2 PRINCIPLES OF FLIGHTTHE HELICOPTEREarlier you saw how aircraft get lift from the airflow overIt’s wings.We will now look at an aircraft that produces lift by rotatingIt’s wings.
3 PARTS OF A HELICOPTER Blades Tail Rotor Rotor Head Rotor Disc PRINCIPLES OF FLIGHTPARTS OF A HELICOPTERBladesTail RotorRotor HeadRotor DiscArea sweptby the blades
4 THE PITCH ANGLE IS THE ANGLE BETWEEN THE PLANE OF PRINCIPLES OF FLIGHTPARTS OF A HELICOPTERSHAFT AXISPITCHANGLETHE PITCH ANGLE IS THE ANGLE BETWEEN THE PLANE OFROTATION AND THE BLADE AND IS A DESIGN FEATURE OFEACH HELICOPTER. THIS IS DIFFERENT TO THE BLADE ANGLE.
5 How A Helicopter Produces Lift PRINCIPLES OF FLIGHTHow A Helicopter Produces LiftThe rotor of a helicopter is actually a number of small wingsattached to a central hub.By rotating the rotor at speed the air is forced over it’saerofoil shape and produces lift.The amount of lift can be varied by changing the angle ofattack of the individual rotor blades. i.e. increase in bladde anglewill increase lift.The helicopter’s engine provides the power, through a gearbox,to turn the rotor.By increasing the speed of the rotor and the angle of attack ofthe blades the rotor can produce enough lift to get thehelicopter airborne.
6 By varying the angle of attack on all the blades the pilot can PRINCIPLES OF FLIGHTBy varying the angleof attack on all theblades the pilot cancontrol the verticalmovement of thehelicopter.
7 The angle of attack of the blades is controlled in the rotor head PRINCIPLES OF FLIGHTThe angle of attack of the blades is controlled in the rotor headand is known as a collective alteration of pitch.The pilot’s control which does this is therefore called thecollective pitch control.CHORD LINEBLADEANGLERELATIVEAIRFLOWTHE BLADE ANGLE IS THE ANGLE BETWEEN THE RELATIVEAIRFLOW AND THE CHORD LINE.
8 Horizontal Helicopter Flight PRINCIPLES OF FLIGHTHorizontal Helicopter FlightTo make the aircraft fly forward, horizontal thrust must beavailable. In a conventional aircraft this thrust is provided bya jet engine or a propeller. In a helicopter it is done by tiltingthe lift in the direction of the required movements.This is achieved not by tilting the whole of the rotor head, asone might think. Instead, each blade is hinged, and can bemade to rise and fall as it goes round the plane of rotation(or ‘disc’).The Disc is the area swept by the rotor blades and is shapedlike a saucer.To make the helicopter go forward, each blade ismade to rise as it reaches the rear of the disc, and descend asit reaches the front.
9 Thus, the disc is tilted forwards, and there is a horizontal PRINCIPLES OF FLIGHTLIFTTHRUSTThus, the disc is tilted forwards, and there is a horizontalcomponent of thrust to propel the helicopter forwards.Conversely, we could tilt the disc backwards by making eachblade rise as it passes over the front and fall as it goes overthe rear; the helicopter would move backwards.It could also move sideways by the same principle.
11 The pitch angle is increased when the blade is required to rise PRINCIPLES OF FLIGHTThe pitch angle is increased when the blade is required to riseand decreased for the blade to descend.Obviously, for the rotor disc to stay tilted in the requireddirection, the pitch of each blade must vary through 360°cycle of travel.Therefore, the pilot’s control used for this is called the cyclicpitch control (or cyclic pitch stick).
13 When the engine of a helicopter drives the rotor in its circular PRINCIPLES OF FLIGHTTORQUE REACTIONWhen the engine of a helicopter drives the rotor in its circularmotion, there is a tendency for an opposing force (called‘torque reaction’) to spin the fuselage of the helicopter theopposite way.Rotor Direction OfRotationTorque ReactionThe normal solution on a single-rotor helicopter is to fit a smallrotor, far back on the tail for leverage, with its rotational discvertical.
