Bionics - learn from nature

How storks are used as models for aviation

© Alexandra, pixabay/ ARTS

It is considered one of the more recent sciences, although it was established more than 500 years ago by Leonardo da Vinci: bionics. Da Vinci was the first to describe the change in shape of the bird's wing with scientific aspects. He thus laid the foundation for a science that increasingly reveals nature's secrets. More blog posts will be published as a series here from the multitude of subjects in the area of bionics.

Aeronautics is "only" a branch of bionics, but still a very exciting one. I will dedicate the first part of this series to the phenomenon that in the future turbulence in the tips of the wings will be more relevant than ever in aviation.

What causes turbulence

Turbulence occurs due to a simple physical cause. The air flows at different rates across the top and underside of the wing which creates buoyancy.1 The shape of the wings, in particular the curvature, causes the particles to travel in a different way on the top than on the bottom. Negative pressure forms on the top and overpressure on the underside. With enough acceleration, the resulting force is sufficient to get several hundred tonnes in the air. On the tips of the wings, high and low pressure areas hit each other, because different pressure conditions always want to balance out and balanced flows result on the wingtips. These two opposing vortices produce no lift, but require energy which is called an induced drag.

Turbulence on the wings is a particular vulnerability for energy efficiency. Wake turbulence caused by the uplift also must be reduced so that the aeroplanes next in the line are not endangered. The waiting times that this causes are particularly inconceivable in high-traffic airports such as London Heathrow (EGGL) and Frankfurt/Main (EDDF).

Reducing air turbulence

By stretching the wings, the end turbulence and thus the induced air resistance can be reduced. A practical example illustrates the comparison: A Cessna 172 has a low wing elongation while a glider has a rather high one. However, elongation has a drawback. If the wings have a lot of elongation, both the stability of the wings as well as the manoeuvrability of the aircraft suffer. The space required would also present a challenge for a lot of aircraft and airports.

Solution from nature

Otto Lilienthal illustrated in his book "Bird flight as the basis of aviation."(1889) a stork in flight, among other things. One small detail above all is impressive: The stork's wing tips are spread. That they are spread apart causes the air turbulence produced on the tips to be significantly reduced. Realising this, aerospace engineers developed winglets (Airbus also calls them sharklets).

stork's wing tips are used as models for aviation - © Alexandra, pixabay/ ARTS

Winglets and Sharklets

With the help of the winglets, the wings are extended and "bent" upwards. The winglets of a Boeing 737-800 are approximately 2.40 m high, which leads to fuel savings of around 5 %. They also increase the stability around the vertical axis (yaw axis) as well as the agility around the longitudinal axis (roll axis).

The first winglets were uncommon and today there are a number of variants. For Boeing, winglets are mostly angular and straight or turned obliquely upwards. Newer versions are blended winglets, which can now be seen on almost all aeroplanes in this country. They form a smooth transition from the wing to the winglet. For example, TUIfly was the first airline in Germany that used split scimitar winglets.2 The Airbus planes also of course fly with winglets. The winglets that have been newly developed since 2009 for the A320 family are however called sharklets. The reason: The shape of the wing spread is like a shark fin.

Small winglets are also called wingtip fences and can be face up or down. These types of winglets are often seen on Airbus planes. Boeing, however, has some planes, including the 777 Dreamliner, that are equipped with raked winglets. These are not winglets in the traditional sense, but specially shaped wingtips. Ultimately, winglets and wing tip fences are used for reducing induced drag.

winglets reduced air turbulence

blended winglets are the newer version of winglets - © Stephan Marc, pixabay

Other types of winglets

A hitherto unfamiliar and not yet used in regular flight operations type of winglets are called spiroids. These loop-shaped wing tips have so far only been made for test vehicles. For example, a Dessault Falcon 50 from Texas, USA, regularly makes test flights. Spiroids are an advanced type of winglet and here, too, nature is used as a model. Recent studies indicate that the multiple spread of the bird wing tips lead to better flight performance. The spread of the wings reduces the induced air drag. Aerospace engineers have modelled this technology after birds and developed spiroids.

The future of bionics

Bionics is always giving engineers and scientists a new approach. Fish, birds, and plants are used as a model for many technical innovations. What technical achievements will be invented in the future? What do you think the most recent use of bionics is? I look forward to hearing your opinion.

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