Angle of Induced downwash

Angle of Induced downwash

Downwash generated through vortex deflects the airflow from horizontal through an angle called as the angle of induced Downwash. This effect not only occurs behind the wing but also impacts the airflow approaching the wing by deflecting in upward from the horizontal through the same angle (ʠ). The resulting airflow is called effective relative airflow and the angle between effective relative airflow and the horizontal is called Ineffective angle of attack.

The resultant lift force which acts perpendicular to the relative airflow is also deflected rear ward through the same angle (ʠ_i). The angle of attack producing this Lift force is called effective angle of attack (ʠ_e) which is the angle between chord line and effective relative airflow. A portion of lift tends to retard the forward motion of the aircraft is called Induced drag which acts horizontally rearwards.

The amount of lift acting vertically upwards is calculated by the effective angle of attack and it is called Effective Lift. If the effective angle of attack is smaller, lift generated is reduced. the amount of lift generated increases from the wing tips in span wise direction.

To recover the lost lift ,angle of attack must be further increased to maintain the effective angle of attack, which also influences the drag component.

Comments

AIRFOIL TERMINOLOGY

Air foil Terminology What is an airfoil? How an air foil is described in modern science, what are the parameters that determines its shape? An Air foil is primary building block of an aircraft which has two edges namely leading edge and trailing edge, the straight line connecting the leading and trailing edge of the air foil is called as chord line. The line which is drawn equidistant from the upper and lower surfaces of the air foil and connecting the leading and trailing edge is called as mean camber line.The distance between the leading and trailing edge is called chord of an air foil. The maximum distance between the mean camber line and chord line is referred as maximum camber. This is one of the variables that determine the aerodynamic characteristics of the wings. Maximum thickness to chord ratio is expressed in terms of percentage. For subsonic wings the ratio is normally 12-14% Depending on the camber (curvature) of the air foil it is d

Form Drag

Form Drag Form drag is experienced in the surface of the aircraft when the streamlined airflow separates and becomes turbulent. To experiment form drag keep a flat plate on the streamlined airflow, now the pressure before the plate is atmospheric and the pressure after it is below the atmospheric which results in sucking effect behind the plate and vortices are formed. It is mandatory to delay the separation point of airflow and this is achieved by altering the shape or streamline of the given object. When the airflow changes its direction rapidly form drag experienced is higher. A fairing is fitted around the fixed undercarriage leg to reduce form drag to considerable extent. The resultant form drag depends on the length and maximum thickness of the streamlined object. The ratio of length to maximum thickness is called the fitness ratio. Fitness ratio = a/b At subsonic speeds fitness ratio of streamlined shapes is

Three dimensional flow around Airfoil

Three dimensional flow around Airfoil When an aircraft is in flight, pressure is not only distributed in chord wise direction but also in span wise direction. Due to span wise distribution of pressure wingtip vortices are created. In atmospheric flight it is the tendency of fluid to move from high pressure area to low pressure area. The same scenario happens when an aircraft is in levelled flight. Pressure of air is lower than atmospheric pressure at upper surface of the wing and higher than atmospheric pressure at the lower surface of the wing. Beyond the wing tips the pressure is normal. This causes the span wise flow of air away from the fuselage on lower surface and an inward flow towards fuselage on upper surface. Now the airflow is on both chord wise and span wise direction. Both meet at trailing edge of the wing, which imparts a twisting motion to the air and series of vortices are formed on the trailing edge. These are known as trailing edge vortices. As the aircraft prop

AEROFORUM

Search This Blog