1. Introduction

The helicopter belongs to the flight machine category with the highest operational efficiency because it does not need special take-off and landing grounds with expensive utilities and logistics equipment. For the short and medium range, the flight efficiency of helicopters is comparable with those of the airplanes. It is able to hover, fly sideward, backward, forward, and perform other desirable maneuvers in civilian field like sea and mountain rescue, police surveillance, and firefighting; or in military missions such as battlefield surveillance, troop transport, assault, and antitank operations. So far with the help of helicopters, lives of over a million of people were saved. In the last years, the results obtained in the scientific research of many aeronautical disciplines has allowed for large increase in the flight dynamics, control, navigation, and lift capabilities of helicopters.

The aerodynamic limitations imposed by the main rotor were understood better and overcome gradually so, the present helicopters are able to fly at about 370 km/h. The continued advance

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

in the computer-aided design, manufacturing, and lightweight materials have permitted new approaches in the helicopter configuration concepts and design. The helicopter lift force is provided by the main rotor with the blades that spin about the shaft and all the flight maneuvers under the pilot's full control suppose a significant mechanical and aerodynamic complexity.

The word "helicopter" comes from two Greek words, "helliko" (spiral) and "pteron" (wing). The idea of vertical flight could be localized in time, in the years of about 400 BC, when was built so called "Chinese top," consisted of feathers at the end of a stick which was spun between the hands to generate lift. In 1483, Leonardo da Vinci proposed a flight device, which comprised a helical surface formed out of iron wire. According to the historical sources, in about 1754, Mikhail Lomonosov of Russia had built a coaxial rotor, modeled after the Chinese top, but powered by a spring device, which flew freely.

A short list of the most important achievements in the historical evolution of helicopters is the following:


Four years after Orville Wright first successful powered flight, which took place in December 17, 1903, a French, named Paul Cornu constructed a helicopter and flew for the first time in the world in November 13, 1907;


1939: Igor Ivanovitch Sikorsky built the helicopter VS-300 which flew in May 13, 1940. He could be considered the most important person in the helicopter design.

#### 1.1. Helicopter configurations

in the computer-aided design, manufacturing, and lightweight materials have permitted new approaches in the helicopter configuration concepts and design. The helicopter lift force is provided by the main rotor with the blades that spin about the shaft and all the flight maneuvers under the pilot's full control suppose a significant mechanical and aerodynamic

The word "helicopter" comes from two Greek words, "helliko" (spiral) and "pteron" (wing). The idea of vertical flight could be localized in time, in the years of about 400 BC, when was built so called "Chinese top," consisted of feathers at the end of a stick which was spun between the hands to generate lift. In 1483, Leonardo da Vinci proposed a flight device, which comprised a helical surface formed out of iron wire. According to the historical sources, in about 1754, Mikhail Lomonosov of Russia had built a coaxial rotor, modeled after the Chinese

A short list of the most important achievements in the historical evolution of helicopters is the

1843: Sir George Cayley (considered the inventor of the airplane) published a paper, where he

1860: Ponton d"Amecourt of France built a number of small steam-powered helicopter models; 1874: Wilheim von Achenbach of Germany built a single rotor model and he had the idea to create a sideward thrusting tail rotor in order to counteract the main rotor torque reaction; 1880: Thomas Alva Edison tested several rotor configurations powered by an electric motor; Four years after Orville Wright first successful powered flight, which took place in December 17, 1903, a French, named Paul Cornu constructed a helicopter and flew for the first time in the

1907: the French brothers Louis and Jaques Breguet built a helicopter (quad rotor, in the form of a horizontal cross) powered by a 40-hp. engine. This helicopter did not fly completely free

1912: Boris Yuriev tried to build a helicopter with a single main rotor and tail rotor configura-

1914: the Danish Jen C. Ellehammer designed a helicopter with coaxial rotors. The aircraft

1922: Georges des Bothezat (USA) designed and built a helicopter for the USA army. He was

1909: Igor Ivanovitch Sikorsky built a nonpiloted coaxial helicopter prototype;

1917: Stephan Petroczy (Austrian) build and flew a coaxial rotor helicopter;

1919: Henry Berliner (USA) built a counter-rotating coaxial helicopter;

tion. He proposed the concept of cyclic pitch for rotor control;

made several short hops but never made a properly flight;

1920: Raul Pescara (Argentina) built a coaxial helicopter;

the first specialist who described the helicopter autorotation;

top, but powered by a spring device, which flew freely.

gives some scientific details about the vertical flight of the aircraft;

complexity.

20 Flight Physics - Models, Techniques and Technologies

following:

world in November 13, 1907;

due to its lack of stability;

The helicopter is a complex aircraft that obtains both lift and thrust from blades rotating about a vertical axis. The term "rotary wing" is often used to distinguish the helicopter from airplane, which is a "fixed wing" aircraft. The helicopter can have one or more engines, and it uses gear boxes connected to the engines by rotating shafts to transfer the power from engines to the rotors (Figure 1).

The most common helicopter configuration consists of one main rotor as well as a tail rotor to the rear of the fuselage (Figure 2a). A tandem rotor helicopter has two main rotors; one at the front of the fuselage and one at the back (Figure 2b). This type of configuration does not need a tail rotor because the main rotors are counter rotating. It was proposed by the Serbian man Dragoljub Ivanovich in 1953.

A variant of the tandem is the coaxial rotor helicopter (Figure 3a) which has the same principle of operation, but the two main rotors are mounted one above the other on coaxial rotor shafts. This constructive solution was developed by Nicolai Ilich Kamov. Another helicopter type is the synchropter, which use intermeshing blades (Figure 3b). This type of helicopter was proposed by Charles Kaman.

Figure 2. The single main rotor (a) and the tandem rotor helicopter (b).

Figure 3. The coaxial rotors (a) and the intermeshing blades (b).

Figure 4. The side by side rotors.

If the two rotors are mounted either side of the fuselage, on pylons or wing tips, the configuration is referred to as side by side (Figure 4).

Another aircraft type that should be mentioned is the autogiro (invented by Huan de la Cievra), which is a hybrid between a helicopter and a fixed wing airplane. It uses a propeller for the forward propulsion and has freely spinning nonpowered main rotor that provides lift.
