Ornithopters
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An ornithopter (from
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
''ornis, ornith-'' 'bird' and ''pteron'' 'wing') is an
aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...
that flies by flapping its wings. Designers sought 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 flying animals. Larger, crewed ornithopters have also been built and some have been successful. Crewed ornithopters are generally powered either by engines or by the
pilot An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its Aircraft flight control system, directional flight controls. Some other aircrew, aircrew members, such as navigators or flight engineers, are al ...
.


Early history

Some early crude flight attempts may have been intended to achieve flapping-wing flight, but probably only a glide was actually achieved. They include the purported flights of the 11th-century Catholic monk
Eilmer of Malmesbury Eilmer of Malmesbury (also known as Oliver due to a scribe's miscopying, or Elmer, or Æthelmær) was an 11th-century English Benedictine monk best known for his early attempt at a gliding flight using wings. Life Eilmer was a monk of Malme ...
(recorded in the 12th century) and the 9th-century poet
Abbas Ibn Firnas Abū al-Qāsim ʿAbbās ibn Firnās ibn Wardūs al-Tākurnī (; c. 809/810 – 887 CE), known as ʿAbbās ibn Firnās () was an Andalusi polymath: Lynn Townsend White, Jr. (Spring, 1961). "Eilmer of Malmesbury, an Eleventh Century Aviator: A C ...
(recorded in the 17th century).
Roger Bacon Roger Bacon (; or ', also '' Rogerus''; ), also known by the Scholastic accolades, scholastic accolade ''Doctor Mirabilis'', was a medieval English polymath, philosopher, scientist, theologian and Franciscans, Franciscan friar who placed co ...
, writing in 1260, was also among the first to consider a technological means of flight. In 1485,
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 1452 - 2 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested o ...
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. He, therefore, sketched 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 successful ornithopter was built by a Polish nobleman and scientist of Italian descent, Tytus Liwiusz Boratyni. In 1648, he built a spring-powered prototype that lifted a cat during a test flight. Tytus Boratyni planned to build a manned version called the "Flying Dragon". The project assumed numerous rescue systems, including a
parachute A parachute is a device designed to slow an object's descent through an atmosphere by creating Drag (physics), drag or aerodynamic Lift (force), lift. It is primarily used to safely support people exiting aircraft at height, but also serves va ...
. The bottom of the ornithopter's fuselage was to be able to float on water in the event of an accident over the sea or a lake. In order to implement the project, he unsuccessfully applied for funding for research from King
Władysław IV Vasa Władysław IV Vasa or Ladislaus IV (9 June 1595 – 20 May 1648) was King of Poland, Grand Duke of Lithuania and claimant of the thrones of Monarchy of Sweden, Sweden and List of Russian monarchs, Russia. Born into the House of Vasa as a prince ...
. In 1841, an ironsmith '' kalfa'' (journeyman), Manojlo, who "came to
Belgrade Belgrade is the Capital city, capital and List of cities in Serbia, largest city of Serbia. It is located at the confluence of the Sava and Danube rivers and at the crossroads of the Pannonian Basin, Pannonian Plain and the Balkan Peninsula. T ...
from
Vojvodina Vojvodina ( ; sr-Cyrl, Војводина, ), officially the Autonomous Province of Vojvodina, is an Autonomous administrative division, autonomous province that occupies the northernmost part of Serbia, located in Central Europe. It lies withi ...
", attempted flying with a device described as an ornithopter ("flapping wings like those of a bird"). Refused by the authorities a permit to take off from the belfry of Saint Michael's Cathedral, he clandestinely climbed to the rooftop of the Dumrukhana (import tax head office) and took off, landing in a heap of snow, and surviving. The first ornithopters capable of flight were constructed in France. Jobert in 1871 used a
rubber band A rubber band (also known as an elastic, gum band or lacky band) is a loop of rubber, usually ring or oval shaped, and commonly used to hold multiple objects together. The rubber band was patented in England on March 17, 1845, by Stephen Perry ...
