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[[Lift (force)|Lift]] is the force that utilises the fluid continuity and [[Newton's laws of motion|Newton's laws]] to create a force perpendicular to the fluid flow. It is opposed by [[weight]], which is the force that pulls things towards the ground. [[Thrust]] is the force that moves things through the air while [[aerodynamic drag|drag]] is the force of flight that is an [[aerodynamic force]] that reduces speed.
[[Lift (force)|Lift]] is the force that utilises the fluid continuity and [[Newton's laws of motion|Newton's laws]] to create a force perpendicular to the fluid flow. It is opposed by [[weight]], which is the force that pulls things towards the ground. [[Thrust]] is the force that moves things through the air while [[aerodynamic drag|drag]] is the force of flight that is an [[aerodynamic force]] that reduces speed.


In order to create an effective ornithopter, it had to be able to flap its wings to generate enough power to get off the ground and travel through the air. Efficient flapping of the wing is characterized by pitching angles, lagging plunging displacements by approximately 90 degrees.<ref>DeLaurier, J.D.. "The development of an efficient ornithopter wing(1993), 152-162, http://www.ornithopter.net/Publications/TheDevelopmentOfAnEfficientOrnithopterWing.pdf. (accessed November 30, 2010).</ref> Flapping wings increase drag and are not as efficient as propeller-powered aircraft. To increase efficiency of the ornithopter, more power is required on the down stroke than on the upstroke.<ref name="ornithopter.net">DeLaurier, James D. "An Ornithopter Wing Design." (1994), 10-18, http://ornithopter.net/Publications/AnOrnithopterWingDesign.pdf. (accessed November 30, 2010).</ref> If the wing on the ornithopter was not flexible and flapped at the same angle while moving up and down, it would act like a huge board moving in two dimensions, not producing lift or thrust. The flexibility and move-ability of the wing let it twist and bend to the reactions of the ornithopter while in flight.
In order to create an effective ornithopter, it had to be able to flap its wings to generate enough power to get off the ground and travel through the air. Efficient flapping of the wing is characterized by pitching angles, lagging plunging displacements by approximately 90 degrees.<ref>DeLaurier, J.D.. "The development of an efficient ornithopter wing(1993), 152-162, http://www.ornithopter.net/Publications/TheDevelopmentOfAnEfficientOrnithopterWing.pdf. (accessed November 30, 2010).</ref> Flapping wings increase drag and are not as efficient as propeller-powered aircraft. To increase efficiency of the ornithopter, more power is required on the down stroke than on the upstroke.<ref name="ornithopter.net">DeLaurier, James D. "An Ornithopter Wing Design." (1994), 10-18, http://ornithopter.net/Publications/AnOrnithopterWingDesign.pdf. (accessed November 30, 2010).</ref> An ornithopter's wing must be able to flex and/or rotate, because if kept at the same angle while moving up and down, it would produce no net lift or thrust. The flexibility and move-ability of the wing let it twist and bend to the reactions of the ornithopter while in flight.


The interest in developing a successful powered ornithopter similar to birds and bats, was one many sought after. In order to get around the problem of not having enough energy for sustained flight, the ornithopter would be required to produce enough lift and thrust to travel through the air. 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.<ref name="ornithopter.net"/>
The interest in developing a successful powered ornithopter similar to birds and bats, was one many sought after. In order to get around the problem of not having enough energy for sustained flight, the ornithopter would be required to produce enough lift and thrust to travel through the air. 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.<ref name="ornithopter.net"/>

Revision as of 13:50, 16 December 2011

Supported by lighter-than-air gases (aerostats)
Ornithopter
File:Cybird.jpg
Cybird radio-controlled ornithopter
UnpoweredPowered
  • Airship
    		•
    Supported by LTA gases + aerodynamic lift
    Unpowered Powered
  • Hybrid airship
    		•
    Supported by aerodynamic lift (aerodynes)
    Unpowered Powered
    Unpowered fixed-wing Powered fixed-wing
  • Airplane (aeroplane)
  • Powered paraglider
  • Flettner airplane
  • Ground-effect vehicle
    • Powered hybrid fixed/rotary wing
  • Tiltwing and Tiltrotor
  • Coleopter
    • Unpowered rotary-wing Powered rotary-wing
  • Rotor kite
    		•
  • Autogyro
  • Gyrodyne ("Heliplane")
  • Helicopter
    • Powered aircraft driven by flapping
  • Ornithopter
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    Other means of lift
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    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 have been successful. The machines are of two general types: those with engines, and those powered by the muscles of the pilot.

