by Dan Hampton
These were individuals like Sir Isaac Newton, who, in his seminal Principia Mathematica of 1687, calculated this limit at 979 feet per second but failed to account for the influence of heat. This error, incidentally, was corrected the following century by Pierre-Simon Laplace. Another Frenchman, Marin Mersenne, calculated the illusive number at 1,380 Parisian feet per second while Robert Boyle, of Boyle’s law fame, arrived at 1,125 Parisian feet per second.* William Derham, a clergyman in Essex, England, came the closest in 1709 at 1,072 Parisian feet per second. Derham had friends fire shotguns from known locations and he painstakingly measured how long it took for sound to travel to his position. Early flintlock firearms, at least as far back as the fourteenth century, were also capable of producing supersonic projectiles.*
The idea of an aircraft flying faster than sound was considered a very real possibility within two decades of Wilbur Wright’s 1904 Kitty Hawk flight. United States Navy Lieutenant Commander Albert Cushing Read, first to fly from America’s East Coast to Europe in 1919, declared that he could see the day when “it will soon be possible to drive an airplane around the world at a height of 60,000 feet and 1,000 miles per hour.” Though belittled at the time, Read and others knew it could happen once technology caught up with vision. This is often surprising to those of us raised with aircraft and air travel as we consider this capability a modern invention; and it is, from a practical standpoint, yet there have been significant, albeit oft-forgotten, aviation milestones stretching back for over 1,000 years.
Man had likely been fascinated by flight from the beginning. One can imagine a heavily muscled, low-browed Homo erectus peering uncomprehendingly at a swooping bird and perhaps dimly wondering why he could not do the same. Jumping from cliffs, later leaping from towers or attaching oneself to a kite—all these efforts to fly, and doubtless many more, had been attempted over the centuries. Though usually resulting in a painful death or lifelong injury, there were some successes nevertheless.
Though the Chinese had been flying kites since the tenth century BCE, the first recorded human flight is generally credited to Abbas ibn Firnas, a Berber polymath living in Moorish Cordoba. After studying kites, and all the known previous attempts at gliding, Ibn Firnas constructed a light, wooden wing, very much like a modern hang glider, from silk and feathers. In 875 CE, at the age of seventy, he jumped from Jabal al-Arus (the Bride’s Hill) outside Cordoba and, by some accounts, glided for ten minutes over the Guadalquivir River valley. It was a successful flight, though Ibn Firnas had neglected to consider the problem of landing and he was badly injured.
In the early eleventh century Eilmer of Malmesbury, a Benedictine monk from southwest England, built a wing from cloth and wood then leaped from the West Tower of his abbey. Gliding downhill against the wind for at least fifteen seconds, he traveled over 200 yards. Unfortunately, as with Ibn Firnas, the monk had not considered the finer points of flying, in this case, control. His apparatus had no tail and was out of balance, so when the wind changed, Eilmer came crashing down, breaking both legs.* Other men followed. All were enamored of flight, were courageous, and had no real idea of what they were truly attempting. Broken legs and necks were common. By the end of the seventeenth century the Italian physiologist and biomechanical pioneer Giovanni Alfonso Borelli definitively concluded in his de Motu Animalium that humans lacked the musculature to sustain flight by flapping wings.
On a moonlit summer night in 1793 a man named Diego Marín Aguilera jumped from Coruña del Conde castle in northern Spain. Soaring at least 1,000 feet across the Arandilla River, his wooden machine very likely caught an updraft from the valley floor and the stress fractured a metal joint. Crashing near Heras, he narrowly escaped being burned as a heretic by the town’s inhabitants, who believed a flying human was an affront to God.
These men, if the accounts are accurate, had at least progressed from near suicide to basic flight. To be sure, gliding can be considered a form of flight, as at its best a glider can have a sustained time aloft and be controlled by a pilot. Elementary as this sounds, it took centuries of trial, error, and death to progress past this basic point. True flight, as we shall see, must have a power source able to propel an aircraft through the air with sufficient velocity to produce lift. The bird or bat has its wings, but man must have something else.