to power a small model bird.
Alphonse Pénaud Alphonse Pénaud (31 May 1850 – 22 October 1880), was a 19th-century French pioneer of aviation design and engineering. He was the originator of the use of twisted rubber to power model aircraft, and his 1871 model airplane, which he called ...
, Abel Hureau de Villeneuve, and
Victor Tatin Victor Tatin (1843–1913) was a French engineer who created an early airplane, the ''Aéroplane'', in 1879. The craft was the first model airplane to take off using its own power after a run on the ground. The model had a span of and weighed ...
also made rubber-powered ornithopters during the 1870s. Tatin's ornithopter was perhaps the first to use active torsion of the wings, and apparently it served as the basis for a commercial toy offered by Pichancourt 1889. Gustave Trouvé was the first to use internal combustion, and his 1890 model flew a distance of 80 meters in a demonstration for the French Academy of Sciences. The wings were flapped by
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, charcoal (which is mostly carbon), and potassium nitrate, potassium ni ...
charges activating a
Bourdon tube Bourdon derives from the French for bumblebee, and may refer to: * Bourdon (bell), the lowest bell in a set * Bourdon (organ pipe), a stopped organ pipe of a construction favored for low pitches * Bourdon (surname) * Drone (music): The lowest cou ...
. From 1884 on, Lawrence Hargrave built scores of ornithopters powered by rubber bands, springs,
steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...
, or
compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air in vehicle tires and shock absorbers are commonly used for improved traction and reduced vibration. Compressed air is an important medium for t ...
. He introduced the use of small flapping wings providing the thrust for a larger fixed wing; this innovation eliminated the need for gear reduction, thereby simplifying the construction. E. P. Frost made ornithopters starting in the 1870s; first models were powered by steam engines, then in the 1900s, an internal-combustion craft large enough for a person was built, though it did not fly.Kelly, Maurice. 2006. ''Steam in the Air''. Ben & Sword Books. Pages 49–55 are about Frost. In the 1930s,
Alexander Lippisch Alexander Martin Lippisch (2 November 1894 – 11 February 1976) was a German aeronautical engineer, a pioneer of aerodynamics who made important contributions to the understanding of tailless aircraft, delta wings and the ground effect in aircra ...
and the
National Socialist Flyers Corps The National Socialist Flyers Corps (; NSFK) was a paramilitary aviation organization of the Nazi Party. History NSFK was founded 15 April 1937 as a successor to the German Air Sports Association; the latter had been active during the years when ...
of
Nazi Germany Nazi Germany, officially known as the German Reich and later the Greater German Reich, was the German Reich, German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a Totalit ...
constructed and successfully flew a series of internal combustion-powered ornithopters, using Hargrave's concept of small flapping wings, but with aerodynamic improvements resulting from the methodical study. Erich von Holst, also working in the 1930s, achieved great efficiency and realism in his work with ornithopters powered by rubber bands. He achieved perhaps the first success of an ornithopter with a bending wing, intended to imitate more closely the folding wing action of birds, although it was not a true variable-span wing such as those of birds. Around 1960, Percival Spencer successfully flew a series of uncrewed ornithopters using internal combustion engines ranging from displacement, and having wingspans up to . In 1961, Percival Spencer and Jack Stephenson flew the first successful engine-powered, remotely piloted ornithopter, known as the Spencer Orniplane. The Orniplane had a wingspan, weighed , and was powered by a -displacement
two-stroke engine A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a Thermodynamic power cycle, power cycle with two strokes of the piston, one up and one down, in one revolution of the crankshaft in contrast to a f ...
. It had a biplane configuration, to reduce oscillation of the fuselage.


