12.6.46. Identify the approximate angle for best L/D ratio.

 The best L/D ratio is at about 4deg angle of attack on most general purpose wings.
Because most light aircraft don’t have angle of attack indicators the only way of knowing that you are operating at the best L/D ratio is to use the airspeeds recommended by the manufacturer.

12.6.44. Describe a typical curve of lift/drag (L/D) ratio versus angle of attack for an asymmetrical aerofoil. 

The Lift to Drag Ratio is the ratio of lift produced to drag created at any given angle of attack.
The maximum lift to drag ratio occurs at the most efficient angle of attack.
The lift to drag ratio increases up to approx 4 deg angle of attack and then decreases as the angle of attack is increased further. (graph)

12.6.42. Identify curves of parasite, profile, induced and total drag versus aerofoil airspeed.

++Diagram++
Parasite drag increases with indicated airspeed – it is proportional to the square of the indicated airspeed
Induced drag decreases with increasing airspeed – it is proportional to 1/IAS squared.

12.6.40(b) . aspect ratio. 

Induced drag decreases as aspect ratio increases.

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