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Thursday, 24 August 2017

FLYING MACHINE SECRETS EXPLAINED.....WHY HELICOPTER FLY??



Helicopter are the true flying machine. They can take up without need of a runway. They can hover in the air. They can manipulate in any direction in air with 360 degree rotation. This blog is on the science behind a flying helicopter. After going through the logic behind a flying helicopter, you will understand the complication of driving a helicopter.
HOW-HELICAPTER-FLY-HELICAPTER-WORKING-MECHANISIM


Helicopter uses the airfoil principle to generate lift. When the blades rotate relative to the air, the special airfoil shape of blade will generate the lift force & make them fly. The blades are driven by a rotation from a engine more specifically a turbo shaft engine.

Inside a turbo shaft engine the compressor sucks the air in & pressurize it. The fuel is burned in the pressurized & hot air. The hot exhaust air leaves the combustion chamber & passes through a series of turbine stages & make them turn. There are 2 set of turbines i.e. 1st turbine set turns compressor & other set rotates helicopter rotor shaft.  Jet engine are mostly used to generate thrust force. The primary function of engine to rotate the main rotor shaft.
The most challenging part of helicopter operation is its control i.e. how can it fly forward , backward , sideways & it can turn . The answer is simple, just rotate the helicopter towards the direction in which you want to move & fly.

When the helicopter is at an angle , the force produce by the blade is not vertical . The horizontal component of force will make the helicopter to move in the desired direction. The vertical component of blade for will balance the gravitational force . Now the real challenge is how to turn the helicopter in desired way. To learn to science behind the turning, we need to learn the airfoil technology.


The lift produce by an airfoil varies with the angle of attack . Generally the greater the angle of attack, the more the lift. Now imagine what happens when a blade with one angle of attack & other blades are with another angle of attack. Well in that matter different lift force will produce on different blades. The variation in the lift force will definitely result in a torque that can turn a helicopter. U can observe the non-uniform blade motion use to generate different lift force by different angle of attack. It is clear that to turn helicopter, the angle of attack should change continuously at a particular position. That will cause the same angle of attack at a particular position. Such completion motion is easily achieve by a swash plate mechanism.

swash plate mechanism

This mechanism consists of 2 plates, a bearing & some connecting.
The bottom swash plate doesn’t move but it can move up & down.

The top swash plate is fitted on the bottom swash plate via a bearing . So the top swash plate will have the all motion of bottom swash plate at the same time it can rotate independently. The top swash plate is attached to the rotor shaft with the help of a driver. So the top smash plate will always move with the rotor shaft.

The blades are connected to the top smash plate with the help of control rods. The interesting part of this mechanism is just by tilting the bottom smash plate we will be able to archive the varying attack angle criteria of the blade. That means with this we will always be able to maintain a positive angle of attack at the rear & -ve angle of attack at the front position of rotor disk. In short smash plate tilting backward produces a torque called as cyclic pitch.

TORQUE & ITS EFFECT

Now back to the basic control of helicopter, how the cyclic torque will affect the helicopter motion. The obvious answer is the helicopter body will turn forward & move . Unfortunately the answer is wrong. In practically the helicopter will turn sideways.  Yes. This is totally weird effect , by applying torque in one direction the object turns in different direction . This affect is known as GYROSCOPIC PRECESSION. GYROSCOPIC PROCESSION is not a new phenomena. This can be predicted by applying newton’s second law of motion to rotary object. The GYROSCOPIC PROCESSION is truly a tricky  phenomena it says if we keep the front position at –ve angle & back position at +ve angle , the helicopter will simply turn sideward not forward.

WHY ALWAYS SAME LIFTING FORCE IS PRODUCE?

The movement of bottom smash plate is controlled by a single mechanism. So that the change lift force produce will be same at each blade. So that the helicopter can up & down without any tilt. This is called COLLECTIVE PITCH.

TAIL ROTOR

If u have ever seen a helicopter u must have thought the use of tail rotor .Every single helicopter needs this rotor for effective operation. Without the tail rotor the helicopter body will rotate along with the blades but in opposite direction due to newton’s third law. We know that the power from engine to rotor shaft is transferred through a bevel gear. According to newton’s law  there will be a reaction force on the engine bevel gear. This reaction force can cause the helicopter body to rotate exactly opposite to the blade rotation along the helicopters canter of gravity. This reaction force is cancelled by the force created by the tail rotor. By properly adjusting the pitch angle of tail rotor blades, the pilot can easily restrict that motion of helicopter body. This is called YAW MOTION.

During flying the pilot have to control the cycle pitch control in order to go forward & backward, with that the pilot have to control the pitch angle of tail rotor simultaneously . Moreover the helicopter doesn’t respond quickly, so that the pilot have to have a good sense of humor & presence sense. Practically, in order to control a helicopter the pilot need a very well co-ordination of all control for good flight.

so that is the complete mechanism how helicopter fly. For better understanding please see google images when reading this.

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4 comments:

  1. Replies
    1. THANKS ...FOR ANY MECHANICAL TECHNICS VISIT HERE.... FEEL FREE TO CONTACT ...THANK U TECHIENGINEER

      Delete
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