Crewed flight

Crewed ornithopters fall into two general categories: Those powered by the muscular effort of the pilot (human-powered ornithopters), and those powered by an engine. One early experimenter was the Dutchman Vincent de Groof in the 1860s and 1870s. Around 1894,
Otto Lilienthal Karl Wilhelm Otto Lilienthal (23 May 1848 – 10 August 1896) was a German pioneer of aviation who became known as the "flying man". He was the first person to make well-documented, repeated, successful flights with gliders, therefore making t ...
, an aviation pioneer, became famous in Germany for his widely publicized and successful glider flights. Lilienthal also studied bird flight and conducted some related experiments. He constructed an ornithopter, although its complete development was prevented by his untimely death on 9 August 1896 in a glider accident. In 1929, a man-powered ornithopter designed by
Alexander Lippisch Alexander Martin Lippisch (2 November 1894 – 11 February 1976) was a German aeronautical engineer, a pioneer of aerodynamics who made important contributions to the understanding of tailless aircraft, delta wings and the ground effect in aircra ...
(designer of the
Messerschmitt Me 163 Komet The Messerschmitt Me 163 Komet is a rocket-powered interceptor aircraft primarily designed and produced by the German aircraft manufacturer Messerschmitt. It is the only operational rocket-powered fighter aircraft in history as well as ...
) flew a distance of after tow launch. Since a tow launch was used, some have questioned whether the aircraft was capable of flying on its own. Lippisch asserted that the aircraft was actually flying, not making an extended glide. (Precise measurement of altitude and velocity over time would be necessary to resolve this question.) Most of the subsequent human-powered ornithopters likewise used a tow launch, and flights were brief simply because human muscle power diminishes rapidly over time. In 1942, Adalbert Schmid made a much longer flight of a human-powered ornithopter at Munich-Laim. It travelled a distance of , maintaining a height of throughout most of the flight. Later this same aircraft was fitted with a Sachs motorcycle engine. With the engine, it made flights up to 15 minutes in duration. Schmid later constructed a ornithopter, based on the Grunau-Baby IIa sailplane, which was flown in 1947. The second aircraft had flapping outer wing panels. The French engineer René Riout devoted himself for three decades to the realization of flapping wing ornithopters. In 1905 he invented his first models. In 1909 he won the gold medal in the Lépine competition for a reduced model. In 1913 he worked on the development of a model ordered by a pilot, the Dubois-Riout. The tests were stopped in 1916. In 1937, he finalized the Riout 102T Alérion, certainly the most successful piloted flapping wing ornithopter until the second decade of the 21st century. Ultimately, the conclusions of the wind tunnel tests were not favorable to the continuation of the project. 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 , observed by officials of the Aero Club de France. 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 Paraplegia, or paraparesis, is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek () "half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neura ...
. A team at the
University of Toronto The University of Toronto (UToronto or U of T) is a public university, public research university whose main campus is located on the grounds that surround Queen's Park (Toronto), Queen's Park in Toronto, Ontario, Canada. It was founded by ...
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 Downsview Park () is a large urban park located in the Downsview, Toronto, Downsview neighbourhood of Toronto, Ontario, Canada. The park's name is officially Bilingualism in Canada, bilingual due to it being federally owned and managed, and was ...
in
Toronto Toronto ( , locally pronounced or ) is the List of the largest municipalities in Canada by population, most populous city in Canada. It is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a p ...
, 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. On August 2, 2010, Todd Reichert of the same institution piloted a human-powered ornithopter named Snowbird. The wingspan, aircraft was constructed from
carbon fibre Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers ( Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon comp ...
, balsa, and foam. The pilot sat in a small cockpit suspended below the wings and pumped a bar with his feet to operate a system of wires that flapped the wings up and down. Towed by a car until airborne, it then sustained flight for almost 20 seconds. It flew with an average speed of . Similar tow-launched flights were made in the past, but improved data collection verified that the ornithopter was capable of self-powered flight once aloft.


