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.

The fast jet navigator in the RAFsolves the vector triangle

using a simplified mental calculation.

In civil airliners an onboard computersolves the triangle

and many other things besides.

Introduction

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

Computers and Numbers

3180

2½150

2120

1⅔100

1½90

1⅓80

9

8

7

6

5

4

3½

540

480

420

360

300

240

210160

nm per minGSnm per minGS

Magic Numbers are ground speeds in nautical miles per minute.

Computers and 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?

Example

2 nm/min120 kts =

Magic Numbers

20 miles at 2 nm per minute

20 divided by 2 = 10

10 minutes to run

( 120 divided by 60 )

Computers and Numbers You are in a Tornado at low levelover Wales doing 420 kts GS.You have 49 miles to run to the next turning point.

How long will this take?

Example

7 nm/min420 kts =

Magic Numbers

49 miles at 7 nm per minute

49 divided by 7 = 7

7 minutes to run

( 420 divided by 60 )

Computers and Numbers 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?

Example

Magic Numbers

1⅓20 mile leg

=2043

20 x 34

=

20 x 34

1

5

= 5 x 3 = 15 min

1⅓ nm/min80 kts =( 80 divided by 60 )

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.

10Ground Speed

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

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 AThe 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.

Check UnderstandingWhat is the name of

the hand held computer still used by navigators in private flying?

Nelson

Newton

Dawson

Dalton

Check UnderstandingFlying at 240 kts ground speed,

how long will it take to cover 40 nm ?

20 mins

6 mins

10 mins

2 mins

Check UnderstandingWhile flying you cover 3 nm every minute,

What is your ground speed?

210 kts

150 kts

180 kts

120 kts

Check UnderstandingIn a Tutor doing 80 knots,

how far will you travel in 6 minutes?

13⅓ nm

8 nm

10 nm

6 nm

Check UnderstandingEstimated Time of Arrival is important.

ETA calculations help the crew to determine . . .

Wind speed and direction

The shortest route

Drift corrections

Fuel calculations

Check Understanding

Contact the departure base

Close down

Initiate overdue action

No immediate action

An aircraft does not arrive at its destination on its ETA,

What action will Air Traffic Control take?

AIR NAVIGATION

End of Presentation