Helicopters:Multi Mission Machine

 

“HELICOPTERS: MULTI MISSION MACHINE”

(Everything about Helicopters)

                             

About Me:         I am Aditya Khamitkar,  I am a student and I am currently in 12th grade. I, with my friends Bijoy Biju Vargeese and Sharada Yashwant Davli made this report on Helicopters for a competition  known as National Aerolympics 2020, conducted by Aeronautical Society of India, Which obviously we won. I love Aeronautics and Aerospace sciences and that is the reason I have written about helicopters in this blog. Actually my father works in Indian Space Research Organisation or ISRO and we live at Sriharikota. And from childhood on wards I have witnessed many rocket launches and this  is what induced an interest of Aeronautics and Aerospace Sciences. I have written this blog for those who are interested to learn about helicopters. Guys, it took a lot of effort so please do read it completely, you will enjoy it.  

 CONTENTS

1.    INTRODUCTION.. 3

2... HISTORY OF HELICOPTERS.. 4

3.   PRINCIPLES BEHIND FLYING.. 7

4... HELICOPTER TECHNOLOGIES.. 9

5.   ADVANTAGES OF HELICOPTERS.. 23

6.   USES OF HELICOPTERS

7.   ADVANCEMENTS

8.   FUTURE FOR HELICOPTERS

9... CONCLUSION.. 37

10. BIBLIOGRAPHY.. 38

1.    INTRODUCTION

               Movement is life. For movement, one requires energy and stamina. Nevertheless, if the distance to be covered were large, then one would require some mode transportation like a two-wheeler, car, bus etc. Transportation happens to be one of the vital contributors to the development of any country. Sophisticated and efficient transportation system reflects the development of the country. Transportation on the surface (roads) is easier to manage and maintain. On the other hand, transportation on waters and in the air becomes difficult to manage and maintain because of unforeseen changes in weather, turbulence etc. However, with the invention of the aero plane (by Orville Wright and Wilbur Wright in the year 1903) and the helicopter (by Igor Sikorsky in the year 1939), the aviation industry has reached a new height. The first Helicopter design by Igor Sikorsky took flight in September 1939 with a single main rotor and tail rotor. The name the model was VS-300 and was built by Vought-Sikorsky Aircraft Division of United Aircraft Corporation. Flight of the first helicopter designed by Igor Sikorsky lasted only for a few seconds. Nevertheless, the improved version with three blade rotor designed in May 1940 became the first ever helicopter to fly.

                    A helicopter has unique features, like (I) being able to hover in the air (ii) being able to take-off vertically (iii) reaching remote and inaccessible areas (iv) the ability to move backwards (v) having enormous agility (vi) the ability to survey the parts of land for military and civilian purposes. For flying, it uses the lift generated by the rotors. These distinct features, has led to a significant increase in the commercial use of helicopters. Its ability to take off and land vertically makes it quite unique and useful. A helicopter does many things that an aero plane cannot do. Advancement in different parts of the helicopter like rotors, engines, structure of the body etc. has enabled helicopters to be used in different fields like transportation, defense forces (Military, Navy and Air Force), agriculture, disaster management, emergency medical transport, reconnaissance, tourism, town & city planning, etc. 

            The growth of the Hindustan Aeronautics Limited is synonymous with the growth and development of the aeronautical industry in India. The major works undertaken by HAL are design, development, manufacture and repair of aircraft, helicopter, engines and the development of related systems like avionics, instruments and other equipment. HAL right from its inception has been actively involved in designing and manufacturing many aircrafts meant for the defense forces. The company which had its origin as the Hindustan Aircraft Limited was incorporated on 23 December 1940 at Bangalore by Sri Wal Chand Harahan, a farsighted visionary in association with the Government of Mysore. Helicopters, thus, not only serve the people of the world but also boost the economy of a country by plunging into commercial activities. Variety, Safety, and Speed are the main characteristics of Helicopters. Nevertheless, research has to take place in making it "fuel-efficient" and its manufacturing process "cost-effective". Under the able guidance and leadership of HAL, one can say assuredly that the country will soon get helicopters with the latest instruments, advancements and sophisticated functioning to cater to the needs of diverse fields.

2.    HISTORY OF HELICOPTERS

2.1 EARLY HISTORY

It is interesting to know that the idea of vertical flight has been around since 400BC. The earliest reference for vertical flight comes from China. Although these are in the form of bamboo flying toys played with by children, they give evidence of prevalence of the idea of vertical flight even during the ancient era.

There have also been references of such helicopter toys in certain Renaissance paintings as well. In the medieval age, Leonardo da Vinci carried forward the idea of vertical flight. He was the first to create a design for a machine that could be described as an ‘aerial screw’. However, he found no means to stop the rotor from making the craft rotate.

The modern era saw many attempts at making vertical flight possible. Although most of these attempts were flawed, all these finally culminated in the helicopter we know today.

The French inventor Gustave de Ponton d’Amecourt coined the word “helicopter” in 1861 (Petrescu et al., 2017). He made a steam-powered model. During this period, technology based on steam power is more popular and most inventors tried to achieve vertical flight through steam power (Petrescu et al., 2017).

In 1878, the unmanned vehicle designed by Enrico Forlanini, powered by steam had risen to a height of 12 meters, hovering for some 20 seconds (Petrescu et al., 2017). Thomas Alva Edison also tried to create a machine capable of flight. In 1885, Edison conducted research using a budget of US$1000 funded by James Gordon Bennett. Jr to develop a flight (Petrescu et al., 2017). Edison built a helicopter that used the power of an internal combustion engine but it was damaged due to an explosion.

2.2 EARLY FLIGHT ATTEMPTS

Two French brothers, Jacques and Louis Breguet, began experimenting with airfoil for helicopters in the year 1906. These experiments resulted in the Gyroplane No.1, which possibly is the first-ever quadcopter. In 1907, Gyroplane No.1 lifted its first pilot into the air about 0.6 meters for a minute.

The same year saw another French inventor Paul Cornu’s helicopter fly. It lifted the pilot to a height of 0.3 meters for 20 seconds. It differed from Gyroplane No.1 by lifting the pilot without any external aid as in the case of Gyroplane No.1.  It was reported to be the first truly free flight with a pilot.

2.3 EARLY DEVELOPMENTS

Engelbert Zaschka, a German inventor, designed a helicopter in 1927, which was equipped with two rotors and a gyroscope to increase stability. The design was not only able to rise and descend vertically but it was also able to remain stationary at a height. In 1928 a helicopter designed by Hungarian Aviation engineer Uszicar Ashoth which took off and landed at least 182 times with minimum flight duration of 53 minutes.

