2 Aim To introduce the Concept and Fundamentals of Visual Navigation 7.1 Form of the earthIn order to apply this knowledge a student should have an understanding of the items listed in (a) to (h) and, if applicable, their effect on:position on the earthtime differencesdistance and direction(a) the shape and rotation of the earth(b) latitude, longitude(c) meridians of longitude, parallels of latitude(d) equator, Greenwich meridian(e) great circles, small circles, rhumb lines(f) difference between true and magnetic north(g) terrestrial magnetism, magnetic variation and the change in variation with time(h) distance on the earth i.e. relationship between a minute of latitude and a nautical mile.
3 Objectives Define “Visual Navigation and Dead Reckoning Navigation” Describe the “Form of the Earth”Identity our position, the direction we wish to travel and the distance we want to flyDescribe and calculate our air speed and velocity through the airCalculate and describe our altitude above the surface of the Earth
4 1. DefinitionsVisual Navigation is fun, challenging and very satisfying if done properly.Australia can be characterised as followsA sparse population with our capital and other major cities concentrated along the coast, principally in the eastern statesMany towns on charts are very small and easy to confuse with other townsA lack once away from the coast of easily recognisable land features due to the generally flat terrain and lack of trees, vegetation, rivers or other easily distinguishable features especially as you move further inlandThere are few Navigation Aids such as a VOR or NDB as you move further inland
5 How to successfully navigate your way around Australia 1. DefinitionsHow to successfully navigate your way around AustraliaUnderstand the concepts and principles involved in Visual NavigationPlan your flight carefully before you departBe organised and disciplined in your approach in flight to navigating from your take off point to your destinationBe “ahead of the aircraft” by which we mean anticipating what needs to be done in the next few minutes and calculating contingencies to cope with unexpected events
6 1. Definitions Visual Navigation Visual Navigation is where pilots use aviation charts (maps) to match observed ground features to determine the position (fix) of the aircraftVisual Navigation is based on a pilot:Being able to sight sufficient ground features be able to fix the position of the aircraft at not less then 30 minute intervalsNavigation Aids such as a GPS, VOR, NDB may be used to assist in determining the position of the aircraft but the prime means of navigating is by Dead Reckoning
7 1. Definitions Dead Reckoning Dead Reckoning (DR) is the process of calculating one's current position by using a previously determined position, or fix and advancing that position based upon known or estimated speeds over elapsed timeDead Reckoning is based on a pilot:Flying accurately the Headings (HDG) which have been previously calculatedKnowing the elapsed time flown since the last known positionBeing able to closely estimate the achieved Ground Speed (GS)Accurate chart (map) reading to initially identify your position based on time elapsed and then confirming your position by reference to ground features
8 2. Form of the Earth Shape and Movement The Earths shape can be described as an “oblate spheroid”It is flattened at the Poles, the surface is constantly changing due volcanic, seismic and tidal activityFor practical navigation purposes we can describe the earth as a perfect sphereThe Earth rotates eastward on its Polar AxisThe 2 points where this axis meets the surface are the North and South Geographical Poles (True North or True South)
9 2. Form of the Earth Great Circles A Great Circle is a circle drawn on the surface of the Earth with a plane that passes through the centre of the EarthExamples include:Meridians of LongitudeThe EquatorHorizontal Paths of Radio WavesA Great Circle divides a sphere into equal partsA Great Circle is the shortest path between 2 points on the surface of a Sphere such as the EarthPoint out that only one parallel of Latitude can be a Great Circle eg the Equator
10 2. Form of the Earth Small Circles A Small Circle is a circle drawn on the surface of the Earth that is not a Great CircleThe centre of a Small Circle is not at the centre of the EarthSmall circle of a sphere
