12.6.40(a) . angle of attack of the aerofoil;
Induced drag increases with an increase in the angle of attack.
In level flight as an aircraft slows down, the angle of attack must be increased to maintain height. Therefore as airspeed decreases and angle of attack increases, induced drag increases to be maximum at the stalling angle of attack.
In manoeuvres such as steep turns where angle of attack is increased, induced drag also increases.
12.6.40. Explain how induced drag varies depending on:
12.6.38. State the factors affecting parasite drag, and profile (form and skin friction) drag.
Skin Friction
The basis of skin friction drag is the viscosity of the air “stickiness” . In flight, a relatively thin layer of air sticks to all of the exposed surfaces
The degree of skin friction drag generated depends on:
– the surface area of the aircraft
– how rough the skin is – damaged/ contaminated surfaces
Form drag:
This is the difference in air pressure in front of the aerofoil and the turbulent wake to the rear
– the greater the turbulent wake, the greater the form drag
– at and beyond the stalling angle the form drag increases massively
Interference Drag:
This is part of parasite drag – where there is interference or mixing of converging airflows at the junctions of various surfaces eg wing / fuselage junctions or wing / engine junctions
12.6.36. List the elements of profile drag.
Profile Drag comprises:
Skin Friction
Form Drag
12.6.34. Distinguish between induced drag, parasite and profile drag.
Induced Drag:
Induced drag is the drag force directly associated with the production of lift which arises from the generation of wingtip and trailing edge vortices
Parasite Drag:
Parasite drag comprises skin friction, form drag and interference drag
Skin friction and form drag are sometimes referred to under the heading of profile drag. (Diagram drag tree )
12.6.32. State the precaution against flying with ice, frost, snow or other contamination of the aerofoil surfaces.
The lifting ability of the wings is significantly reduced by the presence of snow, frost, ice, bird poop, insect remains on the leading edges and upper surfaces
The smooth airflow over the aerofoil is disrupted and results in higher stalling speeds, reduced lift and increased drag
12.6.30. On a typical CL versus angle of attack curve, identify the critical stalling angle.
When the flaps are put down the effective camber of that part of the wing is increased
The effect is to increase the lifting capability of the wing as a whole
(see additional notes)
12.6.28. Describe a typical CL versus angle of attack curve (graph).
On the graph the CL and angle of attack are proportionate until the stalling range is reached at a maximum angle of attack
12.6.26. Identify the primary factors determining the coefficient of lift (CL) for an aerofoil.
The combined effect of the shape of the aerofoil and its angle of attack is represented by the CL
The higher the value of CL the greater the lifting capacity of the aerofoil
12.6.24(b) . summarise the factors affecting lift. (i.e. angle of attack, aerofoil shape, IAS)
Lift is affected by :
The shape of the aerofoil (High lift v High Speed)
The speed and direction of the airflow over the wing.
The angle of attack.
The size (plan area) of the wing.
The density of the air.
From a practical point of view, in a given aircraft lift is related to:
Angle of Attack
The shape of the aerofoil (both design and flaps etc)
Indicated Airspeed.