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What phenomena causes induced drag?
Induced Drag is an inevitable consequence of lift and is produced by the passage of an aerofoil (e.g. wing or tailplane) through the air. Air flowing over the top of a wing tends to flow inwards because the decreased pressure over the top surface is less than the pressure outside the wing tip.
What will increase the drag of an airfoil?
As a wing moves through the air, the airfoil is inclined to the flight direction at an angle. As the angle increases above 5 degrees, the drag quickly rises because of increased frontal area and increased boundary layer thickness. As an object moves through the air, air molecules stick to the surface.
What type of drag is induced drag?
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it.
What affects induced drag the most?
Induced drag will be at its maximum when airspeed is low, thus with a large angle of attack. It decreases with increasing speed where parasite drag will increase to cumulatively form the total drag of an aircraft.
Why induced drag decreases with speed?
m is larger so v must be smaller if mv/t = total lift. The kinetic energy lost to the wake is 1/2mv^2. So at higher speeds where m is larger and v is smaller the kinetic energy lost in the wake is lower. Therefore induced drag decreases as speed increases.
How does an airfoil in a wind tunnel work?
An airfoil in a wind tunnel cannot cause a net downward movement of the air, because of the bottom wall of the wind tunnel. If the airfoil stretches only part way across the tunnel, there can be a downwash behind the airfoil, balanced by an upwash outside its tips, so that the overall mass continues “straight” along the tunnel, with a swirl in it.
How does boundary layer separation affect aerofoil lift?
If an aerofoil is positioned at a sufficiently large angle of attack, separation will occur very close to the point of maximum thickness of the aerofoil and a large wake will develop behind the point of separation. This wake redistributes the flow over the rest of the aerofoil and thereby significantly impairs the lift generated by the wing.
Why was thinner aerofoils better for laminar flow?
Under laminar flow conditions, increasing the thickness of an aerofoil increases the amount of skin-friction drag ( as shown in last month’s post ), and hence thinner aerofoils were considered to be superior. The situation in Germany changed dramatically during WWI.
Skin-friction drag due to the frictional shear stress between the fluid and the surface, and pressure drag due to flow separation and the existence of a downstream wake. As the total drag is the sum of these two effects, the aerodynamicist is faced with a non-trivial compromise: