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PPL > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

Stagnation Point

A

Point at which air cannot decide whether to pass under or over the aerofoil

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2
Q

Constant Total Pressure

A

Constant Total Pressure = Static pressure + Dynamic Pressure

As static pressure increases, dynamic pressure decreases and vice versa

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3
Q

Affect of Temp on Air Pressure

A

As temp increases, total air pressure and density decrease

As temp decreases, total air pressure and density increase

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4
Q

Lift Formula

A 
L = Cl x r/2 x V^2 x S
Cl = AoA + camber
r = air density
v = velocity
S = surface area
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5
Q

Ways of Increasing Lift

A

Increase camber, velocity and AoA

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6
Q

Centre of Pressure

A

The point at which lift acts from, which moves along the chord line as the AoA varies
If AoA increases, the centre of pressure moves forwards

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7
Q

Parasite Drag

A

Caused by movement of the aircraft through the air

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8
Q

Types of Parasite Drag

A

Form: Shape
Interference: Where surfaces meet
Skin Friction: air passing over a surface
Cooling: engine cooling

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9
Q

Induced Drag

A

Caused by the creation of lift

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10
Q

Wingtip Vortices

A

Results from span wise flow

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11
Q

Span Wise Flow

A

Results in airflow above the wing moving towards the wing root and below the wing moving towards the wing tip

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12
Q

Wake Turbulence

A

Due to wingtip vortices

Can be destroyed by wind

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13
Q

Ways to Reduce Induced Drag

A
  1. Wing tapering: smaller wingtip chord line and therefore smaller wingtip vortices
  2. Aspect ratio: a measure of an aircrafts wing span to its wing chord, increased aspect ratio wings produce increased lift for decreased drag
  3. Washout: the ‘angle of incidence’ at the wing root is greater than at the wing tip
  4. Wingtip design: design features such as wingtip fuel tanks, winglets and modified wingtips can help to reduce leakage of airflow around the wingtip and reduce induced drag
  5. Wing fences: reduce span wise flow
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14
Q

Lift/Drag Ratio

A

Most efficient L/D ratio

Min amount of drag created for an x amount of lift

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15
Q

Airspeed

A 
Indicated airspeed (IAS)
Calibrated airspeed (CAS): corrected for aircraft equipment errors
True airspeed (TAS): corrected for temp and pressure, aircrafts true speed
Ground speed (GS): TAS with wind allowance, aircraft speed relative to the ground
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16
Q

Stability

A

The tendency of an aircraft to return to its original state, following a disturbance, without any pilot input

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17
Q

Dynamic Stability

A

Unstable and will get further away from the original path

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18
Q

Longitudinal Stability

A

After a disturbance in pitch it returns to the original AoA, without pilot input

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19
Q

Directional Stability

A

After a disturbance in yaw the aircraft returns to the original heading, without pilot input

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20
Q

Improved Longitudinal and Directional Stability

A

Increase surface area or move the centre of gravity forward

21
Q

Lateral Stability

A

After a disturbance in roll the aircraft returns to its original state, without pilot input

22
Q

Improved Lateral Stability

A

Dihedral
Sweepback
High wing/low centre of gravity

23
Q

Stronger Directional Stability Than Lateral Stability

A

After a roll creates a spiral dive

Spiral instability

24
Q

Stronger Lateral Stability

A

Will cause a dutch roll

25
Q

Ground Effect

A

A cushioning effect caused by the air between the wing and the ground
At a height less than approx a wingspan above the surface
Ground surface restricts airflow by:
- reducing up and downwash
- restricting the formation of wingtip vortices (if not formed fully there is little to no induced drag)
As the aircraft takes off it increases in induced drag, decreases in airspeed and increases in lift

26
Q

Ancillary Controls

A

Flaps
Trim
Engine

27
Q

Flaps - Leading Edge Devices

A

Helps to reenergise the smooth airflow over the leading edge of the wing
Provide additional lift at higher AoAs and allows the aircraft to fly slower and at higher AoAs prior to stalling
Eg. Slats, kruger flaps and leading edge flaps

28
Q

Flaps - Trailing Edge Flaps

A

Are mounted on the trailing edge and move together
Increases the camber of the wing, increases the Cl for any AoA and increases drag, reducing airspeed and decreasing stalling angle and speed, and causes a nose down pitching moment
Simple/Plain/Camber Flap
- The rear section of the wing hinges down
Slotted Flap
- A slot is formed between the wing and the flap
- Re-energises airflow
Split Flap
- Forms part of the lower surface of the wing at the trailing edge
- Undesirable feature: creates a sudden decrease in lift
Fowler Flap
- Extends from the wing, increases area and camber of wings, moves rearwards and downwards
When using flap the centre of pressure moves back

