They’re those fin-like pieces on the wingtips that give aeroplane wings a slightly ‘upturned’ look. These fixtures, known as winglets, are designed to cut fuel consumption by up to 7 per cent. They reduce lift-induced drag by ‘cutting’ through the air, and are most efficient for mid- to long-range flights, during which cruising speed is held for longer periods.
The Physics Behind Winglets
Winglets – also called wingtip devices – were created, primarily, to reduce drag by partially recovering energy from wingtip vortices. Their secondary functions are to improve the aircraft’s handling characteristics and reduce wake vortices which may affect other aircraft that are trailing behind. Winglets also increase lift generated at the wingtips, improving drag-to-lift ratio. This increases fuel efficiency, and consequently, increases range.
Winglets transfer some of the energy from the wingtip vortex into thrust. This energy, if unconverted, would’ve been wasted. On the upper surface of the wing, there is low pressure; and on the bottom surface of the wing, there is high pressure. The confluence of these two intensities of pressure is ‘moved’ away from the surface of the wing, by wingtips. This reduces vortex interference with laminar airflow (smooth, uninterrupted flow of air over the air foil) near the wingtips, and helps achieve increased efficiency.
Tiny Giants
Often times, looking at an aeroplane from afar, the winglets look like little fixtures stuck onto the wingtips. And if you were able to see it from your window seat onboard, the winglets still appear to be fairly small attachments. But take an up-close look and you’ll see that these seemingly tiny pieces are an astounding 2.5 metres tall!
As expected of such large fixtures, the winglets add weight to the aircraft, which inevitably increases fuel burn – but wingtips are supposed to reduce fuel burn. So, in this rather ‘paradoxical’ phenomenon, there is a fine line between fuel savings and fuel consumption.
While installing and maintaining winglets is an additional cost (that can be avoided if airlines opt for aircraft with regular wings), it is a small incurment compared to the benefits it brings to an aircraft’s lifetime.
Shapes and Sizes
The Spiroid (source)
Winglets come in various forms, but all perform essentially the same function of recovering some lost energy in the wingtip vortex.
The Challenger 601 (Bombardier) was a pioneer, equipped with production-standard winglets. Perhaps the most simple of all winglets, these were essentially wingtips that were deflected upwards. Today, there are blended winglets, dual-feather winglets, and Sharklets (by Airbus), among others. These winglets are improved variations of older types of winglets, and provide even higher fuel efficiency (up to 4% improvement on fuel efficiency of previous designs).
The search for the ultimate, most efficient winglet is still ongoing, and is getting more innovative with each concept design. The Spiroid, for example, is a test design created by Aviation Partners, which promises a 10% fuel-burn reduction if successful. Additionally, on Airbus’s side, they have at least three patents assigned to new winglet designs.