# Aerodynamic Theory Review 2

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Aerodynamic Theory Review 2
ATC Chapter 6

Aim To review turning and aircraft speed limitations

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Questions?