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Aim To introduce the Concept and Fundamentals of Visual Navigation.

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Presentation on theme: "Aim To introduce the Concept and Fundamentals of Visual Navigation."— Presentation transcript:

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2 Aim To introduce the Concept and Fundamentals of Visual Navigation

3 Objectives 1.Define “Visual Navigation and Dead Reckoning Navigation” 2.Describe the “Form of the Earth” 3.Identity our position, the direction we wish to travel and the distance we want to fly 4.Describe and calculate our air speed and velocity through the air 5.Calculate and describe our altitude above the surface of the Earth

4 1. Definitions Visual Navigation is fun, challenging and very satisfying if done properly. Australia can be characterised as follows A sparse population with our capital and other major cities concentrated along the coast, principally in the eastern states Many towns on charts are very small and easy to confuse with other towns A 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 inland There are few Navigation Aids such as a VOR or NDB as you move further inland

5 1. Definitions How to successfully navigate your way around Australia 1.Understand the concepts and principles involved in Visual Navigation 2.Plan your flight carefully before you depart 3.Be organised and disciplined in your approach in flight to navigating from your take off point to your destination 4.Be “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 is where pilots use aviation charts (maps) to match observed ground features to determine the position (fix) of the aircraft Visual 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 intervals Visual Navigation Navigation 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 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 time Dead Reckoning is based on a pilot: Flying accurately the Headings (HDG) which have been previously calculated Knowing the elapsed time flown since the last known position Being 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 1. Definitions Dead Reckoning

8 2. Form of the Earth 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 activity For practical navigation purposes we can describe the earth as a perfect sphere The Earth rotates eastward on its Polar Axis The 2 points where this axis meets the surface are the North and South Geographical Poles (True North or True South) Shape and Movement

9 2. Form of the Earth A Great Circle is a circle drawn on the surface of the Earth with a plane that passes through the centre of the Earth Examples include: Meridians of Longitude The Equator Horizontal Paths of Radio Waves A Great Circle divides a sphere into equal parts A Great Circle is the shortest path between 2 points on the surface of a Sphere such as the Earth Great Circles

10 2. Form of the Earth A Small Circle is a circle drawn on the surface of the Earth that is not a Great Circle The centre of a Small Circle is not at the centre of the Earth Small circle of a sphere Small Circles

11 2. Form of the Earth In navigation, a rhumb line is a line crossing all meridians of longitude at the same angle On 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 ship For practical purposes a Great Circle direction and a Rhumb Line direction may for distances under 200 nm be considered the same. Image of a rhumb line, spiralling towards the North Pole Rhumb Lines

12 2. Form of the Earth 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 1851 Meridians of Longitude are specified by their angular difference in degrees East or West of the Prime Meridian The Prime Meridian is either 0° if on the Atlantic side of the Earth or 180° degrees if on the Pacific Ocean side of the Earth If you divide 360° by 24 hours, you find that a point on Earth travels 15° of longitude every hour Longitude

13 2. Form of the Earth Lines of constant latitude, or parallels, run east–west as circles parallel to the equator Latitude is an angle which ranges from 0° at the Equator to 90° (North or South) at the poles Latitude

14 3. Position, direction and distance Latitude is used together with Longitude to specify the precise location of features on the surface of the Earth By convention a position is reported in the following format; Latitude in Degrees, Minutes, Seconds, N or S of Equator Followed by Longitude in Degrees, Minutes, Seconds, W or E of the Prime Meridian Seconds can be replaced by decimal parts of a minute eg 6 Seconds = 0.1 Position Fixing

15 Direction is the angular position of one point to another We 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 destination Direction 3. Position, direction and distance

16 The 4 Cardinal Points are; North as 000, South as 180, East as 090, West as 270 In between are all the other points of the compass A HDG of 300 is where on the diagram? A HDG of 115 is where on the diagram? Describing Direction 3. Position, direction and distance

17 Our initial reference point for calculating the HDG to fly is True North or the North Geographic Pole This makes it easy to measure angles and plot and measure tracks on our Navigation Charts However we normally do not have an instrument in our aircraft that can display our HDG relative to True North True North 3. Position, direction and distance

18 We have in our aircraft a compass that can display our HDG relative to Magnetic North The Iron Core of the Earth acts as a huge magnet with the 2 magnetic poles being Magnetic North and Magnetic South Currently the Magnetic North Pole lies in Hudson's Bay, Canada and it is currently moving toward Russia at between 55 and 60 km per year The difference between True North and Magnetic North is the Magnetic Variation and varies depending on the location of your aircraft Magnetic North Movement of Earth's North Magnetic Pole across the Canadian arctic, 1831– Position, direction and distance