14 Airflow Balancing Force TORQUE REACTION Rotor Direction Of Tail PRINCIPLES OF FLIGHTTORQUE REACTIONAirflowRotor Direction OfRotationTailRotorTorque ReactionBalancing ForceIts horizontal thrust force opposes the fuselage torquereaction and permits balanced flight. The pilot can vary thethrust force provided by the tail rotor, to maintain balancedflight or to yaw the aircraft at will (very useful when hovering).
15 The pilot alters the thrust of the tail rotor by changing the blade PRINCIPLES OF FLIGHTThe pilot alters the thrust of the tail rotor by changing the bladeangle and hence the angle of attack of the tail rotor blades,giving more thrust or less thrust or even negative thrustas required.Helicopters with twin main rotors such as the Chinook haveeach rotor revolving in an opposite direction. The torquereaction from one thus counteracts the other.
17 As it has no fixed wings or tailplane, the helicopter has no PRINCIPLES OF FLIGHTHELICOPTER CONTROLSAs it has no fixed wings or tailplane, the helicopter has nocontrol surfaces (elevators, ailerons, and rudder), and itsflying controls operate differently from those of conventionalaircraft.Collective Pitch ControlThe collective pitch control, (or ‘lever’) which changes theblade angle of all the blades of the rotor by the same amountat the same time, controls the vertical movement of thehelicopter.It is normally on the pilot’s left, for operation by the left hand.The lever is moved up to increase the pitch angle of the bladesand down to decrease the angle.When the blade angle of the blades is increased, the angle ofattack and thus the lift will be increased and the helicopter willrise off the ground.
18 Collective Pitch Control PRINCIPLES OF FLIGHTCollective Pitch Control
19 However, with increased angle of attack the drag of the blades PRINCIPLES OF FLIGHTHowever, with increased angle of attack the drag of the bladesbecomes greater, hence more power is required to keep themrotating at the correct speed.For this reason the lever is attached to a cam arrangementwhich slightly opens the engine throttle as the lever is movedup, and slightly closes it when the lever is moved down.It works well for small movements of the lever, but somethingextra is needed for larger movements and the extra device isthe hand throttle.
20 The hand throttle is situated on the end of the collective PRINCIPLES OF FLIGHTThe Hand ThrottleThe hand throttle is situated on the end of the collectivelever; it is a twist-grip control similar to a motor cycle throttle.The pilot holds the collective pitch control by the twist-griphand throttle and so can operate both at the same time.Hand Throttle
21 By tilting the rotational disc of the main rotor away from the PRINCIPLES OF FLIGHTCyclic Pitch ControlBy tilting the rotational disc of the main rotor away from thehorizontal, the cyclic pitch control is used to make the aircraftmove horizontally.It is normally operated by the pilot’s right hand, and is similar tothe fixed wing aircraft’s control column, (or “stick”).If the stick is moved forward, the disc is inclined forward andthe helicopter moves into forward flight.The stick can be moved in any direction, tilting the disc in thesame direction to move the helicopter forwards, sideways orbackwards.
22 THE ROTOR HEAD PITCH AND BLADE ANGLE INPUTS ROTATING SWASHPLATE PRINCIPLES OF FLIGHTTHE ROTOR HEADPITCH AND BLADEANGLE INPUTSROTATINGSWASHPLATESTATIONARYSWASHPLATECONTROLINPUT
23 The pilot controls the yaw by resting his feet on rudder pedals PRINCIPLES OF FLIGHTTail Rotor ControlThe pilot controls the yaw by resting his feet on rudder pedalssimilar to those of a fixed-wing aircraft.If the left pedal is pushed forward, the nose of the helicopteryaws to the left; right pedal, right yaw.Primarily the purpose of the tail rotor control is to oppose thetendency of the main rotor to make the fuselage rotate - that is,to achieve balanced flight.However, facility to yaw theaircraft (to change thedirection in which it ispointing) can be very usefulin certain Aerobaticmanoeuvres and whenhovering.
