AIR NAVIGATION

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AIR NAVIGATION
Part 1
Distance Speed Time
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LEARNING OUTCOMES

• On completion of this unit, you should
• Be able to carry out calculations to determine
  aircraft distance, speed and time
• Understand the principles of vectors and the
  triangle of velocities to establish an aircrafts
  track and ground speed

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LEARNING OUTCOMES

• Understand the principles of the 1 in 60 rule
• Understand the types of compass systems used for
  air navigation, how they work and their
  limitations
• Know the hazards that weather presents to
  aviation

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RECAP

• Latitude/Longitude grid divides 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

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As a complete circle is 360 then 360 x 60 gives
the circumference of the Earth as 21600
nm (approx 25000 statute miles).
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• Lines of Longitude are sometimes referred to as
  MERIDIANS
• When recording your position the line of
  Latitude must be given first.
• The starting point goes through Greenwich and is
  referred to as the
• Prime Meridian

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Finding Distance Between 2 Points

• Use a ruler and dividers
• If you do not have any equipment, using the marks
  along the edge of any piece of paper

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Change of Latitude

• If two places are on the same meridian then it is
  possible to calculate the distance between them
  rather than having to measure it
• For example Torrejon airfield (near Madrid in
  Spain) is due south of RAF St Athan. These two
  latitudes are N40º29 and N51º24
• How would we calculate the distance between them?

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Calculation
N 51º 24
First Latitude
Second Latitude
N 40º 29
Subtracting gives
10º 55
To convert 10º 55 into nautical miles
10º multiply by 60 600 Add the 55
655 nm
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Aircraft Speed

• The speed for cars, motorcycles and other
  land-based vehicles
• Miles per hour
• For aircraft, the speed is a measure of
• Nautical Miles per hour (Knots)

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Aircraft Speed

• We cannot use a speedometer to record aircraft
  speed.
• The aircraft flies through the air.
• We use an instrument called an Air Speed
  Indicator (ASI)

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Aircraft Speed

• ASI measures the dynamic air pressure
• Dynamic Air Pressure is the pressure caused by
  forward motion of the aircraft

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Aircraft Speed

• In forward flight the pressure above the
  diaphragm will consist of Dynamic Static.
• Below, the pressure is just Static
• The two static pressures cancel out and the
  diaphragm will move due to the dynamic pressure.

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Aircraft Speed

• The movement due to dynamic pressure is amplified
  and displayed on the instrument as Indicated Air
  Speed (IAS), reading in knots.

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Corrections

• The reading on the ASI can be in error because of
  two errors, namely Pressure Error and Instrument
  Pressure.
• Instrument error is caused by poor manufacturing
  tolerances when the instrument was built.

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Corrections

• Pressure Error previously known as position is
  caused by sensing incorrect values of static
  pressure due to the position of the static vents
  relative to the airflow around the aircraft.
• Both errors can be measured by testing the
  aircraft under controlled conditions and a
  calibration card with the combined errors is
  displayed in the cockpit next to the instrument.

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Calibrated Air Speed

• Once the two errors have been accounted for, we
  are left with Calibrated Air Speed (CAS),
  formerly known as Rectified Air Speed (RAS).
• IAS Pressure Error Instrument Error CAS
• Thus an IAS of 118 kts with a correction on the
  calibration card of 2 kts would give a
• CAS of 120 kts.

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True Air Speed (TAS)

• To obtain True Air Speed (TAS) from CAS you need
  to correct for air density changes caused by
  changes in temperature and altitude.
• This can be done by calculation or by
• Navigation Computer.

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TAS

• If you are flying at speeds greater than 300 kts,
  then you need to apply a correction for
  Compressibility Error, which is caused by air
  becoming compressed in the Pitot Tube.
• CAS Density Error Compressibility Error TAS

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Units of Time

• Time is probably the only example of scientific
  measurement where every nation uses the same
  units.
• Everyone is familiar with days, hours and
  minutes it is only necessary to ensure that you
  use hours when working with knots as this speed
  is nautical miles per hour.

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Units of Time

• In military and commercial aviation the 24 hour
  clock is used, set to Greenwich Mean Time GMT or
  Coordinated Universal Time (UTC) as it is now
  known.
• UTC can also be known as Zulu Time
• Summer Time or Daylight Saving Time is always
  ignored.

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Calculation of Time of Flight(Still Air)

• If a car travels 120 miles at 60 mph, it will
  take 2 hours to complete the journey.
• This is calculated using the distance speed time
  formulae

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Provided 2 quantities are known
From Speed Distance and Time
The 3rd one can be calculated using the following
formula
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Calculation Triangle (Still Air)
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SPEED (S) x TIME (T)
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Example
How fast must we go to cover 1500 nm in 5 hours?
Quantities known are
Distance
Time
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Therefore we use the following formulae
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Therefore
1500 nm
S (Knots)
300


5 hours
1
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Check of Understanding
One degree of latitude represents
1 nm
6 nm
60 nm
360 nm
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Glasgow is due north of Plymouth (approximately
on the same meridian). If Glasgow is latitude
5550 and Plymouth is latitude 5025 what
distance are the two places apart?
450 nm
525 nm
275 nm
325 nm
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55 50
-
50 25
55 50 5
5 x 60 300
50 25 25
300 25 325nm
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In the RAF, aircraft speeds are generally
expressed in
metres per second
miles per hour
nautical miles per second
Knots
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An ASI has an instrument correction factor of 3
kts and a pressure correction factor of -1 Kts.
If the instrument reads 130 kts what is the CAS?
130 Kts
132 Kts
133 Kts
134 Kts
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IAS Pressure Error Instrument Error CAS
130 kts 3 kts 1 kts CAS
133 kts 1 kts CAS
132 kts CAS
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A Tornado is flying at a TAS of 400 kts. How far
will it travel in 2 hrs?
200 nm
200 Km
800 nm
800 Km
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SPEED (S) x TIME (T)
D 400 kts x 2 hrs
D 400 x 2 800
Kts Nautical Miles per hour
800 Nautical Miles
800 nm