19 Illustration of the Magnetic Field of the Earth 3. Position, direction and distance

20 Navigation Charts display lines of equal Magnetic Variation, called Isogonals We 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 destination Magnetic Variation Variation 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 true If variation is West, magnetic direction in more than true (East is least, West is best) 3. Position, direction and distance

21 Magnetic 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. Magnetic Deviation The outcome is a calibration chart which is displayed on or by the compass. The deviation is generally minor, less than 2 degrees. 3. Position, direction and distance

22 For Navigation we use Nautical Miles to measure distances 1 Nautical Mile (nm) is the length, at the Earth's sea-level surface, of one minute of arc of a great circle The International Nautical Mile is 1,852 metres or 6,076.1 feet Consequently, one degree of latitude (measured along a meridian) has an equivalent surface distance of 60 nautical miles For other Horizontal Distances we use Kilometres or Metres, for example Runway length, visibility, horizontal distance from cloud For Vertical Distances we use Feet, for example Altitudes to fly and vertical separation from clouds Distance Measurement 3. Position, direction and distance

23 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) Speed 4. Calculate Air speed and Velocity

24 Our 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 = IAS The 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 Indicated Airspeed 4. Calculate Air speed and Velocity

25 Our Airspeed Indicator (ASI) in the C172 is subject to 2 types of errors; Instrument Error This type of error is a result of friction within the instrument and/or bad design. Position Error The 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 Table The 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 Calibrated Airspeed 4. Calculate Air speed and Velocity

26 For 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 Changes The 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 Changes As 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. True Airspeed 4. Calculate Air speed and Velocity

27 The 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. Calculating True Airspeed 4. Calculate Air speed and Velocity

28 A 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) Example A wind of 20 knots travelling from the north would be expressed as 360/20 Wind Velocity 4. Calculate Air speed and Velocity

29 Weather reports will provide wind information in the following format Degrees Magnetic For surface winds eg for take off or landing in an ATIS or TAF Degrees True For navigating through an air mass in an ARFOR This 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. Weather Reports 4. Calculate Air speed and Velocity

30 The 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). Example TAS = 120 knots, HDG = 360, Wind = 360/25 Calculation – 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) Groundspeed 4. Calculate Air speed and Velocity

31 We 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. Example Distance travelled between Alpha and Bravo = 90nm Time Interval to travel between Alpha and Bravo = 45 minutes GS = 90/45 or 2nm per minute therefore GS = 120 knots Time Intervals 4. Calculate Air speed and Velocity

32 The Triangle of Velocities is typically used to calculate HDG and GS In 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) Track and Groundspeed Heading and True Airspeed Wind Triangle of Velocities 4. Calculate Air speed and Velocity

33 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 vertically Terrain Separation: We need to ensure we know where we are in relation to the ground to ensure a safe flight to our destination Traffic Separation: We need to have a common system of determining our altitude to ensure separation from other aircraft Aircraft Performance: How high or low we fly will affect aircraft performance and how efficiently we can get to our destination 5. Altimetry Vertical Navigation

34 5. Altimetry 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 Altitude Height: Measured by reference to a point above the ground For 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 Lofty Flight Level: Measured by reference to a common pressure datum of hPa For example above 10,000 aircraft set 1013 hPa on their Altimeters and fly at “flight levels” such as FL 150 (15,000 feet) Vertical Measurement Ground Sea Height Altitude

35 5. Altimetry QNH: Setting the Altimeter to a specified QNH will indicate aircraft Altitude (AMSL) QFE: Setting QFE (Field Elevation) will determine the altitude above the ground Note: QFE is normally only used in some recreational aviation activities such as aerobatics or parachuting ISA 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 feet Altimeter Settings

36 5. Altimetry We set the actual pressure or “QNH” before take off as the actual pressure is seldom the same as the ISA standard of Setting 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 Changes During 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. QNH Settings

37 VFR Hemispherical Altitudes Below 10,000 Feet Magnetic Tracks Cruising Altitudes (Area QNH) 1,500 3,500 5,500 7,500 9,500 2,500 4,500 6,500 8,500 Hemispherical Cruising Altitudes are optional below 5,000 feet however it is recommend that wherever possible hemispherical altitudes should be flown Why is it important to fly at the correct altitude? IFR aircraft fly at Evens or Odds Altitudes Selection of Altitudes 5. Altimetry

38 VFR Hemispherical Cruising Levels Above 10,000 Feet Magnetic Tracks Cruising Levels (1013 hPa) FL 115 is not available when the Area QNH is less than 997 hPa FL 125 is not available when the Area QNH is less than 963 hPa Oxygen is required for flight above 10,000 feet. VFR flight is prohibited above 20,000 feet. Selection of Cruising Levels 5. Altimetry

39 Questions?


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