Aircraft Design - Propulsion Quiz(MCQ)

1 .

Afterburner is used to ________

A)

increase fuel efficiency

B)

reduce fuel consumption

C)

increase thrust of engine

D)

increase lift produced by tail

Correct Answer : increase thrust of engine

Explanation : Afterburner is used to increase Thrust produced by the jet engine. It is primarily used by fighter aircraft to increase thrust during takeoff and combat. Afterburning will increase fuel consumption and reduces the fuel efficiency.

2 .

Turbofan engine uses a large fan at inlet to _____

A)

increase wing tip lift

B)

increase tailplane lift

C)

increase flow velocity

D)

increase efficiency of the engine

Correct Answer : increase efficiency of the engine

Explanation : To Increase efficiency, more specifically propulsive efficiency of the engine a turbofan engine uses a fan. Some air is bypassed around the engine and not being used for combustion. This helps to increase efficiency.

3 .

At low subsonic speed, we should select _________

A)

turboprop always

B)

always use ram jet

C)

low bypass Turbofan engine

D)

subsonic speed cannot be achieved

Correct Answer : low bypass Turbofan engine

Explanation : At low subsonic speed, low bypass Turbofan engine should be adopted among the given options. Turboprop has speed limitation due to propeller. Ram jet engine cannot be used at low subsonic speed as ram jet will require assistance to achieve adequate design condition. Ramjet can be used for speeds above Mach 2.8.

4 .

Uninstalled engine data is available from ________

A)

manufacturer

B)

stability margin

C)

thin airfoil theory

D)

lifting line theory

Correct Answer : manufacturer

Explanation : Uninstalled engine data is available from an engine manufacturer. It can also be found by using preliminary cycle analysis or by using fudge factor approach. Thin airfoil they is used for airfoils with thin profiles. Lifting line theory is an aspect of Aerodynamics.

5 .

Propulsive efficiency is defined as _________

A)

aerodynamic efficiency

B)

ratio of obtained thrust power to energy expanded

C)

thrust used by compressed energy

D)

lift required to thrust required at each segment

Correct Answer : ratio of obtained thrust power to energy expanded

Explanation : Propulsive efficiency is defined as the ratio of obtained thrust power to the energy expanded. Aerodynamic efficiency is defined as lift to drag ratio. Aerodynamic efficiency is primarily consideration of aerodynamic design.

6 .

Determine thrust power if aircraft velocity is 150 m/s and thrust force is 1000N.

A)

0.0

B)

12.056MW

C)

150KW

D)

1500W

Correct Answer : 150KW

Explanation : Thrust power = thrust*velocity = 150*1000 = 150KW.

7 .

Net thrust is given by ______

A)

drag into velocity

B)

lift to drag ratio

C)

gross thrust divided by weight

D)

gross thrust minus the ram drag

Correct Answer : gross thrust minus the ram drag

Explanation : Net thrust is given by gross thrust minus the ram drag. Drag into velocity will give power not the thrust. This power can be calculated by subtracting the excess power from total available power. Lift to drag ratio is called aerodynamic efficiency of the aircraft.

8 .

Find the acceptable value of ram drag if Turbojet is designed to provide net thrust of 88% of gross thrust. Engine gross thrust is 12.5KN.

A)

1.5KN

B)

2500

C)

4325

D)

23456

Correct Answer : 1.5KN

Explanation : Ram drag = Gross Thrust – net Thrust = 12.5 – 0.88*12.5 = 1.5KN.

9 .

What do you mean by overall pressure ratio?

A)

Ratio of dynamic to normal pressure

B)

Ratio of pressure at engine exhaust and inlet front face

C)

Total pressure divided by stagnation pressure

D)

Stagnation pressure divided by dynamic pressure

Correct Answer : Ratio of pressure at engine exhaust and inlet front face

Explanation : Overall pressure ratio is defined as ratio of pressure at engine exhaust and inlet front face. The overall pressure ratio or opr is used to measure the ability of an engine to accelerate the exhaust. It has direct impact on thrust and propulsive efficiency of the engine.

