hello this is Tim today we will talk about aircraft stability and why stabilizers are needed let's see what is the meaning of stability let's consider an aircraft in flight the ability of this aircraft to withstand any disturbances and continue its normal flight is called a stability stability can be classified into static stability and dynamic stability we will look at static stability in this video what is static stability static stability refers to the initial response of an aircraft after it is subject to a disturbance after the disciplines if the aircraft has a tendency to come back to its original active they let this set to have pasta static stability after the disturbance if the aircraft has a tendency to deviate away from its original attitude then it is said to have negative static stability after the disturbance if the aircraft tends to maintain its new attitude that is not coming back or not deviating from the original attitude then it is said to have neutral static stability on comparing the positive static stability negative static stability and the neutral static stability we understand that the aircraft should have positive static stability this stability is entirely dependent on the aircraft design the positive static stability can be divided into longitudinal stability lateral stability and directional stability let's look at longitudinal static stability this refers to stability of an aircraft after its suppose a disturbance in pitch to understand this stability we will have to take a closer look at the wing airfoil on the air fault there is a point called a center of gravity or CG and another point called a center of pressure or CP at the center of gravity the aircraft's weight force acts downwards and this is a fixed point at the center of pressure the left force of the wing acts and this point moves based on the lift let's keep the CP ahead of the CG now if there is a disturbance in the pitch the tendency of the aircraft would be to deviate from the original attitude this will result in negative longitudinal static stability now let's keep the CP behind the CG if there is a disturbance in pitch the left-hand weight forces will create a tendency to return to the original attitude this is called as positive longitudinal static stability which is required on the aircraft the left-hand weight forces together will form a couple which will push the nose of the aircraft downwards to prevent the aircraft nose down condition the horizontal stabilizer is installed to remove the nose-down condition the horizontal stabilizer needs to give an aircraft nose up this is done by creating a downward force at the tail section this will give us positive longitudinal static stability and level flight next we will look at lateral static stability if the aircraft is subject to a disturbance in drone then it tends to roll with the wind for this disturbance stability is provided by the vertical stabilizer and the wing structure as the aircraft rolls due to the disturbance the lift increases on the downgoing wing as the angle of attack on the swing increases the lift decreases on the upgoing ring as the angle of attack on this wing decreases this will create a tendency on the aircraft to roll back to its original attitude which will give us the posted lateral static stability during the disturbance the vertical stabilizer provides resistance to the roll this will improve the positive lateral static stability next we will look at directional static stability this is important when the aircraft is subject to a disturbance in yawn causing the aircraft to turn the vertical stabilizer becomes the primary surface to provide the directional stability during the disturbance the nose will yawn in the same direction as the wind detail will yawn in the opposite direction of the wind this will result in an increase in drag at the vertical stabilizer this creates a tendency to you're back to the original attitude which will give us the positive directional static stability the static stability of an aircraft includes the longitudinal static stability lateral static stability and the directional static stability the positive static stability is achieved by a good aircraft design or more specifically a good design of the wing and the horizontal and vertical stabilizers thank you for watching and please subscribe [Music] you