Gyroscopic Instruments PDF

I& Intr I o GYROSCOPIC INSTRUMENTS  GYROSCOPIC INSTRUMENTS Objectives: 1. State the main components of a Gyroscope. 2. Explain the Functional Principle of a Gyroscope. 3. Explain the term `Rigidity’ and `Precession’. 4. List the Gyroscope...

I& Intr I o GYROSCOPIC INSTRUMENTS  GYROSCOPIC INSTRUMENTS Objectives: 1. State the main components of a Gyroscope. 2. Explain the Functional Principle of a Gyroscope. 3. Explain the term `Rigidity’ and `Precession’. 4. List the Gyroscope Instrument I& I GYROSCOPIC GI INSTRUMENTS What is a Gyroscope? A gyroscope is a spinning mass mounted in such a way that the spin axis is free to rotate about one or two axes at right angles to the spin axis (3 axes of freedom including the spin axis). I& GI I I& GI I Main Components of a Gyroscope A Gyroscope usually contains 3 movable parts: Inner Outer Rotor gimbal gimbal I& GI I Gyroscope Components Rotor A perfectly balanced rotating mass. Mounted on anti-friction bearings within a ring or frame known as `gimbal’. The rotor axis is called `spin axis Inner Gimbal (Ring) (X-axis)’. The inner gimbal, supports the rotor. The rotor is therefore free to turn relative to the frame which is at right angles to the spin axis. A gyroscope having an inner gimbal only is said to have `one I& GI I Gyroscope Components Outer Gimbal (Ring) Between the inner gimbal and the supporting frame lies a second gimbal which is known as the `outer gimbal’. The type of gyroscope containing both an inner and an outer gimbal is said to have `2 degrees of freedom’. I& GI I 3 AXES OF A GYROSCOPE X- Y- Z- Axis Axis Axis I& I The rotor is free to spin about the X-axis on bearings in the inner frame. The inner ring is free to turn about the Y- axis on pivots in the outer ring. The outer ring is free to turn about the Z- axis on pivots in the support. Such a construction is known as `gimbal rings’. I& GI I When the gyroscope is in its normal position all the axes are at right angles to each other and intersect at the centre of gravity of the rotor. I& I AIRCRAFT AXIS, GYROSCOPE AXIS and GI DISPLACEMENT AIRCRAFT GYROSCOPE Displacement Controls AXIS Longitudin AXIS ? X Roll al Lateral = Y Pitch Vertical Z Yaw I& I FUNCTIONAL PRINCIPLE OF A GI Due to the mass GYROSCOPE inertia of the fast rotating wheel, the direction of the spin axis always remains unchanged (stabilized) in space, even if the suspension is turned or moved. I& FUNCTIONAL PRINCIPLE OF A GI I GYROSCOPE This important property is applied for measuring and indicating several flight characteristics Climbing or Banking Turning Descending (Rolling) (Yawing) (Pitching) I& GI I Properties of a Gyroscope The fundamental characteristics of any gyroscope are : Rigidity Precessi on I& GI I Rigidity Rigidity is the property of a rotating mass to maintain its plane of spin * The spin axis tends to remain in a fixed direction in space as long as the rotational speed is high enough. Axis of Spin Plane of Spin Plane of the Applied Force Plane of Precession I& GI I Precession Precession is the property of a rotating mass to change its axis of spin due to an external force * Precession of a Gyroscope is directly proportional to its rotational speed # On aircraft, Precession is caused by the movement of the mounting or aircraft movement. I& GI I DETERMINE THE DIRECTION OF PRECESSION The direction of Precession depends on: The direction of rotation of the rotor The direction of the applied external force Provided both direction are known The change in direction does not take place in line with the applied force, but always at an angle of 90° in the direction of rotation. Gyro’s speed of rotation must be kept constant, since the precession of the rotor is directly proportional to its speed. I& GI I Types of Precession * Apparent precession: Is the tilt/movement due to the earth’s rotation and curvature Random precession: This precession is created by pivot and bearing friction and out-of-balance assemblies. Actual precession: This is caused by the application of an external force, e.g. whenOn theaircraft, Precession support frame is aircraft) (i.e. the caused is byturned the or moved. of the