2.4 BIRTH OF HELICOPTER INDUSTRY

World war 2 saw a boom in production and development of newer and better helicopters. In United States, there was competition between Igor Sikorsky, a Russian-born engineer and Wynn Lawrence LePage to produce the US military’s first helicopter. Lepage built the XR-1. On the other hand, Sikorsky developed a single rotor design with a tail rotor. This model was called the VS-300. The major milestones achieved in the history of helicopter evolution starting from Chinese flying top to first successful helicopter is shown below in Figure 1.

Sikorsky's R-4 which was developed from the VS-300 was the first large scale mass produced helicopter with a production order for 100 aircraft. The R-4 was the only Allied helicopter to survive in World War 2, which was primarily used for search, and rescue operations. The R-4 was then replaced by R-5 and R-6, which were better variants.

Bell aircraft, a US-based company produced a new helicopter called Model 30 using   Young's two-blade teetering rotor design developed by Arthur Young. Later model 30 was converted into the Bell 47 which become the first helicopter certified for civilian use in the United States.

Figure 1: History of Helicopters

2.5 USE OF TURBINE POWER

In 1915, Charles Kaman modified his K-225 synchropter, (which was a model based on a twin-rotor helicopter developed by Anton Flettner) by using a turboshaft engine rather than a piston engine. This allowed the design to have more power as compared to the piston-powered model while at the same time being lighter than piston-engines. In 1951, the K-225 became the world's first turbine-powered helicopter. In 1954, the HTK-1 became the first twin-turbine helicopter to fly.

It took decades of research and development to build reliable helicopters capable of stable flight after the introduction of fixed-wing aircraft. This is primarily due to the higher engine power density requirements of a helicopter in comparison to a fixed-wing aircraft. Improvements in fuel and engine were also a critical factor in the development of helicopters in the early half of the 20th century. The emergence of the turboshaft engine in the second half of the century gave a boost to these developments resulted in larger, faster and high-performance helicopters today.

2.6.    DEVELOPMENT IN INDIA

In India, Hindustan Aeronautics Limited (HAL) primarily does Helicopter manufacturing. HAL’s Bangalore division had started assembling Alouette helicopters in 1962. Over the years, HAL has made improvements to these helicopters to meet Indian environmental conditions.  Indian armed forces depend heavily on Chetak and Cheetah helicopters for the light helicopter duties for more than four decades. The HAL’s helicopter division has produced 336 Chetaks and 246 Cheetah helicopters so far and has overhauled more than 200 helicopters of both types.

HAL’s experience in manufacturing more than 700 helicopters has provided a solid foundation for its capability to design, develop and manufacture its light helicopters. In effect, it enabled them to develop new helicopters such as the Weapon System Integrated (WSI) version of Dhruv (Christened as “Rudra”), Light Combat Helicopter (LCH) and Light Utility Helicopter (LUH) (HAL, 2019).  HAL’s plans include products such as IMRH (Indian multi-role helicopter), UAV (Unmanned aerial vehicle) and NRUAV (Naval rotary unmanned aerial vehicle)

	Figure 3: Rotary-wing unmanned aerial vehicle   (Defence update, 2019)

3. PRINCIPLES BEHIND FLYING

Helicopter working depends on various principles, which include Torque, Angular Momentum, and Bernoulli’s principle that will be described in the following section.

3.1     CCONCEPTS RELATED TO MECHANICS

3.1.1   TORQUE

It is defined as the cross product of the position vector of the object about and the axis of rotation and the force acting on it.

3.1.2   ANGULAR MOMENTUM

It is defined as the cross product of the position vector of the particle about the axis of rotation and its linear momentum.

3.2     BERNOULLI’S PRINCIPLE

Aircraft works under the Bernoulli’s Principle, which states that an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or decrease in the fluid’s potential energy. Further, the Bernoulli’s Principle also describes the relationship between speed and pressure of air.

3.3     AIRFOIL TECHNOLOGY

The helicopter uses the same principle as any other conventional aircraft for its flight. Aerodynamic forces are produced when air passes about the rotor blades to keep it aloft. The rotor blade, or airfoil, is the structure that enables the flight operations. The shape of an airfoil produces the lift required for the helicopter during movement through the air. Depending on the usage of the helicopter airfoil section are designed to enable certain flight characteristics.

3.3.1   AIRFOIL PRINCIPLE

As the aircraft is heavier than the air occupied in the same volume, there has to be an upward force pushing the aircraft, which is at least equal to the weight of the aircraft. In order to fly, aircraft must have a "lift," a force moving it upward that is created by rotor blades works under the Bernoulli Principle.

Figure 4 : Bernoulli's Principle Applied to Lift (Fitzpatrick,2010)

3.3.2 TYPE OF AIRFOIL

There are two types of Airfoil sections, which are the symmetrical and non-symmetrical airfoils.

Symmetrical airfoils have identical upper and lower surfaces. In symmetrical airfoils, the center of pressure does not travel. The travel remains constant even under a varying angle of attacks thus, providing the best lift to drag ratios. However, the lift produced by a symmetrical airfoil is less as compared to a non-symmetrical airfoil, which results in the undesirable stall characteristics for the design. These airfoils also have to adapt to different airspeeds and angle of attack during each revolution of the rotor. However, it can maintain an acceptable performance level even under varying conditions. Other benefits include lower cost and less complexity in construction.  

Nonsymmetrical (cambered) airfoils have a wide variety of upper and lower surface designs. The non-symmetrical airfoil has increased lift to drag ratios and have better desirable stall characteristics. The large movement of the center of pressure with change in the angle of attack prevented the application of non-symmetric airfoils in the earlier helicopters. Rotor system components that could withstand the twisting force generated due to the movement of the center of pressure had to be developed. Developments in design features and the arrival of new manufacturing materials have helped overcome these drawbacks.

Figure 5: Symmetrical airfoil	Figure 6: Nonsymmetrical (cambered) airfoil

4.    HELICOPTER TECHNOLOGIES

The helicopter uses aerodynamics principles for its operation. The helicopter technologies include the various system and controls to enable its operation under the designed parameters by applying different aerodynamics principles. A high-level picture of various technical components and key working principles are displayed the figure 7 to provide an overview of the overall architecture of the helicopter and it working.

Figure 7:  Helicopter Technologies: System & Control, Working

4.1 SYSTEMS AND CONTROL

The major components of helicopter include a cabin where the payload (passengers, baggage, and cargo) and crew are carried; an airframe, which houses the various components, or where components are attached. In addition to these, a power-plant or engine, a transmission system, rotor system, fuel system, hydraulic and electrical systems are critical for its operation. Some of the key system will be described in the following section.

