Anthony B. Wight
-
“At first we will only skim the surface of the earth like young star lings, but soon, emboldened by practice and experience, we will spring into the air with the impetuousness of the eagle, diverting ourselves by watching the childish behavior of the little men or awling miserably around on the earth below us.’’
|
|
—Jean-Jacques Rousseau, c. 1750
|
(Canby, p.9)
|
Rousseau, romantic philosopher and writer in the 18th century, had no idea
how
man was going to fly, except that he was going to fly like birds of nature. However, for centuries before his statement above, humans had been “flying’’—at least leaving the bounds of earth for measurable periods of time—by one means or another.
Humans first left the earth not on feathered wings, nor even in balloons, but on giant kites. As mentioned above, the invention of kites is attributed to 4th century B.C. China. Long before they were known in the west, kites were used to lift observers high above the sea for navigation and signaling purposes in shipping and military maneuvers—practices witnessed and reported by the explorer Marco Polo from his travels to the Orient in the 14th century A.D. Kites were used in China not only for observation, but even for the dropping of bombs in battle and for the first known parachute jumps. (Taylor & Mondey, p.8) Granted that kites are tethered and such flight is not “free’’; nevertheless, as will be illustrated below, the forces on a kite are similar to those on a bird’s wing or airfoil. (Kite making and kite flying are particularly enjoyable ways to study aerodynamics and might easily be joined to any class picnic, field trip, etc.)
Other than kiting, it is fair to say that man’s first conquest of the air was in balloons. The roots of balloon science really lie in the discoveries made by Greek mathematician and inventor Archimedes who, in about 200 B.C., explained how and why objects float or sink in liquids. The “lift’’ of a floating object depends upon its mass and the mass of the liquid which its volume would displace (i.e., relative densities). For students unfamiliar with Archimedes Principle, mass, volume, and density, some simple laboratory lessons at this point will help them grasp the fundamentals which can then be applied to ballooning. (See any standard General Science or Physical Science text)
The first man to approach flying on a “scientific’’ basis was the English monk Roger Bacon in the 13th century. Studying the work of Archimedes, Bacon envisioned the air about us as a sea of some solid basis. He believed that a balloon could be filled with some lighter substance which he called “ethereal air’’. (Highland, p.6) Four hundred years later, on Italian priest, Francesco de Lana, applied Bacon’s principle of air flight to the design of a boat, complete with mast and sail, which was to be held aloft by four hollow spheres. Each sphere was to be made of very thin copper, 20 feet in diameter. All air was to be removed from the spheres so they would float up in the sky. While impossible to construct, de Lana’s design was an important step in conception.
In Avignon, France (modern new Haven’s sister city!) during November, 1782, Joseph Montgolfier, a paper manufacturer with an inquisitive and inventive mind, observed the upward rush of smoke and hot air from a fire. Constructing a simple cloth bag, he filled it with hot air and watched it rise to the ceiling. The European age of lighter-than-air flight had begun! (see Canby, p.9) Joseph and his brother Etienne had heard about the discovery of a gas lighter than air by the English chemist, Henry Cavendish. Cavendish called his gas “inflammable air’’; it was later renamed hydrogen. (Scarry, p.47) The Mongolfiers at first assumed that a similar light gas was produced by flame; however, they soon realized that the heating of air itself was sufficient to float a balloon and within a year ascents were quite frequent in France by both hot air and hydrogen balloons.
Unknown to the Montgolfiers and to most of the European world, the first demonstration of hot air ballooning is now known to have taken place in 1709—74 years before the Avignon discovery! A brilliant young Jesuit priest, Father Laurenco de Gusmao of Brazil built and displayed before the King of Portugal working models of paper balloons rising above a small basket of flame. The Montgolfiers still have the distinction of being the first to send a person aloft in a balloon; but Gusmao was first to show the principle—even if he did cause a minor fire in the palace chamber during the demonstration! (Taylor & Munson, pp. 19 & 506)
The next 150 years were filled with filled with scientific advances aided by balloons and their more controllable “offspring’’, dirigibles. Though hot-air ballooning gained and still retains great popularity, hydrogen-filled balloons became the favorite for scientific research in the atmosphere and for large dirigible use. Helium, nearly as buoyant as hydrogen and non-flammable was more expensive to produce so remained tragically underutilized until after several spectacular dirigible disasters, including the
Hindenburg
in 1937. By that time the fascination with large dirigibles was on the wane and larger, heavier-than-air craft were in ascendancy. But this is many leaps ahead of our story. We need to return to the English Franciscan monastery of Roger Bacon and pick up the trail of heavier-than-air flight design.
