## Presentation on theme: "Senior/Master Air Cadet"— Presentation transcript:

Learning Outcomes Know the basic features of air navigation and navigational aids Understand the techniques of flight planning Understand the affects of weather on aviation

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: vertical distance weather speed fuel aircraft weight pressure

Vertical Distance and Speed
In aviation horizontal distances are measured in nautical miles and speed in knots One minute of arc measured at the centre of the earth equals 1 nm on the earth's surface These units are based on the length of a “GREAT CIRCLE” on the surface of the earth

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 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 Minute

World-wide the Met Office has changed to metric units
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 For aircraft the units used depend on the country of manufacture In practical terms it is weight (the effect of gravity on mass ) that we use Most US aircraft (70% of the worlds total ) use pounds or imperial tons. The rest use kilograms (kg) or metric tonnes

For fuel the situation is more complicated
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

weight of the same volume of water
Aircraft & Fuel Different types of fuel each have a Specific Gravity ( SG ) Water has a SG of 1.0 A typical jet engine fuel has a SG of 0.80 SG is a measure of the ratio between the weight of the fuel and the weight of the same volume of water

Aircraft & Fuel Conversion is done by calculator, a DR computer or the chart in the RAF flight information handbook This means a litre of jet fuel weighs 80% of the weight of a litre of water

Various gasses & fluids in aircraft are pressurised
Pressure Pressures are expressed in different units according to the country of origin usually PSI or Bars Various gasses & fluids in aircraft are pressurised

Our main concern is the pressure in the atmosphere
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

The average pressure at sea level is 1013 HPA
Air Pressure Air Pressure is measured Hectopascals (HPA) which has recently replaced Millibars (MB) The average pressure at sea level is 1013 HPA Hectopascals is in general use outside the USA which uses Inches of mercury Millimetres of Mercury is also used

If it was not for pressurisation, all aboard would be unconscious
Air Pressure AIR PRESSURE IN HPA ALTITUDE IN FEET SEA LEVEL 1013 10,000 700 18,000 500 24,000 400 30,000 300 34,000 250 39,000 200 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 Until countries agree to common units for their instruments, confusion is always possible in flight There is a slow movement to metrication

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 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

Similar presentations