Applications for uncrewed ornithopters

Because ornithopters can be made to resemble birds or insects, they could be used for military applications such as
aerial reconnaissance Aerial reconnaissance is reconnaissance for a military or Strategy, strategic purpose that is conducted using reconnaissance aircraft. The role of reconnaissance can fulfil a variety of requirements including Artillery observer, artillery spott ...
without alerting the enemies that they are under surveillance. Several ornithopters have been flown with video cameras on board, some of which can hover and maneuver in small spaces. In 2011, AeroVironment demonstrated a remotely piloted ornithopter resembling a large hummingbird for possible spy missions. Led by Paul B. MacCready (of Gossamer Albatross fame), AeroVironment developed a half-scale radio-controlled model of the giant
pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...
, '' Quetzalcoatlus northropi'', for the
Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums, Education center, education and Research institute, research centers, created by the Federal government of the United States, U.S. government "for the increase a ...
in the mid-1980s. It was built to star in the IMAX movie '' On the Wing''. The model had a
wingspan The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the opposite wingtip. For example, the Boeing 777–200 has a wingspan of , and a wandering albatross (''Diomedea exulans'') caught in 1965 had a wingsp ...
and featured a complex computerized autopilot control system, just as the full-sized 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 Research Institute's Robert C. Michelson is developing a reciprocating chemical muscle for use in microscale flapping-wing aircraft. Michelson uses the term " entomopter" for this type of ornithopter.
SRI International SRI International (SRI) is a nonprofit organization, nonprofit scientific research, scientific research institute and organization headquartered in Menlo Park, California, United States. It was established in 1946 by trustees of Stanford Univer ...
is developing
polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
artificial muscles that may also be used for flapping-wing flight. In 2002, Krister Wolff and Peter Nordin of
Chalmers University of Technology Chalmers University of Technology (, commonly referred to as Chalmers) is a private university, private research university located in Gothenburg, Sweden. Chalmers focuses on engineering and science, but more broadly it also conducts research ...
in Sweden, built a flapping-wing robot that learned flight techniques. The balsa-
wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...
design was driven by
machine learning Machine learning (ML) is a field of study in artificial intelligence concerned with the development and study of Computational statistics, statistical algorithms that can learn from data and generalise to unseen data, and thus perform Task ( ...
software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...
technology known as a steady-state linear
evolutionary algorithm Evolutionary algorithms (EA) reproduce essential elements of the biological evolution in a computer algorithm in order to solve "difficult" problems, at least Approximation, approximately, for which no exact or satisfactory solution methods are k ...
. Inspired by natural
evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
, 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. Since 2002, Prof. Theo van Holten has been working on an ornithopter that is constructed like a
helicopter A helicopter is a type of rotorcraft in which Lift (force), lift and thrust are supplied by horizontally spinning Helicopter rotor, rotors. This allows the helicopter to VTOL, take off and land vertically, to hover (helicopter), hover, and ...
. The device is called the "ornicopter" and was made by constructing the main rotor so that it would have no reaction torque. In 2008,
Amsterdam Airport Schiphol Amsterdam Airport Schiphol , known informally as Schiphol Airport (, ), is the main international airport of the Netherlands, and is one of the major hubs for the SkyTeam airline alliance. It is located southwest of Amsterdam, in the municipal ...
started using a realistic-looking mechanical hawk designed by falconer Robert Musters. The radio-controlled robot bird is used to scare away birds that could damage the engines of airplanes. In 2012, RoBird (formerly Clear Flight Solutions), a spin-off of the University of Twente, started making artificial birds of prey (called RoBird®) for airports and agricultural and waste-management industries. Adrian Thomas and Alex Caccia founded Animal Dynamics Ltd in 2015, to develop a mechanical analogue of dragonflies to be used as a drone that will outperform quadcopters. The work is funded by the Defence Science and Technology Laboratory, the research arm of the British Ministry of Defence, and the United States Air Force.


Hobby

Hobby A hobby is considered to be a regular activity that is done for enjoyment, typically during one's leisure time. Hobbies include collecting themed items and objects, engaging in creative and artistic pursuits, playing sports, or pursuing other ...
ists build and fly their own ornithopters. These range from light-weight models powered by rubber bands, 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 United States 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 to present day. 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 Birds of prey or predatory birds, also known as (although not the same as) raptors, are hypercarnivorous bird species that actively predation, hunt and feed on other vertebrates (mainly mammals, reptiles and smaller birds). In addition to speed ...
,
crow A crow is a bird of the genus ''Corvus'', or more broadly, a synonym for all of ''Corvus''. The word "crow" is used as part of the common name of many species. The related term "raven" is not linked scientifically to any certain trait but is rathe ...
s, and even cats. More recent cheaper models such as the
Dragonfly A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threat ...
from
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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. Ornithopters were also of interest as the subject of one of the former events in the American nationwide Science Olympiad event list. The event ("Flying Bird") entailed building a self-propelled ornithopter to exacting specifications, with points awarded for high flight time and low weight. Bonus points were also awarded if the ornithopter happened to look like a real bird.


