1. Aerodynamic Theory Review 2
ATC Chapter 6

2. Aim
To review turning and aircraft speed limitations

3. Objectives State the forces acting in a turn
Define rate and radius of turn
Describe overbanking tendency
Define adverse aileron yaw and state design features to minimise it
Define ‘V’ code airspeeds and explain how they relate to aircraft operation

4. 1. Forces acting in a turn
What are the forces acting on the aircraft during S+L?
As AoB is increased the lift vector is tilted
Lift
Lift
1) Weight acts down towards the earth.
2) Drag acts to pull the aircraft back. R1 = W + D.
3) If we recall the definition of a climb the aircraft is still in equilibrium, therefore there must be a force equal an opposite to R1... R2.
4) R2 = L + T.
5) But T > D. Some other force must also be acting to pull the aircraft back down.
6) Weight can be divided into W1 and a rearward component of weight (RCW) – consider a car rolling backward down a hill...
7) T = RCW + D.
8) But L is also < W so how does the aircraft climb?
9) Some other force must also be acting to pull the aircraft up vertically  Thrust.
10) So climb performance depends on excess thrust  power available. Consider a rocket, it has no wings but can still climb  or consider tilting the lift vector back until the aircraft is climbing due to thrust alone  F/A 18 Hornet.
11) We use full power in light aircraft to climb.
Weight

5. 1. Forces acting in a turn
This creates a vertical and horizontal component of lift (centripetal force), we can see however that the vertical component of lift is no longer equal to weight
In order to maintain level flight we must increase our total lift, this increases both the vertical and horizontal components of lift LH
Lift Lv
Centrifugal Force
1) Weight acts down towards the earth.
2) Drag acts to pull the aircraft back. R1 = W + D.
3) If we recall the definition of a climb the aircraft is still in equilibrium, therefore there must be a force equal an opposite to R1... R2.
4) R2 = L + T.
5) But T > D. Some other force must also be acting to pull the aircraft back down.
6) Weight can be divided into W1 and a rearward component of weight (RCW) – consider a car rolling backward down a hill...
7) T = RCW + D.
8) But L is also < W so how does the aircraft climb?
9) Some other force must also be acting to pull the aircraft up vertically  Thrust.
10) So climb performance depends on excess thrust  power available. Consider a rocket, it has no wings but can still climb  or consider tilting the lift vector back until the aircraft is climbing due to thrust alone  F/A 18 Hornet.
11) We use full power in light aircraft to climb.
Centripetal Force
Weight

6. 1. Forces acting in a turn
Equal and opposite to our lift is the load factor
Equal and opposite to our centripetal force is the centrifugal force LH
Lift Lv
Centrifugal Force
1) Weight acts down towards the earth.
2) Drag acts to pull the aircraft back. R1 = W + D.
3) If we recall the definition of a climb the aircraft is still in equilibrium, therefore there must be a force equal an opposite to R1... R2.
4) R2 = L + T.
5) But T > D. Some other force must also be acting to pull the aircraft back down.
6) Weight can be divided into W1 and a rearward component of weight (RCW) – consider a car rolling backward down a hill...
7) T = RCW + D.
8) But L is also < W so how does the aircraft climb?
9) Some other force must also be acting to pull the aircraft up vertically  Thrust.
10) So climb performance depends on excess thrust  power available. Consider a rocket, it has no wings but can still climb  or consider tilting the lift vector back until the aircraft is climbing due to thrust alone  F/A 18 Hornet.
11) We use full power in light aircraft to climb.
Centripetal Force
Load Factor
Weight

7. 1. Forces acting in a turn In summary: L > W Lv = W L = Load Factor
Centripetal force = Centrifugal force LH
Lift Lv
Centrifugal Force
1) Weight acts down towards the earth.
2) Drag acts to pull the aircraft back. R1 = W + D.
3) If we recall the definition of a climb the aircraft is still in equilibrium, therefore there must be a force equal an opposite to R1... R2.
4) R2 = L + T.
5) But T > D. Some other force must also be acting to pull the aircraft back down.
6) Weight can be divided into W1 and a rearward component of weight (RCW) – consider a car rolling backward down a hill...
7) T = RCW + D.
8) But L is also < W so how does the aircraft climb?
9) Some other force must also be acting to pull the aircraft up vertically  Thrust.
10) So climb performance depends on excess thrust  power available. Consider a rocket, it has no wings but can still climb  or consider tilting the lift vector back until the aircraft is climbing due to thrust alone  F/A 18 Hornet.
11) We use full power in light aircraft to climb.
Centripetal Force
Load Factor
Weight

