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Wing Loading Explained

Author: Adam Woolley

Wing loading is a critical concept in gliding, as it significantly impacts the glider’s polar, handling, and overall performance. Wing loading quickly changes when adding a passenger to that second seat or loading up water ballast before the flight. By understanding the relationship between wing loading and the glider’s polar, pilots can optimise their flights and achieve the best cross-country performance, usually measured in km/hr. Whether flying in strong or weak lift conditions, wing loading is an essential tool for glider pilots to have knowledge of, learn from, and master. I have almost 4000 hours of gliding now, and I’m still trying to master its use!

How does it play a crucial role in the performance and efficiency of gliders? It is a measure of the weight of the glider divided by its wing surface area, and it has a significant impact on the glider’s sink rate reference to its polar curve, that and its (or our) ability to climb! In this article, we will explore the concept of wing loading, its effects on the glider’s polar, and why glider pilots use it to optimise their flights.

Definition of Wing Loading
Wing loading is defined as the ratio of the glider’s weight (W) to its wing surface area (A). It is typically expressed in units of kilograms per square meter (kg/m²) or pounds per square foot (lb/ft²). A higher wing loading indicates a heavier glider with a small wing area (incredibly, the latest Alexander Schleicher AS35 goes to 62 kg/m² or 12.7 lb/ft²), while a lower wing loading (like a training glider, 25 kg/m² or 5.1 lb/ft²) indicates a lighter glider with a larger wing area.

Wing Loading and the Glider’s Polar
The glider’s polar is a graphical representation of its descent rates at various speeds. It is a critical tool for glider pilots, as it helps us understand the glider’s performance and make informed decisions about our flight. Wing loading has a significant impact on the glider’s polar curve, referring to the speed at which we fly and also to our ability to find thermals and then climb in them.

A glider with a high wing loading will have a slower climb rate, while a glider with a low wing loading will have a faster climb rate. This is because a glider with a high wing loading has a smaller lifting surface area, which requires a higher speed to generate the same amount of lift, not to mention the wider turn radius which may be keeping you out of the core of the thermal as a result.

This is where the fun of balancing the optimum wing loading comes in. If you are heavy, then you can cruise faster with the same sink rate of a lower wing loading glider, but… if you can’t find a thermal or struggle to fit inside it, then the lighter glider will cruise straight past you because they are still able to climb, to be able to progress forward.

Why Do Glider Pilots Use Wing Loading?
Glider pilots use wing loading to optimise their flights and achieve the best possible cross-country performance, usually measured in speed across the ground over a pre-set course. There is little need for a higher wing loading glider if you don’t intend to fly cross-country. By understanding the relationship between wing loading and the glider’s polar, pilots can adjust their flying techniques to suit the conditions. For example, in strong lift conditions, a pilot can choose to fly with a higher wing loading to take advantage of the easy-to-find lift with large thermal cores; or, in weak lift conditions, a pilot may choose to fly with a lower wing loading to maximise their chances to find thermals, stay aloft longer & progress further forward towards home.

Additionally, the wing loading range is an important consideration when buying a glider for a particular purpose or region. Fly in strong South African conditions or for high-speed record regions, you’ll want the Jonker Sailplanes JS3; fly in weaker & average areas, or in competitions which have a wide range of conditions, you’ll want the Ventus 3. In my next article on wing loading, I hope to talk about all things regarding launching considerations, communications on the ground, risks, aborted take-offs & the effect on landing ground roll with water ballast; stay tuned and… Source: ‚Adam Woolley on Wings & Wheels‚.