A Definition of Helicopter

 

 By:  Ashob Bahman 

 

Helicopter is an aircraft without wings that obtains its lift from the rotation of power-driven horizontal overhead-blades which enables it to take off and land vertically, move in any direction, or remain stationary in the air.

 

 The sources of the word

The word helicopter was adopted from the French word hélicoptère, a word collected from Greek heliko- and pteron, "wing." Heliko-, the combining form of helix, "spiral," has given us helico-, which can be joined with other words and word forms to create new words. The consonant cluster pt in pteron begins many Greek words but relatively few English words.

  

Historical background of helicopter 

 The Chinese are said to have built the first of all rotary-winged aircraft centuries ago.  Of course, this was not a real helicopter in the sense that it could carry passengers, but rather it was a toy, which has since become known as the Chinese top.

Unsure by historians if he was inspired by the Chinese top toy, according to The Flight of Genius, in 15th century it was the great Italian Leonardo da Vinci (1452 - 1519) who designed his first helicopter called the “shallow saucer-like gondola.”  The model consisted of two upright posts. Both posts carried a double set of wings. (2009, November, p.1).  It is described rather a complicated system of cords, cylinders, and foot pedals.  The pilot would set the wings in motion with movements of his head, hands and feet.  Being a perfectionist with his enormous mental powers, Leonardo da Vinci came to the conclusion that mechanical rather than human power must be used before a successful flying machine could be built.

Stirred by Leonardo’s project, many scientists also tried to build a helicopter in later years but were not successful.  But then, Inventor Biographies describes, it was the Ukrainian born but American citizen engineer Igor Sikorsky (1889 - 1972) who fulfilled Leonardo’s dream in 1909. (2009, p.1 Para. 2).   After many tries and skepticism from others Igor Sikorsky finally proved to the world that vertical flight was possible in 1938. The first successful helicopter to be designed and constructed by him in the United States was the VS-300.

 Compared to a fixed-wing aircraft

The main difference between fixed-wing and rotary-wing aircraft is the way lift is achieved.  The most immediate and obvious difference in the construction of a fixed-wing aircraft versus a helicopter is the use of a rotor instead of a wing. But the common principle to achieve the lift is similar between both aircrafts.  They both rely on airfoil for lift.    A fixed-wing aircraft achieves lift by constant motion “thrust” that is developed by the engine of the aircraft.  The thrust overcomes the force of lower air pressure on the upper surface of the wing more than on the lower surface--which creates lift. The nose of the aircraft changes the angle of attack, and changing the angle of attack causes the aircraft to pivot on its lateral or pitch axis. If the right wing is lowered the left wing will rise. 

But unlike fixed-wing aircraft which gets its lift from a fixed airfoil, the helicopter gets its lift from rotating airfoils called “rotor blades.”  Shaped more like a dragonfly, a helicopter uses two or more engine-driven rotors from which it gets lift and propulsion. Lift is accomplished by rotating the blades through the air at a high rate of speed.  Lift may be changed by increasing the angle of attack or pitch of the rotor blades.  This means that if the rotor is turning and the blades are at (zero angle) “Flat Pitch” no lift is developed.

  

 On the contrary of negation 

Although it can fly in any direction and land almost anywhere without a runway, a helicopter cannot fly as fast or as high as a fixed-wing aircrafts.  And unlike a fixed-wing aircraft, a helicopter cannot fly without a tail rotor that compensates for the main rotor torque. Without some kind of Anti-torque control, a helicopter’s fuselage would spin around in the opposite direction of the main rotor giving it a dysfunctional heading control.

Helicopters are considered more expensive to operate than conventional fixed-wing aircrafts. But in a calculation of the comparison and costs, the advantage granted by the superb vertical flight machines surpasses its competition. Defense systems, medical emergencies, oil drilling rigs, agriculturalists, evacuation rescues, and even vacation tours relay heavily on helicopters.

Despite of being more difficult than a fixed-wing aircraft to control, most helicopter pilots cherish helicopters the cyclic and collective pitch which gives the helicopter its unique ability to fly forward, backwards, sideways, rise, descend vertically, and hover motionless in the air--making it one of the most resourceful vehicles known by man. 

 

 Maneuvering Controls

The flight of a helicopter is governed by the pitch or angle of its rotor blades as they sweep through the air. For climbing and descending, the pitch of all the blades is changed at the same time and in the same degree.
To Climb, the angle at pitch of the blades is increased. To descend, the pitch of the blades is decreased.  Because all blades are acting simultaneously, or collectively--this is known as collective pitch.

For forward, backward and sideways flight, an additional change of pitch is provided.  And this means that the pitch of each blade increases at the same selected point in its circular pathway--this is known as the cyclic pitch.

And finally, the pilot must use the tail rotor pedals (Anti torque Pedals), also known as the Rudder, which are located on the floor--to control the pitch of the tail-rotor. For straight flight, the pitch of the tail rotor is set to prevent the helicopter from turning to the right as the main rotor turns to the left.

 

 

 

 

 

 

 

 

Works cited 

The Flight of Genius. (2009). Leonardo Da Vinci flying machine.                         http://www.leonardo-da-vinci-biography.com/leonardo-da-vinci-flying-machine.html

Inventor Biographies. (2009). Igor Sikorsky Biography (1889-1972).  http://www.madehow.com/inventorbios/17/Igor-Sikorsky.html

All Images and Pictures were retrieved from Google Images. Google.com