A scientific analysis of the evolution of airplanes showed that there are similarities to the way birds and other animals evolved. A new physics principle, named the “constructal law,” was applied to the evolution of airplanes and it was able to predict the documented evolution of aircraft throughout history. Analyzing the evolution of airplanes has been touted as a case of witnessing evolution, which cannot happen with animals because the evolutionary process in nature occurs over a very long period of time. A report on these analyses is published in the Journal of Applied Physics.
Adrian Bejan developed the new law of physics in 1996 and gave it the name constructal law. Bejan is a professor in the Mechanical Engineering and Materials Science Department at Duke University. The constructal law says that a system must evolve toward increasing access to flow in order to survive. Examples of access to flow would be access for blood to flow through the vascular system, water to flow through a river system, tree branches to reach to the sky or highways and roads to flow through a territory. Access to flow in regard to the evolution of airplanes would be allowing more goods and people to flow around the Earth.
Bejan carried out this work based on the recognition that there are theoretical rules on body size related to shape, anatomy and physiology that govern the evolution of birds and animals, and he believed these rules apply to the evolution of airplanes as well. In his report, he stated that the evolution of animal design, river basins and technology is one phenomenon and he said this phenomenon belongs in physics.
According to the rules on body size and shape, larger airplanes are more efficient as carriers, are faster and can fly greater ranges. Also, the mass of the engine must be proportional to the size of the body. Similarly, animal bodies must be proportional as well regarding muscles, lungs, the heart and overall body size. Airplanes must be proportional regarding fuselage length and wing span.
Bejan has reportedly said that larger animals travel farther in their lifetimes and this is true for airplanes as well. In larger airplanes, the engine is proportional to the body size and in larger animals, the heart and other organs are proportional to body size as well. The results from one of the analyses showed that the relationship of the size of an airplane body to its speed was nearly identical to the body size and speed statistics obtained for various mammals, birds, lizards and even insects. This can be interpreted as finding that the evolutionary constraints observed in nature are also at work in the evolution of airplanes.
Aerospace companies may be interested in considering the new law of physics; that is, constructal law, when designing new airplanes in the future. Just as in natural evolution, some designs just do not work well and this has also been the case with airplanes. The Concorde and Howard Hughes’ Spruce Goose are examples of airplanes that have gone extinct. The scientific analysis of the evolution of airplanes has produced information that will undoubtedly be given thought as the aerospace industry considers designing larger sized aircraft.
By Margaret Lutze