AIR NAVIGATION Part 4 Magic Numbers

Introduction So far we have talked about drawing vectors on paper. This is fine in the office or the classroom but impossible in the confines of a small aircraft.

Introduction So for many years, navigators have been using the Dalton hand held computer, and these are still used in the private flying world.

Introduction The fast jet navigator in the RAF solves the vector triangle using a simplified mental calculation. In civil airliners an onboard computer solves the triangle and many other things besides.

Computers and Numbers All Aircrew have to do a lot of mental arithmetic, even in these days of computers. To aid this Magic Numbers are used. It does not matter if you are flying in a Tutor or a Tornado, the method works equally well.

Computers and Numbers nm per min GS Magic Numbers are ground speeds in nautical miles per minute. nm per min GS 60 1 540 480 420 360 300 240 210 9 8 7 6 5 4 3½ 80 1⅓ 90 1½ 100 1⅔ 120 2 150 2½ 180 3

Computers and Numbers 10 minutes to run Example Magic Numbers You are flying at 120 kts GS. You have 20 miles to run before you reach your final destination. How long will this take? Magic Numbers 2 nm/min 120 kts = ( 120 divided by 60 ) 20 miles at 2 nm per minute 20 divided by 2 = 10 10 minutes to run

Computers and Numbers Example Magic Numbers 7 minutes to run You are in a Tornado at low level over Wales doing 420 kts GS. You have 49 miles to run to the next turning point. How long will this take? Magic Numbers 7 nm/min 420 kts = ( 420 divided by 60 ) 49 miles at 7 nm per minute 49 divided by 7 = 7 7 minutes to run

How long will a 20 mile leg take? Computers and Numbers Example You are on a cross-country exercise in a Tutor, heading into wind at 80 kts GS. How long will a 20 mile leg take? Magic Numbers 1⅓ nm/min 80 kts = ( 80 divided by 60 ) 20 mile leg 20 20 x 3 4 = = 1⅓ 4 3 1 5 20 x 3 4 5 x 3 = 15 min =

6 Minute Magic With the slower speeds it is often easier to think in terms of how far do we go in 6 minutes (1 tenth of an hour). This is simply the ground speed with the last zero removed. Ground Speed 10

6 Minute Magic So the Tutor doing 80 knots, will travel 8 miles in 6 minutes. Travelling at 110 knots, You go 11 miles in 6 minutes. An aircraft doing 140 knots. will travel 14 miles in 6 minutes.

6 Minute Magic Despite all the computers, some mental arithmetic is essential, whether you plan to join the RAF as aircrew, become an airline pilot, obtain a PPL, or simply make the most of the available air experience opportunities. The starting point is the 6 times table; no one in their right mind would dream of aviating without this knowledge.

E T A Estimated Time of Arrival (ETA) A by-product of solving the Triangle of Velocities is that by making the DST calculation using Ground Speed and Distance To Go, we can calculate the time that it will take to reach the next turning point or destination. This time is called Estimated Time of Arrival (ETA)

E T A The Estimated Time of Arrival (ETA) is important both for fuel calculations and for Air Traffic control purposes. A particular application of this is the ETA for the destination. If you do not arrive on time, Air Traffic will have to take overdue action; similar to a search party going out to find a group of walkers who have not returned from a trek on time.

still used by navigators in private flying? Check Understanding What is the name of the hand held computer still used by navigators in private flying? Dalton Newton Dawson Nelson

Check Understanding 2 mins 6 mins 10 mins 20 mins Flying at 240 kts ground speed, how long will it take to cover 40 nm ? 2 mins 6 mins 10 mins 20 mins

Check Understanding 120 kts 150 kts 180 kts 210 kts While flying you cover 3 nm every minute, What is your ground speed? 120 kts 150 kts 180 kts 210 kts

how far will you travel in 6 minutes? Check Understanding In a Tutor doing 80 knots, how far will you travel in 6 minutes? 6 nm 8 nm 10 nm 13⅓ nm

Check Understanding Fuel calculations The shortest route Estimated Time of Arrival is important. ETA calculations help the crew to determine . . . Fuel calculations The shortest route Drift corrections Wind speed and direction

Check Understanding No immediate action Close down An aircraft does not arrive at its destination on its ETA, What action will Air Traffic Control take? No immediate action Close down Initiate overdue action Contact the departure base

AIR NAVIGATION End of Presentation