4.1.1 ENGINE

The most commonly used engines in helicopters are the reciprocating engine or piston engines and the turbine engine. Smaller helicopters including training helicopters use reciprocating engines because they are relatively simple and inexpensive to operate. Turbine engines are used in a wide variety of helicopters since they produce a large amount of power for their size but are costlier to operate.

4.1.1.1 TURBOSHAFT ENGINES

A turboshaft engine is designed to produce shaft power to drive machinery instead of producing thrust. Turboshaft engines are most commonly used in applications that require a small, but powerful, lightweight engine, inclusive of helicopters and auxiliary power units.

The gas turbine engine used in helicopters is made up of a compressor, combustion chamber, turbine, and gearbox assembly. The compressor compresses the air, which is then fed into the combustion chamber where atomized fuel is injected into it. The fuel/air mixture is ignited and allowed to expand. The hot exhaust leaves the combustion chamber via a series of turbine stages and makes them turn. The output shaft attached to the turbine wheels turns and provides power to both the engine compressor and the main rotor system. The combustion gas is finally expelled through an exhaust outlet as shown in the figure below.

Figure 8:Working Turbo shaft engine	Figure 9: Turbo shaft engine
Figure 10: Turbo shaft engine (USDOT, 2019)

4.1.1.2   PISTON ENGINES

   

The reciprocating engine consists of a series of pistons connected to a rotating crankshaft. As the pistons move up and down, it creates a rotational motion.   The four-stroke engine is most commonly used which undergoes four different cycles to produce power.

Figure 11: Four stroke reciprocating engine (USDOT, 2019)

When the piston moves away from the cylinder head during the intake stroke, the intake valve opens and a mixture of fuel and air is drawn into the combustion chamber. As the cylinder moves back towards the cylinder head, the intake valve closes, and the fuel/air mixture is compressed. Once the compression is complete, the spark plugs are fixed and the compressed mixture is ignited which then begins the power stroke. The rapid expansion of the gases after combustion pushes the piston away from the cylinder head, thus producing enough power to rotate the crankshaft. The piston then moves back towards the cylinder head on the exhaust stroke where the burned gasses are expelled through the opened exhaust valve. By setting the timing of the power stroke in each cylinder continuous rotation of a crankshaft is maintained.

4.1.2 TRANSMISSION SYSTEMS

The transmission system transfers power from the engine to the main rotor, tail rotor, and other components. The main components of the transmission system are the main rotor transmission, tail rotor drive system, clutch, and freewheeling unit

4.1.2.1 MAIN ROTOR TRANSMISSION

The key objective of the main rotor transmission is to reduce engine output RPM to optimum rotor RPM. Another use of the main rotor system is to alter axis of rotation from horizontal to vertical axis of the rotor shaft where the engine is mounted horizontally.

4.1.2.2 TAIL ROTOR DRIVE SYSTEM

The tail rotor drive system consists of a tail rotor drive shaft powered from the main transmission and a tail rotor transmission mounted at the end of the tail boom. The drive shaft may consist of one long shaft or a series of shorter shafts connected at both ends with flexible couplings. This allows the driveshaft to flex with the tail boom. The tail rotor transmission provides a right angle drive for the tail rotor and may also include gearing to adjust the output to optimum tail rotor RPM.

4.1.2.3 CLUTCH

A clutch allows the engine to be started and then gradually pick up the load of the rotor. Since the weight of the rotor is relatively greater than the power of the engine, rotor and engine must be disconnected at the starting of the engine. On free turbine engines, no clutch is required, as the gas producer turbine is essentially disconnected from the power turbine. On reciprocating engine helicopters, the two main types of clutches are the centrifugal clutch and the belt drive clutch.

4.1.2.4 FREEWHEELING UNIT

Since lift in a helicopter is provided by rotating airfoils, these airfoils must be free to rotate if the engine fails. The freewheeling unit automatically disengages the engine from the main rotor when engine RPM is less than the main rotor RPM. This allows the main rotor to continue turning at normal in-flight speeds. The most common freewheeling unit assembly consists of a one-way “sprag” clutch located between the engine and main rotor transmission.

4.1.3 ROTOR SYSTEMS

Main rotor systems are classified according to the movement of the main rotor blades relative to the main rotor hub. There are three basic classifications: fully articulated, semi-rigid, or rigid. Some modern rotor systems use a combination of these types.

4.1.3.1 FULLY ARTICULATED ROTOR SYSTEM

In a fully articulated rotor system, each rotor blade is linked to the rotor hub through a series of hinges, which allow the blade to move independently of the others. These rotor systems usually have three or more blades.

Figure 12: Fully Articulated Rotor System

The horizontal hinge or the flapping hinge supports the up and down or flapping movement of the blade. The flapping movement is designed to adjust any dissymmetry of lift. The vertical hinge or drag hinge enables the back and forth movement or dragging, or hunting of the blade. Dampers are used around the drag hinge to prevent excess back and forth movement. This ultimately helps to adjust acceleration and deceleration induced by the Coriolis Effect otherwise known as the law of conservation of angular momentum. This is achieved by the feathering of the blade which means changing the pitch angle of the blade and thereby the thrust and direction of the main rotor disc can be controlled.

4.1.3.2 SEMI-RIGID ROTOR SYSTEM

A semi-rigid rotor system is usually composed of two blades which are rigidly mounted to the main rotor hub. The main rotor hub is free to tilt with respect to the main rotor shaft on what is known as a teetering hinge. This allows the blades to flap together as a unit. As one blade flaps up, the other flaps down. Since there is no vertical drag hinge, lead-lag forces are absorbed through blade bending.

Figure 13: semi-rigid rotor system (USDOT, 2019)

4.1.3.3 RIGID ROTOR SYSTEM

In a rigid rotor system, the blades, hub, and mast are rigid with respect to each other. There are no vertical or horizontal hinges so the blades cannot flap or drag, but they can be feathered. Flapping and lead/lag forces are absorbed by blade bending.

4.1.3.4 HYBRID ROTOR SYSTEM

Modern rotor systems may use the combined principles of the rotor systems mentioned above. Some rotor hubs incorporate a flexible hub, which allows for blade bending (flexing) without the need for bearings or hinges. These systems, called “flextures”, are usually constructed from composite material. Elastomeric bearings may also be used in place of conventional roller bearings. Elastomeric bearings constructed from a rubber-type material and have a limited movement that is perfectly suited for helicopter applications.

Figure 14 : Hybrid rotor system (USDOT, 2019)

4.1.4  ANTI-TORQUE SYSTEM

Any time a force is applied to make an object rotate; there will be an equal force acting in the opposite direction. In the case of a helicopter, the motion of the main rotor system in the clockwise direction would lead to the rotation of the helicopter’s fuselage in the counterclockwise direction. In the case of a helicopter, also a torque is produced by the main rotor system. Thus in order to counter this torque, the helicopter uses an anti-torque system.