10 .

What is the limitation of current engine design?

A)

Expansion fan only

B)

Flow velocity over wing

C)

Turbine inlet temperature

D)

Inlet flow velocity reduction limitation

Correct Answer : Turbine inlet temperature

Explanation : Turbine inlet temperature is one of the biggest obstacle of current engine design. For best Thrust and efficiency it is desirable to use stoichiometric air fuel ratio of 15:1. However, this generated tremendous high temperatures. Such high temperatures are beyond the limits of materials used for Turbine.

11 .

Which type of engine should be selected, if required cruise speed is above 2.1M?

A)

Turbojet

B)

Piston

C)

Reciprocating

D)

Piston propeller

Correct Answer : Turbojet

Explanation : If required cruise speed is above Mach 2.1 then turbojet engine is suitable among the given options. Piston and reciprocating engine performance is limited to certain speeds. Piston prop engine is limited by tip speed constraints.

12 .

The actual available thrust used in performance calculations is termed as __________

A)

lift to drag ratio

B)

gross lift and weight

C)

installed weight to reference area

D)

installed net propulsive force

Correct Answer : installed net propulsive force

Explanation : The actual available thrust used in performance calculations is termed as installed net propulsive force. Lift to drag ratio is called the aircraft Aerodynamic efficiency. It is primarily considered for Aerodynamic design. Weight to area is called wing loading.

13 .

Fudge factor is used to obtain __________

A)

lofting

B)

lift to drag ratio

C)

thrust loading and wing loading

D)

manufacturer�s uninstalled engine thrust

Correct Answer : manufacturer�s uninstalled engine thrust

Explanation : Manufacturer’s Uninstalled engine Thrust can be obtained by using fudge factor or by using cycle analysis and/or testing. Thrust loading is defined as the ratio of the aircraft thrust to weight. Lofting is mathematical modelling of skin and it is one of the important factor for designing an aircraft.

14 .

What do you mean by installed engine thrust?

A)

Lifting property

B)

Installed wing lift

C)

Actual thrust produced by an engine when installed

D)

Actual thrust when not installed

Correct Answer : Actual thrust produced by an engine when installed

Explanation : The Actual thrust produced by an engine when installed in the Aircraft can be termed as installed engine thrust. To obtain install thrust we need to correct the thrust for actual inlet pressure recovery and nozzle performance. We also required to consider Thrust losses.

15 .

Following diagram represents ______

A)

uninstalled lift

B)

installed thrust methodology

C)

lift to drag ratio determination

D)

aerodynamic efficiency methodology

Correct Answer : installed thrust methodology

Explaination : A typical installed thrust methodology is shown in the diagram. As shown in the diagram a typical Thrust methodology consists of 3 different processes. Each process has its own significance and is based on some assumptions as well. This can be seen in the diagram. Aerodynamic efficiency is determined by using lift and drag.

16 .

Following diagram represents _______

A)

typical inlet drag trends

B)

drag polar

C)

reynolds number

D)

lift coefficient curve

Correct Answer : typical inlet drag trends

Explaination : Above diagram is showing a typical variation in inlet drag with Mach number. Reynolds number is as non-dimensional quantity. We can use Reynold’s number to get understanding of the fluid flow and more.

17 .

Nozzle drag varies with ______

A)

only with nozzle type

B)

only nozzle flight conduit

C)

position of nozzle, flight conditions, etc

D)

only with nozzle pressure at combustion chamber

Correct Answer : position of nozzle, flight conditions, etc

Explanation : Drag is an opposite forces which resists the forward motion of the aircraft. Nozzle drag depends upon number of the factor such as: Location of nozzle, flight conditions etc. Nozzle is an important device to generate enough velocity and Thrust by expanding the flow.

18 .

If manufacturer's thrust loss requirement is 3% and engine has mass flow of 20 unit then, determine how much bleed mass flow can be used?