8. 2. Define Rate & Radius Rate of Turn Radius of Turn
Alteration of HDG per unit time
Rate 1 = 360o/2min  3o/sec
Radius of Turn
Distance from centre of turn to the aircraft

9. 2. Define Rate & Radius Rate of Turn 1091 x tanƟV
Rate of Turn = (Degrees/Second)
Velocity increases, Rate decreases
AoB increases, Rate increases

10. 2. Define Rate & Radius Radius of Turn V2____ Radius of Turn = (Feet)
11.26 x tanƟ
Velocity increases, Radius increases
AoB increases, Radius decreases

11. Outer wing vs. inner wing
3. Overbanking Tendency
Outer wing vs. inner wing
Outer wing travels a further distance in the same time as inner wing
Faster speed = More lift = Overbanking
L = CL . 1/2.ρ.V2 . S

12. 4. Adverse Aileron Yaw Definition
When the aileron on the up going wing is deflected it creates more lift, it also creates more drag
This imbalance in drag causes the nose of the aircraft to yaw in the opposite direction to the roll
Adverse yaw only occurs when the ailerons are deflected
This is why we apply rudder in the same direction when we apply aileron

13. Differential Ailerons
4. Adverse Aileron Yaw
Differential Ailerons
When the control column is rotated the up going aileron travels through a greater arc than the down going
This will increase the drag produced by the up going aileron (which is on the inner wing) and reduce the drag difference between each wing, reducing adverse yaw
Down going aileron- Outer wing
Up going aileron- Inner wing

14. 4. Adverse Aileron Yaw Frise-type Ailerons
The inner edge of the up going aileron protrudes into the airflow beneath the wing, disturbing the airflow resulting in an increase in drag on the inner wing
This increase in drag on the inner wing will reduce the drag difference between each wing, reducing adverse yaw
Down going aileron- Outer wing
Up going aileron- Inner wing

15. Coupled ailerons & rudder
4. Adverse Aileron Yaw
Coupled ailerons & rudder
The rudder is automatically altered when the ailerons are applied
The rudder is deflected to the direction of turn
i.e. Left turn = left rudder
The subsequent yaw in the direction of the turn counters adverse aileron yaw

16. 5. ‘V’ Code Airspeeds What is the ‘V’ Code?
A standard terms used to define airspeeds important to the operation of all aircraft
Derived from data obtained by aircraft designers and manufacturers during flight testing
Specific to a particular model of aircraft
Expressed in terms of the aircraft's indicated airspeed
Commonly used and most safety-critical airspeeds are displayed as color-coded arcs and lines located on the face of an aircraft's airspeed indicator

17. 5. ‘V’ Code Airspeeds Definitions VNE – Never Exceed Speed
VNO – Maximum speed for normal operations
VF – Flap Speed
VFE – Maximum flap extended speed
VFO – Maximum flap operation speed
VS – Stall Speed
VS0 – Stall speed in the landing configuration
VS1 – Stall speed in the cruise configuration
VX – Maximum angle of climb speed
VY – Maximum rate of climb speed
VA – Maximum manoeuvring speed
VB – Maximum turbulence penetration speed
VLO – Maximum landing gear operation speed

18. VNE – Never Exceed Speed
5. ‘V’ Code Airspeeds
VNE – Never Exceed Speed
Maximum speed under any circumstances
Displayed on the airspeed indicator as a red line
Situations that may result in the aircraft exceeding this speed:
High speed descent
Spiral Dive

19. VNO – Maximum speed for normal operations
5. ‘V’ Code Airspeeds
VNO – Maximum speed for normal operations
Maximum speed for normal operations
This speed may only be in smooth air and when justified by operational requirements
Displayed on the airspeed indicator where the green arc changes to the yellow arc
Situations that may result in the aircraft exceeding this speed:
High speed descent
Spiral Dive

