Airplane vs. Bird
John S. Harris raises some valid points, but I think he also misses or misinterprets a few.
The most significant blind alley induced by mimicking birds lay in the size of the horizontal tail and length of the fuselage; Sir George Cayley and the other early glider builders did not perceive that birds are unstable and are actively stabilized by an extremely sophisticated neural control loop that constantly makes small control movements. For a human pioneer flying solo, this skill would be harder to learn than riding a unicycle. The Wrights, with contributions from Lilienthal and Chanute, changed the proportions to make the machine more stable at considerable expense in maneuverability. Now that computers are approaching bird-brain performance, it is possible to achieve maneuverability improvements with the “relaxed stability” concept of the X-29 aircraft.
It takes advanced mathematics to design a monocoque structure—and industrial-level equipment to manufacture it economically. In an age when airplanes were developed on private budgets, “birdlike” construction made a lot of sense.
There was not the faintest reason for tricycle landing gear until the 1920s, when wing loadings—and hence landing speeds—began to increase and the introduction of the paved runway created crosswinds. Anyway, the bird aspects here are pretty academic, because even tricycle aircraft are landed nose-up.
Ralph Jones
Aurora, Colo.
John S. Harris replies: Mr. Jones raises some interesting points. His strongest argument is for the complexity of the control system of birds; while 1 mentioned the concept briefly in the article, he carried it further. On the issue of the internal skeleton versus monocoque construction, he says the internal skeleton hung on because the engineering was simpler; I still say monocoque construction couldn’t come about anyway until the materials were available. On the tri-gear versus tailwheel landing gear, Mr. Jones is obviously a tail-wheel lover, and I admit to some of the same inclination. But tail wheels hung on well into the era when wing loading would have argued for adoption of tri-gear. Most of the fighter planes of World War II used tail-wheel gear when they would have been much easier to handle with tri-gear. And finally, yes, even a tri-gear lands with its nose up, but landing on the mains with a tri-gear is easy because the center of gravity is ahead of the main gear, and thus the aircraft is inherently stable. | 
