Aero 213

Question 1

Five advantages of thrust reversers

Answer 1

Reduces landing distance, reduces tyre and brake wear (especially in wet/icy conditions), improved ground handling (especially in wet/icy conditions), improves rejected takeoff margins, and allows operation from shorter runways (military), thus increasing operational flexibility.

Question 2

Four issues with thrust reversers

Answer 2

Got gases cannot impinge on the wing, hot gases cannot be re-ingested into the engine, must be impossible to deploy in flight, and can’t generate too much lift, otherwise braking performance is compromised.

Question 3

Two types of thrust reverser

Answer 3

Hot and cold.

Question 4

Hot thrust reversers

Answer 4

Reverse air in/from engine core. There’s two systems. First system is clamshell doors that close within the core, and direct the hot flow through vents out the side in the reverse direction. Other system is bucket doors that extend behind the core exit and direct the hot flow rearwards.

Question 5

pV

Answer 5

mRT

Question 6

h

Answer 6

CpT

Question 7

h0

Answer 7

CpT0 = h + (v^2)/2

Question 8

rho2/rho1

Answer 8

(T2/T1)^(1/(gamma-1))

Question 9

(rho2/rho1)^gamma

Answer 9

p2/p1

Question 10

What do static properties depend on?

Answer 10

The molecules in the gas.

Question 11

What do stagnation properties depend on?

Answer 11

The molecules in the gas, plus any bulk kinetic energy associated with the flow of the gas.

Question 12

T0/T

Answer 12

1 + (M^2(gamma-1)/2)

Question 13

Propulsive efficiency

Answer 13

A measure of how well an engine produces thrust relative to the amount of kinetic energy it adds to the airflow.

Question 14

Requirement for max propulsive efficiency, nuPmax

Answer 14

Jet velocity needs to be low as possible, but still higher than the flight speed in order to produce thrust.

Question 15

Four drawbacks of increasing the BPR

Answer 15

Increased drag, increased weight, installation problems due to size, and requires gearbox after BPR ~ 10.

Question 16

Thermal efficiency

Answer 16

A measure of how well an engine adds kinetic energy to the airflow relative to the total energy input from the fuel.

Question 17

Two methods of increasing the thermal efficiency

Answer 17

Increase the overall pressure ratio, and increase the turbine entry temperature.

Question 18

Overall efficiency, nu0

Answer 18

nuPxnuTh = Tva/m(dot)fQlcv

Question 19

Thrust specific fuel consumption, tsfc

Answer 19

m(dot)f/T

Question 20

Four issues with an unducted fan

Answer 20

Not feasible to install on existing aircraft, airports would have to be adapted, fly slower than normal turbofan, and noisier.

Question 21

Choked flow

Answer 21

M = 1

Question 22

Critical pressure ratio

Answer 22

The pressure ratio required for choked flow.

Question 23

Three benefits of having a three-shaft configuration

Answer 23

Independent shaft speed for optimal blade speed, shorter shafts, and modular for easy maintenance.

Question 24

Turbomachinery cross-sectional area, A

Answer 24

πrt^2 - πrh^2 = πDz, where D is mean diameter and z is blade height.

Question 25

Euler’s turbomachinery equation, P

Answer 25

mdot(Vtheta2U2 - Vtheta1U1) = mdotw(Vtheta2r2 - Vtheta1r1)

Question 26

Blade speed, U

Answer 26

rw

Question 27

SFEE for turbomachinery, P

Answer 27

(mdot)deltah0

Question 28

Conservation of rothalpy

Answer 28

h02 - U2Vtheta2 = h01 - U1Vtheta1

Question 29

V

Answer 29

W + U

Question 30

Vtheta

Answer 30

Wtheta + U

Question 31

Wa

Answer 31

Va

Question 32

Reaction

Answer 32

A measure of the extent to which the rotor contributes to the overall static enthalpy change in the stage.

Question 33

Reaction = 0.5 (turbine)

Answer 33

Pressure drop split evenly, meaning pressure gradients are modest. Sealing is easy.

Question 34

Reaction = 0 (turbine)

Answer 34

Pressure drop entirely across stator, so pressure drop across stator is high, and sealing is difficult.

Question 35

Reaction = 0.5 (compressor)

Answer 35

Pressure rise is split evenly, meaning pressure gradients are modest, so boundary layer is likely to remain attached.

Question 36

Reaction = 0 (compressor)

Answer 36

Pressure rise is entirely over the stator, meaning the pressure gradient across the stator is high, so the boundary layer is prone to separation.

Question 37

Flow coefficient, phi

Answer 37

Va/Um, where Um is mean blade speed.

Question 38

Stage loading, psi

Answer 38

deltah0/Um^2 = deltaVtheta/Um

Question 39

p0/p

Answer 39

(1 + M^2(gamma-1)/2)^gamma/(gamma-1)