AIR NAVIGATION Part 1 Distance & Speed

RECAP Latitude and Longitude lines divide the surface of the Earth into degrees and minutes. One minute of latitude represents one nautical mile (nm) 1 degree of latitude (60 minutes) equals 60nm

RECAP Latitude and Longitude lines divide the surface of the Earth into degrees and minutes. As a complete circle is 360° then 360 x 60 gives the circumference of the Earth as nm (approx statute miles).

RECAP Lines of Longitude are sometimes called MERIDIANS The line of Latitude must be given first. The starting point goes through Greenwich and is referred to as the “Prime Meridian”

Distances Between Points Nautical maps have no scales on the borders, we use the nm scale shown on each meridian.

Distances Between Points If two places are on the same meridian (longitude) then it is possible to calculate the distance between them, rather than having to actually measure it.

Distances Between Points For example: Torrejon airfield (in Spain) is due south of RAF St Athan (in Wales) on the same meridian These two latitudes are N40º29’ and N51º24’ So how do we calculate the distance between them?

Meridian Calculation First Latitude N 51º 24’ Second Latitude N 40º 29’ Subtracting gives 10º 55’ Remember – 60 degrees to a minute Because 29’ is more than 24’ 60’ minus 29’ = 31 As we carry 1 across, we now have 51º – 41º = 10º ? Plus 24’ = 55’

Meridian Calculation Second Latitude: N 40º 29’ Subtracting gives: 10º 55’ Now convert 10º 55’ into nautical miles: 10º multiply by 60 = 600 Add the 55’ = 655 nm First Latitude N 51º 24’

Aircraft Speed What is the measurement of speed for cars, motorcycles and land vehicles: – Miles per hour For aircraft, the speed is a measure of: – Nautical Miles per hour – (Knots) (remember 1’ of latitude is 1 nautical mile (nm))

Aircraft Speed What do we use to show the of speed for cars, motorcycles and land vehicles: – Speedometer For aircraft we use an Air Speed Indicator (ASI)

The Air Speed Indicator (ASI) measures the Dynamic Air pressure caused by forward motion of the aircraft. This is achieved by measuring the air captured in the Pitot Tube Aircraft Speed

The Air Speed Indicator (ASI) measures the Dynamic Air pressure caused by forward motion of the aircraft. The pressure of the air surrounding the aircraft ( “Static Pressure”) and the air pressure captured in the Pitot Tube (“Pitot Pressure”), are measured and compared. Aircraft Speed Pitot Tube Static Tube Airstream A simplified ASI

The Air Speed Indicator (ASI) measures the Dynamic Air pressure caused by forward motion of the aircraft. In forward flight the pressure above the diaphragm is both Dynamic + Static. But below the diaphragm is just Static. Aircraft Speed Pitot Tube Static Tube Airstream A simplified ASI Dynamic + Static Static

The Air Speed Indicator (ASI) measures the Dynamic Air pressure caused by forward motion of the aircraft. The two static pressures cancel each other out, and so the diaphragm moves up and down due only to the Dynamic Air Pressure. Aircraft Speed Pitot Tube Static Tube Airstream Dynamic Static A simplified ASI + Static

Aircraft Speed The Air Speed Indicator (ASI) measures the Dynamic Air pressure caused by forward motion of the aircraft. The movement due to dynamic pressure is amplified and displayed on the instrument as Indicated Air Speed (IAS) in knots.

Check Understanding Distance on the earth’s surface is measured in nautical miles. Which of the following is true? 1 nm = 1 min of Latitude 1 nm = 1/10,000 of the distance from the North pole to the equator 1 nm = 1 min of Longitude 1 nm = 5280 feet

Check Understanding One degree of latitude represents: 1 nm 6 nm 60 nm 360 nm

Check Understanding What time is used as standard in military and commercial aviation? Greenwich Mean Time The local time of the country flying over European Standard Time British Summer Time

Check Understanding Glasgow is due north of Plymouth (approximately on the same meridian). If Glasgow is latitude 55°50’ and Plymouth is latitude 50°25’ what distance are the two places apart? 525 nm 275 nm 450 nm 325 nm 55° 50’ - 50° 25’ 55° – 50° = 5 50’ – 25’ = 25 5 x 60 = = 325nm

Check Understanding What does an ASI measure? Forward thrust of the aircraft engines Dynamic air pressure caused by forward motion of the aircraft Overall speed of the surrounding air Dynamic air pressure caused by speed of the outside air

Check Understanding In the RAF, aircraft speeds are generally expressed in: Nautical miles per hour Miles per hour Metres per second Knots

Check Understanding What is shown on an ASI? Nautical miles per hour True Air Speed in knots Dynamic Air Speed in knots Indicated Air Speed in knots

AIR NAVIGATION End of Presentation