mounting or aircraft movement. movement I& I Methods of Operating GI Gyroscopic Instruments 2 principal methods to drive the rotor: Pneuma Electrica tic l Suction The power created by supply are Engine- either driven 115 V /400 Hz, Vacuum 3-phase AC Pump or a or 28 V DC. Venturi Tube. I& GI I Pneumatic Method Gyroscopic Instrument An air-driven gyroscopic instrument has 2 connections: one to the pump and the other (internally) to a spinning jet system. The instrument is When open vacuum to the is applied to surrounding the instrument, the atmosphere. pressure within the case is reduced to allow the surrounding air to enter through the spinning jets. The jet stream hits the air buckets on the rotor to turn the rotor at high speed. I& GI I Electrical Method Gyroscopic Instrument Power supply is either 115 V/400 Hz, 3-phase AC or 28 VDC. AC system uses the Squirrel-Cage Induction Motor. High frequency of power supply enables high rotor speeds to provide greater rigidity DC system and uses the Permanent-Magnet type of motor. stability. DC is required for the operation of some types of gyroscopic instruments only and for `standby’ gyro instruments. I& GI I Application of Gyroscopes in Aircraft Gyroscope systems establish 2 essential reference datums: a reference against which Pitch and Roll where attitude changes may be detected, and a Directional reference against which changes Turn and about the vertical axis may be Directional detected. Slipreferences These GyroareHorizon established Gyro in the Indicator instruments: following  I& Application of Gyroscopes in Aircraft GI I re 4 References Established by Gyroscope  TYPICAL GYROSCOPIC INSTRUMENT Objectives At the end of this lesson, should be able to:  List the main components and explain the principles of operation of Turn-and-Slip Indicators (Turn Mechanism, the Inclinometer and the Gyro flag)  State the difference between a Turn-and-Slip Indicator and a Turn Coordinator.  List the main components and explain the principles of operation of both Air-driven and Electrically driven Gyro Horizons  State the functional principles of the following types of gyro erecting devices: - air-driven gyro erecting device  Welcome to Turn and Slip Indicator The family of Turn and Slip Indicator Figure 1 Turn-and-Slip Indicators (Examples) I& I TURN and SLIP GI INDICATOR What is a Turn-and-Slip Indicator? Turn-and-Slip indicator displays Rate of Turn and indicates whether the aircraft is in coordinated turn or Slip or Skid.  Main Components of a Turn-and-Slip Indicator The Turn-and-Slip indicator with a DC-driven gyro comprises of the following main parts:  housing with electrical  rate-of-turn needle connector  inclinometer  DC gyro motor  dial  gimbal ring  gyro flag (warning  damping device flag)  reversing mechanism with zero spring I& Independent Mechanism GI I of a Turn-and-Slip Indicator The Turn-and-Slip indicator contains 2 independent mechanisms:  A gyroscopically controlled pointer mechanism for the detection and  indication of the A mechanism forrate the of turn of the detection and aircraft. indication of bank and/or slip/skid. Slip indicator Gyroscope or (Turn) Inclinometer (Bank and/or Slip) I& I Turn Mechanism of a Turn-and-Slip GI Indicator For the detection of rates of turn, the gyroscopic precession against a calibrated spring arrangement is used and it Turn and Slip Indicator is known as uses `Rate RATE GYROSCOPE I& I Principle of Operation of a Turn-and- GI Slip Indicator One gimbal with only one plane (degree) of freedom. Gyro Flag To monitor the gyro’s speed and for assuring accurate indication. Must disappear after 3 minutes of starting and re-appear after 20 seconds of power failure. Turn Mechanism The gimbal pivot is in line with the longitudinal axis of the aircraft, the rotor axis is parallel with the aircraft’s lateral axis. Only when there is rotation about the vertical axis (yawing) influences the gyro (not in role). I& GI I Principle of Operation of a Turn-and-Slip Indicator Principles of precession force affects the rotor at a point which is 90° apart of the point where the force is applied. This causes the gimbal to tilt against a calibrated