TECH TALK – WHY WINGLETS?
Earlier this year we asked our fans what they wanted to see more of in our newsletters and one of the most popular requests was more technical information about our aircraft and team….so the next thing was to consider what to talk about, and without doubt, one of the questions we get asked the most is ‘why do you have winglets and what do they do?’. Here Matt explains in his words. Enjoy getting your #AvGeek on!
Wingtip vortices are created when a wing is at an angle of attack producing lift. It results from the air under the wing being at a higher pressure than the air on top of the wing (ie, how the wing creates lift), that at the wingtip, the high pressure area under the wing mixes with the low pressure air on top of the wing, creating the vortices. The higher the angle of attack, the larger the vortices, which in turn create drag.
The way to reduce wing tip vortices is to make the wing a higher aspect ratio. This means making the wing longer and thinner, much like a glider wing. The longer the wingspan, the more distance the high and low pressure air has to travel to get to the wingtip, and most of it does not make it there. Think of a small chunky wing at high angle of attack, air will be spilling everywhere at the tip, whereas a glider wing will have most of the air come straight off the trailing edge of the wing.
The disadvantages of a glider wing, are that it is not very manoeuvrable, hard to make strong enough to pull large amounts of G, and is generally quite long to create the same amount of lift as a shorter lower aspect wing. Hence, why fighter aircraft have shorter, thicker, lower aspect wings, while airliners are more toward that of a glider.
What do we want when racing? We want a good combination between super strength, great manoeuvrability, but as little drag as possible while under angle of attack. It would be great to just add another 3m to each wing, though we would never fit between the gates, let alone maintain the agility of the race plane. So, we put on winglets.
Winglets have a similar effect as increasing the wingspan or aspect ratio, by creating somewhat of a fence at the end of the wing, thereby delaying the interaction of the low pressure and high pressure air as far away as possible. The air not has to travel up the sides of the winglet to mix on the top of the winglet. While this is not as effective as having an extension on the wing itself, it does have an effect. In rough terms, the winglet gives the same effect of increasing the wingspan by half the height of the winglet.
It must be remembered that the winglet is not giving you extra wingspan, so there is no increase in lift; we are purely reaping the reward of reduction in tip vortices drag with the addition of the winglet, to a value equivalent to an increase of wingspan half the height of the winglet. But, every bit counts when measuring down to 1 / 10 0000 of a second.
Chase your Dreams!