11 2. Form of the Earth Rhumb Lines In navigation, a rhumb line is a line crossing all meridians of longitude at the same angleOn a plane surface this would be the shortest distance between two points.Over the Earth's surface at low latitudes or over short distances it can be used for plotting the course of a vehicle, aircraft or shipFor practical purposes a Great Circle direction and a Rhumb Line direction may for distances under 200 nm be considered the same.Ask what type of charts do we use in NavigatingWAC - Lambert Conformal – 1: 1,000,000VNC – Lambert Conformal – 1: 500,000VTC – Transverse Mercator Projection – 1: 250,000Image of a rhumb line, spiralling towards the North Pole
12 2. Form of the Earth Longitude All Great Circles containing the Polar Axis are “Meridians of Longitude”The prime meridian, based at the Royal Observatory, Greenwich in the UK, was established by Sir George Airy in 1851Meridians of Longitude are specified by their angular difference in degrees East or West of the Prime MeridianThe Prime Meridian is either 0° if on the Atlantic side of the Earth or 180° degrees if on the Pacific Ocean side of the EarthIf you divide 360° by 24 hours, you find that a point on Earth travels 15° of longitude every hour
13 2. Form of the Earth Latitude Lines of constant latitude, or parallels, run east–west as circles parallel to the equatorLatitude is an angle which ranges from 0° at the Equator to 90° (North or South) at the poles
14 3. Position, direction and distance Position FixingLatitude is used together with Longitude to specify the precise location of features on the surface of the EarthBy convention a position is reported in the following format;Latitude in Degrees, Minutes, Seconds, N or S of EquatorFollowed byLongitude in Degrees, Minutes, Seconds, W or E of the Prime MeridianSeconds can be replaced by decimal parts of a minute eg 6 Seconds = 0.1See handout Nav Chapter 1-1
15 3. Position, direction and distance Direction is the angular position of one point to anotherWe need a datum point to establish a reference point and for our purposes we use a North-South Line through our current position (local meridian)By convention we use a flat circle divided into 360 degrees to refer to specific Headings (HDG) to our destinationSee handout Nav Chapter 1-1
16 3. Position, direction and distance Describing DirectionThe 4 Cardinal Points are;North as 000, South as 180,East as 090, West as 270In between are all the otherpoints of the compassA HDG of 300 is where on thediagram?A HDG of 115 is where on theSee handout Nav Chapter 1-1
17 3. Position, direction and distance True NorthOur initial reference point for calculatingthe HDG to fly is True North or theNorth Geographic PoleThis makes it easy to measureangles and plot and measuretracks on our Navigation ChartsHowever we normally do nothave an instrument in our aircraftthat can display our HDG relativeto True North
18 3. Position, direction and distance Magnetic NorthWe have in our aircraft a compass that can display our HDG relative to Magnetic NorthThe Iron Core of the Earth acts as a huge magnet with the 2 magnetic poles being Magnetic North and Magnetic SouthCurrently the Magnetic North Pole lies in Hudson's Bay, Canada and it is currently moving toward Russia at between 55 and 60 km per yearThe difference between True North and Magnetic North is the Magnetic Variation and varies depending on the location of your aircraftMovement of Earth's North Magnetic Pole across the Canadian arctic, 1831–2001
19 Illustration of the Magnetic Field of the Earth 3. Position, direction and distanceIllustration of the Magnetic Field of the Earth
20 3. Position, direction and distance Magnetic VariationNavigation Charts display lines of equal Magnetic Variation, called IsogonalsWe adjust our planned True HDG to a Magnetic HDG by allowing for the Magnetic Variation to give us the Magnetic Track (TR) we need to follow to arrive at our destinationVariation is labelled east or west depending on whether the Isogonal is east or west of the Agonic Line (zero magnetic variation)If variation is East, magnetic direction is less than trueIf variation is West, magnetic direction in more than true(East is least, West is best)Use VNC to illustrate Isogonals
21 3. Position, direction and distance Magnetic DeviationMagnetic deviation refers specifically to compass error caused by magnetized iron within a ship or aircraft.This iron has a mixture of permanent magnetization and an induced (temporary) magnetization that is induced by the Earth's magnetic field.To calculate the magnetic deviation for an aircraft compass is “swung” at regular intervals using specific procedures.The outcome is a calibration chart which is displayed on or by the compass.The deviation is generally minor , less than 2 degrees.