Yet the scientific achievements of very early aviation pioneers are often underestimated or overlooked entirely, and this is quite unfair since we acknowledge debts owed to visionaries from other fields. Antonie van Leeuwenhoek revealed the interior structure of cells in the seventeenth century while Louis Pasteur’s contributions to bacteriology and Gregor Mendel’s to genetics both followed during the next century. Tycho Brahe discovered a supernova in 1572, while Galileo found craters on our moon and identified the Milky Way galaxy. Danish astronomer Ole Rømer correctly measured the speed of light by 1675, and the Royal Society published Ben Franklin’s Experiments and Observations on Electricity in 1751.
Engineering ceilings of all kinds were shattered during the Industrial Revolution, so it should be no surprise that aerodynamics advanced as well. If Boston could implement the first municipal electric fire alarm in 1852, or Thomas Edison could erect the first dedicated research and development laboratory at Menlo Park in 1876, then Francis Wenham’s wind tunnel should be no less revered. Hydroelectric power plants, commercial electrification, and even experimentations with millimeter wave communications were all conducted in the late nineteenth century, therefore Horatio Phillips’s cambered airfoil, or Félix du Temple’s first sustained flight by a true heavier-than-air machine in 1874 ought to be as well known—yet they are not.
Perhaps one reason lies with the mystique surrounding flight. Unlike steam power or electricity, flying was not an activity that benefited the masses until well into the twentieth century, so it largely remained the province of the scientific community or the independently wealthy. Then, less than two weeks after the 1773 Boston Tea Party, a man was born in Yorkshire, Great Britain, who would arguably usher in the modern age of aviation. George Cayley, a self-educated baronet and a man of indefatigable imagination, designed caterpillar tractors and artificial limbs before studying avian physiology to aid his understanding of his true passion: flight.
In 1799 Cayley was the first aerodynamicist to break the process of flight apart into the distinct components of lift, weight, thrust, and drag. He insisted that thrust, or some manner of propulsion, was an independent factor that must be practically solved for man to truly fly. Cayley also correctly envisioned the modern structure of an aircraft with a fuselage, forward wings, and a cruciform tail surface. By 1804 he had constructed a flyable model glider, and five years later his three-part essay “On Aerial Navigation” was published in Nicholson’s Journal of Natural Philosophy, Chemistry and the Arts.
Sir George understood about centers of gravity, and that it was the pressure differential acting on an airfoil that generated lift. Above all, Cayley realized that, unlike a bird, a man must generate lift through a separate form of propulsion. Steam would not suffice; the engine was inefficient and entirely too heavy. Internal combustion, he felt, was the only realistic solution and Cayley spent a good deal of his life theorizing about just such an engine.
He flew models and developed full-scale gliders, including one flown by a ten-year-old boy in 1849. By 1853 he had constructed a craft that could remain airborne, with his unenthusiastic coachman as pilot, for about 500 yards. Upon landing, the unhappy servant told Sir George that “I was hired to drive, not to fly,” and he promptly gave notice.
However, it was Cayley’s methodical evaluation of his concepts that opened the doors to purposeful, systematic testing. With a whirling-arm device used to design windmill blades, he added a paper airfoil and adapted the contraption for surprisingly accurate studies of lift. Dr. John Anderson, the preeminent aerodynamicist of our time, writes that Cayley’s measurements were “accurate to within 10 percent based on modern aerodynamic calculations.” Tow
ard the end of his long and interesting life, Cayley summarized his work by formulating the essence of all modern aircraft within the simple, but as yet undefined principles of lift, propulsion, and control.
With the doorway to flying now framed, the subsequent century of flight research and development was largely a stair-step progression of ideas, techniques, and revelations. There was some cooperation, much jealousy, and often open disdain among the competing worlds of academia, theoretical engineering, and those physically attempting to fly. Yet without an efficient means of propulsion, much of this initial progress necessarily centered on gliders.