Aerodynamics

As demonstrated by birds, flapping wings offer potential advantages in maneuverability and energy savings compared with fixed-wing aircraft as well as potential for vertical take-off and landing. It has been suggested that these advantages are greatest at small sizes and low flying speeds, but the development of comprehensive aerodynamic theory for flapping remains an outstanding problem due to the complex non-linear nature of such unsteady separating flows. Unlike airplanes and helicopters, the driving
airfoil An airfoil (American English) or aerofoil (British English) is a streamlined body that is capable of generating significantly more Lift (force), lift than Drag (physics), drag. Wings, sails and propeller blades are examples of airfoils. Foil (fl ...
s of the ornithopter have a flapping or oscillating motion, instead of rotary. As with helicopters, the wings usually have a combined function of providing both lift and thrust. Theoretically, the flapping wing can be set to zero
angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...
on the upstroke, so it passes easily through the air. Since typically the flapping airfoils produce both lift and thrust, drag-inducing structures are minimized. These two advantages potentially allow a high degree of efficiency.


Wing design

If future crewed motorized ornithopters cease to be "exotic", imaginary, unreal aircraft and start to serve humans as junior members of the aircraft family, designers and engineers will need to solve not only wing design problems but many other problems involved in making them safe and reliable aircraft. Some of these problems, such as stability, controllability, and durability, are necessary for all aircraft. Other problems specific to ornithopters will appear; optimizing flapping-wing design is only one of them. An effective ornithopter must have wings capable of generating both
thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...
, the force that propels the craft forward, and lift, the force (perpendicular to the direction of flight) that keeps the craft airborne. These forces must be strong enough to counter the effects of drag and the weight of the craft. Leonardo's ornithopter designs were inspired by his study of birds, and conceived the use of flapping motion to generate thrust and provide the forward motion necessary for aerodynamic lift. However, using materials available at that time the craft would be too heavy and require too much energy to produce sufficient lift or thrust for flight. Alphonse Pénaud introduced the idea of a powered ornithopter in 1874. His design had limited power and was uncontrollable, causing it to be transformed into a toy for children. More recent vehicles, such as the human-powered ornithopters of Lippisch (1929) and Emiel Hartman (1959), were capable powered gliders but required a towing vehicle in order to take off and may not have been capable of generating sufficient lift for sustained flight. Hartman's ornithopter lacked the theoretical background of others based on the study of winged flight, but exemplified the idea of an ornithopter as a birdlike machine rather than a machine that directly copies birds' method of flight.Aeroelastic Design and Manufacture of an Efficient Ornithopter Wing
" Benedict, Moble. 3–4.
The 1960s saw powered uncrewed ornithopters of various sizes capable of achieving and sustaining flight, providing valuable real-world examples of mechanical winged flight. In 1991, Harris and DeLaurier flew the first successful engine-powered remotely piloted ornithopter in Toronto, Canada. In 1999, a piloted ornithopter based on this design flew, capable of taking off from level pavement and executing sustained flight. An ornithopter's flapping wings and their motion through the air are designed to maximize the amount of lift generated within limits of weight, material strength and mechanical complexity. A flexible wing material can increase efficiency while keeping the driving mechanism simple. In wing designs with the spar sufficiently forward of the airfoil that the aerodynamic center is aft of the elastic axis of the wing, aeroelastic deformation causes the wing to move in a manner close to its ideal efficiency (in which pitching angles lag plunging displacements by approximately 90 degrees.) Flapping wings increase drag and are not as efficient as propeller-powered aircraft. Some designs achieve increased efficiency by applying more power on the down stroke than on the upstroke, as do most birds.An Ornithopter Wing Design
DeLaurier, James D. (1994), 10–18 (accessed November 30, 2010)
In order to achieve the desired flexibility and minimum weight, engineers and researchers have experimented with wings that require carbon fiber, plywood, fabric, and ribs, with a stiff, strong trailing edge. Any mass located aft of the empennage reduces the wing's performance, so lightweight materials and empty space are used where possible. To minimize drag and maintain the desired shape, choice of a material for the wing surface is also important. In DeLaurier's experiments, a smooth aerodynamic surface with a double-surface airfoil is more efficient at producing lift than a single-surface airfoil. Other ornithopters do not necessarily act like birds or bats in flight. Typically birds and bats have thin and cambered wings to produce lift and thrust. Ornithopters with thinner wings have a limited angle of attack but provide optimum minimum-drag performance for a single lift coefficient. Although
hummingbird Hummingbirds are birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With approximately 366 species and 113 genus, genera, they occur from Alaska to Tierra del Fuego, but most species are found in Cen ...
s fly with fully extended wings, such flight is not feasible for an ornithopter. If an ornithopter wing were to fully extend and twist and flap in small movements it would cause a stall, and if it were to twist and flap in very large motions, it would act like a windmill causing an inefficient flying situation. A team of engineers and researchers called "Fullwing" has created an ornithopter that has an average lift of over 8 pounds, an average thrust of 0.88 pounds, and a propulsive efficiency of 54%. The wings were tested in a low-speed wind tunnel measuring the aerodynamic performance, showing that the higher the frequency of the wing beat, the higher the average thrust of the ornithopter.


