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EK24 > Aeroplanlære - Kap 5 (Stall) > Flashcards

Aeroplanlære - Kap 5 (Stall) Flashcards

1
Q

What causes a plane too stall?

A

Stall is caused by an excessive angle of attack combined with a low kinetic energy in the boundary layer and a high energy in the adverse pressure gradient which causes separation closer to the leading edge

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2
Q

How do we unstall an airplane?

A

By reducing angle of attack

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3
Q

Describe the 4 different parts on the model

A
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4
Q

Can a cambered aerofoil with negative angle of attack still generate a positive lift coefficient?

A

Yes

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5
Q

How does the stall angle change with wing aspect ratio?

A

High aspect ratio stalls at a lower angle of attack

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6
Q

Why is highly tapered and/or swept wings dangerous to stall with?

A
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7
Q

Where does a rectangular wing stall first and last?

A
  1. Wing root
  2. Mid span
  3. Wing tip
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8
Q

Where does a tapered wing stall first and last?

A
  1. Mid span
  2. Wing root
  3. Wing tip
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9
Q

Where does an elliptical planform wing stall first and last?

A
  1. Wing root and mid span
  2. Wing tip
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10
Q

Where does a tapered and swept wing stall first and last?

A
  1. Wing tip
  2. Mid span
  3. Wing root
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11
Q

What can we install on the wing, to reduce tip stalling tendencies?

A

We can install a wing fence or vortillion

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12
Q

What can we do to the wing, to reduce tip stalling tendencies?

A

Use notch or washout

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13
Q

What is the best place on the wing to stall first?

A

Wing root since stalling the tip affects our ailerons and our ability to manoeuvre

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14
Q

How do we change the aerofoil shape so that the wing root stalls first?

A

Increase the sharpness of the leading edge

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15
Q

How does wing loading affect stalls?

A

Higher wing loading = Higher adverse pressure gradient
This means that flow energy is lost earlier and thereby earlier stall onset

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16
Q

Does slat and slots increase or decrease the AoA which we stall?

A

Increase

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17
Q

Does trailing edge flaps increase or decrease the AoA which we stall?

A

Decrease

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18
Q

Does leading edge flaps increase or decrease the AoA which we stall?

A

Increase but produce less lift than trailing edge flaps does

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19
Q

Which wing stalls first at high angles of attack in a turn?

A

The side with the down going aileron

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20
Q

Which effect does the weight have on stalling?

A

At higher weights the speed must increase to increase lift or we need a higher angle of attack

This results in stalling speed being higher for heavier aircrafts

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21
Q

How do we calculate the stalling speed on a heavier aircraft than our old one, and why is this possible?

A

The wing always stall at the same AoA which is Clmax
Therefore we can calculate the new stalling speed the following way:

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22
Q

What is the new stalling speed if:
Old stall speed = 60 kts
New weight = 1300 kg
Old weight = 950

A

70 kts

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23
Q

What does slats and flaps do to our Clmax?

A

They increase it

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24
Q

What does slats and flaps do to our stalling tendencies?

A

Slats and flaps increase lift which means:
1. The critical angle occurs at slower speeds
2. Lowering flaps reduce stalling speed

25
Q

What is Vsi?

A
26
Q

What is Vs0?

A
27
Q

Which effect does landing gear have on stalling speed?

A

Drag is increased from gear this cause nose pitch down
Downforce on tail result in lift increase
Lower stall speed

28
Q

Which effect does propellers have on lift?

A

There is increased lift in the area with propeller slipstream

29
Q

Which effect does jets have on lift?

A

Lift is reduced by vertical component of thrust

30
Q

Which effect does CG have on lift?

A

Forward CG increase lift since you need more taildown movement and therefore also have more induced drag

31
Q

Which type of wing is easiest to define stall on?
1. Straight wing
2. Swept wing

A

Straight wing since it occurs more rapidly

32
Q

Which effect does contamination of wings have on stalling speed?

A
33
Q

How do we recover from an accelerated stall?

A

Reduce angle of attack

34
Q

How do we calculate stall speed in turns?

A

Calculate square root of load factor and multiply it with the old stall speed

Example with old stall speed at 60 and a 45 degree turn:

35
Q

What is the stall speed in a 30 degree turn with a normal stall speed at 50 kts?

A

53,7 kts

36
Q

How do we unstall a wing?

A

Reduce angle of attack

37
Q

When does a wing stall?

A

When it exceeds its stalling angle of attack

38
Q

What will an aircraft keep doing in a full developed spin?

A

It keeps rolling, pitching and yawing at a stable low speed, if no control inputs are made from the pilot

39
Q

Which effect does CG have on spin steepness?

A

A forward CG will make a steeper spin
A aft CG will result in a flatter spin

40
Q

What kind of spin is the hardest to get out of?

A

A flat spin, since the angle of attack is greater and it has a rapid rate of yaw

41
Q

What kind of mass distribution has the most dominant factor in a spin?

A

Lateral distribution of mass since it results in more roll and less yaw therefore a steeper pitch attitude

42
Q

How do you prevent a spin?

A

If stalling characteristics are felt reduce angle of attack since a spin is a stalled condition

43
Q

Which phases does a spin consist of?

A

Three phases:
1. Incipient spin - Start of spin - Aircraft starts to auto-rotate
2. Fully developed spin - Spin becomes steady
3. Spin recovery

44
Q

How do you recover from a spin?

A
  1. Close the power
  2. Oppose yaw with full opposite rudder
  3. Unstall the wings by pushing the control stick centrally forwards
45
Q

Is a spiral dive a stalled condition?

A

No

46
Q

How do you recover from a spiral dive?

A
  1. Close power lever
  2. Level wings
  3. Gently ease out of the dive
47
Q

What increase in a spiral dive?

A

Airspeed and load factor

48
Q

Which stall warnings are there in a level flight?

A
  1. Controls become sluggish and unresponsive
  2. A high nose Attitude is seen
  3. Might occur buffeting depending on wing profile (Rectangular)
49
Q

What are the classic aerodynamic indications of a stall (Symptoms)?

A
50
Q

On a swept wing, what are the stall warnings?

A
51
Q

Which artificial stall warning systems do we have?

A
52
Q

What can help a pilot decide the angle of attack?

A

An angle of attack sensor

53
Q

What do the T-17 have to indicate a stall and how does it activate?

A

It has a warning light and a sound to indicate stall

It’s activated by a flapper switch when angle of attack is too high and therefore the stagnation point moves behind the flapper switch

54
Q

Name 3 AoA indicators:

A
  1. The AoA vane
  2. AoA probe
  3. Rotating probe
55
Q

What do almost all aircrafts have to warn of a stall?

A

An audio warning

56
Q

What do a stick shaker and stick pusher do when stalling?

A

Stick shaker - Shakes stick
Stick pusher - Pushes stick forward unless yoke is pulled hard back or system is switched off

57
Q

How do you recover after the first indication of a stall?

A
58
Q

How do you recover from a stall?

A
59
Q

What is Vsw?

A

Velocity for stall warning

Greater than 5 kts or 5%

EK24 (29 decks)

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