22 3. Position, direction and distance Distance MeasurementFor Navigation we use Nautical Miles to measure distances1 Nautical Mile (nm) is the length, at the Earth's sea-level surface, of one minute of arc of a great circleThe International Nautical Mile is 1,852 metres or 6,076.1 feetConsequently, one degree of latitude (measured along a meridian) has an equivalent surface distance of 60 nautical milesFor other Horizontal Distances we use Kilometres or Metres, for example Runway length, visibility, horizontal distance from cloudFor Vertical Distances we use Feet, for example Altitudes to fly and vertical separation from clouds
23 4. Calculate Air speed and Velocity We fly in a mass of air that will move in accordance with the direction of the wind and its velocity.To accurately navigate we need to understand how the wind affects the path and speed of our aircraft over the ground.The 4 speeds we are interested in are:Indicated Airspeed (IAS)Calibrated Airspeed (CAS)True Airspeed (TAS)Groundspeed (GS)
24 Total Pressure – Static Pressure = IAS 4. Calculate Air speed and VelocityIndicated AirspeedOur Airspeed Indicator (ASI) in the C172 compares the total pressure measured by the Pitot Tube of the air due to its movement relative to the aircraft with the static pressure measured by the Static Vent.Total Pressure – Static Pressure = IASThe reading you obtain from the ASI is affected both by the speed and the density of the air.For manoeuvring the aircraft we use IAS as displayed by the ASI. For example flap limiting airspeeds and approach airspeeds
25 4. Calculate Air speed and Velocity Calibrated AirspeedOur Airspeed Indicator (ASI) in the C172 is subject to 2 types of errors;Instrument ErrorThis type of error is a result of friction within the instrument and/or bad design.Position ErrorThe location of the Pitot Tube and the Static Vents are critical to the accuracy of the ASI. Incorrect positioning may lead to errors when the airflow in the vicinity of the Pitot Tube and Static Vents is disturbed for example by lowering flaps.Calibration TableThe ASI is “calibrated” and the results are used to provide a Calibration Table for pilot use to aid in interpreting the ASI. In practice the errors are very small and we can generally assume IAS = CAS
26 4. Calculate Air speed and Velocity True AirspeedFor navigation purposes we need to be able to calculate the effect of changes in air temperature and air pressure on our speed through the air. Once calculated this gives us our True Airspeed (TAS)The ASI is calibrated in accordance with the international standard sea level atmosphere. Changes in the air density (temperature and pressure) will mean that the ASI does not display the TAS.Temperature ChangesThe warmer the air the less dense it is. Which means the aircraft must travel faster through the air to maintain the same IAS, therefore TAS is higher.Pressure ChangesAs we gain altitude there are less molecules of air and therefore the air is less dense. Which means that as we gain altitude we will have a lower IAS for the same TAS.
27 4. Calculate Air speed and Velocity Calculating True AirspeedThe G1000 calculates and displays our TAS (below the IAS indicator).We can however manually calculate the TAS with our Flight Computer.We do that by reference to the Outside Air Temperature and the Pressure Altitude.TAS will always be higher than IAS.
28 4. Calculate Air speed and Velocity Wind VelocityA Velocity is a rate of change of position in a given direction and is therefore a combination of both speed and direction.The speed and direction of an air mass is a velocity.By convention wind speed and direction is provided in the following format;Direction (3 digits)/ Speed (2 or 3 digits)ExampleA wind of 20 knots travelling from the north would be expressed as 360/20
29 4. Calculate Air speed and Velocity Weather ReportsWeather reports will provide wind information in the following formatDegrees MagneticFor surface winds eg for take off or landing in an ATIS or TAFDegrees TrueFor navigating through an air mass in an ARFORThis means that we must adjust the winds we use in navigating from one place to another to take into account the Magnetic Variation.See the Bureau of Meteorology – Aviation section for detailed information on aviation weather reporting.