4.1.4.1 TAIL ROTOR

One method used by a helicopter to counteract torque is to place a spinning set of blades at the end of the tail boom. These blades are called a tail rotor or an anti-torque rotor. Their main purpose is to create a force that acts in the opposite direction of the force exerted by the main rotor system. The tail rotor force, multiplied by the distance from the tail rotor to the main rotor, creates a torque that counteracts the main rotor torque.

Figure 15 : Tail Rotor (FM, 2017)	Figure 16 : Fan-in-tail (FM, 2017)

4.1.4.2 FENESTRON

An alternative method to the tail rotor is known as a fenestron as in figure 14. Since the rotating blades in this design are enclosed in a shroud, they prevent a hazard to personnel on the ground and they create less drag during flight.

4.1.4.3 ANTI TORQUE SYSTEMS (USING ROTORS)

As mentioned in the above section, the anti-torque in helicopters is generally provided by a tail rotor or a fenestron. However, the use of two rotors rotating in the opposite direction would also solve the problem of providing the anti-torque, as the torque exerted by both the rotors would be equal and opposite and thus providing a zero net torque. There are mainly four configurations with two rotors such as Coaxial rotors, Tandem rotors, Intermeshing rotors, Transverse rotors which will be elaborated in the following section.

4.1.4.3.1 COAXIAL ROTORS

Coaxial rotors include a pair of rotors that are mounted one above the other on the same shaft. These rotors have the same axis of rotation but they turn in opposite directions. The major strengths and weakness of coaxial rotors are described below.

Strengths

·        Providing the anti-torque: Since both the rotors in this configuration rotate in the opposite directions and produce a pair of torques, which is equal, and opposite, thus cancelling each other and provide a solution for the torque produced by the main rotor on the fuselage. ·        Preventing dissymmetry of lift: Coaxial rotors prevent dissymmetry of lift by using two rotors rotating in the opposite directions, causes the blades to advance on either side at the same time. ·        Complete power utilization by the rotors: A single-rotor helicopter uses some of its engine power for the tail rotor where as in a coaxial rotor, the entire power is used for generating lift and thereby increases the capacity to carry more load.  ·        Reduction in noise: Due to the absence of Tail rotor noise is reduced compared to a single rotor helicopter.

Weakness

·        High Complexity: Coaxial configurations increase the complexity of the rotor hub. ·        Higher chances of a mechanical failure due to complex structure.

Figure 17 : Coaxial rotor Helicopter, (Wikipedia,2019a)

4.1.4.3.2 TANDEM ROTORS

Tandem rotor helicopters are equipped with two horizontal counter-rotating rotors which are mounted one in front of the other. This configuration is used mainly for cargo helicopters. The only difference between Coaxial rotors and Tandem rotors is that in the case of Coaxial rotors, the counter-rotating rotors are mounted on the shaft whereas in the case of Tandem rotors they are mounted one in front of the other.

Tandem rotors provide the anti-torque by the use of two counter-rotating rotors which cancel out each other’s torque. This allows all the power from the engines to be used for generating lift.

Figure 18: Tandem rotor movement	Figure 19: Tandem rotor Helicopter (Boeing CH-47 Chinook) (Wikipedia, 2019a)

Tandem helicopters attain yaw motion by applying opposite left and right cyclic to each rotor. This effectively pulls both ends of the helicopter in the opposite directions. To achieve pitch, opposite collective applied to both the rotors which increases lift on one end of the helicopter while decreasing the lift on the other end thus tilting the helicopter forward or back. The major strengths and weakness of tandem rotors are as follows.

Strengths	·        Provide a larger centre of gravity range. ·        Better longitudinal stability. ·        Higher weight lifting capacity even with shorter blades (smaller disc area).
Weakness	·        Very complex transmission system. ·        Higher chances of system failure due to complex transmission system.

Some of the tandem helicopters presently in usage are:

Yakovlev Yak-24 (1952), Bell HSL (1953), CH-46 Sea Knight (1960), Boeing CH-47 Chinook (1961), Filper Helicopter (1965), Boeing Model 234 (1981), Boeing Model 360 (1987)

4.1.4.3.3 INTERMESHING ROTORS

Intermeshing rotors include a set of two counter-rotating rotors with each rotor mast mounted on the helicopter such that they make a slight angle with each other, in a transversely symmetrical manner, so that the blades intermesh without colliding. Moreover, since both the rotors do not create lift vertically, the efficiency per each rotor decreases. These type helicopters are also called a synchropter.  

In intermeshing helicopters, the yaw is attained by changing the collective pitch of one of the rotors. The intermeshing helicopter is small and hence there are unmanned versions of it that are currently being used.

Few models of the intermeshing helicopters used widely are:

Flettner Fl 265 (1939), Flettner Fl 282 (1941), Kellett XR-8 (1944), Kaman K-225 (1947), Kellett XR-10 (1947), Praga E-1 (1947)

                 

Figure 20: Intermeshing rotor Helicopter (Kaman K-Max), (Wikipedia, 2019a)

4.1.4.3.4 TRANSVERSE ROTORS

A Transverse rotor helicopter has two horizontal counter-rotating rotors that are mounted side by side. Since the rotors are counter-rotating, they cancel each other's torque. This configuration can be able to hold more weight while having shorter blades as there are two rotors. In addition, all the power from the engines is used for lift, unlike the single rotor helicopter where some of the power is wasted to counter the torque.

Some of the transverse rotor helicopters used currently are:

Focke-Wulf  Fw 61 (1936), Focke-Achgelis Fa 223 (1941),Platt-LePage XR-1 (1941), Landgraf H-2 (1944), Bratukhin G-3 (1946), Bratukhin B-11 (1948), Kamov Ka-22 (1959), Mil Mi-12 (1967)

                                

 

Figure 21: Transverse rotor movement (Wikipedia,2019a)

 4.1.5 CONTROLS

A helicopter has four controls: collective pitch control, throttle control, anti-torque control, and cyclic pitch control.

4.1.5.1 COLLECTIVE PITCH CONTROL

The collective pitch control, changes the pitch angle of all main rotor blades simultaneously, or collectively. As the collective pitch control is raised, there is a simultaneous and equal increase in pitch angle of all main rotor blades; as it is lowered, there is a simultaneous and equal decrease in pitch angle. This is done through a series of mechanical linkages. The collective pitch is changed to increase or decrease the altitude of the helicopter.

