Air Navigation Revision Booklet
Chapter 2 The Triangle of Velocities
Speed and direction together are known as Velocity.
Velocity can be represented by a vector, the length of the line represents
speed and the direction of the line represents the bearing from true north.
The velocity of an aircraft can be affected by the movement of the air resulting
in the aircraft going off of its intended track, this is known as Drift.
The Air Triangle can be used to allow for drift and work out how to get the
aircraft back on track.
Heading and True Air Speed (HDG/TAS)
Drift
Wind speed and Direction
Track and Ground Speed
The six components of the Air Triangle are:
- Heading and True Air Speed
The direction the aircraft is going in and the speed it is travelling through the
air shown by a vector (line) with one arrow
- Wind velocity
A vector showing the speed and direction of where is wind is blowing from
shown with a vector with three arrows
- Track and Ground speed
Where the aircraft is actually going and the speed it is travelling over the
ground, vector shown with 2 arrows
- Drift
The angle at which the aircraft is being blown off of its heading
If we know Track, True Air Speed and Wind Velocity we can work out
Groundspeed and Heading when flight planning. If in the air we know True
Airspeed and Heading so we can work out ground speed and track. The
Dalton computer is used to work out the calculations.
Magic Numbers make calculations easier. There refer to how long it takes to
do 1 nm at different speeds. Remember all speeds at in nautical miles per
hour. So if you travel at 60kts it will take you 1min to do 1nm.
If we were travelling at 540kts how far would be go in 1 min? You need to
know your six times table. Ignore the zero on the end of 540kts and you have
54, 54/6 is 9 so you will go 9nm in 1 min at 540kts.
You can use this to work out how long it would take to do certain distances at
certain speeds e.g.
Flying at 420kts and you need to turn in 49nm to turn at the correct time you
need to know how long it will take to get to your tuning point. At 420kts you
will go how far in 1 min? Ignore the zero = 42/6 = 7 so you go 7nm in 1 min.
So how long will it take to do 49nm? 49/7=7 so it is 7min until you need to
turn.
If you need to know how far you will go in 6mins and the speed ends in a zero
just remove the zero and you will have the distance in nm for 6mins!
By working out the time to your next turning point you can also work out your
estimated time of arrival (ETA). This is important to make sure you have
enough fuel and for Air Traffic control to know when to expect you so they can
start overdue action if necessary.
Air Navigation The Triangle of Velocities Revision Questions
1. A single line, drawn on paper, representing speed and direction is known
as:
a. A vector
b. A velocity
c. A vertical
d. A vector triangle
2. A velocity consist of:
a. Speed and direction together
b. speed only
c. several speed vectors together
d. direction only
3. A vector is a line, drawn to represent a velocity. This is achieved by:
a. The bearing represents knots at all times
b. The bearing represents speed and the length represents direction
c. The length represents mph at all times
d. the bearing of the line represent the direction and the length of the line
represents the speed
4. In the Air Triangle, the heading vector includes 2 components. They are:
a. Heading and Wind velocity
b. Heading and Groundspeed
c. Heading and drift
d. Heading and true airspeed
5. In the airspeed triangle drift is:
a. The angle between the heading and track vectors
b. the bearing of the wind vector
c. the angle between the wind and track vectors
d. the angle between the heading and wind vectors
7. In the air triangle of velocities the angle between heading and track vectors
is known as:
a. Drift
b. Wind velocity
c. Groundspeed
d. Track made good
8. The air triangle of velocities can be used to calculate flight data. There are
6 elements in total. How many elements are needed to calculate those
missing?
a. 4
b. 5
c. 6
d. 2
9. You are flying at 120kts groundspeed. How long will it take to fly 20nms?
a. 6 mins
b. 60 mins
c. 2 mins
d. 10 mins
10. You fly between 2 features on the ground and note that it takes 3 minutes.
If the features are 18nm apart what is your groundspeed.
a. 360kts
b. 280kts
c. 180kts
d. 54kts
11. You are flying in a tornado at 420kts groundspeed. How many nms do you
travel each minute?
a. 7nm
b. 8nm
c. 42nm
d. 6nm
12. Aircrew are always aware of their Estimated time of arrival (ETA) Why is
this?
a. Fuel flow rate depends on ETA
b. ETA is important for fuel calculations and air traffic control purposes
c. It is the easiest calculation to do
d. A revised ETA tells them that the wind has changed
13. An aircraft departs from base but does not arrive at the destination on its
estimated time of arrival. What action will Air Traffic Control take:
a. Initiate overdue action
b. No immediate action is required
c. Close down
d. contact the departure base
14. Regular checks of estimated time of arrival are important. ETA
calculations helps the crew to determine that:
a. The drift is correct
b. they are flying the shortest route
c. the wind velocity will not change
d. the aircraft has sufficient fuel to reach the destination