22.10.2
Identify and explain the components of total drag.

Total drag is made up of:

• Induced drag
• Parasite drag

         

Parasite drag is made up of 

22.8.18
Define aspect ratio (AR) and describe the effect of AR on CL.

• Wingspan to chord ratio

• Calculated by dividing the wingspan by mean aerodynamic chord
• or span² divided by the gross wing area (A)

• High AR wing produces a higher CL for a given geometric A of A
• High AR wing stalls at a lower geometric A of A 

                         CL vs Geometric Angle of Attack graph

Aspect ratio is the ratio of the wingspan to the chord of the wing. It is used to give a comparison between varying wing shapes. 

Aspect ratio is often measured by span² divided by the gross wing area (A), or wingspan divided by the mean aerodynamic chord. It includes any area ‘cut out’ by the fuselage.

It has an effect on C_L due to the changes in the effective airflow. A high aspect ratio wing will meet its maximum C_L at a lower angle of attack than when compared to a low aspect ratio wing. Although it may have a higher C_L overall compared to a low aspect ratio wing. (see diagram below)

22.8.16
Explain the effect of induced downwash on α

• Created by the wingtip and trailing edge vortices 
• Decreases effective A of A
• Tilts TR rearwards, resulting in a reduction of lift and increased induced drag 

The higher the induced downwash, the smaller the effective angle of attack, the further tilted aft the Total Reaction will be and therefore the higher the induced drag will be.

22.8.14
Describe three-dimensional flow over a wing and explain how wingtip and trailing edge vortices are formed.

• Chordwise flow follows the camber of the wing 
• A third dimensional flow travels the wing span 
• Spanwise flow on top, moves from wing root to wing tip
• Spanwise flow on the bottom, moves from wing tip to wing root 

• Wingtip vortices are caused by the air spilling from high pressure to low pressure around the wing tips
• Trailing edge vortices are caused by airflows meeting at the trailing edge at slightly different angles 

When considering three-dimensional flow over a wing we need to consider spanwise flow. The air under the wing is at a higher pressure than the air on top and therefore air which obeys the gas laws will try to flow from high pressure to low pressure. This sets up a flow around the wing tips from beneath the wing to the top. As the two airflows come together at differing angles a vortex is formed.

22.8.12
With respect to the CL curve, describe the effect of:
(a) increased camber;
(b) surface roughness (e.g. contamination).

• As camber is increased, the wing will produce a higher CL
• As camber is increased, the wing will stall at a lower A of A

• As surface roughness is increased, CLmax is reduced 
• As surface roughness is increased, the stall Angle of Attack is reduced 

An increase in camber will increase C_Lat all normal operating angles of attack

An increase in surface roughness, especially over the first 20-30% of the wing will cause lift to break down at an earlier stage, effectively reducing C_L.

22.8.10
Explain the meaning of a high CLmax.

• Produces more lift over all normal operating angles of attack
• Fly at slower speeds without stalling 
• More manoeuvrable 

All other factors being equal, a wing with a high C_L max will produce more lift than a wing with a lower C_L max. This means the aircraft with the higher C_L max will be able to fly at a lower speed without stalling and has more manoeuvrability 

22.8.8
Given a typical CL versus Angle of Attack curve for a GP (general purpose)-type aerofoil, identify:
(a) the zero lift angle;
(b) the angle for maximum CL (CLmax).

• X-axis = Angle of Attack
• Y axis = CL 
• Zero lift = Less than zero
• Max CL = Top of curve (Approximately 15˚)

               CL vs Angle of Attack Graph for GP type (Cambered) Wing

For a typical training aircraft airfoil the zero lift is typically -4˚

The angle for maximum angle of attack is usually around 16˚

22.8.6
Describe the meaning of the term, coefficient of lift (CL).

Coefficient of lift is a number derived in a wind tunnel, factoring: 

• A given shape of wing
• Angle of Attack

This gives us as pilots an indication of the amount of lift created by an aerofoil.

22.8.4
State the lift formula, and the three basic functions contained within it.

The Lift formula is Lift=C_L1/2 ρ v² S

This can be broken down to:

22.8.2
Identify the factors affecting lift (low-subsonic speed airflow) 

The size of the total aerodynamic reaction depends on a number of factors, these are

• Freestream air density
• Freestream velocity
• Size of the wing: in aerodynamics the plan form area used
• The shape of the wing, both in section and in plan form
• Condition of the surface, whether rough or smooth
• Angle of attack

In practice this can be reduced to three factors, as follows

• The free stream density and velocity are incorporated in the expression for dynamic pressure 1/2 ρ v², which for all practical purposes is IAS.
• The effect of wing area is straightforward. Lift is produced as a result of the pressure differential above and below the wing. The greater the area a given pressure differential can act upon, the greater the lift produced.
• The remaining variables are combined into a single factor called the coefficient of lift (C_L)