In this article, we will learn about how helicopters fly with the help of an animation tutorial video. Helicopters are the true flying machines. They can take off and land without the need for a runway. They can hover in the air, it can maneuver in any direction in a 360 degree space.
This video will unveil the complexity in science behind how helicopters fly. After going through the physics behind the helicopter flying. You will also understand why helicopter pilots are doing an incredibly complex job. Helicopters use the Airfoil principle to generate lift. When the blades rotate relative to the air, the unique airfoil shape will create lift force. Which make them fly. The blades derive rotation from an engine. More specifically a turbo shaft engine. The compressor sucks the air in and pressurizes it. Fuel is burned in this pressurized and hot air. The hot exhaust leaves the combustion chamber and passes through a series of turbine stages. This makes them turn.
There are two Sets of turbines, one turbine set turns the compressor, and the other set turns the helicopters rotor shaft. Jet Engines of Airplanes are used to generate thrust force. However, the primary function of the helicopters jet engine is to rotate the rotor shaft. The most challenging part in helicopter operation is its controls. That means, how can it fly forward? How can it fly backward, side ward Or how can it take a turn. The answer is quite simple. Just rotate the helicopter towards the direction you want to move and just fly When the helicopter is at an angle. The force produced by the blade is not vertical. The horizontal component of this force will make the helicopter move in the desired direction. The vertical component of the blade force will balance the gravitational force.
Now the real challenge is, how to turn the helicopter in the desired way?
To learn the science behind helicopter turning, we need to learn more about the airfoil principle. The lift produced by an airfoil varies with the angle of attack. Generally the higher the angle of attack the more the lift. Now think for a moment what happens if the one blade were at one angle of attack and others were at a different angle. The lift forces acting on the blades will be different in this case. The variations in the lift forces will undoubtedly result in a torque that can turn the helicopter. You can observe the beautiful blade motion required to achieve this non-uniform lift force distribution. It is clear that the blades must keep on changing the angle of attack. So that at one particular location the angle of attack is always the same. Such complexity of the blades is easily achieved by a swash plate mechanism.
Understanding the basic components.
In this exploded view in the video, you can see the bottom swash plate does not spin. But it can move and tilt as shown. A top swash plate is fitted on the bottom swash plate via a bearing. So the top swash plate inherits all the motion of bottom Swash plate while at the same time it can rotate independently. Top swash Plate is attached to the rotor Shaft with the help of a driver. So the top swash plate will always move with the blades. The blades are connected to the top swash plate with the help of control rods.
The exciting thing about this arrangement is that. Just by tilting the bottom swash plate. We will be able to achieve the varying angle criterion of the blades. That means, with this swash plate tilt, we will always be able to maintain a positive angle of attack at the rear and a negative angle at the front portion of the rotor disk.In short, swash plate tilting backward produces torque as shown. This kind of control is known as cyclic pitch.Now back to the basic helicopter control.
How will this torque affect the motion of the helicopter?
The most obvious answer is that the helicopter will turn forward and move as shown. Unfortunately, this answer is entirely wrong. What happens, in reality, is the helicopter will turn side ward as shown. This is definitely a weird effect. By applying torque in one direction to a rotating object, the object turns in a different direction. This effect is known as gyroscopic precession. Gyroscopic precession is not a new phenomenon of physics. If you carefully apply Newton’s second law of motion to rotary objects. You will be able to predict this phenomenon. According to Newton’s second law. Force is the rate of change of linear momentum? Similarly, torque is the rate of change of Angular Momentum.
Let’s consider this rotating blade as shown in the video. It will have angular momentum. As shown in the video, assume that the helicopter has tilted, as shown due to some torque action. If you subtract the first angular momentum from the second, you can figure out the torque required for this operation. It Is interesting to note that, to turn the helicopter forward the torque applied should be towards side wards. That means to tilt the helicopter? Forward the swash plate should lean side wards. As shown, you can again verify from Newton’s second law of motion. That if you keep the front portion at a negative angle of attack and the back portion at positive Angle. The Helicopter will merely turn side wards.
Gyroscopic precession is a genuinely intriguing phenomenon. But it conforms perfectly with Newton’s second law of motion. If you just lift the bottom swash plate without tilting it. You can see how the angle of attack of all three blades will vary by the same amount. This means that the helicopter lift force will be the same in all three blades and the helicopter can move up or down without any tilt. Such blade control can be called as collective pitch.
If you have ever seen a helicopter, you are all sure to have seen a tail rotor. Every single rotor helicopter needs this tail rotor for effective operation. Without the tail rotor, the helicopter fuselage would have spun as shown in the video. This is due to a consequence of Newton’s third law of motion.
To understand it, let’s focus on the force transmission part of the rotor. We know the rotor get the force of rotation from the bevel gear and connected to the engine. The bevel gear transmits force to the rotor bevel gear as shown. However, according to Newton’s third law of motion, the rotor bevel gear should transmit an equal and opposite force to the engine bevel gear.
This reaction force will make the whole helicopter turn opposite the blade rotation along the helicopter center of gravity. The function of the tail rotor is to prevent such helicopter rotation by producing a force at the tail. By appropriately adjusting the pitch angle of the tail rotor blades. The pilot can easily manipulate the tail rotor force this way with the help of the tail rotor. Yaw motion of the helicopter can also be achieved. All the physics behind helicopter operation means that. Flying a helicopter is a truly challenging task. Minute variations in blade Angles make considerable changes in Helicopter behavior. Often the pilot has to do two or more operations together to achieve the desired motion. Moreover, the helicopter does not respond instantaneously to your inputs. So the pilot should possess a good sense of balance and coordination to navigate the Helicopter properly.
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