In 1250, Bacon completed a book titled “Secrets of Art and Nature’’ in which he makes the first known reference to a flying machine with “artificial wings made to beat the aire’’, known today as an ornithopter (bird-like craft). (Taylor & Mondey, p.8) However, it was Leonardo da Vinci, the versatile mathematician, painter, sculptor, architect and engineer and musician who made the first detailed analysis of the mechanics of flight. He studied birds in flight and made drawings to show his ideas on flight, including several sketches of flapping wing planes and ornithopters which he felt a human could operate. Da Vinci assumed that man’s muscular power was adequate for this purpose. Except for their reliance on human-powered flapping, da Vinci’s designs look remarkably like modern lightweight aircraft.
Following da Vinci, many inventors tried to make ornithopters, the most successful being Robert Hooke in England about 1650. Hooke claimed to succeed in flying, but he also wrote of the great difficulty in remaining in the air. None of the early experimenters realized that the human body is not built for bird-like flying. The human heart is only 0.5 percent of total body weight, whereas that of the golden eagle is 8 percent and that of the hummingbird up to 22 percent. Compared with man’s normal heartbeat of 70 times per minute, even that of a sparrow throbs at an astounding 800 times per minute in flight. The limitations of human physiology were spelled out in 1680 by the Italian Giovanni Borelli. His
De Motu Animalium
describes at length why man could never hope to sustain his weight in the air
without mechanical assistance
. (Taylor and Munson, p.11) Borelli’s assessment was later confirmed by an American engineer, Octave Chanute, who in his 1894 publication
Progress in Flying Machines
, stated that man could not develop sufficient power to fly with only his arms and legs. (Taylor and Munson, p.45). Chanute was a railway engineer whose work on steam and other engines proved a valuable guide to the Wright brothers. However, as we shall see, Borelli proved a much more accurate forecaster, for, less than 100 years after Chanute’s publication, man flew substantial distances using the power of his legs and mechanical, but not motorized assistance.
Prior to 1800 there were few attempts at flight with heavier-than-air craft. The designs of Bacon, da Vinci, Hooke and others did not prove feasible. The most promising work—that of da Vinci—was not even published until late in the 19th century. (Taylor & Munson, p. 34) The man now recognized as the “father of aeronautics’’, Sir George Cayley, was an English inventer and student of flight who unknowingly retraced much of da Vinci’s path. Cayley, however, made a major breakthrough in aircraft design. He decided that it would be possible to make a plane fly through air if: 1. the plane were light enough, 2. the air could be forced against its wings by moving the plane through the air, and 3. stability could be provided by placement of crossed vertical and horizontal “tail’’ wings. By using diagonal bracing to reinforce the wings and body of the craft, Cayley was able to greatly reduce the weight. Moving the ship through the air was to be accomplished by a propeller driven engine. Cayley even designed a new lightweight engine, but he never built and applied it. However, he did construct successful gliders and significant advanced understanding of flight theories of lift and drag. His separation of the means of propulsion from the aircraft itself pointed the way for later developments after his death in 1857.
Little more need be covered here about early aircraft. Immediately after Cayley, many experimenters built models to which small engines were attached for flight. The four forces acting on a craft: lift, drag, gravity and thrust were reasonably understood. All that remained was for development of an engine of sufficient power and lightness to provide the needed thrust to put a manned glider into flight. The Wright brothers in 1903 had the honor of being the first to achieve “true flight’’—
powered, sustained
and
controlled
.
———
Determining Power Output
Students will, no doubt, be interested in the actual power output of a human body and their own output for familiar tasks. A calculating exercise is provided among the suggested classroom activities. However, the table below may prove helpful for students who are not familiar with the metric (MKS or SI) system of measurement.
|
Quantity
|
U.S. System
|
Metric System
|
|
1. gravity
|
32 ft/sec2
|
9.8m/sec2
|
|
2. mass
|
slugs (lb/32)
|
kilograms
|
|
3. weight (mg)
|
pounds
|
newtons
|
|
4. force
|
pounds
|
newtons
|
|
5. distance
|
feet
|
meters
|
|
6. time
|
seconds
|
seconds
|
|
7. work (=f x d)
|
footpounds
|
joules
|
|
8. Power (=w/t)
|
horsepower
|
watts
|
one horsepower = 550 foot pounds per second one horsepower = 746 watts
