Aviation 1052 Propeller Controls Tutorial PDF

AVIA-1052 1 Previously On AVIA-1052  Well there is no “previously”, this is our first class together.  Now this is first class 2 Today On AVIA-1052  We are going to talk about…  You guessed it,...

AVIA-1052 1 Previously On AVIA-1052  Well there is no “previously”, this is our first class together.  Now this is first class 2 Today On AVIA-1052  We are going to talk about…  You guessed it, Propellers  Some general prop stuff  Aircraft Propeller Theory  Basic Propeller Controls 3 Where are we?  Powerplant (Vol. 2) 7-2 to 7-6   Start at  General  Stop at  Propeller Location  FAA-H-8083-30A, Aviation Maintenance Technician Handbook-General  FAA-H-8083-31A, Aviation Maintenance Technician Handbook-Airframe Volume 1  FAA-H-8083-31A, Aviation Maintenance Technician Handbook-Airframe Volume 2  FAA-H-8083-32A, Aviation Maintenance Technician Handbook-Powerplant Volume 1  FAA-H-8083-32A, Aviation Maintenance Technician Handbook-Powerplant Volume 2 4 AVIA-1052 5  Powerplant 7-2 Propellers  the unit that must absorb the power output of the engine  Propeller development  the propeller has passed through many stages of development  propeller development has encouraged many changes as propulsion systems have evolved  the first propellers were fabric- covered sticks  Designed to force air in a rearward direction 6  Powerplant 7-2 Propellers  propellers started as simple two-bladed wood propellers  have advanced to the complex propulsion systems of turboprop aircraft that involve more than just the propeller  more complex propellers  a variable-pitch, constant-speed feathering and reversing propeller system  allows the engine rpm to be varied only slightly during different flight conditions  increases flying efficiency 7  Powerplant 7-2 Propellers  constant-speed systems  a basic constant-speed system consists of:  a flyweight-equipped governor unit that controls the pitch angle of the blades so that the engine speed remains constant 8  Powerplant 7-2 Propellers  a flyweight-equipped governor unit  that controls the pitch angle of the blades so that the engine speed remains constant  can be regulated by controls in the cockpit so that any desired blade angle setting, and engine operating speed can be obtained at  takeoff  low-pitch  high-rpm setting  flight  higher pitch  lower rpm setting 9  Powerplant 7-2 Propellers  This figure shows normal propeller movement with the positions of  low pitch  high pitch  Feather-used if the engine quits to reduce drag  zero pitch into negative pitch-reverse pitch 10  Powerplant 7-2 Common Propeller Types  Propellers 11  Powerplant 7-2 Propellers  most propellers are two-bladed  great increases in power output have resulted in the development of  four-bladed propellers  six-bladed propellers of large diameters  all propeller-driven aircraft are limited by the revolutions per minute (rpm) at which propellers can be turned 12  Powerplant 7-2 Propellers  forces acting on the propeller as it turns  centrifugal force  tends to pull the blades out of the hub at high rpm  blade weight is very important to the design of a propeller 13  Powerplant 7-2 Propellers  excessive blade tip speed  rotating the propeller too fast may result in  poor blade efficiency  fluttering  vibration 14  Powerplant 7-2 Propellers  since the propeller speed is limited, the aircraft speed of a propeller driven aircraft is also limited approximately 400 miles per hour (mph) (644 kilometers per hour)  as aircraft speeds increased, turbofan engines were used for higher speed aircraft 15  Powerplant 7-2 Propellers  propeller-driven aircraft have several advantages  takeoff and landing can be  shorter  less expensive to maintain  new blade materials and manufacturing techniques have increased the efficiency of propellers  widely used for applications in  turboprops  reciprocating engine installations  many smaller aircraft will continue to use propellers well into the future 16  Powerplant 7-2 Propellers  propeller systems  many different types of propeller systems have been developed for  specific aircraft installation  speed  type of operation 17  Powerplant 7-2 Propellers  diagrams  basic nomenclature of the parts of a simple fixed-pitch, two-bladed wood propeller  aerodynamic cross-section of a blade (next slide)  includes terminology to describe certain areas shown 18  Powerplant 7-2 Propellers  aerodynamic cross-section of a blade 19 AVIA-1052 20  Powerplant 7-2 Basic Propeller Principles  the aircraft propeller consists of:  two or more blades  each blade is essentially a rotating wing  produce forces that create thrust to pull or push the airplane through the air  the power needed to rotate the propeller blades is furnished by the engine  a central hub to which the blades are attached 21  Powerplant 7-3 Basic Propeller