29
Q

Trim

A

Relieves pilot of control loads

Creates a small aerodynamic force which holds the elevator in place

30
Q

Forces in a Climb

A

L < W
T = D + Rcw
T > D

31
Q

Types of Climb

A

Normal Climb: Increased visibility, better engine cooling, increased airspeed
Max Rate of Climb (Vy): Best rate, best L/D ratio
Max Angle of Climb (Vx): Avoid Obstacles and controlled airspace

32
Q

Factors Decreasing Climb Performance

A 
Reduced power
Increased weight
Inaccurate airspeed being maintained
Increased air temp
Decreased air density and pressure
33
Q

The Cruise Descent

A

Helps to ensure engine warmth and passenger comfort

34
Q

The Glide Descent

A

Max range and endurance for engine failure
L < W
D + L = W
D = FCW
Performance will vary due to: flaps, weight, inaccurate speed maintenance and wind

35
Q

Forces in a Turn

A

Centripetal force pulls into a turn
Load factor = how hard the wing is working
G-factor = 1 in straight and level flight

36
Q

Range

A

Best range - Vimd (indicated speed for min drag)
When aiming for max range, we are achieving:
- max distance per litre of fuel
- max fuel burn over a given distance
To max, we need to min the fuel burn per mile
- fuel burn/distance = fuel burn per hour/distance per jour = fuel flow/groundspeed
Fuel flow is directly related to power and groundspeed to TAS, so:
- Fuel flow/GS is directly related to Power/TAS
Also power = thrust/drag, so thrust = power/TAS
Min fuel burn means min thrust
Thrust = drag in level flight, max range is achieved by flying at the speed for min drag (best L/D ratio)

37
Q

Endurance

A

With max endurance, we achieve:
- Max time aloft for a given amount of fuel
- A given time in flight for the min amount of fuel
Aiming for min fuel flow
Fuel flow is directly related to power, therefore the best speed for max endurance is the speed for min power

38
Q

Best Range and Endurance

A

Must account for aerodynamics and engines
Normally aspirated engines
- Best range: at full throttle height (power setting gives min drag speed)
- Best endurance: flying as low as possible (when TAS is almost = to IAS, air more dense and therefore less power to maintain IAS
Supercharged Engine
- Best range = high altitude
- Best endurance = flying low

39
Q

Lack of Stability on the Lower Speed Range

A

Between stall speed and min power speed, it is difficult to maintain constant speed
If a gust decreases speed, total drag increases, reducing the speed further, therefore increasing power
If a gust increases speed, opposite applies and decreased power is required
Must be quick on the throttle to maintain airspeed

40
Q

Effects of Changes in Weight On AoA and IAS in level flight

A
  • As weight decreases, less lift is required, therefore IAS decreases by reducing power
  • Or maintain power, decrease AoA and therefore, increase IAS
41
Q

Effect of Altitude On IAS and AoA

A
  • Will be the same (same amount of lift required)

- Same IAS will give increased TAS with Increased altitude

42
Q

Effect of Wind On Endurance and Range

A

On endurance:
- Not affected as time airborne
On range and glide range:
- To achieve max range: fly faster than best range speed to minimise the effect of headwind or fly slower than best range speed to max the effect of a tailwind

43
Q

Power

A

Min power required to keep airborne means: min fuel flow which gives max endurance

44
Q

Thrust

A

Needs to = drag to maintain airspeed
The difference in airspeed before and after the propellor disk, therefore thrust decreases as IAS increases
Max thrust when we have min drag gives max range (min fuel per nm)
Speed that gives max ‘excess’ thrust is max angle of climb

45
Q

Effects of Changes in Weight On Range and Endurance in Level Flight

A
  • As weight decreases and less lift is required we can either decrease IAS by reducing power = greater endurance or decrease AoA while maintaining IAS, drag decreases and therefore range increases
46
Q

Effects of Changes in Weight On Glide Range and Endurance

A
  • Maintain AoA (optimum), therefore decreased weight = decreased lift and IAS to maintain best glide speed (constant), therefore glide range is not affected but with a lower speed rate of descent will decrease, increasing endurance
47
Q

Effects of Changes in Weight on Turn Performance

A

No effect

48
Q

Effect of Altitude On Range and Endurance

A
  • Little effect on range as no affect on drag and thrust
  • Best endurance = maintain a certain IAS, therefore increase TAS required at increased height. As power required depends on TAS, endurance decreases with increased height
  • Fly at the altitude with most favourable wind
49
Q

Effect of Altitude On Turn Performance

A
  • Turn at certain angle of bank and IAS, TAS will increase with height, therefore the radius of the turn increases and it is a lower rate of turn

PPL (4 decks)

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