When the Red Bull Air Race returned in 2014 there was only one pilot that had winglets on his raceplane: Nigel Lamb. He'd added them 2010, but very few people took notice. However, after the 2014 season had finished, Lamb was World Champion and winglet fever had struck the Red Bull Air Race!
Since then every Master Class team has gone on to try wingtips of various shapes and sizes. From Petr Kopfstein's small wingtips to Ben Murphy's downturned version, everyone has their variation that works for them. But what exactly do they do?
When a raceplane is in flight there is high pressure below the wings and an area of low pressure above the wings created by the airflow. The area of high pressure will try to move to the low pressure area because it's unbalanced. This is what generates lift.
The air will move below, along the length of the wings and then upwards over the wings. The winglets disturb this movement and reduce drag, as it stops the two types of pressure meeting. Because of the difference in air pressure, when they meet it disturbs the air and this takes energy away from the raceplane – causing drag. With the winglets this disturbance is minimised and the drag is reduced. When pulling high Gs, more pressure is created under the wing and therefore more drag. This is when the winglets will be the most useful.
Basically you have two types of drag – profile and induced. These are completely opposite in their action. Profile drag increases with speed, while induced drag is the result of the 'angle of attack' (the angle between the oncoming air/wind and a reference line on the raceplane). The winglet is a barrier to stop the high pressure disturbing the lower pressure, which has a direct impact on the level of induced drag. As the high pressure disperses it will try to enter the area of low pressure, creating what's known as a vortex. The quickest way for these vortices to form is when the air moves over the end of the wing. The winglets lessen the impact, meaning the airflow is smoother and the raceplane can fly faster.
If you're still confused, let Jim Reed, the Red Bull Air Race's Technical Director explain more...