PILOT NAVIGATION

1. PILOT NAVIGATION Senior/Master Air Cadet

2. 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

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

4. Units

5. 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

6. Units This unit will look at the units commonly used for: vertical distance weather fuel speed aircraft weight pressure

7. 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

8. 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

9. 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

10. 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’!

11. Vertical Distance and Speed Terrain clearance is done with great care & the navigators number one priority The calculation of the safety altitude there should be no doubt

12. Vertical Distance and Speed Vertical Speed uses the same units as Vertical Distance Feet

13. Vertical Distance and Speed Vertical speed indicators which show rate of climb or descent are calibrated in thousands of feet for most military aircraft

14. 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

15. 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

16. 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!!!

17. Aircraft & Fuel You cannot measure fuel 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 )

18. AVTUR AVGAS 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 Even if one type of fuel is always used, its density will change with temperature changes In other words the density of fuel varies from type to type

19. 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 1.0 A typical jet engine fuel has a SG of 0.80

20. 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

21. Pressure Several different units are used to express pressures - according to the country of origin Various gasses & fluids in aircraft are pressurised

22. 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

23. Pressure Pressure is measured in PSI, Inches of mercury (US) , in MM of mercury, or millibars (MB) The average pressure at sea level is 1013 MB Millibars is in general use outside the USA

24. ALTITUDE IN FEET AIR PRESSURE IN MB Pressure SEA LEVEL 1013 10,000 700 18,000 500 24,000 400 30,000 300 34,000 250 39,000 200 Note an aircraft at 34000’ is pressurised to 5000’ and so the amount of oxygen at that height is a quarter of that at sea level If it was not for pressurisation all aboard would be unconscious

25. 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

26. Conclusion Aviation is the only major area of science still using such a wide variety of units Until countries agree to common units to their instruments, and whilst longitude & latitude remain so will the confusion There is a slow movement to metrication

27. Check of Understanding In aviation how are horizontal distances and speeds measured? horizontal distances are measured in nautical miles speed in knots

28. Check of Understanding How do the majority measure vertical distances? the majority of countries use feet to measure height or altitude

29. Check of Understanding How are Vertical Speed Indicators calibrated? Vertical speed indicators which show rate of climb or descent are calibrated in thousands of feet for most military aircraft

30. Check of Understanding In practical terms, how are aircraft and fuel measured? In practical terms it is weight

31. 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