Tutorials

Question 1

Notation for coefficient of lift of a) wing b) aerofoil

Answer 1

a) CL
b)Cl

Question 2

Notation for lift and drag of a) wing and b) horizontal tail

Answer 2

a) Lw, Dw
b)Lt, Dt

Question 3

Are pitching moment coefficient notation Cm and CM different?

Answer 3

No, they are used interchangeably

Question 4

What does ε represent

Answer 4

the downwash angle behind the wing, i.e. the angle by which the airflow is deflected behind a wing due to the effects of vortices

Question 5

What is the angle of incidence, i?

Answer 5

The angle between the chord line of the wing where the wing is mounted to the fuselage, and a reference axis along the fuselage

Question 6

What is xac,w?

Answer 6

The wing aerodynamic centre location from the wing leading edge

Question 7

What is xcg?

Answer 7

The location of the centre of gravity from the leading edge of the aircraft

Question 8

How are wing reference area, wing span, and mean aerodynamic chord denoted?

Answer 8

S or Sw
b
Cbar

Question 9

What symbols correspond to a) ailerons, b) elevators, and c) rudders

Answer 9

a) ξ (xi)
b) η (eta)
c) ζ (zeta)

Question 10

What are the sign conventions for control surface movement?

Answer 10

1) positive aileron=> port wing down
2) Positive elevator=>nose down
3)positive rudder=>nose to port

Question 11

Which side is port and which is starboard

Answer 11

port=left
starboard=right

Question 12

What rotation does a) elevator, b) ailerons, c) rudder provide

Answer 12

a) pitch
b) roll
c) yaw

Question 13

Where is the body fixed coordinate system centred?

Answer 13

At the centre of gravity of the aircraft

Question 14

Is centre of gravity fixed?

Answer 14

No it moves as payload changes, fuel is consumed and as other factors changes

Question 15

The simplest trim condition is straight and level flight, what does this mean?

Answer 15

The forces are balanced and the moments about the CoG sum to zero. Accelerations and angular accelerations are all zero.

Question 16

Which surface most strongly influences longitudinal trim

Answer 16

The elevator

Question 17

What is the best way to begin discussing airplane trim and stability?

Answer 17

With quasi-static analysis:
pitching moment about CoG is first considered, followed by the changes in pitching moment generated when the vehicle changes pitch

Question 18

What does quasi-static mean

Answer 18

Unsteady aerodynamic and inertial effects are neglected

Question 19

When is an aircraft said to be statically stable?

Answer 19

When the direction of the moment is restorative.

Question 20

When is an aircraft said to be neutrally stable?

Answer 20

When no moment is produced

Question 21

When is an aircraft said to be statically unstable?

Answer 21

When the moment produced further increases the angle of attack

Question 22

Where is the aerodynamic centre usually positioned?

Answer 22

1/4 aft of the leading edge

Question 23

What happens as CoG moves forward and why

Answer 23

the longitudinal static stability increases because:
a) the moment arm of the horizontal stabiliser increases
b) the contribution of the wing

Question 24

Where is the most convenient place to locate lift, drag, and moment?

Answer 24

Aerodynamic centre

Question 25

Define longitudinal static stability

Answer 25

It characterises the initial tendency of an aircraft to return to equilibrium after a pitch disturbance

Question 26

Where is the trim point for a longitudinally marginally stable aircraft

Answer 26

Cm,cg=0

Question 27

What 2 conditions have to be satisfied for an aircraft to be longitudinally statically stable? (numerical)

Answer 27

Cm,0 = Cm,α|α=0 > 0 and 2) Cmα < 0.

Question 28

How can CLw be determined

Answer 28

CLαw*αw
WHere CLαw is the slope of the lift curve and αw is wing angle of attack

Question 29

What are the two conditions for static stability? (wordy+numerical)

Answer 29

Cm,αw = dCm,cg,w/dαw < 0, meaning aerodynamic centre must lie aft of the centre of gravity, i.e.
xcg-xac,w < 0
Cm,0w > 0, this requires a negative-cambered airfoil section or a an airfoil section that has a reflexed
trailing edge.

Question 30

If the eigen values are complex (have real and imaginary) and real is minus what do you say about free response

Answer 30

damped sinusoid

Question 31

Comment on the impact of the short- and long-period longitudinal modes on aircraft handling
and pilot workload.

Answer 31

[Emily’s made up answer couldn’t find answers] If short period is unstable pilot will be unable to correct it.. tbc

Briefly explain, using diagrams if appropriate, the effect of varying the centre of gravity
position on the longitudinal dynamic stability.
5) Discuss, using examples as appropriate, the implications of flying qualities on the design
of aircraft

Question 32

What type of flow does a) a canard and b) an aft tail experience?

Answer 32

a) upwash flow
b) downwash flow

Question 33

Is it correct to assume elliptical lift distribution for an aft tail?

Answer 33

Yes

Question 34

What is the efficiency equation for the horizontal tail?

Answer 34

Ratio of dynamic pressure at the tail to dynamic pressure at the wing
η=(ρVt^2)/(ρVw^2)
Where Vt=velocity at tail
Vw= velocity at wing

Question 35

Cm0 is negative for an aerofoil with positive camber. How can an aft tail be used to create a positive Cm0 for the whole aircraft?

Answer 35

By ensuring it is properly designed to change the overall Cm0 to be positive, and Cmα is negative. This ensures static stability.

Question 36

2 advantages and 1 disadvantage of a canard

Answer 36

A:
Relatively free from wing and engine flow interference
Better at trimming nose-down moment of high lift devices
D:
Destabilising contribution to static stability

Question 36

How does the position of CoG impact stability at the stick fixed neutral point?

Answer 36

When CoG is forward of the SFNP the aircraft is neutrally stable.
If CoG moves after of SFNP the aircraft will be statically unstable- as the slope of the pitching moment curve becomes positive

Question 36

What is the stick fixed neutral point?

Answer 36

The point at which Cmα=0

Question 37

What is the equation for steady state roll response?

Answer 37

pss=-((Lδa)/Lp)Δδa
Where Lδa and Lp are defined according to the equation sheet
Subbing these in and cancelling terms
pssb/2u0=-(Clδa/Clp)Δδa

Question 38

What is the characteristic equation for pure yawing?

Answer 38

λ^2+Nrλ+Nβ=0
where Nr=(∂N/∂r)/Iz
and Nβ=(∂N/∂β)/Iz
where Iz=moment of inertia

Question 39

What is the value for ωn and ζ when comparing the yawing characteristic equation to the second-order characteristic equation?

Answer 39

ωn=√Nβ
ζ=-(Nr)/2*√Nβ
Note: frequency only depends on static stability, and damping ratio depends on yaw rate too so is a function of aerodynamic damping

Question 40

What is the basic idea of inertial cross-coupling?

Answer 40

That rotation about one axis can cause unwanted rotation about the other axes

Question 41

When can Ixz not be assumed as zero?

Answer 41

In fighter aircraft

Question 42

What two static stability characteristics allow for high rates of roll and which type of coupling they lead to? Give an example of each

Answer 42

1: Small longitudinal and large directional static stabilities e.g slender supersonic aircraft at subsonic speeds: roll-pitch
2: Small directional and large longitudinal static stabilities e.g slender supersonic aircraft at supersonic speeds: roll-yaw

Question 43

Why does Roll-Yaw inertial coupling happen

Answer 43

P=roll vector
q=pitch vector
w=new axis of rotation
w=p+q
The pitching moment is resisted by the large LSS. As the aircraft has small DSS it rotates to align with w. This causes a large yawing moment