Principles  mounted on a shaft  low-horsepower engines  which may be an extension of the crankshaft  high-horsepower engines  mounted on a propeller shaft that is geared to the engine crankshaft  the engine rotates the airfoils of the blades through the air at high speeds  the propeller transforms the rotary power of the engine into thrust 22  Powerplant 7-3 Propeller Aerodynamic Process  an airplane moving through the air creates a drag force  opposing its forward motion  there must be a force applied to it that is equal to the drag but acting forward  if an airplane is to fly on a level path this force is called thrust  the work done by thrust is equal to the thrust times the distance it moves the airplane  work = thrust × distance  the power expended by thrust is equal to the thrust times the velocity at which it moves the airplane  power = thrust × velocity 23  Powerplant 7-3 Propeller Aerodynamic Process  the power expended by the thrust is termed thrust horsepower if the power is measured in horsepower units  the engine supplies brake horsepower through a rotating shaft  the propeller converts it into thrust horsepower  some power is wasted in this conversion  the propeller must be designed to keep this waste as small as possible for maximum efficiency  (image to the right is for a boat prop) 24  Powerplant 7-3 Propeller Aerodynamic Process  propeller efficiency is the ratio of thrust horsepower to brake horsepower since the efficiency of any machine is the ratio of the useful power output to the power input the usual symbol for propeller efficiency is the Greek letter η (eta)  propeller efficiency varies from 50-87% depending on how much the propeller slips 25  Powerplant 7-3 Propeller Aerodynamic Process  pitch is not the same as blade angle  because pitch is largely determined by blade angle  the two terms are often used interchangeably  an increase or decrease in one is usually associated with an increase or decrease in the other  blade angle  the angle between the face or chord/ chord line of a blade section and the plane in which the propeller rotates  usually measured in degrees 26  Powerplant 7-3 Propeller Aerodynamic Process  geometric pitch  is the distance a propeller should advance in one revolution with no slippage  usually expressed in pitch inches  calculated by using the following formula:  GP = 2 × π R × tangent of blade angle at 75% station  R = Radius at the 75% blade station  π = 3.14  based on no slippage 27  Powerplant 7-3 Propeller Aerodynamic Process  effective pitch  is the distance it advances  recognizes propeller slippage in the air  propeller slip is the difference between the geometric pitch of the propeller and its effective pitch  geometric pitch – effective pitch = slip 28  Powerplant 7-3 Propeller Aerodynamic Process  the chord line of the propeller blade is determined in about the same manner as the chord line of an airfoil  a propeller blade can be considered as being composed of an infinite number of thin blade elements  each of which is a miniature airfoil section whose chord is the width of the propeller blade at that section  the chord line is often drawn along the face of the propeller blade because most propellers have a flat blade face 29  Powerplant 7-3 Propeller Aerodynamic Process  the typical propeller blade can be described as a twisted airfoil of irregular planform  a blade can be divided into segments that are located by station numbers in inches from the center of the blade hub  for purposes of analysis 30  Powerplant 7-4 Propeller Aerodynamic Process  the cross-sections of each 6-inch blade segment are shown as airfoils on the right side 31  Powerplant 7-4 Propeller Aerodynamic Process  also identified are:  blade shank  thick, rounded portion of the propeller blade  near the hub  designed to give strength to the blade  blade butt  also called the blade base or root  the end of the blade that fits in the propeller hub  blade tip  part of the propeller blade farthest from the hub  generally defined as the last 6 inches of the blade 32  Powerplant 7-4 Propeller Aerodynamic Process  this section or blade element is an airfoil comparable to a cross-section of an aircraft wing  blade back  cambered or curved side of the blade  like the upper surface of an aircraft wing  blade face  flat side of the propeller blade  chord line  an imaginary line drawn through the blade from the leading edge to the trailing edge  leading edge  thick edge of the blade that meets the air as the propeller rotates 33  Powerplant 7-4 Propeller Aerodynamic Process  the principal forces acting on a rotating propeller  centrifugal force  a physical force  tends to throw the rotating propeller blades away from the hub  the most dominant force on the propeller 34  Powerplant 7-4 Propeller Aerodynamic Process  torque bending  tends to bend