AERODYNAMICS:forces on a flying body

Its swirling in.Things seems complex from the snap .But obviously this is what is required to make a body fly.
Flight simply implies motion that can be considered in two directions.
1.motion that gives change in position in the horizontal direction or thrust
2.motion that makes the body lift
Thus there are two forces needed for the flight or in other words work has to be done by these forces against some other forces
According to Newton's 3rd law "every action has an equal and opposite reaction".
in this case the reactions are :
1.DRAG:acting in opposite direction
2.GRAVITY: in vertically downward direction

So our primary aim is to MINIMIZE THE DRAG AND REDUCE THE EFFECT OF GRAVITY.




DRAG


Drag can be considered as a kind of friction caused by air on the body.In usual motion on earth ,this air friction or air drag is very minimum amount  and  it is generally not considered.Equation for drag is given below

                                                   
                                             Fd=0.5(density)(velocity^2)(Cd)(area of cross section)

the above equation implies that the drag can be reduced
1.Decrease the density
2.Decrease the velocity
3.Decrease the area of cross section
4.Cd is coefficient of drag and is depended on shape of body and Reynolds(Re) no.The typical curve between Cd and Reynolds no. for a sphere is given below.

The drag for a smooth and rough sphere is given in the above figure.It is found that there is considerable difference in the value of drag at higher velocities for smooth and rough spheres.Reynolds no. increases directly with velocity.

Drag is generally not preferred as it is considered as a loss of input power and thus it has to be minimized for economical and efficient motion of the body.

Of the factors affecting the drag on a body,the changes we can make on the density,speed,cross sectional area is limited.
Density for a particular material body is constant.
Velocity will depend on the purpose of flight.
Area of cross section is also limited to the purpose.

The only factor that can be practically changed is the shape.The shape that is considered most efficient today is the streamline.Here the surface of the body is aligned along the streamlines of the flowing air.This is found to reduce Drag .