20. 5. ‘V’ Code Airspeeds VF – Flap Speed
VFE – Maximum flap extended speed
This limit is to prevent overstressing the flap structure
Displayed on the airspeed indicator at the higher end of the white arc
Situations that may result in the aircraft exceeding this speed:
Too Fast on approach
Not retracting the flaps after take off (if deployed)
Not retracting the flaps in the event of a go-around

21. 5. ‘V’ Code Airspeeds VF – Flap Speed
VFO – Maximum flap operation speed
This speed limit is only applicable when the flaps are in motion
This airspeed limitation is not displayed on the airspeed indicator
Airspeed is found in the pilot operating handbook
Situations that may result in the aircraft exceeding this speed:
Not knowing the speed limitation
Not checking the speed prior to deploying the flaps

22. 5. ‘V’ Code Airspeeds VS – Stall Speed
VS0 – Stall speed in the landing configuration
This is the lowest speed permissible in level flight in the landing configuration
There are a number of certification limits under which the stall speed for an aircraft is tested and certified to:
MTOW
Most forward CoG
Power Idle 1G
Flaps Retracted
This airspeed limitation is displayed on the airspeed indicator at the lower end of the white arc
Situation that may result in the aircraft slowing to less than Vs0:
The flare

23. 5. ‘V’ Code Airspeeds VS – Stall Speed
VS1 – Stall speed in the cruise configuration
This is the lowest speed permissible in level flight
There are a number of certification limits under which the stall speed for an aircraft is tested and certified to:
MTOW
Most forward CoG
Power Idle 1G
Flaps Retracted
This airspeed limitation is displayed on the airspeed indicator at the lower end of the green arc
Situation that may result in the aircraft slowing to less than Vs0:
Climb

24. VX – Maximum angle of climb speed
5. ‘V’ Code Airspeeds
VX – Maximum angle of climb speed
The speed, during a climb, that gives the best altitude gain for the shortest horizontal distance
This is the lowest climb speed that is used
This speed is achieved at the maximum surplus between thrust available and thrust required
This airspeed is not displayed on the airspeed indicator
Airspeed is found in the pilot operating handbook
Situations that may require this climb speed:
To clear obstacles after take off
Make an ATC requirement

25. VY – Maximum rate of climb speed
5. ‘V’ Code Airspeeds
VY – Maximum rate of climb speed
The speed, during a climb, that gives the best altitude gain for the shortest time
This is the climb speed that is primarily used
This speed is achieved at the maximum surplus between power available and power required
This airspeed is not displayed on the airspeed indicator
Airspeed is found in the pilot operating handbook
Situations that may require this climb speed:
Normal take off
Change in altitude

26. VA – Maximum manoeuvring speed
5. ‘V’ Code Airspeeds
VA – Maximum manoeuvring speed
The highest speed at which full control deflection will not overstress the aircraft
At or below VA the aircraft will stall before structural damage
This airspeed is not displayed on the airspeed indicator
Airspeed is found in the pilot operating handbook
Situations that may result in the aircraft exceeding this speed:
Spiral dive
Uncorrected undesired aircraft states

27. VB – Maximum turbulence penetration speed
5. ‘V’ Code Airspeeds
VB – Maximum turbulence penetration speed
The highest speed permissible in turbulent air to avoid overstressing the aircraft
Fast enough to prevent a gust causing a stall
This airspeed is not displayed on the airspeed indicator
Airspeed is found in the pilot operating handbook
Situations that may result in the aircraft exceeding this speed:
Not aware of weather conditions conducive to turbulence
Not reducing speed in turbulence

28. VLO – Maximum landing gear operation speed
5. ‘V’ Code Airspeeds
VLO – Maximum landing gear operation speed
This speed limit is only applicable when the landing gear is in motion
This airspeed limitation is not displayed on the airspeed indicator
Airspeed is found in the pilot operating handbook
Situations that may result in the aircraft exceeding this speed:
Not knowing the speed limitation
Not checking the speed prior to deploying the landing gear

29. Questions?