Have you ever wondered how the Aircraft fly with so much stability?
Well, the answer lies in its design
The cruise of the Aircraft is not as smooth as we think it will be. Aircrafts are designed to travel through the Gusty winds, Thunderous storms and Hurricanes. And for this to happen the aircraft must be designed in such a way that it withstands these disturbances and maintain its stability.
Well, let us first talk about the stability of the aircraft.
As i have mentioned above the aircraft has to withstand many disturbances in the weather and has to come to its equilibrium position to maintain its stability.
Let us consider the case of Gusty winds, the air through which the aircraft is travelling will be imposing certain angle of attack on the airplane. If you are no familiar with this terminology then i will put it this way, it is the angle at which the air is coming and hitting the wings and the body. So coming back to our Gusty winds, when these hit our aircraft they actually change the angle of attack and there by creating a nose up movement. Nose up movement means the aircraft will be lifted upwards.
If this situation is not handled, the airplane may have difficulties to fly and may even crash also. So to handle this situation the airplane must be brought back to its original/equilibrium position.
But how can we achieve that????
Here comes the design part. The nose up and nose down movement will be about the center of gravity of the aircraft. Center of gravity is the point where all the weight of the body will be acting. There will be another point called aerodynamic center.
Aerodynamic center is the point on the aerofoil about which the pitching movement is independent to the angle of attack. The pitching moment means the nose up and nose down movement.
So when the angle of attack is increased there will be an increase in the lift co-efficient which will be generating a moment. This moment actually decides the stability of the aircraft.
If the Aerodynamic center is located ahead of the center of gravity then it will just amplify the nose up pitching movement and the plane will crash.
But if the Aerodynamic center is located before the center of gravity as shown in the figure then the moment is generated in the opposite direction of the nose up movement and the plane is brought back to its original state.
So to maintain the stability of the Aircraft the Aerodynamic center must lie before the center of gravity
There are other cases where the Aerodynamic center actually lies ahead of the center of gravity but the stability is mainly determined by the stabilizer which lie at the tail.
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