4.1.5.2 THROTTLE CONTROL

The function of the throttle is to regulate engine RPM. In case the correlator or governor system does not maintain the desired RPM when the collective is raised or lowered, or if those systems are not installed, the throttle has to be moved manually with the twist grip in order to maintain RPM. Twisting the throttle outboard increases RPM, twisting it inboard decreases RPM.

4.1.5.3 CYCLIC PITCH CONTROL

The cyclic pitch is used to tilt the rotor disk in the desired direction. The cyclic pitch control tilts the main rotor disc by changing the pitch angle of the rotor blades in their cycle of rotation. When the main rotor disc is tilted, the horizontal component of the lift moves the helicopter in the direction of tilt. The rotor disc tilts in the direction that pressure is applied to the cyclic pitch control. When the cyclic is moved forward, the rotor disc tilts forward. Similarly the cyclic is moved aft (towards the tail) when the disc tilts aft.

4.1.5.4 ANTI-TORQUE PEDALS

The anti-torque pedals, control the pitch, and therefore the thrust, of the tail rotor blades. The pedals are connected to the pitch change mechanism on the tail rotor gearbox and allow the pitch angle on the tail rotor blades to be increased or decreased thus increasing or decreasing the torque produced by the tail rotor. Besides the counteracting torque of the main rotor, the tail rotor is also used to control the yaw movement of the helicopter.

4.2     HOW A HELICOPTER WORKS?

The force created by air moving over an object (or moving an object through the air) is called aerodynamic force. Accordingly, by moving the air over an airfoil we can change the static pressures on the top and bottom thereby generating an aerodynamic force. The portion of the aerodynamic measured perpendicular to the air flowing around the airfoil is called "lift" and is used to oppose weight. Drag is the portion of aerodynamic force that is measured as the resistance created by an object passing through the air (or having the air passed over it). Drag retards forward movement.

Figure 22: Four forces acting on a helicopter in forward flight (USDOT, 2019a).

Once a helicopter leaves the ground, it is acted upon by four aerodynamic forces; thrust, drag, lift, and weight as shown in the figure.

4.2.1. LIFT

The dynamic effect of the air acting on the airfoil produces lifts which acts in the opposite direction of the weight and also perpendicular to the flightpath through the center of lift. Lift is generated when an object alter the direction of the flow of a fluid or when the fluid is forced to move by the object passing through it. When there is a relative movement between the object and fluid and the object change the flow direction perpendicular to that flow, the force required to do this work creates an equal and opposite force that is called lift. The lift generated by an airfoil depends on these factors such as speed of the airflow, density of the air, total area of the segment or airfoil, and angle of attack (AOA) between the air and the airfoil.

The sudden change in the direction of the flow over the object creates an area of low pressure  behind the leading edge on the upper surface of the object (Figure 21).This in turn  accelerate the flow along the over surface of the object due to this pressure gradient and the viscosity of the fluid.  Meanwhile a high-pressure area is created under the object due to the slowing down of the flow along the lower surface of the object. This result in producing lift by the two sections of the fluid each leave the trailing edge of the object with a downward component of momentum.

Figure 23: Lift created  by wing	Figure 24 Lift created  by airfoil

4.2.2 WEIGHT

Weight is the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Weight pulls the aircraft downward because of the force of gravity. It opposes lift and acts vertically downward through the aircraft’s center of gravity.

4.2.3 THRUST

Thrust is the force produced by the power plant/ propeller or rotor. It opposes or overcomes the force of drag. Generally, it acts parallel to the longitudinal axis.

4.2.4 DRAG

Drag is a rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects. Drag opposes thrust and acts rearward parallel to the relative wind.

4.2.3 GYROSCOPIC PRECESSION

Gyroscopic precession is a phenomenon happening in rotating bodies in which an applied force is displayed 90 degrees later in the direction of rotation from where the force was applied. The following diagram shows how precession affects the rotor disk when force is applied at a given point.

Figure 25: Effect of Gyroscopic precession (Cantrell, 2004).

 A downward force applied to the disk at point A results in a downward change in disk attitude at point B. And upward force applied at Point C results in an upward change in disk attitude at point D.               

This behavior explains some of the fundamental effects occurring during various helicopter maneuvers. For example, the helicopter behaves differently when rolling into a right turn than when rolling into a left turn. During roll into a left turn, the pilot will have to correct for a nose-down tendency in order to maintain altitude. This correction is required because precession causes a nose-down tendency and because the tilted disk produces less vertical lift to counteract gravity. Conversely, during a roll into a right turn, precession will cause a nose up tendency while the tilted disk will produce less vertical lift. Pilot input required to maintain altitude is significantly different during a right turn than during a left turn because gyroscopic precession acts in opposite directions for each.

5. ADVANTAGES OF HELICOPTERS

5.1 ADVANTAGES

5.1.1 ABILITY TO HOVER

The ability to hover makes the helicopter a game-changer in case of rescue and emergency operations, Fixed-wing aircraft have to continuously move in the atmosphere in order to achieve lift to continue flying. However, in the case of helicopters, it is the rotor alone which moves in the atmosphere to generate lift which can be utilized for achieving vertical flight, this also allows the craft to hover over a region. Thus in case of emergencies such as wildfires, rescue operations,etc..The helicopter can hover over the spot and conduct the operation with great precision as compared to the conventional fixed-wing aircraft. For example, in the case of wildfire, the helicopter can hover exactly over the region where there are intensive flames and release the fire suppressant right over the flames. In the case of fixed aircraft, they move with great speed, as a result, the released fire suppressant have more chances of missing the target.

5.1.2 LESS LAND REQUIREMENTS

Helicopters can perform takeoff and landing vertically and thus require very less space to takeoff. This allows the helicopter to reach and land on narrow strips of plain land in remote and mountainous regions, where fixed-wing aircraft cannot land.

5.1.3 FASTER MOBILIZATION

Helicopters can be mobilized fast as compared to fixed-wing aircraft which require a lot of time and checks of the equipment to get ready for an emergency. Faster mobilization implies better services in case of emergency. Helicopters can be made ready in a shorter time and thus can rush within few minutes to the emergency site.

5.1.4 HIGHER EFFICIENCY AT LOWER ALTITUDES

Fixed-wing aircraft move at very high speeds and thus experience a lot of drag at lower altitudes. Thus, they burn a lot of fuel at lower altitudes and hence are forced to fly at higher altitudes where they experience less drag because of the thinner atmosphere. However, because of lower speed helicopters experiences less atmospheric drag and hence are more efficient at lower altitudes.

