Two methods of flight we are technologically familiar with are the lighter-than-air flight, such as a hot-air balloon or a gas-filled zeppelin, and the heavier-than-air flight, for which you need wing span and air speed. That is the entire breadth of our current understanding of flight, the miracles of modern technology notwithstanding. We know everything there is to know on the subject of flying, right? Wrong. Any bird knows more than we do.
As confirmed by visual observation and stop-photography, the take-off speed of a bird, which is always a heavier than air object, is too low to create the aerodynamic force sufficient to take that bird off the ground and sustain flight. The birds in their flight follow both the lighter-than-air and the heavier-than-air patterns. Well, that is something new. We could possibly learn a thing or two from the birds.
The phenomenon of near-zero-speed plight in birds is particularly evident when birds are landing onto or hover over a swaying perch, such as electrical wires or tree branches. Birds spread their wings, move individual feathers apart and thus can maintain their position, demonstrating that the wings themselves create the needed lifting force even at near-zero speed. The structure of the wings itself creates lifting force.
Wing feathers are composed of tiny nets that break the air column above the wing into micro- and nano-cells. Nano-dimensions of the net allow us to consider Van der Waals’ forces of attraction between the air columns over the net to the net’s edges resulting in narrowing of the air column above the wing, creating the difference in pressure upward from below the wing and downward from above. In other words, the lifting force is created by increasing the number of nano-cells of the net in direct contact with air achieved by spreading apart individual feathers.
Per the science not included in this article, the lifting force of a wing can be regulated. For a bird to take off it is only necessary to narrow the air column above the wings by less than 1%.
Overlapping, wing feathers markedly increases lifting force because the grooves of the overlapping feather cross at certain angles, which increases the number of the cells in the net, thus further dividing up the air column.
A bird with ends of the feathers cut off can no longer fly. Therefore, by varying the surface area of the feathers overlap we can regulate the lifting force of the wing. Birds use this during landing on a stationary target, like a nest, whereby the lifting force of the wings and tail have to be reduced to zero.
The cells of the net that narrow the air column are spread evenly over the entire surface of the wing, symmetrical in relation to the central axis of the bird’s body on both wings. That helps create the vertical vector of the lifting force. Increase of the wing area with the increase of the mass of the bird is another indicator of the way they magnify the lifting force by increasing the number of the narrowing air columns over the flapping feather cells.
The altitude regulation can be achieved through varying the lifting force in the following ways:
First, by changing the surface area of the feathers;
Second, by varying angle of the wing in relation to horizontal plane;
Third, by varying the frequency of flaps.
Airplanes with flapping wings are not practical but other factors open interesting possibilities for near-zero-speed take-offs and landings and super-fuel-efficient flight.
Wouldn’t it be interesting to see a prototype of a mesh-constructed wing with surface segments capable of overlapping and spreading out, changing the surface area, and where the pitch of the wing can be regulated in flight? Could this be the wing of the future? After all, birds had been using this design for about 150 million years so far and doing fine!