spring. The amount of tilting is proportional to the rate of rotation about is Precession the aircraft’s caused by vertical changeaxis. of aircraft’s attitude. When starting a turn, the pointer deflects according to the rate of turn and indicates the direction of turn. The deflection of one pointer width corresponds to a standard rate of turn of 3° per second (= 2 min for a 360-turn). I& GI I Principle of Operation of a Turn-and-Slip Indicator Slip Indicator or Inclinometer Indicates whether the aircraft is correctly banking or not for a Its principle particular of operation turn. is based on the effect of: Gravitational force and Centrifugal force in order to indicate whether the aircraft experiencing a: coordinated turn I& GI I Inclinometer It indicates the resultant of: – Gravitational force and – Centrifugal force during each moment of a turn. If coordinated / correctly banked turn is flown, the ball remains centered. If the turn is too shallow /under bank or too steep (over bank) the ball moves away from the centre position indicating a skid or slip attitude. Aircraft is turning to the ……… Shallow Steep Correct Turn Turn bank (under (over I& GI I Turn Coordinator A Turn coordinator may be installed in small types of aircraft instead of a Turn-and-Slip indicator. Coordination of the turn is indicated by the inclinometer.  Turn Coordinator The annotation 2 MIN means what? It means that a indication of one pointer width corresponds to a standard rate of turn of 3° per second turn or The annotation a turnofof`no 360pitch information’ deg in 2 min. is given to avoid confusion in pitch control due to the similarity of a gyro horizon. What type of gyro is used in a Turn and Slip Indicator? RATE GYROSCO PE Explain the following indications A B C D E F GYRO HORIZON I& GI I GYRO HORIZON What is a Gyro Horizon? Gyro horizon (AH) indicates the Pitch and Roll/Bank attitude of an aircraft relative Gyro Horizon uses to the vertical. DISPLACEMENT GYROSCOPE I& GI I GYRO HORIZON The Pitch and Bank/Roll attitude are presented by 2 elements  One is fixed which symbolizes the aircraft.  The bar, is stabilized by the gyroscope and symbolizes the natural horizon. Bank indications presented by the position of a fixed pointer and a bank angle scale attached to the outer gimbal. The scale of the gyro horizon is calibrated in degrees. I& GI I Air-Driven Gyro Horizon Air-driven gyro horizon comprises the following main parts:  Case with air-inlet/outlet  Filter adapter assembly  Vertical-axis gyroscope  Outer gimbal (360⁰ freedom)  Inner gimbal (= rotor case, ±85⁰ freedom)  Fast-erection unit  Horizon Figure 6dial - Gimbal and Rotor Assembly of an Air-driven I& GI I The Operation of Air-Driven Gyro Horizon During operation the vacuum system creates a depression so that the surrounding air enters the inlet and passes through the channels to the jets I& GI I The Operation of Air-Driven Gyro Horizon When leaving the jets, the air hits on the rotor buckets, thus creating a force to spin the rotor at approx 15,000 rpm. After spinning the rotor, the air passes through a pendulous vane unit. Finally, it is drawn off by the vacuum source. I& GI I Functional Principle of a Gyro Horizon A Displacement Gyroscope whose spin axis is maintained Vertical by a gravity sensing device. The inner ring (gimbal) forms the rotor casing. It is pivoted parallel to the aircraft’s lateral axis. The outer ring is pivoted parallel to the aircraft’s longitudinal I& GI I Functional Principle of a Gyro Horizon The curved slot (`magnifying lever system’) determines the amount of magnification of the horizon bar movement presented to the pilot. The aircraft symbol may be either: rigidly fixed to the case or manually adjustable for pitch trim setting. I& GI I Functional Principle of a Gyro Horizon A background plate symbolizing the sky is fixed to the front end of the outer ring. It carries the bank pointer which indicates the actual bank on the bank-angle scale. The horizon bar and pointer are an accurately balanced assembly pivoted on the outer ring.  