Aero 317

Question 1

Surge

Answer 1

Linear movement along the x-axis

Question 2

Sway

Answer 2

Linear movement along the y-axis

Question 3

Heave

Answer 3

Linear movement along the z-axis

Question 4

Aileron

Answer 4

Controlled by rotation of the stick. Primary control for roll.

Question 5

Elevator

Answer 5

Controlled by fore/aft stick. Primary control for pitch.

Question 6

Rudder

Answer 6

Controlled by pedals. Primary control for yaw.

Question 7

Stability

Answer 7

The tendency of a system to return to its initial condition when disturbed from an equilibrium/trim position.

Question 8

Two types of stability

Answer 8

Static and dynamic

Question 9

Static stability

Answer 9

The initial tendency of an aircraft following a disturbance.

Question 10

Three possibilities of static stability

Answer 10

1. Return towards trim position (statically stable).
2. Diverge away from trim position (statically unstable).
3. Neither (statically neutral).

Question 11

Dynamic stability

Answer 11

How an aircraft behaves once it enters an oscillation.

Question 12

Two dynamic stability possibilities

Answer 12

1. Oscillation damps out (dynamically stable).
2. Oscillation amplifies over time (dynamically unstable).

Question 13

Centre of pressure

Answer 13

The point on a body where the pressure field acts, i.e. where lift and drag act from if modelled as single forces.

Question 14

Aerodynamic centre

Answer 14

The point on a aerofoil where the moment doesn’t change with lift, i.e. dCm/dCl = 0. It’s denoted xac.

Question 15

Finding the moment at the aerodynamic centre.

Answer 15

Cmac = Cm0

Question 16

If A.C. is in front of the C.G., an increase in alpha will…

Answer 16

1. Increase lift
2. Increase nose-up moment
3. Increase alpha further, hence statically unstable (dM/dL > 0).

Question 17

If A.C. is behind the C.G., an increase in alpha will…

Answer 17

1. Increase lift
2. Increase nose-down moment
3. Decrease alpha back towards trim, hence statically stable (dM/dL < 0).

Question 18

Dimensionless form of the pitching moment equation

Answer 18

Cm = Cl(h-hac) + Cm0wb - CltVt

Question 19

Vt (v bar, technically)

Answer 19

ltSt/Sc

Question 20

Effective tailplane angle of attack, alphat

Answer 20

alpha + phit - epsilon

Question 21

Epsilon

Answer 21

(∂epsilon/∂alpha)*alpha

Question 22

Neutal point, hn

Answer 22

hac + Vt(a1/a)(1-(∂epsilon/∂alpha))

Question 23

Static margin, Hn

Answer 23

hn - h, where hn is the neutral point and h is the centre of gravity location.

Question 24

Controls free neutral point, hn’

Answer 24

hac + Vt(a1/a)(1-(∂epsilon/∂alpha))*(1-(a2b1/a1b2))

Question 25

Controls free static margin, Hn’

Answer 25

hn’ - h

Question 26

Alpha

Answer 26

Cl/a

Question 27

Cmh

Answer 27

Cmh0 + (b2/a2)(1/Vt)(h-hn’)Cl

Question 28

Load factor, n

Answer 28

L/mg

Question 29

Tail lift coefficient, Clt

Answer 29

a1alphat + a2eta + a3*beta

Question 30

Three traits of the phugoid dynamic mode

Answer 30

1. Long period
2. Large amplitude
3. Low frequency, characterised by large changes in flight speed and altitude.

Question 31

Determinant of a 2x2 matrix, det(A)

Answer 31

ad - bc

Question 32

If A is a 2x2 abcd matrix, what’s the adjugate of A, adj(A)?

Answer 32

d -b
-c a

Question 33

Open loop system

Answer 33

No feedback outside of the pilot applying control inputs to change the aircraft state as they want.

Question 34

Closed loop system

Answer 34

Use feedback about aircraft states to apply control inputs to the aircraft system.

Question 35

Limited authority system

Answer 35

The feedback control law is only allowed to make small adjustments to the pilot’s control inputs to modify the response of the aircraft.

Question 36

Full authority system

Answer 36

Allows the control law jurisdiction over the entire range of control surface deflections.

Question 37

Root locus rules 1-5

Answer 37

1. The number of lines (loci) is equal to the greater of m or n (the orders of the numerator or denominator) and hence the number of zeros or poles.
2. As K increases from zero to infinity, the roots of the characteristic equation move from the open loop poles of G(s) to the open loop zeros of G(s).
3. If m=n, then roots move from poles to zeros in pairs, but if there are excess poles (n>m), then the poles migrate along asymptotes towards infinity. The number of asymptotes is equal to the number of excess poles, n-m.
4. The portion of the real axis to the left of odd numbers of open loop poles are part of the loci.
5. The angle that the asymptotes make is a function of the number of asymptotes, N: thetan = (180-360N)/(n-m).

Question 38

Root locus rules 6-8

Answer 38

6. The asymptotes meet at a point defined by the centroid of the real parts of the roots and zeros: sigma = (∑real parts of poles - ∑real parts of zeros)/n-m
7. Lines break out, or in to, the real axis at 90˚
8. The points on the locus where the poles leave the real axis are the values of s which satisfy: (d/ds)G(s) = 0.

Question 39

What’s the modulus of complex number equal to?

Answer 39

The gain.

Question 40

What’s the phase of a complex number equal to?

Answer 40

The argument/angle.

Question 41

Nichols plot

Answer 41

Plots the gain and phase of a transfer function.

Question 42

Nyquist plot

Answer 42

The frequency response in the complex plane.

Question 43

Nyquist stability criterion

Answer 43

The Nyquist plot must not enclose the critical point if the closed loop system is to be stable.

Question 44

Phase margin

Answer 44

The amount of phase lag a system can experience before the Nyquist locus will touch the critical point.

Question 45

Gain margin

Answer 45

The gain multiplier required to cause a loss of stability, defined by the control gain, K, and the system gain where the phase = -180˚.