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POF > Stalling > Flashcards

Stalling Flashcards

1
Q

Reducing IAS does what do CL

A

CL need to increase to maintain level flight

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2
Q

Straight Wing Stall

A

Distinct Symptoms (nose drop/buffering)

  • Lift reduces
  • Total drag much greater from large increase in form drag
  • CP moves aft
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3
Q

You stall what you gonna do

A

REDUCE AOA
DO NOT USE AILERON OR RUDDER UNTIL YOU UNSTALL

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4
Q

Factors Contributing To Wing Drop

A

Manufacturing differences between each wing
Small Lateral imbalances in lift prod
Loss of lift at tip rather than root (moment)

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5
Q

Ellipetical Wing Stall Category

A

Same vortex spanwise = same downwash spanwise
All area of wing working equally as hard

! Sudden stall - controls become ineffective quickly
! Large roll rates

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6
Q

Stalling With Tapered Wings

A

Mid section vortex least so least downwash here (greatest EAOa at mid section)
Stall starts in mid section
Not as bad as Ellipetical wing

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7
Q

Stall With Swept Wing

A

Less vortices at tip - EAOA greatest at tip
Tip will stall first
CP moves forward and inwards
AC pitches further up (Deep stall)
Increased Downwash on tailplane adding to the deep stall conditions

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8
Q

Deep Stall

A

Wake of wing impinges tail surfaces making them ineffective

Worse on high T tail planes
A/C with sweepback wings

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9
Q

Anti Stall Devices

A

Vortilon - Generate vortex to help spanwise flow
Wing Fence - Physical barrier to spanwise flow
Reduce camber/washout towards tip to reduce local CL and prevent tip stall
Cross Section - Thicker more progressive inboard stall
Nacelle Stakes - Located on engine tight vortex to reenergise
Stall Strips - Used on tip to sharpen LE at root

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10
Q

Wing Loading on stall speed

A

Greater Wing Loading = Higher Stall Speed
Lower Wing Loading = Lower Stall Speed

Weight/area

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11
Q

Flaps/Slats on Stall Speed

A

CLMAX increased + VS speed decreases
LE - Increase stalling Angle
TE - Reduce Stalling Angle
Slates/Slots - Increase delaying flow separation to higher AOA

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12
Q

Measures to delay flow separation

A

Vortex Generators
Engine nacelle strakes (lift vanes)

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13
Q

Sharper vs Larger radius leading edge

A

Sharper LE the tighter the radius of turn more energy consumed

Large radius from LE less energy loss by flow

Stagnation point moves backward onto underside of aerofoil as alpha increases

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14
Q

Critical Angle Of Attack

A

Highest achievable AOA before the stall
No the actual stall
Maximum lift produced at the critical angle
AC will always stall at the same critical angle of attack

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15
Q

Aspect Ratio on stalling angle

A

High aspect ratio produces same lift with less span wise flow/less downwash = shallower effective airflow

High aspect ratio the effective angle of attack = low wing angle of attack

Low aspect ratio produces more span wise flow and more downwash for same lift = small effective angle of attack and therefore stalling angle of attack is much larger

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16
Q

Rectangular Wing on stalling

A

Stalls at the roots first then the tips

Shallower effective airflow at wing root produces a greater effective angle of attack and therefore stalls first

Spread from root to the tip as alpha increases

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17
Q

Why does a sweep back wing pitch up at the stall

A

Wings CP moves forward and inwards
Increased downwash on horizontal stabiliser (inner wing has to produce more lift increasing downwash airflow onto tail)

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18
Q

CS25 Stall Criteria

A

Nose down pitch that cannot be readily arrested
Buffeting of magnitude to deter further speed reduction
Pitch control reaches aft stop no more pitching

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19
Q

Deterrent Buffet

A

Point at which buffet becomes a strong and effective deterrent

Vertical accelerations of 0.5g+

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20
Q

Engine nacelle (Lift vanes)

A

Reduces upwash ahead of wing delaying onset of seperation locally in area of wing influenced by nacelle

Create large vortex over upper surface which reenergises boundary layer locally delaying separation to high alpha

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21
Q

Cross section on stalling

A

Sharper thinner leading edge stalls more sudden (high-speed wing)

High-thickness chord ratio with greater leading edge has a more gradual stall

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22
Q

VS1

A

Minimum steady flight speed in obtained config

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23
Q

VS0

A

Stall speed in landing config

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24
Q

EASA regs for MEP aircraft in class B

A

VR = 1.1vs1
T/O Screen = 1.2vs1
L/D(vref) = 1.3vs1

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25
Q

EASA regs for stall speeds in class A

A

VR = 1.1vs1
VSRI (T/O Screen) = 1.13VSR1
VSRD (Landing) = 1.23VSRD

10%
13%
23%

26
Q

EASA C25 Reg for stall warning speed

A

VSW must be 5kt or 5% greater

27
Q

What happens towards the stall

A

AOA is increasing
Stagnation point moving rearward
Kinetic energy airflow over the wing is reducing
Seperation point moving forward
Adverse pressure gradient increasing

