Pilotage is flying by reference to a aviation maps and ground references using a prepared flight plan. Basically, one uses aviation maps to determine course headings and distances between waypoints. A good waypoint is a clear visual reference that can be identified from the air. It's best to space them approximately 10 minutes apart so there is little chance of getting off course or lost completely. After determining course heading and distance between waypoints, the flight plan is then adjusted for wind. If there was no wind, airplane navigation would be mush simpler, but that is a rare condition. A Wind Correction Angle (WCA) must be calculated for each course heading. From the map, it can be determined the heading to fly on the compass, but unless the wind is either directly ahead or directly behind, the plane will move laterally off course some what. Think of it like trying to swim across a flowing river. If you wanted to arrive on the other side directly across from where you started, you would need to swim at an angle up river to offset the effects of water flowing downstream. That angle is determined by how fast you're swimming and how fast the river is flowing. In aviation, the river is the wind and the plane is the swimmer. If I want to fly a heading of 90 degrees over the ground, but the wind is blowing from North (O degrees), I would need to angle the nose of the plane into the wind to some degree. That's the WCA!
The wind also effects an airplanes speed over the ground. Most planes fly at a very predictable airspeed given a particular power setting. This is great for planning purposes. The Cessna Skyhawk I fly travels approximately 120kts per hour. So if I have a distance between two waypoints of 20 nautical miles (nm), it should take 10 minutes to fly that leg. Unfortunately, our friend the wind messes with this simple math too. The plane flies through the air at 120kts, but what is the air doing relative to the ground? If the plane is flying directly downwind (with the wind) which is blowing at 10kts, the plane's speed over the ground would be 130kts. And on the trip home, the plane would be traveling at 110kts over the ground. OK, not so hard, just add or subtract the speed of the wind to the airspeed of the plane. But that only works if the wind is directly in front or behind. What about if the wind is coming from a 45 degree angle to our route of flight? Well we know from above, we will need to calculate a WCA and fly a heading slightly different than the intended course over the ground, but what about speed over the ground? A wind blowing at an angle to the direction of flight can be mathematically broken into 2 parts: the headwind portion and the crosswind portion. A simple example would be a 10 kt wind blowing from 45 degrees to your intended course is made up of 5kts of headwind and 5kts of crosswind. The headwind portion is used to calculate speed of the ground and the crosswind portion is used to determine WCA.
So, creating a flight plan requires the pilot to understand these concepts, be good at math, plot accurate courses on the maps with clearly identifyable waypoints, measure the distances between those waypoints accurately, use the WCA & headwind calculations to determine the headings to fly and the time in route between waypoints. Got it? lol
The worst part of all of this is every bit of creating an accurate flight plan and navigating successfully by pilotage is dependent on knowing the winds direction and speed. How do we do this in advance of getting up there and feeling it? Well, the government weather service publishes predictions of the "winds aloft" for various altitudes. To their credit, they do a good job and the predictions are usually close to what the winds actually are, but when they're not, the flight plan quickly falls apart and it is very easy to get off course and lost! Welcome to aviation.
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