Leishman J.G. Principles of Helicopter Aerodynamics. Файл формата pdf; размером 74,79 МБ. Добавлен пользователем hel_mi26t. Basic Helicopter. Aerodynamics. Second Edition. An account of first principles in the fluid mechanics and flight dynamics of the single rotor helicopter. J. Seddon. Helicopter blades have airfoil sections designed for a specific set of flight . a low pressure area above the airfoil according to Bernoulli's Principle, and the.
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Principles of helicopter portal7.info Pages. Principles of helicopter portal7.info Uploaded by. Izzet Aydemir. Download with Google Download. Principles of helicopter aerodynamics / J. Gordon Leishman. p. cm. Includes bibliographical references (p.). ISBN (hardcover). 1. Helicopters . [PDF] Download Principles of Helicopter Aerodynamics (Cambridge Aerospace Series) eBooks Textbooks. Description An internationally recognized expert explains the aerodynamic principles of helicopters and other rotating-wing vertical lift aircraft. Besides the history of helicopter.
Introduction: a history of helicopter flight; 2. Fundamentals of rotor aerodynamics; 3. Blade element analysis; 4. Rotating blade motion; 5. Helicopter performance; 6.
As the helicopter begins to move into forward flight, the blades on the side of the rotor disk that advance into the relative wind will experience a higher dynamic pressure and lift than the blades on the retreating side of the disk, and so asymmetric aerodynamic forces and moments will be produced on the rotor. Articulation helps allow the blades to naturally flap and lag so as to help balance out these asymmetric aerodynamic effects.
However, the mechanical complexity of the rotor hub required to allow for articulation and pitch control leads to high design and maintenance costs. With the inherently asymmetric flow environment and the flapping and pitching blades, the aerodynamics of the rotor become relatively complicated and lead to unsteady forces. These forces are transmitted from the rotor to the airframe and can be a source of vibrations, resulting in not only crew and passenger discomfort, but also considerably reduced airframe component lives and higher maintenance costs.
However, with a thorough knowledge of the aerodynamics and careful design, all these adverse factors can be minimized or overcome to produce a highly reliable and versatile aircraft.
Boulet takes a unique approach in that he gives a first-hand account of the early helicopter developments through interviews with the pioneers, constructors, and pilots of the machines. A remarkably detailed history of early helicopter developments is given by Liberatore , , As described by Liberatore , the early work on the development of the helicopter can be placed into two distinct categories: inventive and scientific.
The former is one where intuition is used in lieu of formal technical training, whereas the latter is one where a trained, systematic approach is used. Prior to the nineteenth century there were few scien- tific investigations of flight or the science of aerodynamics. The inherent mechanical and aerodynamic complexities in building a practical helicopter that had adequate power and control, and did not vibrate itself to pieces, resisted many ambitious efforts.
The history of flight documents literally hundreds of failed helicopter projects, which, at most, made 1. Some designs provided a contribution to new knowledge that ultimately led to the successful development of the modern helicopter.
Yet, it was not until the more scientific contributions of engineers such as Juan de la Cierva, Heinrich Focke, Raoul Hafner, Igor Sikorsky, Arthur Young, and others did the design of a truly safe and practical helicopter become a reality. Six fundamental technical problems can be identified that limited early experiments with helicopters.
These problems are expounded by Sikorsky , and various editions in his autobiography. In summary, these problems were: 1. Understanding the aerodynamics of vertical flight.
The theoretical power required to produce a fixed amount of lift was an unknown quantity to the earliest experi- menters, who were guided more by intuition than by science. The lack of a suitable engine. This was a problem that was not to be overcome until the beginning of the twentieth century, through the development of internal combustion engines.
Keeping structural weight and engine weight down so the machine could lift a pilot and a payload. Early power plants were made of cast iron and were heavy. Counteracting rotor torque reaction. A tail rotor was not used on most early designs; these machines were either coaxial or laterally side-by-side rotor configurations. Yet, building and controlling two rotors was even more difficult than for one rotor. Providing stability and properly controlling the machine, including a means of defeating the unequal lift produced on the advancing and retreating blades in forward flight.
These were problems that were only to be fully overcome with the use of blade articulation, ideas that were pioneered by Cierva, Breguet, and others, and with the development of blade cyclic pitch control. Conquering the problem of vibrations. This was a source of many mechanical failures of the rotor and airframe, because of an insufficient understanding of the dynamic and aerodynamic behavior of rotating wings. The relatively high weight of the structure, engine, and transmission was mainly re- sponsible for the painfully slow development of the helicopter until about However, by then gasoline powered piston engines with higher power-to-weight ratios were more widely available, and the antitorque and control problems of achieving successful vertical flight were at the forefront.