28
Q

What causes a swept wing to pitch up at the stall

A

Roots are having to generate more lift are tips have stalled
More downwash on tailplane
Increasing AOA on horizontal tailplane
Increased downforce
Causing nose to pitch up

29
Q

Swept wing “pitch up” phenomenon

A

Cp moves forward with AOA
Beyond critical AOA CP continues to move forward due to swept wings stalling at tips
Further nose up pitch

30
Q

Centre of pressure of straight wing at stall

A

CP moves forward with AOA
Beyond critical AOA the CP moves aft
Nose down pitch moment

31
Q

Swept Wing CP movement at stall

A

Swept wing moves forward with AOA
Beyond critical AOA keeps moving forward
Further nose up pitch

32
Q

Common method to reduce tip stalling

A

Modify cross section
Washout and reduced camber at tips to reduce local CL

33
Q

Landing Gear effect on stall speed

A

Extension increases stall speed
Creates a drag force which forms an arm with CG causing a nose down pitching moment

Increased downforce produced by tailplane the counter so more lift needed

Speed needs to be increased

34
Q

Where are stall speed determined

A

With the least favourable cg position.
The most forward cg limit
This leads to downwards force which needs to be compensated for
Higher stall speed at aft cg

35
Q

How are minimum controls speed determined (conditions)

A

Cg on aft limit will provide small arm and least ability to oppose yawing moments on engine failure

36
Q

Flapper Switch

A

Mounted on LE - on/off device that activates audio warning when AOA exceeds set value

Works by:
AOA increasing stagnation point moves down and aft once stagnation point is behind flapper switch airflow pushes flapper switch into its up position

37
Q

AOA Vane

A

Pivots around its own axis to align with airflow
Angle is detected relative to longitudinal axis electrically
Processed by computer to give a calculated wing AOA and provide continuous display of aoa and trigger warning on approach to stall

38
Q

Fixed Prob Stall warner

A

Two ports which measure pressure
When aoa increases airflow into each port differs
Different pressure sensed at each port sent to computer to determine AOA

Works even if pitot tube freezes

39
Q

Rotating Probe

A

Probe with two ports that rotates to null out pressure difference at both ports. Orientation is then measured by computer to calculate wing AOA.

40
Q

Stick Shakers Role

A

At computed AOA stick shaker forcefully vibrate control yoke to stimulate light buffet in ac with no natural buffet

Operates until pilot reduces AOA

41
Q

Low Mounted Engine hazards at the stall

A

Below ac CG therefore full power at the stall could pitch up

42
Q

CS23 Stall Measured by

A

Engines at idle/throttle closed
CG at max stall speed - forward limit and max mass

43
Q

Vr

A

Speed at which pilot begin to apply control input on T/O

1.1 x vs1

44
Q

VToss (50ft)

A

Speed you must be at 50ft after take off

1.2 x VS1

45
Q

VREF

A

Landing speed
1.3 x VS0

46
Q

Minimum speed at 35ft after take off on CS25

A

1.113 x VSR1

47
Q

Minimum landing speed C25

A

Referred to as Vref

1.23 x vs0

48
Q

CS23 Single engine Vr speed

A

For must not be less than VS1

49
Q

CS23/25 rules for stall warning speeds

A

Must be activated 5kt or 5% above relevant stall speed and operate until above the limit

50
Q

Airbus 3 AOA protection systems

A

Alpha protection
Alpha Floor
Alpha Maximum

51
Q

What do you do if you experience buffeting after lowering the flaps

A

Return flaps to previous setting

52
Q

Vne

A

Never exceed speed used on smaller ac - CS23

53
Q

Vmo

A

Maximum operating speed/maximum operating Mach number - used on cs25

54
Q

Vmc

A

Minimum control speed - calibrated airspeed of ac below which directional or lateral control of ac can no longer be maintained after failure of one engine.

Maintain straight flight with bank angle of no more than 5 degrees with max thrust on engine

55
Q

Vmca established conditions

A

Max take off power
Aeroplane trimmed for takeoff
Unfavourable CG position
Max seal level take off weight
Critical take off config (gears ups)
Ground effect negligible

56
Q

Washout

A

To stall the root first

57
Q

3 AOA protections in normal Law of a320

A

Alpha protection
Alpha floor
Alpha maximum

58
Q

Power increase from idle in stall will do what to clmax and the stall speed

A

CLMAX unchanged

Stall speed will decrease

59
Q

Angle of sweep on stall speed

A

Swept wing less efficient at producing lift than straight wing therefore as cl decreases speed must increase.

Decrease in clmax from swept wing increases the stall speed

60
Q

Vortilons

A

Fixed aerodynamic devices on ac winds to improve handling at low speed - energises the boundary layer over the wing turbulent flow

Usually fitted under the wings leading edge

Help improve aileron performance at high AOA also

61
Q

What does weight do to critical alpha

A

No effect on critical alpha only the design of the wing will change the critical alpha

POF (25 decks)

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