It was not long ago that people could only dream of being able to fly.
The dream was the subject of great myths and stories such as that of
Icarus and his father Daedalus and their escape from King Minos' prison
on Crete. Legend has it that they had difficulty with structural materials
rather than aerodynamics.
(Picture from a woodcut of 1493.)
In medieval times further work in applied aerodynamics and flight were made. Some rather notable people climbed to the top of convenient places with intent to commit aviation.
Natural selection and survival of the fittest worked very effectively in preventing the evolution of human flight.
|As people started to look before leaping, several theories of flight were propounded (e.g. Newton) and arguments were made on the impossibility of flight. This was not a research topic taken seriously until the very late 1800's. And it was regarded as an important paradox that birds could so easily accomplish this feat that eluded people's understanding. Octave Chanute, in 1891 wrote, "Science has been awaiting the great physicist, who, like Galileo or Newton, should bring order out of chaos in aerodynamics, and reduce its many anomolies to the rule of harmonious law."|| |
(A Galapagos hawk -- Photo by Sharon Stanaway )
Papers suggested that perhaps birds and insects used some "vital force" which enabled them to fly and which could not be duplicated by an inanimate object. Technical meetings were held in the 1890's. The ability of birds to glide without noticeable motion of the wings and with little or negative altitude loss was a mystery for some time. The theory of aspiration was developed; birds were in some way able to convert the energy in small scale turbulence into useful work. Later this theory fell out of favor and the birds' ability attributed more to proficient seeking of updrafts. (Recently, however, there has been some discussion about whether birds are in fact able to make some use of energy in small scale air motion.)
The figure here is reproduced from the 1893 book, First International Conference on Aerial Navigation. The paper is called, "The Mechanics of Flight and Aspiration," by A.M. Wellington. The figure shows the flight path of a bird climbing without flapping its wings. Today we know that the bird is circling in rising current of warm air (a thermal).
Designs were made before people had the vaguest idea about how aircraft flew. Leonardo Di Vinci designed ornithopters in the late 1400's, modeled on his observations of birds. But apart from his work, most designs were pure fantasy.
The first successes came with gliders. Sir George Cayley wrote a book entitled "On Aerial Navigation" in 1809. He made the first successful glider in 1804 and a full-size version five years later at the age of 36.
|For many years thereafter, though, aeronautics was not taken seriously, except by a small group of zealots. One of these was William Henson who patented the Aerial Steam Carriage, shown here, in 1843. The aircraft was never built, but was very well publicized (with the idea of raising venture capital). Both the design and the funding scheme were ahead of their time.
In England, Henson worked with John Stringfellow and Federick Marriott, each of whom who continued development of related concepts after Henson. Stringfellow built several models including steam-powered monoplanes (which flew in 1848) and triplanes in the 1860's.
Marriott continued work on flying machines, while becoming a well-known publisher in San Francisco. He built several large models (28 feet long) of partially-buoyant air vehicles (Avitor) and a triplane that he named after Leland Stanford in the 1870's. He popularized the idea of aviation long before it became feasible. From a Marriott biography by Richard A. Hernandez in 1963 and quoted at TwainQuotes.com:
"A young reporter from Nevada with a noticeable drawl and a large red mustache often accompanied Mr. Marriott down to the basement of the building where he was working on the 'Avitor.' The reporter was astounded by the stamina and enthusiasm of the editor as he worked hour-after-hour with only the light of a row of candles stuck in beer bottles. The reporter was the young Mark Twain. (Hernandez, p. 405-407)."
For a wealth of additional information on these early pioneers see the websites cited in the reference section.
Henson's Aerial Steam Carriage
Image courtesy Carroll F. Gray Aeronautical Collection
Some rather ambitious designs were actually built. The enormous aeroplane built in 1894 by Sir Hiram Maxim and shown below, weighed 7,000 lbs (3,200 kg) and spanned over 100 ft (30 m).
In Germany in the 1860's Otto Lilienthal took a more conscientious approach with tests on a whirling arm, ornithopter tests suspended from a barn, and finally flight tests of a glider design. He studied the effect of airfoil shape, control surfaces, propulsion systems, and made detailed measurements of bird flight. His book, "Birdflight as the Basis of Aviation" was an important influence on later pioneers.
This was one of Lilienthal's last flights. He was killed in 1896 by a gust-induced stall too near the ground.
From Lilienthal's first flights in the 1890's, to the Wright brother's glider flights and powered aircraft, evolution was quick.
Orville Wright soars a glider in 50 mi/hr (80 km/hr) winds for 10 minutes at Kitty Hawk, Oct. 24, 1911. This was one of the first applications of a aft horizontal tail on the Wright aircraft. From Aero Club of America Bulletin, Jan. 1912.
The first 'Aerial Limousine', 1911. "The limousine has doors with mica windows and seats for four persons fitted with pneumatic cushions, the pilot seats in front. A number of flights have been made, with and without passengers, with entire success."
The Boeing 777, Courtesy Boeing Commercial Airplane Group.
It is truly amazing how quickly this has happened: we tend to think of the dawn of flight as something from Greek mythology, but it has been only about 100 years since people first flew airplanes.
Of course other things happen quickly too. When the 747 was designed calculators were big whirring contraptions which sat on desks and could not do square roots. The earlier transports, still flying today, were designed when calculators were women who worked the computing machines.
The picture below shows the computational grid for a modern calculation of the flow over 737 wing with flaps and slats deployed.
Image from NASA Ames Research Center
The revolution in computing has changed the way we do computational applied aerodynamics, but we still utilize a variety of methods. Computation, ground-based testing, and finally, flight tests.
The plot shows the computer power required to perform the indicated calculations in about 15 minutes using 1985 algorithms. Using more modern supercomputers and now, parallel machines, this time is dropping dramatically. Yet, we are still a long way from routine applications of direct Navier-Stokes simulations or LES.
The Cray C916 Supercomputer
Projects such as NASA's Numerical Aerodynamic Simulation program continue to develop simulation software that takes advantage of recent advances in computer hardware and software.
In this class we will talk about the methods used to compute aerodynamics flows. We will use simple methods on personal computers and design airfoil sections. We will analyze wings and talk about the elements of wing design. We will be talking about fundamental concepts that can be demonstrated with simple programs but which form the basis for modern computational methods. We will discuss how these methods work, what they can and cannot do. We will use results from analytical studies, wind tunnel tests, and CFD to discuss wing and airplane design.
While we discuss aircraft a great deal, the concepts and methods are relevant to a wide range of applications: Weather prediction, boat design, disk drive aerodynamics, architectural applications, and land-based vehicles.
The aerodynamics of bumble bees, disk heads, weather, and many other things is not a solved problem. While it is impressive that the methods in use today do so well, we are still not able to predict many flows.