As seen earlier, helicopters have a number of exceptional capabilities that aeroplanes and motor vehicles lack. The greatest of the chopper’s agility is its potential 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 directions; it can also fly backwards in addition to the sideways just as easily. A helicopter that is flying forward can also stop in mid-air and begin hovering very quickly, all of these manoeuvres are impossible in an aeroplane, which must fly forward at all times in order to develop lift from its wings (as seen in our article of “How Aeroplanes Work”). In that article, we saw one important factor in the flight of an aeroplane is the fact that, it must have a drag and speed in order for it to displace its own weight and hence taking off the ground into its flight! As for the helicopter, the story is totally different! How do the different abilities influence the design and the controls of a helicopter? Assume that we need a machine that can simply fly straight upwards (ignore getting back to the ground for the time being), all we need is to ascend. In order to provide the upward force with a wing, then the wing has to be in motion in order to create lift. Wings create lift by deflecting air downward and benefiting from the equal and opposite reaction that results. As for aeroplanes, the plane and its winds are in motion! In the case of a chopper, all we need is to create a rotary motion by keeping the 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. That way, the rotating wings of a helicopter are shaped much in the same way as the airfoils of an aeroplane wing, but generally the wings on a helicopter’s rotor are narrow and thin because they must spin so quickly. 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 (rotation) and spin the shaft, the wings start to develop lift. In order to accomplish the spin on the shaft with enough force to lift vehicle, you need an engine of some sort and the fuel that powers it. The engine’s power is channeled through a transmission to the main rotor shaft. This works well until the vehicle leaves the ground, then, there is the risk of the whole vehicle spinning just like the main rotor does is very likely unless something is done about it. The usual way to provide a force to the body of the vehicle is to attach another set of rotating wings to a long tail like boom. These wings are known as the tail rotor. The tail rotor produces thrust just like an aeroplane’s propeller does. By producing thrust in a sideways direction, this counters the engine’s tendency to spin the body; the tail rotor keeps the body of the helicopter from spinning. In order to exercise control, both the main rotor and the tail rotor need to be adjustable. This 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. As already indicated, it is the tail that is used in the manoeuvring of the chopper in the spinning or rotating motion (can rotate or spin from front to sideways or back through an angle of 360˚), all this is done by the foot pedals. One does a clockwise and the other an anti-clockwise motion; both balance the motion to a required spin! As seen before, the helicopter’s main rotor is the most important part of the vehicle as it provides the lift that allows the helicopter to fly, as well as the control that allows the helicopter to move laterally, make turns and change altitude. In order to manage all these tasks, the rotor is very strong and robust. It also has must be able to adjust the angle of the rotor blades with each revolution of the hub, this is made possible by a device known as the swash plate assembly in-charge of the following roles:- Under the direction of the collective control, the swash plate assembly can change the angle of both blades simultaneously. Doing this increases or decreases the lift that the main rotor supplies to the vehicle, allowing the helicopter to gain or lose altitude. Under the direction of the cyclic control, the swash plate assembly can change the angle of the blades individually as they revolve. This allows the helicopter to move in any direction around a 360-degree circle, including forward, backward, and left and right. 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. eddie@afrowebs.com
