WIND TRIANGLE

In our early days of flying after going solo and having experienced the joy and responsibility of flying alone, we feel confident about ourselves and build a good relation with our aircraft. The next thing on any aspiring aviators agenda would be to fly for hours and explore new places and aerodromes .Navigation and flight planning are key subjects in aviation because no matter how good we fly the aircraft we yet have to reach our destination and most importantly reach on time.Before the advent of various radio aids that help us in navigation, pilots used to find their way with the help of visual landmarks (pilotage) or dead reckoning.

Dead reckoning is navigation solely by means of calculations based on time, airspeed, distance, and direction.Except for flights over water, dead reckoning is usually used with pilotage for cross-country flying. The heading and ground speed, as calculated from the variables before the flight, are constantly monitored and corrected by pilotage as observed from checkpoints.

Understanding a Few Terms

• HEADING: Heading is the direction in which the aircraft is pointing. It can also be said that it is the direction in which the fore and aft axis of the aircraft points.It is expressed in three digits and unit is degrees.
• TRACK: Track is the direction of our aircraft over the ground. The lines we draw on our map before we set out to fly are called tracks.Tracks are also expressed in three digits and unit is degrees.Now , as discussed above in case of no wind condition, the value of track and heading will be the same.
• WIND DIRECTION: It simply means the direction from which wind is coming.It is expressed in degrees.The wind direction is obtained from the forecast reports and can be provided by the Air Traffic Controller as well.
• TRUE AIRSPEED (TAS):It is the speed of the aircraft with reference to the surrounding air. The TAS is expressed in knots.
• GROUND SPEED (GS):The speed of the aircraft in relation to the ground. The ground speed will always be derived from the true air speed . it is expressed in knots as well.As discussed above, in no wind conditions, the TAS and GS will be equal.
• WIND SPEED:The speed with which the wind flows is provided in knots and given along with the wind direction information.

Effect of Wind

A very important aspect in navigation is the impact wind has on our journey.Wind is a mass of air moving over the surface of the earth.In our day to day life, we observe the effect of wind with the moving trees , dust, balloons and clouds. Wind has a similar effect on aircraft’s movement as well. Most of the navigation in aviation is derived from the navigation of the sea, it is easier to explain the impact of wind on air travel by comparing it to sea travel.

Lets assume that our boat is to leave the shore from place A and is destined for placed B. As the boat departs from place A, the water current is observed to be moving from left to right of the boat and due to this movement, the boat begins to drift to the right with the current. This results in the boat arriving at place C instead of place B.

The same logic applies in aviation but instead of the current , it is the wind that affects us. It is important to note that if the winds are calm, then the aircraft will point where the nose is pointed. In this case, we assume the wind coming from the left side.The aircraft departs from place A and even though it is pointing (heading) towards place B, the aircraft actually travels (track) to place C.

In the above examples, we have considered the wind from the side , that is, crosswind.The wind can be head on (headwind) or from the behind (tailwind) as well. To explain the effect of wind in those scenarios, we consider our aircraft flying north from point A to B with a True Airspeed of 120 Knots.Lets assume our wind is also from the north at a speed on 20 knots, this would result in our Ground Speed to become 100 knots as we have a headwind. On our return leg from place B to A, we are travelling south and our wind direction and speed remains the same. This would result in a tailwind of 20 knots and our resultant Ground Speed would be 140 knots.

What is Drift ?

Now that we know the difference between heading and track, it is understandable that in case of wind, the heading of the aircraft and the track to be followed will vary. The difference in angle between heading and track is known as drift angle.Lets consider our aircraft heading and track are same and track are the same but there is a wind from the left. The wind from the left will cause the aircraft track to push (drift) to the right of the desired track even though we maintain the same heading.

An easy way to recognize if our drift is left or right if to check if the track is to the left or right of our heading.If the track is to the left of the heading, there will be left drift.If the track is to the left of the heading, there will be left drift.

WIND TRIANGLE COMPONENTS

A wind triangle, the pilot’s version of vector analysis, is the basis of dead reckoning.
The wind triangle is a graphic explanation of the effect of wind upon flight. GS, heading, and time for any flight can be determined by using the wind triangle. It can be applied to the simplest kind of cross-country flight, as well as the most complicated instrument flight.The vectors required for constructing the wind triangle are Air vector, Wind Vector and Ground Vector.

