PILOT NAVIGATION Part 1 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

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 speed weather 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 uses the same units as Vertical Distance Feet/ Min

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 & 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 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 in lbs or kgs and the measuring system compensates 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 1.0 A 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 switch between millibars and inches of mercury.

Pressure 20039, , , , , , SEA LEVEL AIR PRESSURE IN MB ALTITUDE IN 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.

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

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