5.2 DISADVANTAGES

The Helicopter has some disadvantage over fixed-wing aircraft. The main disadvantages are

·        Slower than fixed-wing aircrafts

·        Less capacity in terms of power

·        Less fuel efficiency

·        Mechanical complexity  for flying

6. USES OF HELICOPTERS

The advantages brought by the helicopter over other aircraft enable its usage in various fields. The major utilization of helicopters in day-to-day-life includes Agriculture, Cargo, Firefighting, Military, Rescue and Relief Operations, Medical emergencies, Construction, Law enforcement, Tourism, Aerial Observation.

Figure 26: Usage of Helicopter in various fields

6.1 AGRICULTURE

Helicopters are also being used in the field of agriculture. Usually they are used for agricultural works in plantations or fields span across a vast geographic area.  Some of the small helicopters can be also controlled using remote systems. Helicopters are used to spray pesticides, weedicides, herbicides, fertilizers, etc. on the crops from a low height, which are called “air tractors” as well.

Figure 27: A Helicopter spraying pesticides

6.2 CARGO

Helicopters as a result of having powerful engines can create a strong lift force thus enabling them to carry heavy cargo apart from countering its weight. Helicopters that are used for cargo are known as aerial cranes. These aerial cranes are used to place heavy equipment such as radio transmission towers; large air conditioning units, etc. on top of tall buildings or a hill or mountain. Aerial cranes are also used for construction purposes as well.

Some of the commonly used helicopter models for cargo transport are Mil Mi 26, Sikorsky S-64 Sky Crane, Boeing CH-47 Chinook, and CH-55 Tarhe The model named CH-55 Tarhe has no fuselage (the main body of a helicopter) which enables it to carry more cargo. This model was developed especially for the transport of cargo.

	Figure 29: Mil Mi26 Carrying a space capsule

Disc area is the area swept by the blades of a rotor. The lift produced is directly proportional to the disc area and since cargo helicopters are required to produce a larger lift force, these helicopters have a larger disc area.

6.3 FIREFIGHTING

Helicopters are also used in combating fires and especially forest fires. These helicopters are fitted with Heli buckets which are also known as Bambi buckets. These are usually filled by submerging the buckets in lakes or rivers. These helicopters are also used for the movement of firefighters to inaccessible regions. Sometimes these helicopters are fitted with foam cannons to fight fires easily.

Popular firefighting helicopters include variants of models the Bell 204, Bell 205, Bell 212, Boeing Vertol 107, BoeingVertol 107, Boeing Vertol 234 and Sikorski S-64 Aircrane helitanker, which features a snorkel for filling from a natural or man-made water source while in hover. Currently the world's largest helicopter, Mil Mi 26 uses a Bambi bucket.

Figure 30: The Erickson Sky crane is extinguishing the fire (Wikiwand,2019)

6.4 MILITARY

Helicopters are also used widely in militaries around the world. Military helicopters are of two types, attack helicopters, and transport helicopters. Attack helicopters are equipped with missile launchers and miniguns and are used to conduct aerial attacks on the ground targets. Transport helicopters are used for the quick transportation of troops, ammunition and other resources in and out of the war zone. Helicopters are also used for reconnaissance and surveillance duties as well.  

6.4.1 USE OF HELICOPTERS IN INDIAN MILITARY

The Indian armed forces use both foreign helicopters and many indigenously developed helicopters from HAL. The following are the helicopters used by the Indian armed forces:

·        Boeing:  Apache AH-64E, Chinook.

·        Mil: MI-17 V5, MI-25/MI-35, MI-26.

·        HAL: Chetak., Cheetah, ALH (advanced light helicopter) DHRUV, Rudra.

6.5. OTHER USES

We have seen the major uses of the helicopter. It has many other uses, which include aerial observation, construction, law enforcement, media, medical emergencies, and rescue and relief operations as described below.

6.5.1 RESCUE AND RELIEF OPERATIONS

Helicopters, as mentioned in the section, can hover over a region. In case people are stuck up in a remote area where other forms of transport cannot reach, the helicopter can be used to rescue them, as the helicopter can hover over them and then airlift them.

6.5.2 MEDICAL EMERGENCIES

The helicopter can also be used for medical emergencies. In case there is an emergency, a helicopter can airlift the patient and take them to the nearest hospital. They can also be used to transfer a patient from one hospital to another.

6.5.3 CONSTRUCTION

Helicopters are capable of lifting very heavy materials to a higher altitude, which enables them to be used in construction projects as well. They can also be used to hold heavy construction material in place for fixation. They can be used to lift prefabricated walls and rods to higher heights than conventional cranes, which enable the construction of high-rise buildings and other structures.

6.5.4 LAW ENFORCEMENT

Helicopters are also used in supporting law enforcement activities. Helicopters brought a number advantage to law enforcement authorities due to its inherent flying capabilities. As a result, it can be used for many law enforcement activities such as traffic surveillance, riot control, narcotics detection (detection of narcotics smuggling and distribution activities), night patrols for crime prevention (using high-intensity lights), and covert surveillance.

6.5.5 TOURISM

Helicopters are slowly becoming synonymous with tourism. Helicopters are being used to provide the tourists with a bird’s eye view of the surroundings be it a glacier, mountain, cities, etc. Aerial tours are becoming quite popular nowadays. The increased use of helicopters in tourism helped in improving the growth of the tourism industry in many parts of the world.

6.5.6 AERIAL OBSERVATION

Helicopters can also be used for aerial observation and reconnaissance, which include the observation of forest fires. Further, they are also used for refraction seismology, which is a branch of the study of the surface of the earth as well as in atmospheric studies to carry equipment.

6.6. ACTIVITIES IN INDIA INVOLVING THE APPLICATION OF HELICOPTERS

6.6.1 MILITARY

Steps are being taken by the Union government towards the operation of helicopter services for the CRPF personnel serving in Jammu and Kashmir in order to facilitate the movement of troops.

6.6.2 RESCUE AND RELIEF

During the Uttarakhand floods in 2013, HAL made helicopters Dhruv, Cheetah and Chetak have a pivotal role in the rescue of stranded people and transport of troops, food and medicines. Helicopters were also used extensively during the Kerala floods in August 2018. Thirty-eight helicopters were involved in the air-lifting of stranded people and dropping relief materials.

6.6.3 FIRE FIGHTING

Forest fires, which erupted in Sikkim’s Fambanglho Wildlife Sanctuary in 2017, were doused-off by helicopters provided by the Indian Air Force. The helicopters undertook 18 missions to control the spread of the fire.

6.6.4 HELICOPTER AIRLINE SERVICES

Companies such as Pawan Hans Limited, a public service unit company and Global Vectra Helicorp Limited provide helicopter airline service that include transport for passengers or cargo, or both. They also offer helicopter services for Off-Shore operations in oil and gas industry, inter-island transportation, Heli-pilgrimage tourism, charter services, etc.

