Bionics  Ė  Building on Bio-Evolution

Ingo Rechenberg

Bionicists are convinced of the performance of natureís way of optimization. This sophisticated method is running already 3 billion years, in the biggest laboratory we can imagine: The surface of the earth. Now, the laboratory is large enough and the time is long enough to find good solutions (perhaps optimal solutions) under the biological constraints.

I define bionics as the science for the utilization of results of biological evolution. Not always but very often the result of biological evolution is also the optimum solution for the engineer. I start with 9 solutions of biological evolution to demonstrate that evolution develops incredible tricks. I like to speak of Wondrous Technologies in Nature.

The spider throws a lasso with a sticky droplet at the end to catch an insect. Thatís the well-known technique of a cowboy.

  Lasso spider waiting for a chance

The deep-see fish angles small fishes using an illuminated lure. Therefore the flashing spoon bait isn't an invention of the angler.

  Angler-fish with an illuminated lure

The bombardier beetle has something like a flame-thrower. The ejected gas jet is really hot.

  Bombardier beetle in shooting position

The archerfish shoots down a fly with a water pistol. 

  The archer-fish aims at an insect

The bombardier beetle and the archer fish show that shooting is not an invention of mankind. Similarly: Weaving a fishing net and digging of a pitfall are trapping-techniques invented in nature.

  The net of the larva of a caddis fly.

  An ant-lion lurking in the pitfall.

The wheel hasnít been invented in nature, due to the lack of streets. However, if the rolling movement is energy-saving, this technique is employed also at nature. Spiders roll down the dunes and with the rolling technique the scarab saves energy.

  The scarab is rolling the gathered food away.

People walk in religious traditions over the water. A lizard is doing it today.

  Jesus lizard sprinting over the surface of water 

Million years ago nature has invented the technique to fly. Engineers of the last centuries thought that the bird feather includes the mystery of flight. It is difficult to mimic the feather. The bat could be imitated more simply.

  The bat: A biological model simply to be mimicked.

Therefore Leonardo da Vinci designed his flight machine like a bat.

  Part of the outline for a flying machine (1497 - 1500).

Clement Ader, the French flight pioneer, mimicked the bat with high precision. But his Avion III made only small jumps.

  The AVION III Before the examining board

Igo Etrich used the seed of a tropical liana as a model for a tailless airplane.

The seed of Macrozanonia macrocarpa


as a model for the tailless airplane of Igo Etrich

A tail was attached later. Finally, Otto Lilienthal, the German flight pioneer, used the bird as a model to design his glider. He mimics already the slotted wing tips of a bird.

  Otto Lilienthal on August 16th, 1894.

Why I do tell you this? Now, I find it very remarkable that after 100 years development a modern aircraft still looks like a bird: a spindle body, the wing in front and the elevator behind. Thatís the solution of biological evolution and thatís still the basic concept of a modern aircraft. The airplane is the showpiece of the Bionicist. And the airplane is still an object for modern research in the field of Bionics.


 Spindle body !

 Wing in front !

 Elevator behind !

Solution of biological evolution


and the engineering solution after 100 years development.


Look to an aerodynamic detail at a bird wing. During a 3-month stay in Antarctica I made nearly 2000 photos of the Brown Skua. The birds fly near enough to you to make such photos. About 30 pictures show what I wanted to see: The raising of the covering feathers.


  Brown Skua: Aeroflexible covert feathers act as a non-return valve


  The reverse flow opens - just before stall - the Reflux-Bags


What happens if an airplane moves too slowly or if the wind speed in front of a bird decreases suddenly? The airplane and the bird must fly with a high angle of attack to produce enough lift. Then there is a low-pressure peak in front of the upper-side of the wing. Fluid elements near the wall, which have been decelerated by the wall friction, move back to the low-pressure region. The flow separates from the wing surface. The separation point moves to the leading edge of the wing and the lift breaks down.


Movement of the separation point
to the region of minimum pressure

Braking the reverse flow throught
the covert feathers


The aeroflexible covert feathers now act as non-return valve. The reverse flow opens, just before separation, the so-called reflux-bags. Stall will be prevented. Look to the reflux bags of a bird in action. Stall with a break­down of the lift is still the main reason that airplanes fall from the sky. The ideal aerofoil for safety in flight keeps its maximum lift for high angles of incidence.


                     Research goal for aircraft safety


This research goal in aircraft aerodynamics has been reached with artificial covering feathers, an innovation of Bionics.


          The covert-feather effect


I continue my tutorial with some basic considerations to the theory of Bionics. I was claiming that biological evolution must have optimized biological struc­tures. Can this be proved mathematically? Yes it can. We look to the branching geometry of blood vessels. Physiologists have measured very exactly the bran­ching geometry of the blood vessels for a dog. They found an exponential law. If z is the number of vessels having equal diameter then the diameters decrease proportional to z raised to the power of Ė1/3. Now, and that is the point, you can derive the optimum bran­ching geometry with minimum energy losses mathe­matically. Indeed, you get just this exponential law.




