ornithopter n : heavier-than-air craft that is propelled by the flapping of wings [syn: orthopter]

English

Noun

1. a machine that generates lift through the flapping of its wings.

An ornithopter (from Greek ornithos "bird" and pteron "wing") is an aircraft that flies by flapping its wings. Designers seek to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, they are usually built on the same scale as these flying creatures. Manned ornithopters have also been built, and some successful flights have been reported.

Early history

The idea of constructing wings in order to imitate the flight of birds dates to the ancient Greek legend of Daedalus and Icarus. Roger Bacon, writing in 1260, was among the first to consider a technological means of flight. Around 1490, Leonardo da Vinci began to study the flight of birds. He grasped that humans are too heavy, and not strong enough, to fly using wings simply attached to the arms. Therefore he proposed a device in which the aviator lies down on a plank and works two large, membranous wings using hand levers, foot pedals, and a system of pulleys.

The first ornithopters capable of flight were constructed in France in the 1870s. Gustav Trouvé's 1870 model flew a distance of 70 meters in a demonstration for the French Academy of Sciences. The wings were flapped by gunpowder charges activating a bourdon tube. Jobert in 1871 used a rubber band to power a small model bird. Alphonse Penaud, Hureau de Villeneuve, Victor Tatin, and others soon followed with their own designs.

Around 1890, Lawrence Hargrave built several ornithopters powered by steam or compressed air. He introduced the use of small flapping wings providing the thrust for a larger fixed wing. This eliminated the need for gear reduction, thereby simplifying the construction. To achieve a more birdlike appearance, this approach is not generally favored today.

In the 1930s, Erich von Holst carried the rubber band powered bird model to a high state of development and great realism. Also in the 1930s, Alexander Lippisch and other researchers in Germany harnessed the piston internal combustion engine.

Manned flight

Perhaps because the prevailing culture favors fixed-wing aircraft, people are mainly aware of the failed attempts at flapping-wing flight. This article describes only the more successful attempts. The machines are of two general types: those with engines, and those powered by the muscles of the pilot.

In 1929, a man-powered ornithopter designed by Alexander Lippisch flew a distance of 250 to 300 meters after tow launch. The flight duration was necessarily short due to the limitations of human muscle power. Since a tow launch was used, some have questioned whether the aircraft was capable of sustained flight, however brief. Lippisch asserted that the aircraft was actually flying, not making an extended glide. Later tow-launched flights include Bedford Maule (1942), Emil Hartmann (1959), and Vladimir Toporov (1993). All faced similar limitations due to the reliance on human muscle power.

In 1942, Adalbert Schmid flew a motorized, manned ornithopter at Munich-Laim. It was driven by small flapping wings mounted at the sides of the fuselage, behind a larger fixed wing. Fitted with a 3 hp Sachs motorcycle engine, it made flights up to 15 minutes in duration. Schmid later constructed a 10 hp ornithopter based on the Grunau-Baby IIa sailplane, which was flown in 1947. The second aircraft had flapping outer wing panels.

In 2005, Yves Rousseau was given the Paul Tissandier Diploma, awarded by the FAI for contributions to the field of aviation. Rousseau attempted his first human-muscle-powered flight with flapping wings in 1995. On 20 April 2006, at his 212th attempt, he succeeded in flying a distance of 64 metres, observed by officials of the Aero Club de France. Unfortunately, on his 213th flight attempt, a gust of wind led to a wing breaking up, causing the pilot to be gravely injured and rendered paraplegic.

A team at the University of Toronto Institute for Aerospace Studies, headed by Professor James DeLaurier, worked for several years on an engine-powered, piloted ornithopter. In July 2006, at the Bombardier Airfield at Downsview Park in Toronto, Professor DeLaurier's machine, the UTIAS Ornithopter No.1 made a jet-assisted takeoff and 14-second flight. According to DeLaurier, the jet was necessary for sustained flight, but the flapping wings did most of the work.

Recent developments

Practical applications capitalize on the resemblance to birds or insects. The Colorado Division of Wildlife has used these machines to help save the endangered Gunnison Sage Grouse. An artificial hawk under the control of an operator causes the grouse to remain on the ground so they can be captured for study.

Because ornithopters resemble birds or insects, they could be used for military applications, such as spying without alerting the enemies that they are under surveillance. AeroVironment, Inc., led by Paul B. MacCready (Gossamer Albatross), has developed a remotely piloted ornithopter the size of a large insect for possible spy missions.

MacCready also developed in the mid-1980s, for the Smithsonian Institution, a half-scale radio controlled replica of the giant pterosaur, Quetzalcoatlus northropi. The model had a wingspan of 5.5 meters (18 feet) and featured a complex, computerized autopilot control system, just as the full-size pterosaur relied on its neuromuscular system to make constant adjustments in flight.

Researchers hope to eliminate the motors and gears of current designs by more closely imitating animal flight muscles. Georgia Tech scientist Robert C. Michelson is developing a Reciprocating Chemical Muscle for use in micro-scale flapping-wing aircraft. Michelson uses the term "entomopter" for this type of ornithopter. SRI International is developing polymer artificial muscles which may also be used for flapping-wing flight.

In 2002, Krister Wolff and Peter Nordin of Chalmers University of Technology in Sweden, built a flapping wing robot that learned flight techniques. The balsa wood design was driven by machine learning software technology known as a steady state linear evolutionary algorithm. Inspired by natural evolution, the software “evolves” in response to feedback on how well it performs a given task. Although confined to a laboratory apparatus, their ornithopter evolved behavior for maximum sustained lift force and horizontal movement.