30 4. Calculate Air speed and Velocity GroundspeedThe GS is one of the most important pieces of information a navigator needs to accurately fly to your destination.GS is found by adjusting your TAS for the effect of wind (direction and velocity).ExampleTAS = 120 knots, HDG = 360, Wind = 360/25Calculation – 120 knots – 25 knots of wind = GS of 95 knots(As there is nil cross wind the calculation is simple. We will try more complex examples using the Flight Computer to calculate our GS in future lessons)
31 4. Calculate Air speed and Velocity Time IntervalsWe use the GS to calculate a TI which in turn dictates your fuel requirements, the time you will arrive and the payload you can carry.We can check our GS as the flight progress by comparing the time it takes to fly over 2 known points with the distance actually travelled.ExampleDistance travelled between Alpha and Bravo = 90nmTime Interval to travel between Alpha and Bravo = 45 minutesGS = 90/45 or 2nm per minute therefore GS = 120 knots
32 4. Calculate Air speed and Velocity Triangle of VelocitiesThe Triangle of Velocities is typically used to calculate HDG and GSIn order to use the triangle we must know at least two of the following:Track (TR) and Groundspeed (GS)Wind (Direction and Strength)Heading (HDG) and True Airspeed (TAS)WindHeading and True AirspeedTrack and Groundspeed
33 5. Altimetry Vertical Navigation Unlike driving a car when flying we operate in a 3 dimensional environment and we need to have some way to navigate both horizontally and verticallyTerrain Separation: We need to ensure we know where we are in relation to the ground to ensure a safe flight to our destinationTraffic Separation: We need to have a common system of determining our altitude to ensure separation from other aircraftAircraft Performance: How high or low we fly will affect aircraft performance and how efficiently we can get to our destinationSee handout Nav Chapter 1-1
34 5. Altimetry Vertical Measurement Altitude: Measured by reference to Mean Sea Level (MSL)For example at Parafield we fly our circuit altitude is 1,000 feet Above Mean Sea Level (AMSL) so all aircraft are at the same AltitudeHeight: Measured by reference to a point above the groundFor example if we were flying above Mount Lofty at an altitude of 3,500 feet we would be at a height of 727 feet above Mount LoftyFlight Level: Measured by reference to a common pressure datum of hPaFor example above 10,000 aircraft set 1013 hPa on their Altimeters and fly at “flight levels” such as FL 150 (15,000 feet)See handout Nav Chapter 1-1AltitudeHeightSeaGround
35 5. Altimetry Altimeter Settings QNH: Setting the Altimeter to a specified QNH will indicate aircraft Altitude (AMSL)QFE: Setting QFE (Field Elevation) will determine the altitude above the groundNote: QFE is normally only used in some recreational aviation activities such as aerobatics or parachutingISA Pressure: The International accepted standard pressure at sea level is “ hPa”This is used to establish “flight levels” for aircraft flying at high altitude, for example in Australia above 10,000 feet, in the USA above 18,000 feetSee handout Nav Chapter 1-1
36 5. Altimetry QNH Settings We set the actual pressure or “QNH” before take off as the actual pressure is seldom the same as the ISA standard ofSetting the QNH on the Altimeter sub scale will provide the pilot with the actual altitude of the airfield and in flight the altitude of the aircraft AMSL.Pressure ChangesDuring the day the actual pressure will change and according the actual QNH will change.Pressure changes are advised in aviation weather forecasts, by ATC and by an airfield ATIS.If we are on the ground we can determine the QNH by setting the known airfield height above mean sea level and reading the QNH off the altimeter sub scale.See handout Nav Chapter 1-1
37 5. Altimetry Selection of Altitudes VFR HemisphericalAltitudes Below 10,000 FeetMagnetic TracksCruising Altitudes(Area QNH)1,5003,5005,5007,5009,5002,5004,5006,5008,500Hemispherical Cruising Altitudes are optional below 5,000 feet however it is recommend that wherever possible hemispherical altitudes should be flownSee handout Nav Chapter 1-1Why is it important to fly at the correct altitude?IFR aircraft fly at Evens or Odds Altitudes
38 VFR Hemispherical Cruising Levels Above 10,000 Feet 5. AltimetrySelection of Cruising LevelsVFR Hemispherical Cruising Levels Above 10,000 FeetMagnetic TracksCruising Levels(1013 hPa)115135155175195125145165185FL 115 is not available when the Area QNH is less than 997 hPaFL 125 is not available when the Area QNH is less than 963 hPaSee handout Nav Chapter 1-1Oxygen is required for flight above 10,000 feet.VFR flight is prohibited above 20,000 feet.