7. ADVANCEMENTS

7.1 NOTAR

NOTAR has been one of the most significant advancements in the last decade. NOTAR, which abbreviates to no-tail rotor has eliminated the use of a tail rotor. A tail rotor's main function is to counteract the torque produced by the main rotor. But this tail rotor produces a lot of noise and can easily be damaged. NOTAR solves both these problems.

7.1.1 HOW NOTAR WORKS

The system has a fan inside the tail boom which is used to build a huge volume of low-pressure air. This low-pressure air then exits through two slots, creating a boundary layer flow of air along with the tail boom. Now the Coanda effect comes into play. The Coanda effect is the tendency of a fluid jet to stay attached to a convex surface. As a result of the Coanda effect, the downwash from the main rotor is made to hug the tail boom which in turn produces lift. This creates a thrust opposite to the motion of fuselage caused by the torque produced by the main rotor. This is augmented by the presence of a direct jet thruster and vertical stabilizers

7.1.2 SIGNIFICANCE OF NOTAR

Tail rotors are easily damaged as their blades are quite delicate. This would lead to a rotation of the fuselage and cause a lot of instability and would finally lead to a crash. Thus the use of NOTAR prevents such a situation. The tail rotor also causes a lot of noise. Thus using NOTAR would decrease the noise produced by helicopters. For example, let us consider a military helicopter having a tail rotor. In this case, the tail rotor would be the weak spot as once it is damaged the fuselage would start rotating and the helicopter would spiral out of control. Thus in such cases, the application of NOTAR would provide a structural advantage.

Figure 31: NOTAR Helicopter (Wikipedia,2019)

1 Air intake ,2 Variable pitch fan 3 Tail boom with Coanda Slots,4 Vertical stabilizers, 5 Direct jet thruster, 6 Downwash, 7 Circulation control tail boom cross-sections, 8 Anti-torque lift
Figure 32: Notar System (Wikipedia,2019)	Figure 33: Airmovement in NOTAR System

7.2 USE OF TWO ENGINES

Certain models of helicopters have two engines of which one is the secondary and is used in case the primary or the main engine suffers a mechanical failure. Although they are named primary and secondary both the engines have the same capacity. Either of the engines can keep the helicopter in flight, thus enabling the pilot to land safely in case of any emergency.

7.3 PIEZOELECTRIC ACTUATORS AND ROTOR BLADES

The high complexity of the motor system and a large number of moving parts of the main rotor assembly has been a major concern as they have a high chance of failure and thus many attempts have been made towards simplifying this intricate system. One way of doing so was to incorporate piezoelectric actuators. Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure and latent heat.

Piezoelectric materials can change shape when subjected to an electric field. Piezoelectric actuators are fixed on the rotor blades that change its shape as it spins thus improving a helicopter's aerodynamic performance.

7.3.1 APPLICATION OF PIEZOELECTRIC ACTUATORS

As a helicopter blade passes through the air, it creates a wake that is left behind the blade. The blade behind it then intercepts this wake. As this blade passes through this wake, it experiences a periodic vibration, which leads to slight instability. Here is where piezoelectric actuators can be used. If these piezoelectric actuators are fixed to the blades, one can incorporate a periodic motion into the blade flaps via the actuators. These periodic motions can be made to have the right amplitude, phase and frequency to cancel out this vibration, thus improving the quality of flight and making the engine more fuel-efficient. Before piezoelectric actuators, hydraulic actuators were used which proved to be too heavy.

7.3.2 WORKING OF A PIEZOELECTRIC ACTUATOR IN THE BLADE

The piezoelectric actuator sits inside the frame of the rotor blade near its tip where the aerodynamic forces are the greatest. The actuator is used to turn a flap at the tip of the blade. The actuators are activated using power amplifiers that then transmit an electric field to the piezoelectric material inside the actuators. The material in response to the electric field changes its length by expanding a very small amount (about 10 to 20 thousandths of an inch). This, in turn, moves a rod that is kept perpendicular to the flap. The movement of the rod then pushes the flap and the flap moves.

The movement of the flap during flight causes a lot of aerodynamic change to the blade. The flaps can be used to generate lift and change airspeed. This also allows the helicopter to use the flaps anytime during the flight whereas other fixed-wing aircraft can use flaps only for takeoff and landing.

Another important reason why this is a game-changer is the fact that these actuators are quite lightweight and do alter the rotor system much and thus are easy to incorporate.

Figure 35: Piezoelectric actuator	Figure 36: Components of  Piezoelectric actuator in the rotor blade

7.4 TILTROTORS

The development of tiltrotors is one of the more considerable advancements in the field of helicopters. A tiltrotor is an aircraft that generates lift and propulsion by using one or more powered rotors. These rotors are mounted on rotating engine pods or nacelles usually at the ends of a fixed-wing. This allows the movement of the rotors from the horizontal position to the vertical position. A tiltrotor combines the vertical lift capability of a helicopter with the speed and range of a conventional fixed-wing aircraft.

For achieving vertical lift, the rotors are angled in such a manner that the plane of rotation of the rotor blades is horizontal. This lifts the aircraft similar to a helicopter. Once the aircraft gains some speed, the rotors are progressively tilted forward, slowly making the plane of rotation of the blades vertical. In this configuration, the lift is achieved by the fixed-wing and the rotor is used to provide propulsion to move forward. Since this configuration avoids a helicopter's issue of retreating blade stall, a tiltrotor can achieve higher speeds than helicopters.

7.4.1 WHY TILTROTORS CAN MOVE AT HIGHER SPEEDS?

In the case of a helicopter, the maximum forward speed is decided by the turn speed of the rotor. As the forward speed of the helicopter increases, a point is reached when the helicopter will be moving forward at the same speed as the spinning of the backward-moving side of the rotor. This results in that side of the rotor experiencing zero or negative airspeed, which makes it to stall. This limits the speed of modern helicopters to about 150 knots. Nevertheless, in the case tiltrotors, the rotors can be made perpendicular to the direction of motion during the forward motion. This prevents the stalling experienced by helicopters. This, in turn, allows tiltrotors to achieve nearly double the speed of helicopters about 300 knots.

Figure 37: Tiltrotor Helicopter

7.5. SB>1 DEFIANT

          The SB>1 DEFIANT is a helicopter that is designed and developed by both Sikorsky and Boeing. It is a military helicopter and is designed for attack and assault missions along with long transportation of troops, infiltration and resupply mission.