    Early history of the ornithopter

    The Sanskrit epic Ramayana (4th Century BC) describes an ornithopter, the Pushpaka Vimana. The ancient Greek legend of Daedalus (Greek demigod engineer) and Icarus (Daedalus's son) and The Chinese Book of Han[1] (19 AD) both describe the use of feathers to make wings for a person but these are not actually aircrafts. Some early manned flight attempts may have been intended to achieve flapping-wing flight though probably only a glide was actually achieved. These include the flights of the 11th century monk Eilmer of Malmesbury (recorded in the 12th century) and the 9th century poet Abbas Ibn Firnas (recorded in the 17th century).[2] Roger Bacon, writing in 1260, was also among the first to consider a technological means of flight. In 1485, 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 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.

    Leonardo da Vinci's ornithopter design.

    The first ornithopters capable of flight were constructed in France. In 1858 Pierre Jullien's model flew an estimated forty feet.[3] Gustave Trouvé's 1870 model flew a distance of 70 metres 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, Abel Hureau de Villeneuve, and Victor Tatin, also made rubber-powered ornithopters during the 1870s. Tatin's ornithopter (now in the US Air & Space Museum) 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 c. 1889.

    From 1884 on, Lawrence Hargrave built scores of ornithopters powered by rubber bands, springs, steam, or compressed air.[4] 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. In the 1930s, Alexander Lippisch and the NSFK in Germany constructed and successfully flew a series of internal combustion powered ornithopters using a similar overall design, with aerodynamic improvements resulting from methodical study.

    Erich von Holst also working in the 1930s, achieved great efficiency and realism in his work with ornithopters powered by rubber band. This includes perhaps the first success of an ornithopter with a bending wing, intended to more closely imitate the folding wing action of birds although it was not a true variable span wing like birds have.[5]

    Manned flight

    Otto Lilienthal on August 16, 1894 with his kleiner Schlagflügelapparat
    Schmid 1942 Ornithopter

    Manned ornithopters fall into two general categories: Those powered by the muscular effort of the pilot (human-powered ornithopters), and those powered by an engine.

    Around 1894, Otto Lilienthal 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.

    In 1929, a man-powered ornithopter designed by Alexander Lippisch (designer of the Me163 Komet) flew a distance of 250 to 300 metres 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 900 metres, maintaining a height of 20 metres throughout most of the flight. Later this same aircraft was fitted with a 3 hp Sachs motorcycle engine. With the 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.[6]

    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.[7]

    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,[8] the jet was necessary for sustained flight, but the flapping wings did most of the work.[9]

    On August 2, 2010, Todd Reichert of the University of Toronto Institute for Aerospace Studies piloted a human-powered ornithopter named Snowbird. The 32 metres (105 ft 0 in) wingspan 42 kilograms (93 lb) aircraft was constructed from carbon fibre, 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 145 meters with an average speed of 25.6 km/h (7.1 m/s) [10] 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.[11]

    Applications for unmanned ornithopters

    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 can be made to resemble birds or insects, they could be used for military applications, such as aerial reconnaissance 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, Inc. announced a remotely piloted ornithopter resembling a large hummingbird for possible spy missions.

    AeroVironment, Inc., then led by Paul B. MacCready (Gossamer Albatross) developed in the mid-1980s, for the Smithsonian Institution, a half-scale radio controlled replica of the giant pterosaur, Quetzalcoatlus northropi. It was built to star in the IMAX movie On the Wing. The model had a wingspan of 5.5 metres (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.[12][13][14]

    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.[15] 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.[16]

    Since 2002, Prof. Theo Van Holten has been working on an ornithopter which is constructed like a helicopter. The device is called the ornicopter [17] and was made by constructing the main rotor so that it would have no reaction torque at all.

    In 2008, Schiphol Airport started using a real 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.[18][19]

    In March 2011, scientists and engineers in Festo have created a robotic SmartBird,[20] based on a seagull's motion. The SmartBird weighs only 450 grams and is controlled by a radio handset.

    Ornithopters as a hobby

    File:FlyTech Dragonfly 1.jpg
    The Dragonfly is a toy made by Wow-Wee.

    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 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.[21] 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, 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. To see video examples of a remote control Ornithopter visit the Birds You Fly website.

    Ornithopters are also of interest as the subject of one of the events in the nationwide Science Olympiad event list. The event ("Flying Bird") entails building a self-propelled ornithopter to exacting specifications, with points awarded for high flight time and low weight. Bonus points are also awarded if the ornithopter happens to look like a real bird.

