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 21600 nm
(approx 25000 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
Plus 24’ = 55’
As we carry 1 across,
we now have 51º – 41º = 10º
Meridian Calculation
First Latitude
N 51º 24’
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
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)
Aircraft Speed
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.
A simplified ASI
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.
Pitot Tube
Airstream
Static Tube
Aircraft Speed
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.
A simplified ASI
Dynamic
+ Static
Static
But below the diaphragm is just Static.
Pitot Tube
Airstream
Static Tube
Aircraft Speed
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.
A simplified ASI
Dynamic
+ Static
Static
Pitot Tube
Airstream
Static Tube
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 = 1/10,000 of the distance
from the North pole to the equator
1 nm = 1 min of Longitude
1 nm = 5280 feet
1 nm = 1 min of Latitude
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?
The local time of the country flying over
British Summer Time
European Standard Time
Greenwich Mean 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?
275 nm
55° 50’ - 50° 25’
325 nm
50’ – 25’ = 25
55° – 50° = 5
5 x 60 = 300 450 nm
300 + 25 = 325nm
525 nm
Check Understanding
What does an ASI measure?
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
Forward thrust of
the aircraft engines
Check Understanding
In the RAF, aircraft speeds are
generally expressed in:
Knots
Miles per hour
Metres per second
Nautical miles per hour
Check Understanding
What is shown on an ASI?
Indicated Air Speed in knots
True Air Speed in knots
Dynamic Air Speed in knots
Nautical miles per hour
AIR NAVIGATION
End of Presentation