7.5.1 DESIGN

           This helicopter is powered by a coaxial rotor system. The two coaxial rotors, which rotate in the opposite directions apart from canceling each other’s torque, also provide extra lift. This extra lift from each rotor's advancing blade balances out the diminished lift from the opposite side's retreating blade to eliminate retreating blade stall. The forward thrust in this helicopter is provided by a pusher propulsor, thus allowing the aircraft to fly twice as fast and twice as far as compared to today’s helicopters. This technology also increases the overall maneuverability and agility required for certain mission objectives.

Figure 39: SB>1 DEFIANT Helicopter (24heures, 2018)

8. FUTURE FOR HELICOPTERS

8.1 USE OF HELICOPTER IN SPACE EXPLORATION

8.1.1 MARS HELICOPTER SCOUT

         The Mars Helicopter Scout is a robotic helicopter that is planned to be launched to Mars in 2020 along with the Mars 2020 rover. The helicopter will be used to scout targets of interest on the Martian surface for study and would help in planning the best driving route for future Mars rovers. The helicopter would land along with the rover on Mars in 2021 and is expected to fly up to five times during its 30-day testing period.

8.1.1.1 OBJECTIVES OF THE MARS HELICOPTER SCOUT

           The main objective of this helicopter is to test whether the technology can fly safely and provide better mapping and guidance that would allow future mission controllers to plan better travel routes and would help in avoiding hazardous routes. The helicopter is also expected to identify points of interest for the rover. The helicopter is equipped with a high-resolution camera that would provide overhead images with nearly ten times the resolution as compared to the images provided by the orbiters and would display features that the rover's camera may miss. It is expected that such scouting would help in increasing the distance traveled by the rover to nearly three times the current travel distance per Martian day or Sol.

8.1.1.2 DESIGN

             The helicopter is equipped with counter-rotating coaxial rotors. The payload of the helicopter will be a high-resolution camera that faces downwards for navigation, landing and surveying the Martian terrain. It also has a communication system to relay data back to the rover. The helicopter also has radiation-resistant systems capable of operating in the frigid environment of Mars.

               Mars' inconsistent magnetic field prevents the use of a compass for navigation, so the helicopter will use a solar tracker for navigation. Some additional inputs include gyros, visual odometers, tilt sensors, altimeters, and hazard detectors. The helicopter is powered by six Li-ion batteries that are recharged by solar panels.

8.1.1.3 FUTURE

              This technology will form the foundation for the development of helicopters for ambitious missions to planets and moons having an atmosphere. Future helicopters could be used to explore special regions with exposed water-ice or brines where life may survive.

Figure 40: Mars Helicopter Scout (Wikiwand,2019)	Figure 41: Mars Helicopter Scout (Wikiwand,2019)

8.1.2 DRAGONFLY: A HELICOPTER TO TITAN

                 Dragonfly is an ambitious plan of sending a mobile robotic rotorcraft to Titan which Is Saturn’s largest moon, in order to study prebiotic chemistry and extraterrestrial habitability.

8.1.2.1 WHY TITAN?

                Titan has an abundant, complex, and diverse carbon-rich chemistry on the surface. Moreover, it is a water-ice dominated world with an interior ocean. All this makes Titan a good target for astrobiology and the origin of life studies. Titan is an analogy to the very early Earth, thus may provide clues to how life may have begun on Earth.

8.1.2.2 DESIGN

                Dragonfly is a rotorcraft lander that would be powered by four double-rotors i.e. it will be an octocopter. The aircraft will travel at a speed of 36 km/hr. and would be able to climb to an altitude of 4km. The aerial flight on Titan is plausible aerodynamically as Titan has low gravity, low winds, and a dense atmosphere. Thus, Dragonfly will be able to fly without any constraints. The craft will be designed to cope with space radiation and temperatures as low as 94K. The high aerodynamic drag created by the dense atmosphere is to be considered while designing the shape of the helicopter.

               The craft is powered by a battery that will be recharged by a Multi-Mission Radioscopic Thermoelectric Generator during the night at Titan. These generators convert the heat from the natural decay of radioisotope into electricity. The craft will weigh nearly 450kgs and will be equipped with two sample acquisition drills and hoses, for delivery to the mass spectrometer instrument.

               The craft will remain grounded during the Titan night, which is approximately 8 Earth days or 192 hours long. Activities during the night may include sample collection and analysis, seismological studies, meteorological monitoring, and local microscopic imaging. The craft will communicate directly to Earth with a high-gain antenna.

Figure 42: Dragonfly rotorcraft-lander	Figure 43: Dragonfly rotorcraft-lander  (Davis,2019)

8.2 APPLICATION OF ARTIFICIAL INTELLIGENCE

The application of artificial intelligence would lead to the development of self-driving helicopters in the future.  For instance, SkyRyse a California based company has built a first-of-its-kind advanced pilot assistance system (APAS) that combines artificial intelligence, a flight perception suite, and decision-making algorithms.

8.3 SUSTAINABILITY IN HELICOPTERS

The copter concept namely "Racer," for Rapid and Cost-Effective Rotorcraft — has been designed as a part of the Clean Sky 2 European research program, which focuses on reducing carbon dioxide emissions and lesser noise levels during operation (Dreamer, 2017).  The helicopter design incorporates an “eco-mode” which would increase fuel efficiency. This design also allows an electrically powered "start and stop" of one engine in flight to save fuel. This would also increase range along with low-weight body to have better fuel efficiency and aerodynamics (Deamer, 2017). Considering the long term benefits which can be brought by a sustainable helicopter, research on this area is to be encouraged and promoted.

9.    CONCLUSION

           The helicopter is undoubtedly a unique form of transportation. With its special features like flexibility, adaptability and agility and small size, they are being used extensively by private and government agencies in different parts of the world. It has helped in the improvement of the economy as it is used in different fields like cargo transportation, small-scale industries, medical field, tourism department, military purposes, and civilian purposes. Advancements in technology, processes, and training are further increasing the extensive use of helicopter safely and effectively. Helicopters fitted with modern equipment like computers, robots, and lasers have helped many people, professionals, soldiers, civil servants, private and government service personnel, doctors, and personnel working in disaster management council. 

         In the times of war, during natural calamities, fight against wildfires, rescue operations, for surveying offshore resources and other sources of renewable energy, news gathering, event coverage, inspection and reconnaissance, construction & utility work, etc.---the list for the service provided by helicopters is endless. The hallmark of the modern helicopter is its ability to adapt to the latest developments and advancements related to its design and other features. Unmanned aerial systems provide additional unique unmanned capabilities. Although there have been many developments in the design of the rotors and design and working of the engine of late there is still a scope for further improvement. Thus, one can say that helicopters contribute both directly and indirectly towards the country’s economy, which is depicted in the big picture, shown in figure 44.

Figure 44: Big picture of Helicopter’s contribution to National Development

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