pilot navigation part 1 senior/master air cadet. learning outcomes understand the affects of weather...
TRANSCRIPT
Learning Outcomes
Understand the affects of weather on aviation
Know the basic features of air navigation and navigational aids
Understand the techniques of flight planning
Units
At school you will have been taught that in the modern world everything is
measured in metric units
However in real life many people use non metric measures. An example of this is the
use of miles & mph in the UK
Units
This lesson will look at the units commonly used for:
pressure
vertical distance
speedweather fuel
aircraft weight
Vertical Distance and Speed
In aviation horizontal distances are measured in nautical miles and speed in knots
These units are based on the length of a “GREAT CIRCLE” on the surface of the
earth
One minute of arc measured at the centre of the earth equals 1 nm on the earth's surface
Vertical Distance and Speed
In the vertical axis the majority of countries use feet to measure height or altitude. Only the former communist countries use metres
Vertical Distance and Speed
It must be noted that many countries who use feet have changed their maps to show
elevation in metres, - such as the UK OS maps
Vertical Distance and Speed
Great care is needed because an aircraft flown in thousands of feet can be in a very
dangerous position
!if a navigator reads a mountain top at 2000’ when it is 2000 metres which is
about 6000’!
Vertical Distance and Speed
Terrain clearance is done with great care and is the pilots/navigators
number one priority.
When calculating the safety altitude there should be no doubt.
Vertical Distance and Speed
Vertical speed indicators which show rate of climb or descent are calibrated in thousands of feet/ min for most military
aircraft
Meteorological Units
World-wide the met office has changed to metric units
With the major exception of the USA
However even the met office must continue to use feet for altitude &
knots for windspeed
Aircraft & FuelStrictly speaking aircraft & fuel should be
measured by mass
In practical terms it is weight (the effect of gravity on mass ) that we use
For aircraft the units used depend on the country of manufacture
Most US aircraft (70% of the worlds total ) use pounds or imperial tons. The rest use
kilograms (kg) or metric tonnes
Aircraft & Fuel
For fuel the situation is more complicated
In theory it should be measured by mass as the amount of thermal energy in one unit of fuel relates directly to its mass!!!
Aircraft & Fuel
You cannot measure fuel mass when an aircraft is in flight, so it is measured by
volume,
as in cars.
In cars we measure the fuel volume in litres (or gallons) & then calculate the fuel use in
km per litre (or mpg )
Aircraft & Fuel
However the use of volume in the air is not accurate enough as the type of fuel
& the temperature affect the mass per unit volume
AVTUR
AVGAS
In other words the density of fuel varies from type to type
Aircraft & Fuel
Even if one type of fuel is always used, its density will change with temperature changes.
AVTUR
AVGAS
On modern aircraft the fuel is indicated inlbs or kgs and the measuring systemcompensates for density and temperature.
Aircraft & Fuel
Different types of fuel each have a Specific Gravity ( SG )
This is a measure of the ratio between the weight of the fuel and the
weight of the same volume of water
Water has a SG of 1.0A typical jet engine fuel has a SG of 0.80
Aircraft & Fuel
This means a litre of jet fuel weighs 80% of the weight of a litre of water
Conversion is done by calculator, a Dalton computer or the chart in the RAF flight
information handbook
Pressure
Various gasses & fluids in aircraft are pressurised
Several different units are used to express pressures - according to the
country of origin
Pressure
Our main concern is the pressure in the atmosphere
The higher we go the less air there is & so pressure reduces as we gain height
Pressure
Pressure is measured in Pounds Per Square Inch PSI, Inches of mercury (US) , in MM of
mercury, or millibars (MB)
Millibars is in general use outside the USA
The average pressure at sea level is 1013 MB
Most modern electronic altimeters can switchbetween millibars and inches of mercury.
Pressure
20039,000
25034,000
30030,000
40024,000
50018,000
70010,000
1013SEA LEVEL
AIR PRESSUREIN MB
ALTITUDEIN FEET
Note: An aircraft at 34000’ has a quarter the amount of oxygen of one at sea level, which is why the aircraft is pressurised to about 5000ft.
If it was not for pressurisation all aboard would be unconscious
Pressure
At a cruising altitude of 39,000 feet, a Boeing 767's cabin will be pressurized to an altitude
of 6,900 feet¹
¹Commercial Airliner Environmental Control System: Engineering Aspects of Cabin Air Quality.
http://www.boeing.com/commercial/cabinair/ecs.pdf
Conclusion
Aviation is the only major area of science still using such a wide variety
of units
There is a slow movement to metrication
Until countries agree to common units to their instruments, and whilst longitude &
latitude remain so will the confusion
Check of Understanding
In aviation how are horizontal distances and speeds measured?
horizontal distances are measured in nautical miles
speed in knots
Check of Understanding
How do the majority of countries measure vertical
distances?
the majority of countries use feet to measure height or altitude
Check of Understanding
In what units do Vertical Speed Indicators their informationdisplay?Vertical speed indicators which show rate of climb or descent are calibrated in thousands
of feet/min for most military aircraft
Check of Understanding
In practical terms, in what units are aircraft and fuel measured?
In practical terms it is weight