PILOT NAVIGATION Senior/Master Air Cadet. Learning Outcomes Understand the affects of weather on aviation Know the basic features of air navigation and.

PILOT NAVIGATION

Senior/Master Air Cadet

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

Introduction

This portion of the syllabus will now tie the previous 3 subjects together

Units

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 unit 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 & the navigator’s number one

priority

For the calculation of the Safety Altitude there should be no doubt

Vertical Distance and Speed

Vertical Speed uses similar units to Vertical Distance

Feet per MinuteFeet per Minute

Vertical Distance and Speed

For most military aircraft, Vertical speed Indicators which show rate of climb or

descent are calibrated in

Thousands of Feet per MinuteThousands of Feet per Minute

Meteorological Units

World-wide the Met Office has changed to metric units

With the major exception of the USA

However even the Met Ofice must continue to use feet for altitude &

knots for windspeed

Aircraft & Fuel

Strictly 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

The fuel delivered to the aircraft, from the bowser, 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

Even if one type of fuel is always used, its density will change with temperature

changes

Aircraft & Fuel

Different types of fuel each have a Specific Gravity ( SG )

SG 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 DR computer or the chart in the RAF flight

information handbook

Pressure

Various gasses & fluids in aircraft are pressurised

Pressures are expressed in different units according to the country of origin

usually PSI or Bars

Air 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

Air Pressure

Air Pressure is measured Hectopascals (HPA) which has recently replaced Millibars (MB)

Hectopascals is in general use outside the USA which uses Inches of mercury

The average pressure at sea level is 1013 HPA

Millimetres of Mercury is also used

Air Pressure

20039,000

25034,000

30030,000

40024,000

50018,000

70010,000

1013SEA LEVEL

AIR PRESSUREIN HPA

ALTITUDEIN FEET

Note an airliner at 34000ft is pressurised to 5000ft and so the amount of oxygen at that

altitude is a quarter of that at sea level

If it was not for pressurisation, all aboard would be unconscious

Air Pressure

At a cruising altitude of 39,000 ft, a Boeing 767's cabin will be pressurised to an altitude

of 6,900 ft

Combat aircraft cockpits are usually pressurised considerably less than airliners,

with crews breathing a pressurised air/oxygen mix through masks

Conclusion

Aviation is the only major area of science still using such a wide variety

of units

There is a slow movement to metricationUntil countries agree to common units for

their instruments, confusion is always possible in flight

Check of Understanding

In aviation how are horizontal distances and horizontal speeds measured?

horizontal distances are measured in nautical miles

speed in knots

Check of Understanding

How do the majority measure vertical

distances?

the majority of countries use feet to measure height or altitude

Check of Understanding

How are Vertical Speed Indicators calibrated?

For most military aircraft Vertical Speed Indicators, showing rate of climb or descent are calibrated in

Thousands of Feet per MinuteThousands of Feet per Minute

Check of Understanding

In practical terms, how are aircraft and fuel measured?

In practical terms it is weight

Check of Understanding

What is Specific Gravity?

a measure of the ratio between the weight of the fuel

and the weight of the same volume of water

End of Learning Outcome 1