    Aerodynamics

    See also: Aerodynamics

    As demonstrated by birds, flapping wings offer potential advantages in maneuverability and energy savings compared with fixed-wing aircraft, as well as potentially vertical take-off and landing. It has been suggested that these advantages are greatest at small sizes and low flying speeds.[22]

    Unlike airplanes and helicopters, the driving airfoils 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 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.

    In propeller- or jet-driven aircraft, the propeller creates a relatively narrow stream of relatively fast moving air. The energy carried by the air is lost. The same amount of force can be produced by accelerating a larger mass of air to a smaller velocity, for example by using a larger propeller or adding a bypass fan to a jet engine. Use of flapping wings offers even larger displaced air mass, moved at lower velocity, thus improving efficiency.[citation needed]

    Wing design

    Birds inspired Leonardo da Vinci when he designed his ornithopter in 1490. Leonardo da Vinci was interested in flying during 1488–1514. He never saw his dream of flight take place because his ornithopter was too heavy and required too much energy to produce lift or thrust. In 1929, the human-powered ornithopter constructed by Alexander Lippisch was towed into the air and glided around. In 1959, in England, another ornithopter was towed into the air and demonstrated the ornithopter being a birdlike machine.[23] By the 1960s, there were powered unmanned ornithopter flights of various sizes demonstrating how ornithopters flew. In 1991 Harris and DeLaurier flew the first successful engine-powered remotely piloted ornithopter in Toronto, Canada. By 1999, there was an ornithopter design that was designed to take off from a level pavement.[23]

    Lift is the force that utilises the fluid continuity and Newton's laws to create a force perpendicular to the fluid flow. It is opposed by weight, which is the force that pulls things towards the ground. Thrust is the force that moves things through the air while drag is the force of flight that is an aerodynamic force that reduces speed.

    In order to create an effective ornithopter, it had to be able to flap its wings to generate enough power to get off the ground and travel through the air. Efficient flapping of the wing is characterized by pitching angles, lagging plunging displacements by approximately 90 degrees.[24] Flapping wings increase drag and are not as efficient as propeller-powered aircraft. To increase efficiency of the ornithopter, more power is required on the down stroke than on the upstroke.[25] An ornithopter's wing must be able to flex and/or rotate, because if kept at the same angle while moving up and down, it would produce no net lift or thrust. The flexibility and move-ability of the wing let it twist and bend to the reactions of the ornithopter while in flight.

    The interest in developing a successful powered ornithopter similar to birds and bats, was one many sought after. In order to get around the problem of not having enough energy for sustained flight, the ornithopter would be required to produce enough lift and thrust to travel through the air. 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.[25]

    The wing design is designed with the spar as far forward of the airfoil but still having acceptable dimensions of strength. Engineers and researchers have experimented with wings that require carbon fiber, plywood, fabric, ribs, and the trailing edge to be stiff, strong, and for the mass to be as low as possible.[26] Any mass located to the aft or empennage, reduce the wings performance and hinder the design of the ornithopter. In order to calculate the performance of the ornithopter, the wings lift is determined by the lift of the wing versus weight, drag and thrust. A smooth aerodynamic surface with a double-surface airfoil is more efficient then a single-surface airfoil to produce more lift.

    A variation of ornithopters has the wings and flapping surfaces towards the empennage to increase stabilizing forces and thrust. With different designs, ornithopters do not 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 in a single value of lift coefficient.[27]

    Although hummingbirds fly with fully extended wings, an ornithopter would not be able to effectively fly that way. If an ornithopter wing were to fully extend and twist and flap in small movements it would cause a stall but if it were to twist and flap in very large motions, then it would act like a windmill causing an inefficient flying situation.[28]

    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 has a propulsive efficiency of 54%.[29] The wings were tested in a low speed wind tunnel measuring the aerodynamic performance. Discovering that the higher the frequency of the wing beat, the higher the average thrust of the ornithopter.

