• Great Circle Route and Rhumb Line: Looking for the shortest path

If you’re not familiar with the terminology used in navigation, chances are you’ve never heard of great circle route and rhumb line, let alone isozimuthal curves. But fear not! That’s about to change.

Following the theme we started with our post on why planes don’t fly in a straight line, today we delve into the fundamental aim of flight planning: finding the shortest path.

So, if you’re curious about great circle routes and rhumb lines, or why isozimuthal sounds like a tongue twister, keep reading as we explain it all. Let’s get started!

What are Great Circle Routes?

The great circle route, derived from the Greek words orthos (straight) and dromos (way), is a navigation technique based on finding the great circle route, which is the shortest line between two points on the surface of a sphere.

And what are great circle routes? They are those traced along a great circle, i.e., the imaginary circle obtained by dividing the Earth in half. Thus, each meridian would be a great circle route, as they all divide the Earth into two vertical halves; as well as the equator, which divides it horizontally.

Due to the Earth’s round shape, if you were to travel in a straight line from one point to another, you would follow what is known as a great circle route. This line represents the shortest distance between two points on the surface of a sphere and is the path that airplanes usually take to minimize flight time and fuel consumption.

In reality, this route, although appearing curved on a flat map, would follow a straight line when placed on a sphere. Because, as we already know, the Earth is not flat.

Adapting the Great Circle Route

Now, calculating this great circle distance may seem like a challenge from another world, but thanks to mathematics and modern technology, it has become a fairly accessible task.

For flight planning, it is used the great circle formula, which takes into account the curvature of the Earth, to determine the most efficient route.

This calculation is vital, especially on long-distance flights, where even small deviations can result in significant additional fuel and time consumption.

How to calculate the Great Circle distance between airports

Calculating the great circle distance between airports is a fascinating process involving mathematics and geography. The geographic coordinates of both airports, latitude and longitude, are used, and the great circle formula is applied.

This formula takes into account the curvature of the Earth, using the Earth’s radius to calculate the shortest arc between two points on the surface of a sphere.

What are Rhumb Lines?

Unlike the great circle route, a rhumb line, also known as a constant bearing or course line, is one that cuts all meridians at the same angle. In practice, this means that if you are navigating along a rhumb line, you will maintain a constant bearing relative to true north.

This type of navigation is especially useful when using compasses or navigation systems that do not account for the curvature of the Earth. Although not the shortest path, as in the case of the great circle route, the simplicity of maintaining a fixed course makes it attractive for certain types of maritime navigation and, in some circumstances, aerial navigation.

However, on long-distance flights, the difference in travel length can be considerable, making it preferable to opt for great circle routes.

Rhumb Lines vs. Great Circle Routes: What sets them apart?

The main difference between rhumb line and great circle navigation lies in efficiency and course. While the great circle route offers the shortest and most direct path between two points, taking advantage of the Earth’s sphericity, the rhumb line adheres to a constant course, simplifying navigation but extending the total distance of the journey.

In the vast sky that connects continents, this difference is crucial for flight planning, where efficiency and resource savings are paramount.

Why is the Great Circle Route chosen sometimes and the Rhumb Line others?

And you may wonder, why is one route chosen over another at times? Well, the reason lies in how the plane intersects each meridian. In the great circle route approach, the flight path involves cutting each meridian at a unique angle, requiring constant course adjustments, as navigation routes are designed for straight segments rather than curves.

On the other hand, in the rhumb line approach, the plane flies straight on the sphere without constantly changing its course during displacement.

The great circle route offers advantages in terms of time and fuel savings, although it requires continuous course adjustments. On the other hand, the rhumb line, being easier to follow as it does not require course changes, is commonly used on short flights. However, on long flights, where the priority is to minimize fuel consumption, the great circle route is usually preferred.

Did you know about Great Circle Routes and Rhumb Lines?

And you, had you heard of navigation through great circle routes and rhumb lines before? It’s incredible how they reveal the complexity and, at the same time, the beauty of moving around our planet.

The next time you’re on a plane, remember the calculations that have made that flight possible.

Did you enjoy this article? Well, you’re going to love our aviation blog. There you’ll find more posts on air navigation, like Jeppesen navigation charts.

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