With theory and practice warring with each other, the focus shifted as various problems were addressed and eventually solved. By the late eighteenth century, lift was well understood so the emphasis moved to creating thrust and mastering control. If you recall, Cayley pointedly separated propulsion from lift and this was a crucial point. Flying requires thrust, whether it is self-generated like a bird, bat, and insect, or via some type of artificial propulsion such as an engine. If you are not flying under power, then you are not flying; you are gliding or, even worse, you are floating.
Early experiments in flying sought to emulate birds, which was reasonable enough as they were the most obvious examples of successful flight, yet it was impractical. Birds are able to fly due to a combination of evolutionary advantages, such as honeycombed bones that yield a very strong, yet extremely light frame. This frame is covered with keratin feathers that are molded, or preened, into highly efficient airfoils capable of producing lift. But a bird, like a man, still needs to generate thrust in order to produce lift. In the bird’s case, this is possible due to a high metabolism that enables its muscles to work more than twice as fast as other mammals. This permits flapping that generates enough thrust to get air moving over the wings, which in turn produces lift.
Once it was understood that man could not replicate these natural advantages, then artificial methods of generating thrust were explored, and the quest for powered flight moved forward. The results speak for themselves with the nineteenth century witnessing the advance of theoretical aerodynamics into workable flying machines. Some of these, like William Henson and John Stringfellow’s aerial steam carriage (also called the Aeriel), were wildly impractical; how could a 30-horsepower engine propel a machine weighing well over a ton? Indeed, its 150-foot wingspan and gigantic 4,500-square-foot wing area exceeded that of a modern Airbus 320.*
It never flew, of course, but was nonetheless influential by inspiring others through its form and potential. Dr. Anderson says of Henson’s monstrosity, “Here is an excellent example of the still technically undeveloped state of the art of airplane design in the first part of the 19th century.” Yet Henson’s machine also seemed to graphically illustrate the rather profound differences between aerodynamic theorists, academicians, and the designers of aircraft. One problem was to separate flight from propulsion—and no one had a really clear idea how either worked.
Clément Ader, on the other hand, actually did get a machine airborne under its own power: a 20-horsepower steam engine. A French electrical engineer, Ader specifically looked to nature for inspiration and by 1890 completed a machine he named the Éole. On October 9, the bat-winged contraption staggered into the air near Armainvilliers and managed to remain aloft for 165 feet. Though this event was a startling aviation first, a manned craft flying under its own power, it still did not qualify as a “flight” since Ader had no way to control, or physically “fly,” the aircraft.
Neither did Hiram Maxim. Arrogant and vain, Maxim was unquestionably brilliant, and behind his unpleasant façade lay a first-class brain coupled to a fertile imagination. A self-educated inventor, he patented the original machine gun in 1883 and incorporated the Maxim Gun Company the following year. After emigrating from America to the United Kingdom, his wealth permitted the freedom to pursue other interests, including aviation. When asked if he could build a flying machine, Sir Hiram replied, “the domestic goose is able to fly and why should man not be able to do as well as the goose.”
Methodical and precise, he was the first aviation pioneer to derive specific wind tunnel data toward a specific design. Like Ader, Maxim’s immediate goal was to get a manned aircraft aloft under its own power, so he leased Baldwyns Park outside London, and built a hangar to accommodate his project. The result was a four-ton flying machine powered by a 362-horsepower steam engine that would propel the craft down 500 yards of railway track. Maxim mounted extra raised wheels on his apparatus that would catch a wooden safety rail running parallel with the track. This, he reasoned, would keep the machine from getting more than a few feet above the ground and prevent crashes.
On July 31, 1894, he did just that.