In fiction

Ornithopters have been depicted in fiction several times, including
Frank Herbert Franklin Patrick Herbert Jr. (October 8, 1920February 11, 1986) was an American science-fiction author, best known for his 1965 novel Dune (novel), ''Dune'' and its five sequels. He also wrote short stories and worked as a newspaper journalist, ...
's ''Dune'' series, where they are the primary form of air transportation used by House Atreides in the desert climate of the planet Arrakis.


See also

*
Cyclogyro The cyclogyro, or cyclocopter, is an aircraft configuration that uses a horizontal-axis cyclorotor as a rotor wing to provide lift and, sometimes, also propulsion and control. In principle, the cyclogyro is capable of VTOL, vertical take off and ...
*
Gyroplane An autogyro (from Greek and , "self-turning"), gyroscope, gyrocopter or gyroplane, is a class of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. A gyroplane "means a rotorcraft whose rotors are not engine-dr ...
*
Human-powered aircraft A human-powered aircraft (HPA) is an aircraft belonging to the class of vehicles known as human-powered transport. As its name suggests, HPAs have the pilot not only steer, but power the aircraft (usually propeller-driven) by means of a system ...
* Insectothopter *
Micro air vehicle A micro air vehicle (MAV), or micro aerial vehicle, is a class of man-portable miniature UAVs whose size enables them to be used in low-altitude, close-in support operations. Modern MAVs can be as small as 5 centimeters - compare Nano Air Vehi ...
* Micromechanical Flying Insect * Nano Hummingbird *
Rotary-wing aircraft A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotary wings that spin around a vertical mast to generate lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapter I of Title 14 of the ...


References


Further reading

* Chronister, Nathan. (1999). ''The Ornithnopter Design Manual''. Published b
The Ornithopter Zone
* Mueller, Thomas J. (2001). "Fixed and flapping wing aerodynamics for micro air vehicle applications". Virginia: American Inst. of Aeronautics and Astronautics. * Azuma, Akira (2006). "The Biokinetics of Flying and Swimming". Virginia: American Institute of Aeronautics and Astronautics 2nd Edition. . * DeLaurier, James D.
The Development and Testing of a Full-Scale Piloted Ornithopter.
Canadian Aeronautics and Space Journal. 45. 2 (1999), 72–82. (accessed November 30, 2010). * Warrick, Douglas, Bret Tobalske, Donald Powers, and Michael Dickinson.
The Aerodynamics of Hummingbird Flight.
American Institute of Aeronautics and Astronautics 1–5. Web. 30 Nov 2010. * Crouch, Tom D. Aircraft of the National Air and Space Museum. Fourth ed. Lilienthal Standard Glider. Smithsonian Institution, 1991. * Bilstein, Roger E. Flight in America 1900–1983. First ed. Gliders and Airplanes. Baltimore, Maryland: Johns Hopkins University Press, 1984. (pages 8–9) * Crouch, Tom D. ''Wings. A History of Aviation from Kites to the Space Age.'' First ed. New York: W.W. Norton & Company, Inc., 2003. (pages 44–53) * Anderson, John D. ''A history of aerodynamics and its impact on flying machines.'' Cambridge: United Kingdom, 1997.


External links

* , two-minute flight of an eight-foot radio-controlled ornithopter {{Authority control Aircraft configurations