GI Climbing Horizon bar moves below the aircraft miniature Diving Horizon bar moves above the aircraft miniature I& GI I Gyro Erection Device The spin axis of a artificial horizon must be maintained Vertical. This is done by the erecting device consisting of 4 discharge ports in a chamber below the rotor. 4 vanes are suspended and hang vertically due to gravity One pair of ports is located laterally and the other pair of ports is situated for and aft of the chamber Figure 8 Air-driven Erection Device I& GI I Gyro Erection When the rotor spin axis Device is vertical all the 4 vanes are half covered. Air discharged from all the 4 ports are equal i.e. there will not be any resultant force which could affect the gyroscope’s vertical axis. If the spin axis is out of the vertical, the chamber will tilt with the rotor, but the vanes (due to gravity) will remain vertical. This causes one port to be opened fully and the opposite port to be closed fully. The air, leaving from one port only, creates a precessive force Figure 8 Air-driven Erection Device that will bring the gyro spin axis back to its vertical position I& GI I Electrically Driven Gyro Horizon The electrically driven gyro horizon In general, the comprises the following function and  Case main with an electrical parts: principle of connector  Vertical-axis gyroscope operation and  Outer gimbal (360 freedom) indications are the  Inner gimbal (= rotor case, 85 freedom) same as an Air-  Fast-erection unit The maindriven differences Gyro  Horizon dial (or drum) are:  Horizon bar Horizon.  Roll scale the way the rotor is  Aircraft symbol rotated and  Power warning flag. the gyro erection  Pitch trim adjusting knob. device. I& GI I Electrically Driven Gyro Horizon The gyroscope in ’any’ artificial horizon has the spin axis vertical. Gyro Erection Device 2 Types of Gyro Erection Device Ball-type Erection Unit ue Motor and Levelling Switch System I& GI I Gyro Erection Ball-type Erection Unit Device The ball-type erection unit utilizes the precessional forces which arise when steel balls within a rotating holder are affected by gravity. It contains 5 to 8 balls which are free to roll across a round disc with profiled hooks. When the Gyro tilts, the balls are release from the profiled hooks due to gravity. Figure 9 Ball-type Erection Unit I& GI I Gyro Erection Ball-type Erection Unit Device Since the centre of masses is shifted, the gravitational force exerts at the centre of masses, resulting in precessive force which pushes the gyro back to the vertical position (principle of precession). Figure 9 Ball-type Erection Unit I& GI I Gyro Erection Device Torque Motor and Levelling Switch System It consists of 2 torque control motors which are operated independe ntly by One switch levelling is mounted switches parallel to the lateral axis, the other parallel to the longitudina l axis I& GI I Gyro Erection Device Torque Motor and Levelling Switch System Each switch is connected to one torque motor and causes the application of a corrective torque to the required axis. The laterally mounted switch detects and corrects displacement in roll. Longitudinally mounted switch detects and corrects displacement I& GI I Gyro Erection Device Torque Motor and Levelling Switch System Each levelling switch consists of a sealed glass tube which contains 3 electrodes and a small quantity of mercury. They are mounted beneath the gyro housing. Filled with inert gas to prevent arcing. I& GI I Torque Motor and Levelling Switch System When the gyro is in operation, the mercury in the levelling switches lies at the centre Should the of the tubes. gimbals wander, the mercury switches close the circuits to the appropriate torque motor The ’fast erecting’ push button at the front of the and cause the gyro horizon may only be operated if the erection of the gyroscope has toppled after a hard manoeuvre gyro by and the aircraft is once again flying straight and application of level. a corrective EMERGENCY HORIZON I& GI I EMERGENCY HORIZON Powered by Used as a static inverter standby 115 V AC instrument. or 28 V DC from The gyro spin axis can be erected bybattery. pulling the ’fast erecting’ knob at the front of the instrument. The difference A red and white striped warning flag is displayed when,  the `Fast Erecting’ knob is pulled.  