Ornithopters as a hobby

Hobbyists can build and fly their own ornithopters. These range from light-weight models powered by rubber band, to larger models with radio control.

The rubber-band-powered model can be fairly simple in design and construction. Hobbyists compete for the longest flight times with these models. An introductory model can be fairly simple in design and construction, but the advanced competition designs are extremely delicate and challenging to build. Roy White holds the US national record for indoor rubber-powered, with his flight time of 21 minutes, 44 seconds.

Commercial free-flight rubber-band powered toy ornithopters have long been available. The first of these was sold under the name Tim Bird in Paris in 1879. Later models were also sold as Tim Bird (made by G de Ruymbeke, France, since 1969).

Commercial radio controlled designs stem from Percival Spencer's engine-powered Seagulls, developed circa 1958, and Sean Kinkade's work in the late 1990s. The wings are usually driven by an electric motor. Many hobbyists enjoy experimenting with their own new wing designs and mechanisms. The opportunity to interact with real birds in their own domain also adds great enjoyment to this hobby. Birds are often curious and will follow or investigate the model while it is flying. In a few cases, RC birds have been attacked by birds of prey, crows, and even cats. More recent cheaper models such as the Dragonfly from WowWee have extended the market from dedicated hobbyists to the general toy market,

Some helpful resources for hobbyists include The Ornithopter Design Manual, book written by Nathan Chronister, and The Ornithopter Zone web site, which includes a large amount of information about building and flying these models.

Aerodynamics

Unlike fixed-wing aircraft (which derive their lift from the wings and thrust from the propellor or jet), an ornithopter's wings themselves provide both lift and thrust, and have a flapping motion instead of rotary. Theoretically, the flapping wing can be set to zero angle of attack on the upstroke, so it passes easily through the air. Since the flapping airfoils produce both lift and thrust, drag-inducing structures are minimized. These two advantages potentially allow a high degree of efficiency.

As demonstrated by birds, flapping wings offer potential advantages in maneuverability and energy savings compared with fixed-wing aircraft.

From general aerodynamic considerations, ornithopters appear to make more efficient use of power than rotating propeller or jet aircraft do. However, this is only the case at low velocities and masses, as wing area required for lift at high speeds is very small as is the ideal pitch of propeller, turboprop or turbofan engines. Other difficulties that have prevented major practical application appear to be the required mechanisms and structures, and the comfort of passengers since the ornithopter body typically oscillates counter to the wing motion.

However, the main issue in constructing large manned ornithopters is the problem of wing loading. For similarly shaped flyers, the weight increases as the cube of linear dimension, while the lift-producing surface area increases only as the square of linear dimension. Thus as the payload portion of the flyer gets larger, the wings must increase in size disproportionately in order to maintain wing loading at levels where lift can overcome the craft's total weight. These much larger wings are then more difficult to flap.

While difficulties arise from larger wings, flapping is not impossible. King Vulture and the Stork, are fully capable of flight. Some of the largest flying animals to have ever existed are now extinct. These include, the Pteranodon, the Quetzalcoatlus, and the Hatzegopteryx, all of which had massive wingspans fully capable of flapping to achieve flight.

Notable popular culture

• Robert Altman's 1970 movie, Brewster McCloud, centers around a young man and his project to build a manned ornithopter.
• Frank Herbert's Dune universe featured ornithopters (colloquially called thopters) as one of the primary modes of transportation on Arrakis.
• Many of the movies made by Hayao Miyazaki feature ornithopters, many featuring wings like insects.
• The Magic the Gathering trading card game features a card named Ornithopter which is considered one of its staples.
• The Star Wars film Revenge of the Sith depicts a dragonfly-like vehicle being operated by the Wookies during battle on their home planet of Kashyyyk.
• In Nick Park's feature film Chicken Run the "crate" that they end up escaping on, is an ornithopter.

See also

• Fixed-wing aircraft
  • variable geometry wing
  • variable-incidence wing
  • variable camber wing
• Rotary-wing aircraft
  • Gyroplane
  • Helicopter
  • FanWing
• STOL/VTOL/STOVL/VSTOL
• Micromechanical Flying Insect
• FlyTech Dragonfly from WowWee
• Interactive Toy Concepts iFLY VAMP

References

Further reading

• Hallion, Richard P. (2003). Taking Flight: Inventing the Aerial Age from Antiquity through the First World War. New York: Oxford University Press. ISBN 0-19-516035-5.

• Chronister, Nathan. (1999). The Ornithopter Design Manual. Published by The Ornithopter Zone.

External links

• The Ornithopter Zone web site
• Creation of a learning, flying robot by means of Evolution
• University of Toronto ornithopter project
• University of Arizona ornithopter-Video
• Design Engineering article about UTIAS project
• Fly UTIAS Ornithopter with FlightGear open-source flight simulator
• Photographs from 1927 From the State Library& Archives of Florida
• The French Ornithopter web site
• web site of a member of URVAM
• gfraise ornithopter site (French)
• Entomopter web site
• BYU students fly tiny, birdlike 'ornithopter' at competition
• Lawrence Hargrave's ornithopters - State Library of NSW
• DelFly - an MAV ornithopter by a team of Delft University of Technology and Wageningen University