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Helicopters are the most versatile flying machines in existence today. This versatility gives the pilot complete access to 3-dimensional space in a way that no airplane can. If you have ever flown in a helicopter you know that its abilities are exhilarating! The amazing flexibility of helicopters means that helicopters can fly almost anywhere. However, it also means that the machines are complicated to fly. The pilot has to think in three dimensions and must use both arms and both legs constantly to keep a helicopter in the air! Piloting a helicopter requires a great deal of training and skill, as well as continuous attention to the machine.
In this edition of How Stuff Works you will learn about all of a helicopter's different capabilities, and you will also learn how the machine is able to do such amazing things!
Comparing Helicopters to Planes, Trains and Automobiles
To understand how helicopters work and also why they are so complicated to fly, it is helpful to compare the abilities of a helicopter with those of trains, cars and airplanes. By looking at these different modes of transportation you can come to understand why helicopters are so versatile!
If you have ever been inside of the cab of a locomotive, you know that trains are fairly simple to drive. After all, there's only two directions that a train can travel -- forward and reverse! There is a brake to stop the train's travel in either direction, but there is no steering mechanism of any kind on a train. The tracks take the train where it needs to go.
Because a train has only two directions in which it can travel, you can drive a train with one hand.
As we all know, a car can go forward and backward like a train. While you are traveling in either direction you can also turn left or right:
To handle the steering a car uses a steering wheel that the driver can turn clockwise or counterclockwise. It is possible to drive a car with one hand and one foot.
Anyone who has taken pilot lessons or looked inside the cockpit while boarding a jumbo jet knows that planes are a lot more complicated to fly than a car is to drive. However, a plane is really only one step away from a car:
A plane can move forward and turn left or right. It also adds the amazing ability to go up and down. However, it loses the ability to reverse. So a plane can move in 5 different directions instead of a car's 4 directions. The ability to go up and down adds a whole new dimension to a plane, and this dimension is what makes airplanes so different from a car. To control the upward and downward motion of the plane, either a joystick replaces the steering wheel or the steering wheel gains the ability to move in and out (in addition to turning clockwise and counterclockwise). In most planes (but not all) the pilot also has access to two pedals to control the rudder. Therefore a pilot could fly a plane with one hand and two feet.
A helicopter can do three things that an airplane cannot:
The Special Capabilities of Helicopters
Helicopters have a number of unique abilities that airplanes do not have. Several of these capabilities are shown in the following videos (if you have a high-speed Internet connection, these videos are fun to watch!).
The signature of a helicopter is its ability to hover over one point on the ground. While hovering a helicopter can also spin on its axis so that the pilot can look in any direction.
Another unique feature of a helicopter is its ability to fly backwards. A helicopter can also fly sideways just as easily.
Since a helicopter can fly backwards and sideways it can do a number of interesting tricks. The following video shows a helicopter performing a pirouette in which it rotates 360 degrees while it travels down a straight line relative to the ground:
A helicopter that is flying forward can also stop in mid-air and begin hovering very quickly, as demonstrated in this video:
All of these maneuvers are impossible in an airplane, which must fly forward at all times in order to develop lift from its wings (see How Airplanes Work for details).
How Helicopters Fly
You can begin to understand how a helicopter flies by thinking about the abilities displayed in the previous section. Let's walk through the different abilities and see how they affect the design and the controls of a helicopter.
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I would like to express my gratitude to Glenn Brown, the president of Raleigh Helicopters, and Ellen Turcio, my pilot and the star of the videos shown in this article. Both were extremely helpful and went out of their way to assist me with this article. If you are in the Raleigh, NC area and need helicopter services or instruction, you can reach Raleigh Helicopters at (919) 497-1870. |
A rotary motion is the easiest way to keep a wing in continuous motion. So you can mount two or more wings on a central shaft and spin the shaft, much like the blades on a ceiling fan. The rotating wings of a helicopter are shaped just like the airfoils of an airplane wing, but generally the wings on a helicopter's rotor are narrow and thin because they are spinning so fast. The helicopter's rotating wing assembly is normally called the main rotor. If you give the main rotor wings a slight angle of attack on the shaft and spin the shaft, the wings will start to develop lift.
In order to spin the shaft with enough force to lift a human being and the vehicle, you need an engine of some sort. Reciprocating gasoline engines and gas turbine engines are the most common types. The engine's driveshaft can connect through a transmission to the main rotor shaft. This arrangement works great until the moment the vehicle leaves the ground. At that moment there is nothing to keep the engine (and therefore the body of the vehicle) from spinning just like the main rotor does. So, in the absence of anything to stop it, the body will spin in an opposite direction to the main rotor. To keep the body from spinning you need to apply a force to it.
The normal way to provide a force to the body of the vehicle is to attach another set of rotating wings to a long boom. These wings are known as the tail rotor. The tail rotor produces thrust just like an airplane's propeller does. By producing thrust in a sideways direction, counteracting the engine's desire to spin the body, the tail rotor keeps the body of the helicopter from spinning. Normally the tail rotor is driven by a long drive shaft that runs from the main rotor's transmission back through the tail boom to a small transmission at the tail rotor.
What you end up with is a vehicle that looks something like this:
In order to actually control the machine, both the main rotor and the tail rotor need to be adjustable. The following two sections explain how the adjustability works.
The Tail Rotor
The adjustability of the tail rotor is straightforward -- what you want is the ability to change the angle of attack on the tail rotor wings so that you can use the tail rotor to rotate the helicopter on the drive shaft's axis. The pilot has two foot pedals that control the angle of attack. These two videos let you take a look at the pedals and see how they affect the tail rotor:
You can also see the pedals in this shot of the cockpit:
The Main Rotor
A helicopter's main rotor is the most important part of the vehicle. It provides the lift that
allows the helicopter to fly and it also provides the control that allows the
helicopter to move laterally, make turns and change altitude. To handle all of these
tasks, the rotor must first be incredibly strong. It must also be able to adjust the angle
of the rotor blades with each revolution of the hub. The adjustability is provided
by a device called the swash plate assembly, as shown in this photograph:
The swash plate assembly has two primary roles:
The collective control changes the angle of attack on both blades simultaneously:
The cyclic control tilts the swash plate assembly so that the angle of attack on one side of the helicopter is greater than it is on the other, like this:
Hovering in a helicopter requires experience and skill. The pilot adjusts the cyclic to maintain the helicopter's position over a point on the ground. The pilot adjusts the collective to maintain a fixed altitude (especially important when close to the ground, as shown in the videos). The pilot adjusts the foot pedals to maintain the direction that the helicopter is pointing. You can imagine that windy conditions can make hovering a real challenge!
The following videos help you understand the relationship between the cyclic and collective controls and the swash plate assembly. In general:
Other Important Components
Links
Sponsored links to interesting websites:
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