Aeroplanlære - Kap 5 (Stall)

Question 1

What causes a plane too stall?

Answer 1

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

Question 2

How do we unstall an airplane?

Answer 2

By reducing angle of attack

Question 3

Describe the 4 different parts on the model

Answer 3

Question 4

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

Answer 4

Yes

Question 5

How does the stall angle change with wing aspect ratio?

Answer 5

High aspect ratio stalls at a lower angle of attack

Question 6

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

Answer 6

Question 7

Where does a rectangular wing stall first and last?

Answer 7

1. Wing root
2. Mid span
3. Wing tip

Question 8

Where does a tapered wing stall first and last?

Answer 8

1. Mid span
2. Wing root
3. Wing tip

Question 9

Where does an elliptical planform wing stall first and last?

Answer 9

1. Wing root and mid span
2. Wing tip

Question 10

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

Answer 10

1. Wing tip
2. Mid span
3. Wing root

Question 11

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

Answer 11

We can install a wing fence or vortillion

Question 12

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

Answer 12

Use notch or washout

Question 13

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

Answer 13

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

Question 14

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

Answer 14

Increase the sharpness of the leading edge

Question 15

How does wing loading affect stalls?

Answer 15

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

Question 16

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

Answer 16

Increase

Question 17

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

Answer 17

Decrease

Question 18

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

Answer 18

Increase but produce less lift than trailing edge flaps does

Question 19

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

Answer 19

The side with the down going aileron

Question 20

Which effect does the weight have on stalling?

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

70 kts

Question 23

What does slats and flaps do to our Clmax?

Answer 23

They increase it

Question 24

What does slats and flaps do to our stalling tendencies?

Answer 24

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

Question 25

What is Vsi?

Answer 25

Question 26

What is Vs0?

Answer 26

Question 27

Which effect does landing gear have on stalling speed?

Answer 27

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

Question 28

Which effect does propellers have on lift?

Answer 28

There is increased lift in the area with propeller slipstream

Question 29

Which effect does jets have on lift?

Answer 29

Lift is reduced by vertical component of thrust

Question 30

Which effect does CG have on lift?

Answer 30

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

Question 31

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

Answer 31

Straight wing since it occurs more rapidly

Question 32

Which effect does contamination of wings have on stalling speed?

Answer 32

Question 33

How do we recover from an accelerated stall?

Answer 33

Reduce angle of attack

Question 34

How do we calculate stall speed in turns?

Answer 34

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:

Question 35

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

Answer 35

53,7 kts

Question 36

How do we unstall a wing?

Answer 36

Reduce angle of attack

Question 37

When does a wing stall?

Answer 37

When it exceeds its stalling angle of attack

Question 38

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

Answer 38

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

Question 39

Which effect does CG have on spin steepness?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

How do you prevent a spin?

Answer 42

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

Question 43

Which phases does a spin consist of?

Answer 43

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

Question 44

How do you recover from a spin?

Answer 44

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

Question 45

Is a spiral dive a stalled condition?

Answer 45

No

Question 46

How do you recover from a spiral dive?

Answer 46

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

Question 47

What increase in a spiral dive?

Answer 47

Airspeed and load factor

Question 48

Which stall warnings are there in a level flight?

Answer 48

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

Question 49

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

Answer 49

Question 50

On a swept wing, what are the stall warnings?

Answer 50

Question 51

Which artificial stall warning systems do we have?

Answer 51

Question 52

What can help a pilot decide the angle of attack?

Answer 52

An angle of attack sensor

Question 53

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

Answer 53

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

Question 54

Name 3 AoA indicators:

Answer 54

1. The AoA vane 2. AoA probe 3. Rotating probe

Question 55

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

Answer 55

An audio warning

Question 56

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

Answer 56

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

Question 57

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

Answer 57

Question 58

How do you recover from a stall?

Answer 58

Question 59

What is Vsw?

Answer 59

Velocity for stall warning Greater than 5 kts or 5%