24 PRINCIPLES OF FLIGHTHELICOPTER CONTROLSCyclicYaw PedalsCollective
25 WHEN A HELICOPTER ROTOR IS DRIVEN IN A CIRCULAR MOTION PRINCIPLES OF FLIGHTQUESTIONSWHEN A HELICOPTER ROTOR IS DRIVEN IN A CIRCULAR MOTIONTHERE IS AN OPPOSING FORCE, WHAT IS THIS FORCE CALLED?A. DRAGB. LIFTC. TORQUE REACTIONC. TORQUE REACTIOND. LIFT REACTION
26 WHAT IS THE PURPOSE OF THE TAIL ROTOR? PRINCIPLES OF FLIGHTQUESTIONSWHAT IS THE PURPOSE OF THE TAIL ROTOR?A. COUNTER TORQUE REACTIONA. COUNTER TORQUE REACTIONB. REDUCE DRAGC. PROVIDE THRUSTD. CONTROL THE HELICOPTER IN THE ROLLING PLANE
27 WHAT ARE THE 3 CONTROLS A HELICOPTER USES TO PRINCIPLES OF FLIGHTQUESTIONSWHAT ARE THE 3 CONTROLS A HELICOPTER USES TOCONTROL THE AIRCRAFT’S ATTITUDE?A. AILERONS, RUDDERSB. COLLECTIVE, CYCLIC, YAW PEDALSB. COLLECTIVE, CYCLIC, YAW PEDALSC. CYCLIC, ELEVATORS, THROTTLED. YAW PEDALS, FIN, ROTOR
28 WHAT DOES A HELICOPTER COLLECTIVE CONTROL DO: PRINCIPLES OF FLIGHTQUESTIONSWHAT DOES A HELICOPTER COLLECTIVE CONTROL DO:A. CONTROLS HORIZONTAL FLIGHT IN ANY DIRECTION.B. CONTROLS VERTICAL FLIGHT.B. CONTROLS VERTICAL FLIGHT.C. CONTROLS THE TAIL ROTOR.D. CONTROLS THE ENGINES.
29 A HELICOPTER ROTOR DISC IS: PRINCIPLES OF FLIGHTQUESTIONSA HELICOPTER ROTOR DISC IS:A. CONTROLLED BY THE YAW PEDALS.B. THE AREA SWEPT BY THE ROTOR BLADES.B. THE AREA SWEPT BY THE ROTOR BLADES.C. USED TO OPERATE THE COLLECTIVE.D. USED TO PROGRAMME THE FLIGHT PLAN.
30 THE LIFT OF A HELICOPTER ROTOR BLADECAN BE INCREASED BY: PRINCIPLES OF FLIGHTQUESTIONSTHE LIFT OF A HELICOPTER ROTOR BLADECAN BE INCREASED BY:A. DECREASING THE BLADE PITCH ANGLE.B. INCREASING THE TORQUE REACTION.C. DECREASING THE ROTOR SPEEDD. INCREASING THE BLADE PITCH ANGLE.D. INCREASING THE BLADE PITCH ANGLE.
31 WHAT DOES A HELICOPTER CYCLIC CONTROL DO: PRINCIPLES OF FLIGHTQUESTIONSWHAT DOES A HELICOPTER CYCLIC CONTROL DO:A. CONTROLS HORIZONTAL FLIGHT IN ANY DIRECTION.A. CONTROLS HORIZONTAL FLIGHT IN ANY DIRECTION.B. CONTROLS VERTICAL FLIGHT.C. CONTROLS THE TAIL ROTOR.D. CONTROLS THE YAW PEDALS.