the propeller blades in the direction opposite that of rotation  in the form of air resistance 35  Powerplant 7-4 Propeller Aerodynamic Process  thrust bending  loads that tends to bend propeller blades forward as the aircraft is pulled through the air  at least two of these forces acting on the propeller's blades are used to move the blades  on a controllable pitch propeller  centrifugal twisting  aerodynamic twisting 36  Powerplant 7-4 Propeller Aerodynamic Process  aerodynamic twisting  tends to turn the blades to a high blade angle  used to move the blades into high pitch 37  Powerplant 7-4 Propeller Aerodynamic Process  a rotating propeller is acted upon by:  centrifugal twisting  greater than the aerodynamic twisting force  tends to force the blades toward a low blade angle  sometimes used to move the blades to the low pitch position 38  Powerplant 7-4 Propeller Aerodynamic Process  a propeller must be capable of withstanding severe stresses  greater near the hub  caused by centrifugal force and thrust  increase in proportion to the rpm  the blade face is also subjected to tension from:  the centrifugal force  the bending  nicks or scratches on the blade may cause very serious consequences  these could lead to:  cracks  failure of the blade 39  Powerplant 7-4 Propeller Aerodynamic Process  a propeller must also be rigid enough to prevent fluttering  a type of vibration  the ends of the blade twist back and forth at high frequency around an axis perpendicular to the engine crankshaft  the constant vibration tends to weaken the blade and eventually causes failure  accompanied by a distinctive noise  often mistaken for exhaust noise 40  Powerplant 7-4 Aerodynamic Factors  consider first its motion  to understand the action of a propeller  which is both rotational and forward  a section of a propeller blade moves downward and forward 41  Powerplant 7-4 Aerodynamic Factors  the result is the same as if the blade were stationary and the air coming at it from a direction opposite its path  as far as the forces are concerned, the angle at which this air (relative wind) strikes the propeller blade is called angle of attack(AOA)  the air deflection produced by this angle causes the dynamic pressure at the engine side of the propeller blade to be greater than atmospheric pressure, therefore creating thrust 42  Powerplant 7-4 Aerodynamic Factors  the shape of the blade also creates thrust  because it is shaped like a wing, as the air flows past the propeller, the pressure on one side is lower than the pressure on the other side  this difference in pressure produces a reaction force in the direction of the lesser pressure  Example: the area above a wing has less pressure, the force (lift) is upward  the area of decreased pressure is in front of a propeller which is mounted in a vertical instead of a horizontal position  the force (thrust) is in a forward direction  thrust is the result of the propeller shape and the AOA of the blade aerodynamically 43  Powerplant 7-4 Aerodynamic Factors  another way to consider thrust is in terms of the mass of air handled  thrust = the mass of air handled x the slipstream velocity - the velocity of the airplane  in these terms, the power expended in producing thrust depends on the mass of air moved per second 44  Powerplant 7-4 Aerodynamic Factors  the amount of air displaced (moved) depends on the blade angle  for any single revolution of the propeller which determines the quantity or amount of mass of air the propeller moves, the blade angle is an excellent means of adjusting the load on the propeller to control the engine rpm  if the blade angle is increased, more load is placed on the engine tending to slow it down unless more power is applied 45  Powerplant 7-4 Aerodynamic Factors  thrust constitutes approximately 80% of the torque  total horsepower absorbed by the propeller balances the horsepower delivered by the engine for any speed of rotation  the other 20% is lost in friction and slippage 46  Powerplant 7-4 Aerodynamic Factors  as an airfoil is moved through the air, it produces two forces:  lift and drag  increasing propeller blade angle:  increases the AOA  produces more lift and drag  increases the horsepower required to turn the propeller at a given rpm  slows the propeller down (since the engine is still producing the same horsepower) 47  Powerplant 7-4 Aerodynamic Factors  decreasing propeller blade angle:  speeds the propeller up  the engine rpm can be controlled by increasing or decreasing the blade angle  lift versus drag curves drawn for:  propellers  wings 48  Powerplant 7-4 Aerodynamic Factors  indicate that the most efficient AOA is a small one varying from 2° to 4° positive  the actual blade angle necessary to maintain this small AOA varies with the forward speed of the airplane  due to a change in the relative