium during straight-and-level, unaccelerated flight. LIFT THRUST DRAG WEIGHT
LiftLift is the force created by the interaction between the wingsand the airflow. It always act upwards. It is considered to bethe most important force as without it, an aircraft cannotascend from ground and maintain altitude. Lift is an aerodynamic force Lift must exceed weight for flight Generated by motion of aircraft through air Created by the effects of airflow past wing Aircraft lift acts through a single point called the center of pressure.
Lift: Wing Section Lift Equation: L=CL × ½ ρ × A × V2
Angle of Attack • The angle of attack is the angle between the chord line and the average relative wind. • Greater angle of attack creates more lift (up to a point).
Angle of Attack and Lift Force High velocity Low pressure Low velocity High pressure
Angle of Incidence • The angle of incidence is the angle between the chord line and the longitudinal axis of aircraft. • It is the angle of wing setting. • When the leading edge of the wing is higher than the trailing edge, the angle of incidence is said to be positive. It is negative when the leading edge is lower than the trailing edge of the wing. Angle of incidence Chor d lineAircraft longitudina l axis
Lift and Induced Drag • Lift acts through the center of pressure, and perpendicular to the relative wind. • This creates induced drag. induced drag cho rd effective total line lift lift aver a ge re l ative wind
WeightThis force acts on an aircraft due to the interaction betweenthe aircrafts body weight and Earths gravity. Weight is adownward force. Weight is not constant Varies with passengers, cargo, fuel load Decreases as fuel is consumed or payload off-loaded Direction is constant toward earth’s center Acts through a single point called the center of gravity (the CG)
ThrustThis force is created by an aircrafts engine and is required forforward motion. Forward-acting force opposes drag Direction of thrust depends on design Propulsion systems produce thrust Equal to drag in straight, constant speed flight
DragThis force acts in reverse direction to that of Thrust andhinders forward motion. Drag is considered as a negative forceand all engineers try their best to reduce drag. An aerodynamic force. Resists forward motion. Increases with the square of speed. Two broad drag classifications. – Parasite drag: drag created by airplane shape. A result of air viscosity. – Induced drag: by-product of lift generation. Caused by the wingtip vortices.Drag Equation: D=CD × ½ ρ × A × V2
Shape of the Airfoil• The shape of the airfoil determines the amount of turbulences or skin friction that it will produce. The shape of a wing consequently affects the efficiency of the wing. A wing may have various airfoil section from root to tip, with taper, twist, sweep back and sweep forward.
StabilityAn aircraft must have sufficient stability to maintain a uniformflight path and recover from the various upsetting forces alsoto achieve the best performance. There are two types of stability Static Stability - The initial movement of an object after being disturbed. – Positive Static Stability – returns to position before displacement. – Neutral Static Stability – tendency to remain in displaced position. – Negative Static Stability – tends to continue away from displaced position in same direction.
Dynamic stabilityDynamic Stability - The behavior of theobject over time. Positive Dynamic Stability – the oscillations or phugoids dampen themselves out. Neutral Dynamic Stability – the oscillations or phugoids carry on with out increasing in severity. Negative Dynamic Stability – the oscillations or phugoids increase in severity and diverge.
CONTROLTo achieve the best performance, the aircraft must have theproper response to the movement of the controls. Control is theaction taken to make the aircraft follow any desired flight path.Different Control surfaces are used to control the aircraft abouteach of the three axes.Flight Control Surfaces – Hinged or moveable airfoilsdesigned to change the attitude of the aircraft during flight. 1. Primary group 3. Auxiliary group - ailerons - wing flaps - elevators - spoilers - rudder - speed brakes 2. Secondary group - slats - trim tab, spring tab - leading edge flaps - servo tab, balance tab - slots
Flight Control Surfaces Spoiler SpoilerFlap Flap
Control around the Longitudinal AxisROLLINGAilerons – The ailerons form a part of the wing and are located inthe trailing edge of the wing towards the tips. The control stick isconnected by means of wires or hydraulics to the wings’ ailerons. Byturning the stick, the pilot can change the positions of the ailerons.
Control around the Vertical AxisYAWINGRudder – The rudder is amoveable control surfaceattached to the trailing edge of thevertical stabilizer. The foot pedalsare connected by means of wiresor hydraulics to the rudder of thetail section. The rudder can alsobe used in controlling a bank orturn in flight. Moving rudder to the Moving rudder to the right forces tail to the left forces tail to the left, nose to the right right, nose to the left.
Control around the Lateral AxisPITCHINGElevators – Elevators are themovable control surfaces hinged tothe trailing edge of the horizontalstabilizer. The control stick isconnected by means of wires orhydraulics to the tail section’selevators. - Stabilator - Ruddervator