A science fiction story: Astronaut biologists land on a planet where they discover extraterrestrial beings, the necklings. Their extremely long neck consists of the very light magnesium and their ball-shaped heads of the heaviest metal osmium. The biologists investigate the various species of the necklings. The plot of the neck weight against the head weight shows the exact validity of an exponential law (exponent = 7/6).


       Allometric law ofthe extraterrestrial necklings

Our fiction biologists recollect that the same relation­ship is valid for earth mammals. The so-called mouse elephant diagram has the exponent 7/6.


         Allometric law of mammals


Now, the necklings are in fact cantilevered beams with an osmium sphere as a load at the end of the beam. Using the Evolution Strategy I have minimized the neck weight under the constraint that the geometry of the system changes similarly. The exact exponent 7/6 is derived by a corresponding theory. The mouse elephant diagram with the exponent of 7/6 proves that the evolution has optimized biological systems with mathematical accuracy.


Some remarks to the philosophy of Bionics. Before transferring an evolutionary solution in the engineering you should think about the questions:

1. Is the biological function similar to the engineering function?

2. Are the biological constraints similar to the engineering constraints?

3. Is the biological quality similar to the engineering quality? 

If in some question your answer is no, then you stop better. Otherwise you may do a lot of nonsense.


          Seven steps in thinking of bionics         


I call it Pseudo-Bionics. Butterfly scales and roofing tiles may look quite similar. But they have different functions. Bird wing profiles are not a model for an aerofoil section of an airliner. The boundary conditions, expressed by the Reynolds number, are completely different. And the usage of a poppy capsule as a saltshaker arises a problem: During a dinner you salt the breads of your neighbors. Why that? Now, biological evolution has designed the poppy capsule to spread the seed as far away as possible. The evolution strategist would state: The quality functions are different.



    Pseudo Bionics




We come back to the aerodynamics of the bird flight. Why do birds fly with slotted wing tips? The answer: An ordinary wing produces at the wing tip a strong vortex. It is the low pressure on the upper side of the wing and the high pressure on the lower side, which causes a flow round the wing end. With a slotted wing this vortex will be split into small vortices. A vortex coil will be formed producing thrust. I explain later what a vortex coil is.


Black Vulture


To mimic the formation of the primary feathers we need very good snapshots of an eagle, stork or vulture in the flight. I never got them. Better is a method I call Neo-Bionics. We use the principle found in biology as the starting configuration for a computer aided post-evolution under the enginee­ring constraints.

The experiment started with a flat configuration (not staggered) of the five wing-ears. Flexible lead stripes at the roots of the winglets made the system mutable. The angle of attack and the angle of staggering of each wing-ear could be altered manually by means of a special mechanical device.



Post-Evolution under engineering constraints


Let me explain the course of action in the closed loop experiment: A computer program outputs the data of 12 mutated wing configurations. These will be adjusted and measured (lift and drag) Ė one after the other Ė in the wind tunnel. After the evaluation by the experimenter the 4 offspring numbers with the highest quality (lift to drag ratio) are then transmitted via the keyboard to the computer. The (4/4,12)-ES program declares these offspring to be the parents and outputs the next generation of wing configurations.

Here the gallery of ancestral portraits of the wings. After 27 generations the solution couldn't be improved any more.


        27 generations post-evolution of a birdlike wing


I show you the polar diagram of this experiment.


        Spread wing versus normal wing


What does a bird win with a slotted wing tip? Imagine there are two birds in 1000-meter height. They are tired and glide to the ground like a sailplane. We would like to note down the time up to the ground touch. We enter the data of a buzzard into the formula for the descent rate.



Bird (a) hovers 13 min 33 sec, bird (b) 14 min 30 sec. Bird (b) with evolved multi-winglets has 57 sec. more time to detect a mouse and thatís an evolutionary plus. I can show you the application of our outcome of the wind tunnel experiment for a sailplane.


        Multiwinglets at a glider designed with the Evolution Strategy


During the air show in Berlin I made these photos of the winglets of a big military airplane (a Boeing Globemaster III). This design is in my opinion the pre-stage of the complete imitation of the primary feathers of a bird.



Pre-stage of the spread primary feathers of the bird


Now the innovation goes on: From the primary feathers to the wing tip loop. The idea is to multiply the feathers and then to cut the inside out. What a pity: Louis B. Gratzer, formerly chief of aerodynamics at Boeing, has invented it a short time before us.



The title of the new chapter: Vortex-structures in nature and their application. There exists a strange analogy between the well-known magnet coil and a coil, which is made of a vortex. In the corresponding formulas the magnetic intensity becomes the flow velocity and the electric current has to be replaced by the vortex circulation. We take in mind: The magnet coil amplifies the magnetic intensity and the vortex coil amplifies the flow intensity.


Continued ...


Bionics & Evolutiontechnique