wind direction which varies with aircraft speed 49  Powerplant 7-4 Aerodynamic Factors  the blade angle  an excellent method of adjusting the AOA of the propeller  the blade angle must be adjusted to provide the most efficient AOA at all engine and airplane speeds on constant-speed propellers  fixed-pitch and ground-adjustable propellers are designed: for best efficiency at:  One rotation speed  One forward speed 50  Powerplant 7-4 Aerodynamic Factors  to fit a given airplane and engine combination, a propeller may be used that provides the maximum propeller efficiency for: takeoff climb cruising high speeds  any change in these conditions results in lowering the efficiency of both the propeller and the engine 51  Powerplant 7-4 Aerodynamic Factors  A constant-speed propeller keeps the blade angle adjusted for maximum efficiency for most conditions encountered in flight  during takeoff, when maximum power and thrust are required:  the constant-speed propeller is at a low propeller blade angle or pitch  the low blade angle keeps the AOA small and efficient with respect to the relative wind  it allows the propeller to handle a smaller mass of air per revolution 52  Powerplant 7-4 Aerodynamic Factors  this light load allows the engine to turn at high rpm and to convert the maximum amount of fuel into heat energy  the high rpm also creates maximum thrust  the engine rpm is high  the slipstream velocity (air coming off the propeller) is high  the thrust is maximum with the low airplane speed 53  Powerplant 7-6 Aerodynamic Factors  after liftoff, as the speed of the airplane increases  the constant-speed propeller changes to a higher angle (or pitch)  the higher blade angle keeps the AOA small and efficient with respect to the relative wind  the higher blade angle increases the mass of air handled per revolution  this decreases the engine rpm, reducing fuel consumption and engine wear, and keeps thrust at a maximum 54  Powerplant 7-6 Aerodynamic Factors  for climb after takeoff  the power output of the engine is reduced to climb power by decreasing the manifold pressure and increasing the blade angle to lower the rpm  the torque (horsepower absorbed by the propeller) is reduced to match the reduced power of the engine  the AOA is kept small by the increase in blade angle  the greater mass of air handled per second is more than offset by the lower slipstream velocity and the increase in airspeed 55  Powerplant 7-6 Aerodynamic Factors  at cruising altitude, when the airplane is in level flight and less power is required than is used in takeoff or climb  engine power is reduced by lowering the manifold pressure and increasing the blade angle to decrease the rpm  this reduces torque to match the reduced engine power  it is more than offset by a decrease in slipstream velocity and an increase in airspeed  the AOA is still small because the blade angle has been increased with an increase in airspeed 56  Powerplant 7-6 Aerodynamic Factors  pitch distribution is the twist in the blade from the shank to the blade tip, due to the variation in speeds that each section of the blade is traveling  the tip of the blade is traveling much faster than the inner portion of the blade 57 AVIA-1052 58 Propeller Controls and Instruments  https://youtu.be/0bP2MH3LqvI  The Propeller Explained (24.04)  https://www.youtube.com/watch?v=GNsnXjxopJM  ConstantSpeedPropPart1 (14:23) Landed valve=pilot valve=spool valve  https://youtu.be/-KyxxrEJBH0  HOW PROPELLERS ARE MADE: Hartzell Propeller (8:42)  https://youtu.be/HHXlhJlPqKg  She is a Builder! Wood Worker! Prop Maker! Machinist! (36:40)  https://www.youtube.com/c/CulverProps 59  Powerplant 7-6 Propeller Controls and Instruments  fixed pitch propellers:  have no controls  require no adjustments in flight  constant-speed propellers:  have a propeller control in the center pedestal between the throttle and the mixture control (typically a blue knob)  the two positions for the control are:  increase rpm  (full forward)  decrease rpm  (pulled aft) 60  Powerplant 7-6 Propeller Controls 61  Powerplant 7-6 Propeller Controls and Instruments  Controls are directly connected to the propeller governor and adjusts the tension on the governor speeder spring by moving the control  can be used to feather the propeller in some aircraft by moving the control to the full decrease rpm position  controls rotations per minute (rpm)  the two main instruments used are:  the engine tachometer  the manifold pressure gauge  adjusted by the throttle 62  Powerplant 7-6 Speed Sensing  tachometer generator  measures the rotational rate of a shaft using an internally generated electrical signal  reference signal or voltage is generated by rotating the generator's internal mechanism  generated alternating current (AC) is then read by tachometer circuitry and displayed 63