The subject matter of aerodynamics is finding there are determining the forces and moments, that acts on anybody that moves through a fluid. In our case we are mostly interested in air, but the basic principles are same irrespective of what fluid. It is considering the bodies as an aircraft; see when aircraft moves through a body. It experiences certain force as, you know that aircraft exerts, forces on the air and air in turn exerts forces on it, and this force and moments and estimation of their contribution to the motion that is what, the subject matter of aerodynamics.
Since, this force on moments comes, because of the pressure, and viscous stress that is develops on the surface of the aircraft. So, aerodynamics tries to determine these pressure and viscous stresses on the surface, and of course these pressure and viscous stresses are dependent on the overall flow. So, you can say that aerodynamics is the study of the flow about, anybody that is emerged in a fluid and moving through it.
We are mostly interested, in the body of aircraft and if we consider aircraft is say, what are the forces that act us on an aircraft. We know that there is a buoyancy force, but usually the buoyancy force is so small that, it is hardly considerable when compared to the total weight of the aircraft, and we can neglect it for further motion. Now, aircraft considering the simplest possible flight, which is that aircraft flying in a straight level flight. That it is going straight, and keeping it is altitude more or less fixed under this condition.
You know that the forces need a balance, the wait force needs to be balanced by some force similarly, the engine thrust is also balanced by some other forces, and these forces are in this configuration of flight are known as the lift and drag force. That is when the aircraft is in a
steady level flight, it is weight is balanced by the lift force, and thrust is balanced by a drag force. Both of these forces are aerodynamics nature that is they come, because of the relative motion of the aircraft and the air or the fluid.
Now, if there is any disturbance in the flight of course the moment develops, and the configuration of the aircraft changes. The force coming from the pressure distribution, and viscous stress distribution, and they are distributed over the entire surface of the aircraft. It is not necessarily aircraft it can be any body, which is emerged in fluid. Now, as you know that a distributed force can be represented by a system of force, and moments same thing can be done here also. And, these force and moments, they can be resolved in any three mutual orthogonal directions.
If, we consider these three mutual orthogonal directional like this, particular remember these direction, the let us call it x axis the x axis is along the relative wind. It is along the relative wind that means it is along the direction of the relative velocity between the body and the fluid is neither horizontal nor vertical or anything, it is along the direction of relative velocity between the body and the fluid. So, as an example if we consider that an aircraft is moving in atmosphere, which is at rest then the relative wind is simply the direction of or opposite of the direction of the aircraft speed. So, in that case the x axis is opposite to the direction of the aircraft velocity.
If, an aircraft is flying through an atmosphere at rest, the x axis is along the opposite of the direction of aircraft velocity or aircraft speed. However, in general we will call it is the direction of the relative wind. The x axis is relating the direction relative to the wind. And let us, call at this stage the z axis, which is upward, but not vertical it is normal two of course the x axis, so it is upward, but it is not vertical. Since, x axis is not vertical horizontal the z axis is not vertical, and the y axis is which is perpendicular to the plane formed by x and z.
Usually, for an if we consider the body to be an aircraft, we call it the direction to the right wing, right side of the wing with respect to the pilot, to the right side can be with respect to an observer. The observer may be as in front observer may be behind, so of course the right will change. So, it is right side with respect to the pilot, usually that is called the starboard side. These names came from shipping, where they have the left is usual called the portside, as ships comes in to a port, it is left side usually faces the port towards the port. So, that left side is called the port side, and the right side is called the starboard side.
Since, this force on moments comes, because of the pressure, and viscous stress that is develops on the surface of the aircraft. So, aerodynamics tries to determine these pressure and viscous stresses on the surface, and of course these pressure and viscous stresses are dependent on the overall flow. So, you can say that aerodynamics is the study of the flow about, anybody that is emerged in a fluid and moving through it.
We are mostly interested, in the body of aircraft and if we consider aircraft is say, what are the forces that act us on an aircraft. We know that there is a buoyancy force, but usually the buoyancy force is so small that, it is hardly considerable when compared to the total weight of the aircraft, and we can neglect it for further motion. Now, aircraft considering the simplest possible flight, which is that aircraft flying in a straight level flight. That it is going straight, and keeping it is altitude more or less fixed under this condition.
You know that the forces need a balance, the wait force needs to be balanced by some force similarly, the engine thrust is also balanced by some other forces, and these forces are in this configuration of flight are known as the lift and drag force. That is when the aircraft is in a
steady level flight, it is weight is balanced by the lift force, and thrust is balanced by a drag force. Both of these forces are aerodynamics nature that is they come, because of the relative motion of the aircraft and the air or the fluid.
Now, if there is any disturbance in the flight of course the moment develops, and the configuration of the aircraft changes. The force coming from the pressure distribution, and viscous stress distribution, and they are distributed over the entire surface of the aircraft. It is not necessarily aircraft it can be any body, which is emerged in fluid. Now, as you know that a distributed force can be represented by a system of force, and moments same thing can be done here also. And, these force and moments, they can be resolved in any three mutual orthogonal directions.
If, we consider these three mutual orthogonal directional like this, particular remember these direction, the let us call it x axis the x axis is along the relative wind. It is along the relative wind that means it is along the direction of the relative velocity between the body and the fluid is neither horizontal nor vertical or anything, it is along the direction of relative velocity between the body and the fluid. So, as an example if we consider that an aircraft is moving in atmosphere, which is at rest then the relative wind is simply the direction of or opposite of the direction of the aircraft speed. So, in that case the x axis is opposite to the direction of the aircraft velocity.
If, an aircraft is flying through an atmosphere at rest, the x axis is along the opposite of the direction of aircraft velocity or aircraft speed. However, in general we will call it is the direction of the relative wind. The x axis is relating the direction relative to the wind. And let us, call at this stage the z axis, which is upward, but not vertical it is normal two of course the x axis, so it is upward, but it is not vertical. Since, x axis is not vertical horizontal the z axis is not vertical, and the y axis is which is perpendicular to the plane formed by x and z.
Usually, for an if we consider the body to be an aircraft, we call it the direction to the right wing, right side of the wing with respect to the pilot, to the right side can be with respect to an observer. The observer may be as in front observer may be behind, so of course the right will change. So, it is right side with respect to the pilot, usually that is called the starboard side. These names came from shipping, where they have the left is usual called the portside, as ships comes in to a port, it is left side usually faces the port towards the port. So, that left side is called the port side, and the right side is called the starboard side.
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