4. LESSON 31 - NAVIGATION

Key points of attention:
  • Prepare your flight well so you don’t need to spend too much time looking at your map or flight computer
  • Practice using and changing the flight computer settings on the ground; read the manual beforehand
  • Try and memorize landscape features while flying – this will make it easier to find your way back
  • Keep your finger on your last known position on the map so you can quickly find your position if you get lostNavigation is easier if you fly a bit higher
  • Always keep an eye on the wind direction

Just as you can get lost in a busy city, you can lose your sense of direction in the air. You will probably soon know your way around your training airfield, you will recognize landscape features (natural or man-made) and you will know where the airfield is in relation to a village or city. But how can you find your way back if you are flying further away or somewhere you haven’t been before?

There are several ways of navigation in gliding:
  • Just ‘knowing’ your way around (this only works if you know the local area very well)
  • Determining your course on a traditional map (called “dead reckoning”, see below)
  • Using a GPS-based flight computer
  • Using both a flight computer and a map

When you are flying alone, you will need to know how you can always find your way back home. In this lesson, your instructor will show you how to use the flight computer and the aeronautical chart. But remember that proper flight preparation is equally important, as this will give you a better idea of what to expect as well as more time to concentrate on flying (rather than navigating).

DEAD RECKONING

This is the process of calculating your current position by using estimates of groundspeed and track over time. Important factors that make ‘dead reckoning’ a bit more difficult and that you have to take into account are: the wind, circles in thermals along the way and a varying airspeed (because you will fly at the optimal speed to not waste altitude). As resources you need at least an aeronautical chart (a three-dimensional map) and compass.

By carefully studying the legend you already get a good idea of what you can find on an aeronautical chart. It is basically a regular map of towns, cities, rivers, roads and railways. In addition, there are marked landscape elements that you can see from the air, such as power stations and racetracks, and large drawn boxes that indicate airspace restrictions. Each restriction has an upper and lower limit and airspace classification. Because of these extra features, the map becomes three-dimensional. Some airspace restrictions mean that you can cross the area only at a certain height. You will learn about this in detail before you take your exam for your license.

 

The large boxes and coloured circles indicate the airspace restrictions around Lasham airfield.

Four important basic terms for navigating an aeroplane:

 Heading: The direction the glider’s nose is pointing. If you look at your compass, you are using the magnetic properties of the earth and you are flying a “compass heading.”
 Track: The track refers to the path you are following over the ground, thus taking drifting off by the wind into account.
 Bearing: The bearing is the direction in which a location on your map is, indicated in degrees on a 360-degree scale. When you align the track and the bearing you fly straight to that location.
 Course:  The course is the desired direction of travel over the ground.


It’s wise to keep your finger on your last known position along the way. If you do get lost, you can compare striking landscape features with the part of the map near your finger to quickly re-establish your position. 

Your actual track will always differ slightly from the route you have prepared.

FLIGHT COMPUTERS

There are many different flight computers on the market, and most gliders nowadays have a flight computer on board.They all use satellites (the Global Positioning System) to determine your position very accurately. In addition to GPS, some computers also use pressure, temperature, acceleration and even live weather data to make even more accurate calculations. Often you will see a moving map that also shows you the airspace restrictions. There are also portable flight computers for sale. Alternatively, you can install flight computer software as an application on your mobile phone. These two options are often cheapest, but have the disadvantage that they take up extra space in the cockpit. Flight computers generally make navigation a lot easier.

A modern flight computer can perform hundreds of calculations simultaneously. But really, only a couple of things are really important when you want to get from A to B:
  1. Whether your track matches the desired course. Most flight computers calculate your drift very accurately and indicate how many degrees you have to turn left or right to reach your goal.
  2. What your estimated arrival height will be. Based on your settings and circumstances, you may need to gain height to arrive safely.
  3. (If you have a moving map) If your route remains clear of restricted or prohibited airspace. Airspace restrictions can be temporary and often change; remember to regularly update the airspace database of your flight computer.

Other calculations that modern flight computers can make are: wind direction and strength, distance to your goal, height above ground level, ground speed, optimal flying speed based on the McCready theory (see Lesson 26), ETA (= estimate time of arrival) and so forth.

Example of a modern flight computer. The possibilities are endless.

Practice using and changing the flight computer settings on the ground and always read the manual before using the computer during flight. Make sure you don't have to figure out how a new system works while you are flying, that would be too much of a distraction from flying.

In addition to a flight computer, most glider pilots use the most recent aeronautical chart to find things quickly and easily. Eventually, you will need to master both ways of navigating. One of the advantages of a traditional map is that the battery can’t run out.

THE WIND
Two important things to constantly be aware of while navigating are wind direction and wind strength. Not only do they determine how much drift you will experience, they are also fundamental in case you have to make a field landing (see Lesson 32). There are several ways of determining the wind direction when you cannot see a windsock:
  • smoke from fires or chimneys
  • clouds of sand or dust: sometimes dust is clearly visible when a farmer is mowing a field
  • windmills: these are generally facing the wind
  • digital indication of the wind on a flight computer (but be aware that this is not always very reliable).

Without a windsock it is difficult to see what the strength of the wind is at ground level. You can roughly estimate the wind strength based on how much drift you experience when flying. But you can also compare your ground speed (from the flight computer) to your airspeed when flying parallel to the wind.

LOW AND LOST

You will soon find out that navigating is much easier when you fly a bit higher. After all, when you are flying low, you can’t see as far, you will generally be busier flying the glider and trying to find thermals, and you may have to decide to make a field landing. If you do get lost, stay calm and remember that this has happened to most other glider pilots at least once. Focus on flying the plane first and make a plan after that. Often it is wise to just fly in the direction of the planned course until you come across something that you recognize again. But keep in mind that you don't accidentally enter prohibited airspace, because this could be dangerous for you and for other traffic. Sometimes it also helps if you can climb a little higher so you can look for clues further ahead. A third option is to make one big turn, which might allow you to identify eye-catching landscape elements that correspond to those on your map. If none of these options has been helpful, then you can use the feature on your flight computer that lets you choose from a list of nearest airports. We recommend, again, finding out how this feature works on the ground before you might need it during flight.

Two last tips that can help you getting back on track when you are lost: before entering a thermal, it is wise to take in some of the landscape features on your route to make it easier to resume on the same track later. And if you are flying at the beginning and end of the day, then you can determine your course roughly by looking at the position of the sun: the sun rises in the east and sets in the west.