Constructal Design of Aircraft

New fronts of research using Constructal Theory

“Body-freedom flutter characteristics of flying wing aircraft vary with engine placement. Here, we show why a certain design parameter (engine placement) influences the aeroelastic flight envelope of the aircraft. The approach is based on the constructal law and the principle that a design that avoids stress strangulations provides better access to the flows that inhabit the system. This is in sharp contrast with trial-and-error techniques such as optimization, which means to opt from among different choices, cases, and designs. Under the same flight condition, the flow of stresses through the aircraft wings is investigated for several configurations including those with maximum and minimum flutter speeds. The results reveal that when the stresses flow smoothly in the wings the stability of the aircraft improves. On the other hand, in the cases in which the engine location causes stress strangulation, the flutter speed decreases considerably. The most severe stress strangulation corresponds to the aircraft configuration with minimum flutter speed (i.e., engine placement at 20% span behind the reference line). The smoothest flow of stresses happens in the configuration with maximum flutter speed (i.e., engine placement at 80% span forward of the reference line).”


Link to the paper at AIAAJ


The Tortoise and the Hare

41598_2018_30303_Fig9_HTML.png “The fastest animals and vehicles are neither the biggest nor the fastest over lifetime” is the subtitle of A. Bejan, U. Gunes, J. D. Charles, and B. Sahin in their Nature Scientific Report published the 27 August 2018.

Thanks to their theory, in this article, the authors explained phenomena such as the emergence of animal “outliers”:  higher speed at smaller body mass.

They show that what accounts for the animal outlier also accounts for the vehicle outlier: military jet fighter are smaller and reach speeds higher than the biggest commercial aircraft. Yet, like the cheetah, the jet fighter spends most of its active life at rest, on the ground, out of sight.  This new view gives the word ‘outlier’ a different meaning: the jet fighter is the outlier because, during its overall lifetime, it is slower than the bigger commercial aircraft, which spend most of its time flying.

This new meaning is in fact the oldest, taught by Aesop in his fable “The Tortoise and the Hare”: what matters in the life of the mover is the movement – i.e. the territory covered, the speed averaged – over the whole lifetime.

Thermodynamics Today

In a recent paper published in the prestigious “Energy”, Bejan presents his view on Thermodynamics and Science itself.

“Science is like a civilized territory that improves, prospers and expands because it makes life better for the people who belong to it. It expands as long as it keeps producing useful things, which attract people. The civilized welcome the newcomers, the nobodies, provided that they obey the laws, the discipline. People join because their lives become better that way.”

“To fight the barbarians who pillage on the perimeter is a necessary and unpleasant effort, a nuisance, not the objective. As the defeated barbarians are assimilated and civilized, the civilized territory expands and, as a result, life, peace, movement and freedom flourish. The civilized territory that does not fight the pillagers is destined to disappear along with the good way of life that it was sustaining.”

“Thermodynamics, like all the useful artifacts (e.g., science) produced by the civilized, is no different.” (open access for one month)