Under full power the three-man crew reached 42 miles per hour, and the giant seventeen-foot, ten-inch propeller kept the craft airborne (at two feet) for over 300 yards. Yet for all his considerable talents Maxim, like many others, could not conceive of the aircraft in more than diversionary terms, an engineering challenge. “But I do not think,” Maxim once stated, “the flying machine will ever be used for ordinary traffic and for what may be called ‘popular’ purposes. People who write about the conditions under which the business and pleasure of the world will be carried on in another hundred years generally make flying machines take the place of railways and steamers, but that such will ever be the case I very much doubt.”
But since Maxim and Ader succeeded in getting into the air under their own power, why did they not get credit for the first flight? Obviously a few basics were understood, at least as far as building an airfoil that produced sufficient lift to overcome weight and get airborne. Maxim’s machine was powerful enough to generate a very respectable unit of horsepower for each twenty-two pounds of weight, and Ader’s subsequent designs were quite similar.
In the end, this comes down to how true flight is defined. Whereas getting airborne under power is quite different from gliding, so too is piloting your aircraft as you choose once aloft. When inventors, engineers, and others expanded on Cayley’s separation of lift, thrust, and drag, a final component was eventually realized: control. Ader and Maxim did produce thrust, which in turn generated lift, so in this respect they were definitely a bridge between the world of gliding and that of true flight. To truly fly, one must have control of the aircraft. To “feel” the plane and adapt to the continuously changing circumstances around it.
In other words, to be a pilot.
By the close of the nineteenth century those most successful in aircraft development were harnessing the theoretical aspects of the new science with the ability to conduct the experiments themselves, to fly their own machine. From this point of view Otto Lilienthal was arguably the first test pilot in the modern sense of the title. A mechanical engineer by training, he believed that each component of flight—lift, propulsion, and control—had to be fully understood and the issues with each solved to arrive at a comprehensive solution.
Using practical, engineering-based processes, Lilienthal was specifically concerned with the variations in air pressure on a wing resulting from changes in the angle of attack. He systematically measured this, and other hypotheses, during some 2,000 flights in sixteen types of gliders near his home in Steglitz, or his testing area over the Rhinow Mountains. He even constructed a small hill in Lichterfelde near Berlin so he could always launch himself into the wind. A monument was constructed on the site of Lilienthal’s research shed in 1932 and it is there still, a delightfully Germanic Stonehenge surrounding a stone globe that overlooks a rectangular pond.
Perhaps Lilienthal’s greatest contribution was the formulation of aerodynamic coefficients that permitted the use of dimensionless quantities to characterize forces acting on an airfoil. This greatly simplified lift and drag calculations and permitted progression into modern aerodynamic design. Like Horatio Phillips, Lilienthal arrived at the conclusion that cambered airfoils were a necessity for an effective wing. Interestingly,
this was done independently, so Lilienthal was unaware of any competing work until he filed a patent application in 1889 and discovered it had already been granted to the Englishman. That same year he also published Birdflight as the Basis of Aviation, a compendium of verified aerodynamic data that included results from his own experiments and the seminal work on flight.
Yet despite his visionary efforts, Otto Lilienthal suffered from the rather serious delusion that the ideal solution for powered flight would be an ornithopter; that is, a machine that flies by flapping mechanical, rather than static wings, which generate lift while being propelled through the air. Unlike Ibn Firnas and Eilmer the monk, Lilienthal was aware that a man could not produce sufficient muscular force to sustain flight by flapping since our bodies are too heavy relative to the muscular force produced, and we have the wrong type of muscles. He actually constructed a one-cylinder engine to flap his glider’s wings and commenced testing in Berlin during the spring of 1894. Having absolutely no success with this, he returned to gliders with hopes of producing them commercially for sport.
In common with his predecessors, Lilienthal had looked to birds for answers and this partially explains his ornithopter fixation. In any event, as his gliders had no control surfaces he, like the birds, relied on shifting his own weight to maintain altitude and direction. On a sunny Sunday afternoon in August 1896 he caught an updraft and the glider stalled, sending Lilienthal into a fifty-foot fall that broke his back. He died the following day, a stark reminder that with no control, lift is a force that can kill.