Stability 😱

Question 1

What increases longitudinal stability

Answer 1

Larger tailplane area

Further forward cg

Question 2

What does reduced stability do to manoeuvrability and controllability

Answer 2

Increases manoeuvrability but reduces controllability

Question 3

Where does the aerodynamic centre need to be for it to be stable

Answer 3

Behind the cg

Question 4

What does forward cg do to drag

Answer 4

Increase trim drag

Question 5

What is absolute AOA

Answer 5

Angle between zero lift line and the raf

Question 6

What is the most significant factor for pitching coefficient

Answer 6

Dynamic pressure

Question 7

What type of gradient will a longitudinally stable aircraft have

Answer 7

Negative

Question 8

What is the most important contributor to longitudinal stability

Answer 8

Tailplane

Question 9

What is the area of the tailplane and the distance from aircraft cg collectively known as

Answer 9

Tail volume

Question 10

What effect does the fuselage have on the stability of a aircraft

Answer 10

Destabilised

Question 11

Do the engine nacelles have a stabilising or destabilising effect

Answer 11

As AOA increases air catches on the lips of the intake = upwards moment = less stable

Question 12

How does cg position in relation to engines affect stability

Answer 12

Closer cg is to engines = less instability

Further away cg is to engines = more instability

Question 13

What is a static margin

Answer 13

Safety margin between the neutral point and aft cg

Question 14

What affect do trailing edge flaps THEMSELVES have on the stability

Answer 14

Stabilise

Question 15

What effect do flaps have on the overall stability of the aircraft

Answer 15

Increase in downwash

= reduced effectiveness at tailplane

= less stable

Question 16

How does flaps affect the neutral point

Answer 16

Flaps extended results in neutral point further forward resulting in reduced longitudinal static stability

Question 17

What is stick position stability

Answer 17

The position you expect the stick to be in for a certain phase of flight

Question 18

What would be a unstable stick position stability

Answer 18

Push forward when you slow down and want to increase AOA

Question 19

Does trim affect stick position stability or over all stability

Answer 19

No

Question 20

What is stick force stability

Answer 20

Size of force required is greater for further distance from trim position

Question 21

What is manoeuvre stability

Answer 21

Having the right amount of control force to produce a given pitch rate

Question 22

What are the risks of light manoeuvre stability

Answer 22

Overstress

Question 23

What is stick force gradient

Answer 23

The amount of extra stick force that must be applied per unit increase in load factor

Question 24

Do airliners have a high or low stick force gradient

Answer 24

High

Question 25

How does cg affect stick force gradient

Answer 25

Bigger if cg is forward

Question 26

How does aerodynamic damping affect stick force gradient

Answer 26

More aerodynamic damping at low level = more stickforce required

Question 27

How does aerodynamic damping work

Answer 27

During manoeuvre = reduces effectiveness of tailplane

Question 28

How does being stick free of stick fixed affect the manoeuvre point

Answer 28

Stick fixed = manoeuvre point further back

Question 29

What is the manoeuvre point

Answer 29

The neutral point adjusted for aerodynamic damping (only during the actual manoeuvre) Always aft of neutral point

Question 30

Is the aircraft more or less stable during a manoeuvre

Answer 30

More stable due to damping

Question 31

Can a aircraft be dynamically stable and statically unstable

Answer 31

No for dynamic stability it must be statically stable

Question 32

How do you work out the degree of dynamic stability

Answer 32

Time taken for oscillations to reduce by half

Question 33

What are short period oscillations

Answer 33

Little variation in height or airspeed Large variations in AOA and load factor

Question 34

What is pilot induced oscillations

Answer 34

Pilot trying to correct for short period oscillations but being behind the aircraft and making it worse

Question 35

What is long period oscillations (phugoid)

Answer 35

Little change of AOA or load factor Large variations in height and airspeed

Question 36

How does altitude affect dynamic and static stability

Answer 36

Altitude decreases static and dynamic stability

Question 37

For directional stability what does a positive gradient mean

Answer 37

Positive directional stability

Question 38

What will a aircraft with positive directional stability do

Answer 38

Yaw into the direction of sideslip

Question 39

What is the biggest contributing factor to directional stability

Answer 39

Fin

Question 40

When will the directional stability yawing moment be stronger

Answer 40

Cg further forward Fin is larger Higher IAS Size of side slip angle

Question 41

How does the shape of the fin affect cl and AOA

Answer 41

Straight fin with high aspect ratio = Higher lower AOA and higher Cl

Question 42

What does a dorsal fin do

Answer 42

Increases directional stability Greater sweepback Lower aspect ratio

Question 43

What does a ventral fin do

Answer 43

Increase directional stability

Question 44

What do strakes do

Answer 44

In slow flight rear of aircraft dips into air = creates ventral fin

Question 45

How does sweep back affect directional stability

Answer 45

One wing is more straight on to airflow = more lift (but more drag) therefor yaws towards raf = more stable

Question 46

What does a fuselage do to stability

Answer 46

Destabilises

Question 47

What does weak lateral stability mean

Answer 47

Slow to recover from wing drop

Question 48

What will happen if you have positive lateral stability during a sideslip

Answer 48

Roll in opposite direction of sideslip

Question 49

What gradient does positive lateral stability have

Answer 49

Negative gradient

Question 50

What affect does a dihedral wing have on lateral stability

Answer 50

Increases it

Question 51

What effect does sweepback have on lateral stability

Answer 51

More stable

Question 52

What effect does High wing have on lateral stability

Answer 52

More stable Centre of pressure moves slightly down the downgoing wing creating a moment

Question 53

What affect does High keel surface have on lateral stability

Answer 53

More stable

Question 54

What is spiral instability

Answer 54

When directional stability is strong Lateral stability is weak

Question 55

What is a Dutch roll

Answer 55

Strong lateral stability Weak directional stability Wing drop = wings level (however more drag with extra lift = yaw in direction of wing drop)

Question 56

What does a aircraft that suffers from Dutch roll require

Answer 56

Yaw damper which inputs rudder to prevent yaw

Question 57

Can you fly with an inoperative yaw damper

Answer 57

No

Question 58

How does altitude affect dynamic stability

Answer 58

Reduces with altitude

Question 59

For a canard where must the AC and neutral point me

Answer 59

Forward or the cg

Question 60

What must you remember when calculating stick force per G

Answer 60

To take of 1G for normal gravity