    See also

    References

    1. ^ Joseph Needham and Ling Wang, Science and civilisation in China: Physics and physical technology. Mechanical engineering, Volume 4, Part 2, Cambridge University Press, 1965, p. 588.
    2. ^ White, Lynn. "Eilmer of Malmesbury, an Eleventh Century Aviator: A Case Study of Technological Innovation, Its Context and Tradition." Technology and Culture, Volume 2, Issue 2, 1961, pp. 97–111 (97–99 resp. 100–101).
    3. ^ W. Hudson Shaw and Olaf Ruhen. 1977. Lawrence Hargrave: Explorer, Inventor & Aviation Experimenter. Cassell Australia Ltd. p. 53.
    4. ^ W. Hudson Shaw and Olaf Ruhen. 1977. Lawrence Hargrave: Explorer, Inventor & Aviation Experimenter. Cassell Australia Ltd. pp. 53-160.
    5. ^ http://ornithopter.org/history.real.shtml Ornithopter Zone history of bird-like ornithopters
    6. ^ Bruno Lange, Typenhandbuch der deutschen Luftfahrttechnik, Koblenz, 1986.
    7. ^ FAI web site.
    8. ^ Dr. James DeLaurier's report on the Flapper's Flight July 8, 2006
    9. ^ University of Toronto ornithopter takes off July 31, 2006
    10. ^ Human-Powered Ornithoper Flight in Flapping Wings: The Ornithopter Zone Newsletter, Fall 2010.
    11. ^ Human-Powered Ornithopter Project
    12. ^ Anderson, Ian (10 October 1985), "Winged lizard takes to the air of California", New Scientist (No.1477): 31, retrieved 20 October 2010 {{citation}}: |issue= has extra text (help)
    13. ^ MacCready, Paul (November 1985), "The Great Pterodactyl Project" (PDF), Engineering & Science: 18–24, retrieved 20 October 2010
    14. ^ Schefter, Jim (March 1986), "Look! Up in the sky! It's a bird, it's a plane it's a pterodactyl", Popular Science: 78–79, 124, retrieved 20 October 2010
    15. ^ Winged robot learns to fly New Scientist, August 2002
    16. ^ Creation of a learning, flying robot by means of Evolution In Proceedings of the Genetic and Evolutionary Computation Conference, GECCO 2002 (pp. 1279-1285). New York, 9–13 July 2002. Morgan Kaufmann. Awarded "Best Paper in Evolutionary Robotics" at GECCO 2002.
    17. ^ Ornicopter project
    18. ^ Article in Dutch newspaper Trouw, partial translation:..."The so-called 'Horck', an electrical controllable bird is the newest means to scare birds. Because they can cause much damage to airplanes. (...) ...it is a design by Robert Musters, a falconer from Enschede"
    19. ^ A picture of the bird with English description
    20. ^ Article in Daily Mail
    21. ^ "FLYING HIGH: Bird Man". Scientific American Frontiers Archive. Retrieved 2007-10-26.
    22. ^ T.J. Mueller and J.D. DeLaurier, "An Overview of Micro Air Vehicle Aerodynamics", Fixed and Flapping Wing Aerodynamics for Micro Air Vehicle Applications, Paul Zarchan, Editor-in-Chief, Volume 195, AIAA, 2001
    23. ^ a b Benedict, Moble. "3-4." http://uwmav.uwaterloo.ca/Aeroelastic%20Design%20and%20Manufacture%20of%20an%20Efficient%20Ornithopter%20Wing.pdf
    24. ^ DeLaurier, J.D.. "The development of an efficient ornithopter wing(1993), 152-162, http://www.ornithopter.net/Publications/TheDevelopmentOfAnEfficientOrnithopterWing.pdf. (accessed November 30, 2010).
    25. ^ a b DeLaurier, James D. "An Ornithopter Wing Design." (1994), 10-18, http://ornithopter.net/Publications/AnOrnithopterWingDesign.pdf. (accessed November 30, 2010).
    26. ^ DeLaurier, J.D. 1993 "The development of an efficient ornithopter wing", 152-162, http://www.ornithopter.net/Publications/TheDevelopmentOfAnEfficientOrnithopterWing.pdf. (accessed November 30, 2010).
    27. ^ 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. <http://dbs.umt.edu/research_labs/flightlab/documents/Warrick_Tobalske_Powers_Dickinson_2007_AIAA.PDF>.
    28. ^ Liger, Matthieu, Nick Pornsin-Sirirak, Yu-Chong Tai, Steve Ho, and Chih-Ming Ho. "LARGE-AREA ELECTROSTATIC-VALVED SKINS FOR ADAPTIVE FLOW CONTROL ON ORNITHOPTER WINGS." (2002): 247-250. Web. 30 Nov 2010.
    29. ^ DeLaurier, James D. "An Ornithopter Wing Design40. 1 (1994), 10-18, http://ornithopter.net/Publications/AnOrnithopterWingDesign.pdf. (accessed November 30, 2010).

    Further reading

    • Chronister, Nathan. (1999). The Ornithopter Design Manual. Published by The Ornithopter Zone.
    • Mueller, Thomas J. (2001). "Fixed and flapping wing aerodynamics for micro air vehicle applications". Virginia: American Inst. of Aeronautics and Astronautics. ISBN 1-56347-517-0
    • Azuma, Akira (2006). "The Biokinetics of Flying and Swimming". Virginia: American Institute of Aeronautics and Astronautics 2nd Edition. ISBN 1-56347-781-5.
    • 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.
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