• AIR VECTOR: The Air Vector consists of heading and True Airspeed (TAS) information. The TAS as we have already spoken above is the speed of the aircraft through air (not the indicated speed ). The air vector is drawn with one direction arrow.
• WIND VECTOR:The Wind Vector consists of wind direction and wind speed.It is important to know that the wind direction is always given in terms of the direction wind is coming from.For example, if the wind direction is 270 degrees, the wind is coming from the west .The Wind Vector is always is also given by three direction arrow.
• GROUND VECTOR:The Ground Vector consists of track and Ground Speed (GS).The ground vector is drawn by joining the air and wind vector.The vector is drawn with a two direction arrow.

WIND TRIANGLE EXAMPLE

In practice, pilots do not normally draw it out to scale on graph paper, but solve it using an analogue navigation computer. However, the Navigation Computer is merely a device for quickly producing a scale drawing and is actually drawing the Triangle of Velocities for you.It is necessary to consider a practical scale for representing speed as it will be important to draw the triangle on a convenient piece of paper if we are not using the navigation computer.The scale can be of our choice.For example, one inch can represent one knot or one cm can equal one knot.

Lets consider we are flying our aircraft with a TAS of 100 knots and heading north (000 degrees). The wind observed is coming from 240 degrees with a speed of 30 knots.With the help of our wind triangle, find out our track and ground speed ?

STEP 1: On a piece of paper (graph paper, ideally), draw in the Air Vector. It will have a direction of
000 degrees and a vector length equivalent to 100 knots (say, 100 mm).

STEP 2: It is time to draw our wind vector. The wind direction is from 240 degrees.Whatever units you used in proportion to 100 knots TAS (100 mm), draw the length of the wind vector in the same units (30 mm).

STEP 3: The final step is to join the air vector and the wind vector to obtain our ground vector.The ground vector will give us the resultant track and ground speed.

When you do that on your piece of graph paper, if you measure the track with a protractor you
will find that it is 012° and if you measure the length of the ground vector you will find a vector
length equivalent to 118 knots (118 mm).

What this entire problem tells us is that if we fly a heading of a 000 degrees and maintain a TAS of 100 knots, then with the wind mentioned in our example, the resultant path over the ground will actually be a track of 012°T at a ground speed of 118 knots.This is the very basics of flying, navigation and calculating the missing components of the wind triangle.With the advancements in technology and or with the use of the navigation computer you might never draw the wind triangle on a piece of graph paper. Even though you might never use it ,with the help of this technique we can be sure of never getting lost if navigation systems fail in our aircraft.

Here is a practice question for you to have a go at the wind triangle. Our aircraft is on a heading of 053 degrees with a TAS of 132 knots. The wind direction and speed are 205 degrees and 15 knots respectively.Find out the track and ground speed of the aircraft ? Type your answers in the comments down below or if you have any doubts regarding it.

FACT OF THE WEEK

The Hong Kong International Airport opened on July 6, 1998 and is located 30 kilometers northwest of Hong Kong Island. When it first opened its doors to the public, the airport was regarded as having the world’s largest passenger terminal buildings.  According to reports, the 1,255-hectare site area contributed nearly 1% to the total surface area of Hong Kong.

The airport has consistently received awards for its top-notch service, including at least 70 “Best Airport Awards,” according to its website. 

From 2016 to 2019, HKIA was named the “Best Global Airport” by Asia Cargo News. It also received the “Freighter Hub of the Year” award in 2019. 

In 2018, it was named “Airport of the Year” by International Airport Review and “Best Airport in Asia” by Monocle. – Rappler.com

Click the link to know more about Hong Kong International Airport https://www.hongkongairport.com/iwov-resources/file/the-airport/hkia-at-a-glance/facts-figures/HKIA_FactSheet_EN_200518A.PDF

We are done for this weeks post. I hope you gained a few more insights from the world of aviation.I appreciate you giving a few minutes of your day reading this post.Please don’t forget to solve the wind triangle question and drop your answers down below in the comments section.If you liked this post please share it with your fellow aviation lovers. Until next week stay safe and stay healthy.

YOUR COPILOT

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