This resulted in the development of a vast number of proto- type helicopters. Many of the early designs were built in Great Britain, France, Germany, Italy, and the United States, who led the field in several technical areas. However, with all the various incremental improvements that had been made to the basic helicopter concept during the pre—World War II years, it was not until the late inter war period that significant technical advances were made and more practical helicopter designs began to appear.
The most important advances of all were in engine technology, both piston and gas turbines, the latter of which revolutionized both fixed-wing and rotating-wing flight. A time-line documenting the evolution of rotating-wing aircraft through is shown in Fig.
The ideas of vertical flight can be traced back to early Chinese tops, a toy first used about BC. Everett-Heath and Liberatore give a detailed history of such devices. The earliest versions of the Chinese top consisted of feathers at the end of 1 The first significant application of aerodynamic theory to helicopter rotors came about in the early s.
It was not used in aeronautical applications until about It is also recorded that Mikhail Lomonosov of Russia had developed, as early as , a small coaxial rotor modeled after the Chinese top but powered by a wound-up spring device. In , the French mathematician 1.
Amongst his many intricate drawings, Leonardo da Vinci shows what is a basic human- carrying helicopterlike machine, an obvious elaboration of an Archimedes water-screw.
He also describes in some detail how the machine should be built using wood, wire, and linen cloth. Although da Vinci worked on various concepts of Figure 1.
Sir George Cayley is famous for his work on the basic principles of flight, which dates from the s — see Pritchard By the end of the eighteenth century, Cayley had con- structed several successful vertical-flight models based on Chinese tops driven by wound-up clock springs. He designed and constructed a whirling-arm device in , which was prob- ably one of the first scientific attempts to study the aerodynamic forces produced by lifting wings.
Cayley —10 published a three-part paper that was to lay down the foundations of aerodynamics — see Anderson Also, in the s, another Englishman, Horatio Phillips, constructed a steam-driven vertical flight machine, where steam generated by a miniature boiler was ejected out of the blade tips. Other notable vertical flight models that were constructed at about this time include the coaxial design of Bright in and the twin-rotor steam-driven model of Dieuaide in Wilhelm von Achenbach of Germany built a single rotor model in , and he was probably the first to use the idea of a tail rotor to counteract the torque reaction from the main rotor.
Later, Achenbach conducted experiments with propellers, the results of which were published by NACA — see Achenbach About a Russian helicopter concept was developed by Lodygin, using a rotor for lift and a propeller for propulsion and control. Around , Enrico Forlanini of Italy also built a flying steam-driven helicopter model. This model had dual counterrotating rotors, but like many other model helicopters of the time, it had no means of control. He tested several rotor configurations driven by a guncotton engine, which was an early form of internal combustion engine.
Later, Edison used an electric motor for power, and he was one of the first to realize from his experiments the need for a large diameter rotor with low solidity to give good hovering efficiency [Liberatore ].
In , Edison patented a rather cumbersome looking full-scale helicopter concept with boxkite-like blades, but there is no record that it was ever constructed. Boulet gives a good account of the work.
The airframe was very simple, with a rotor at each end 1. Power was supplied to the rotors by a gasoline motor and belt transmission. Each rotor had two blades, and the rotors rotated in opposite directions to cancel torque reaction. A primitive means of control was achieved by placing small wings in the slipstream below the rotor.
The machine was reported to have made several tethered flights of a few seconds at low altitude. Also in France, the Breguet brothers had begun to conduct helicopter exper- iments about By , Sikorsky had built a nonpiloted coaxial prototype.
This machine did not fly because of vibration problems and the lack of a powerful enough engine. Sikorsky abandoned the helicopter idea and devoted his skills to fixed-wing conventional airplane designs at which he was very successful.
Although he never gave up his vision of the helicopter, it was not until the s after he had emigrated to the United States that he pursued his ideas again. Another early design was patented by Gaetano Crocco of Italy in Introduction: a history of helicopter flight; 2.
Fundamentals of rotor aerodynamics; 3. Blade element analysis; 4.
Rotating blade motion; 5. Helicopter performance; 6. Aerodynamics design of helicopters; 7. Aerodynamics of rotor airfoils; 8. Unsteady airfoil behavior; 9. Dynamic stall; Rotor wakes and blade tip vortices;