Why did George Cayley never crack the stability problem?

Question

George Cayley, aka "The Father of Aerodynamics" essentially, invented the field of heavier-than-air aerodynamics and built a number of model and man-carrying gliders, all in the first half of the 19th century. He defined the four forces acting on a plane, understood aerofoils and invented a device to test them. The layout of a modern plane can be traced back to him. He even invented the "tension wheel" to keep undercarriage weight down - an invention still found on virtually all bicycles today.

However he never built a true plane. Two problems alluded him: stability/control, and power. Both problems were only truly cracked by the Wright Brothers, and it could be argued that solving these problems were essentially the Brothers' main achievement.

Cayley had no hope of cracking the power problem. Steam engines were far too heavy and internal combustion engines were decades away (even the Wright Brothers had to build their own engine).

However the problem of stability and control (they are two sides of the same coin) were definitely within his grasp. If you look at the tail on his man-carrying machine, he appears to be thinking along the right lines - his tail is more like that of most aircraft, rather than the split tail used by the Wright Brothers (which was probably the more practical considering the technology available).

So how did he manage to miss this important step? He built a lot of models over an extended period of time (almost 50 years by some estimates) - how come he didn't come up with the idea of warping the wings or adding control surfaces? I think everyone who has built paper aeroplanes has accidentally warped their wings! Isn't Cayley likely to have made essentially the same mistake?

Answer 1

A main conclusion presented in the article Sir George Cayley: The Invention of the Aeroplane near Scarborough at the Time of Trafalgar (Ackroyd, 2011) was that

Although certain of his arguments have been shown to be over-simplistic, even on occasions faulty, he nonetheless arrived at many of the basic aerodynamic, structural and stability features of the successful aeroplane, tested them, and showed that they worked

and interestingly, Ackroyd notes that if people had paid more attention and if there was a wider adoption and expansion of his work, then many of the problems may have been overcome.

Like the power problem, some aspects of stability/control were beyond his time also. In particular, from the article

subject of centre of pressure movement was a further topic to retain its “dark nature” for a considerable period.

According to the webpage Sir George Cayley, The Father of Aviation (Dwyer, 2009), it seems that

He found that setting the wings at a slight dihedral gave the glider lateral stability and that a tail plane set behind the main wings gave longitudinal stability.3 This was the discovery of Inherent Stability that, although demonstrated but not fully understood by Cayley, would be theorized in greater detail by Alphonse Pénaud.

A vital aspect that the Wright brothers worked out in 1901. Another aspect that eluded Cayley was that he

failed to grasp the stabilising function of the tail’s fixed surfaces and is rather limited in his understanding of the functions of the tail’s movable surfaces.

This is something that he realised and applied a bit later in his life, when he successfully tested a flight of the 'Boy Carrier' in 1849 up to the Coachman Carrier around 1853.

The issue is not so much that Cayley did not make a successful model of a plane (which he did in the form of gliders), he was not able to, to quote Dwyer (2009), achieve

Cayley never achieved his final goal of sustained heavier-than air, manned flight, but his contributions clearly furthered advancement of the modern airplane.