the power failure to the Indicator (loss of power). I& GI I I& GI I DIRECTIONAL GYROSCOPE What is a Directional Gyroscope? The purpose of Directional Gyro is to indicate the direction of the aircraft heading. Directional Gyroscope uses Directional Gyro I& GI I Introduction to Directional Gyro It is the first gyroscopic instrument introduced in aviation. Serves as a heading indicator. Replaced by Remote-Reading Compass Systems and Flight Director Systems. Employs a horizontal-axis gyroscope, and is always used in conjunction with the magnetic compass. DG provides short-term heading reference, while the magnetic compass provides a reliable long-term I& GI I List of main components of a Directional Gyro The air-driven Directional gyro comprises the following main parts: 1. Case with air-inlet/outlet ports 2. Filter adapter assembly 3. Horizontal-axis gyroscope (DG) 4. Inner gimbal ring 5. Synchronizer gear/ring 6. Caging and setting knob 7. Compass card. I& GI I Principle of Operation of Directional Gyro The Directional gyro consists of an outer ring pivoted about the vertical axis Z and carrying a circular card graduated in degrees. The card is referenced against a lubber line/index fixed to the gyroscopic frame. I& GI I Principle of Operation of Directional Gyro The Air-driven rotor: Has 3 degree of freedoms. is enclosed in a case (or: shroud) and spins axis is horizontal (X). The rotor is: supported in an inner ring and free to turn about the The inner ring is: horizontal axis Y. mounted in the vertical outer ring which carries the compass card and which is pivoted on the The gimbal verticalring axisassembly Z. (including Rotor) has freedom to rotate 55° either side of the horizontal axis Y. I& GI I Principle of Operation of Directional Gyro As the rotor spins: the gimbal system and the compass card are stabilized, the heading is read on the card against the lubber line. The rotor rotates at about 12, 000 and 18,000 rpm by the inlet air hitting rotor buckets via air jets. Figure 14 Air-driven I& GI I Due to gyroscopic inertia, the rotor’s spin axis maintains the same direction even during yawing. The relative movement between the gyro and the instrument case is seen Defines the short-term on compass card. heading reference. To synchronise DG heading with Magnetic Compass heading, a caging and setting knob is provided at the front of the case. Figure 14 Air-driven I& GI I Principle of Operation of Directional Gyro Reasons for caging the inner ring:  To prevent it from precessing when the outer ring is rotated manually.  To ensure that, on caging, its axis is at a right angle to the outer ring I& GI I Overall View of a Gyro I& GI I Indicato Purpose Types of Gyro Rotor Freedo r used spin m of moveme nt Turn and Turn Rate gyro Y axis 1 degree Slip Gyro Pitch & Displacement Z axis 2 Horizon Roll gyro degrees Direction Direction Directional gyro X axis2 al Gyro Gyro Properties degrees GYROSCOPE DRIVEN OPERATION Precessi Rigidity on PNEUMATI 3.5 - 4.5 Eng.drive Apparent C in Hg n vacuum Precession Random pump Actual ELECTRICA 115vAC Squirrel L 400Hz 3 cage Precession directly Phase induction proportional to Rotor ELECTRIC 28 VDc Conventio motor speed AL nal Precess 90° from the permanen point of force applied t magnet  CHECK 1. State the main components of a Gyroscope? 2. Explain the Functional principle of a Gyroscope. 3. Explain the term `Rigidity’ and `Precession’. 4. List the Gyroscopic instrument used in aircraft. 5. A Gyroscope is defined as ________________ 6. State the 3 axes of freedom in Gyroscope. 7. State the 3 moveable parts of a Gyroscope. 8. State and describe the 3 types of Precession of a Gyroscope. 9. The direction of Presession is always __________ 10. What determine the Precession of the Gyroscope. 11. The 2 principle methods used for driving the rotors of Gyroscope? 12. Vacuum pump provides a suction of ___________ in Hg. 13. The Gyroscopes of instruments using AC utilize the principle of the ______ 14. DC operated Gyroscope is based on the principle of the _______________ 15. The Turn and Slip indicator (Turn coordinator) is designed to indicate ____ The END