A)

0.3 unit

B)

0.4 unit

C)

0.8 unit

D)

0.9835 unit

Correct Answer : 0.3 unit

Explaination : Bleed correction factor C can be approximated as 2 when it is not mentioned in the question.
Bleed mass flow = Thrust loss*Engine mass flow / C = 0.03*20/2 = 0.3 unit.

19 .

The installed net propulsive force is defined as ______

A)

installed lift by drag

B)

installer wing loading

C)

uninstalled thrust plus drag due to inlet and nozzle

D)

installed engine thrust minus the drag due to inlet, nozzle and throttle dependent trim drag

Correct Answer : installed engine thrust minus the drag due to inlet, nozzle and throttle dependent trim drag

Explanation : The installed net propulsive force is defined as installed engine thrust minus the drag due to inlet, nozzle and throttle dependent trim drag. This thrust value can be used to determine aircrew performance. Wing loading is defined as the ratio of weight of the aircraft to the reference area.

20 .

A manufacturer's uninstalled engine is required to operate at 1.8M. Find the reference pressure recovery based on military standard.

A)

12.56%

B)

45.97%

C)

94.45%

D)

100%

Correct Answer : 94.45%

Explanation : Reference pressure recovery is defined as,
Reference pressure recovery = 1 – 0.075(M – 1)^1.35
= 1 – 0.075(1.8 – 1)^1.35 = 0.9445 = 94.45%.

21 .

A supersonic aircraft is designed to operate at 2.0M if thrust loss is required to be less than 2% then determine the reference value of inlet pressure recovery. Given ram recovery Correction factor C is 1.2.

A)

70

B)

95%

C)

99

D)

102

Correct Answer : 95%

Explaination : Reference pressure recovery = (Thrust loss/C) + actual pressure recovery
= 0.02/1.2 + 0.93
= 0.016+0.93 = 0.95 = 0.95*100% = 95%.

22 .

A subsonic flight has actual inlet pressure recovery of 0.975. Estimate the thrust loss by this subsonic engine.

A)

2.5%

B)

3.37%

C)

11.22%

D)

56%

Correct Answer : 3.37%

Explanation : Given, subsonic Aircraft, actual inlet pressure recovery = 0.975.
Thrust loss can be approximated as follows,
% Thrust loss = C*(reference pressure recovery – actual inlet pressure recovery)*100
Since, C is not given we will consider it as 1.35. 1.35 is a typical value of C for subsonic aircraft.
Hence,
% Thrust loss = 1.35*(1-.975)*100 = 3.37%.

23 .

Mass flow rate will be affected by ______

A)

altitude

B)

longerons weight

C)

induced drag only

D)

weight of the aileron

Correct Answer : altitude

Explanation : Typically, Mass flow rate can be expressed as follows: mass flow rate = density*Area*Velocity. Density is function of altitude. It depends on the altitude and changes as per the international standard atmosphere. Hence, if density varies then, the mass flow rate will also vary. Hence, we can say that the mass flow rate is affected by the altitude.

24 .

A piston engine has bhp of 600 at sea level. Now, if engine is operating at an altitude where density ratio is 0.816 then, find the value bhp at that altitude.

A)

37

B)

89

C)

100

D)

289

Correct Answer : 37

Explanation : Given, sea level bhp, p1 = 600, density ratio d = 0.816
Now, bhp at an altitude = p1*(d – ((1-d)/7.55))
= 600*(0.814-((1-0.814)/7.55))
= 600*(0.814-(0.1836/7.55)
= 600*0.0616 = 37.

25 .

Supercharger is used to improve ______

A)

outlet pressure

B)

expansion of exhaust velocity

C)

intake manifold pressure

D)

to increase charging capacity of an electric charger

Correct Answer : intake manifold pressure

Explanation : Supercharger is used to increase intake manifold pressure. We can increase manifold pressure by small amount by using forward facing air intake scoop. Supercharger or turbocharger is used to increase manifold pressure by large amounts.

26 .

Following diagram represents ______

A)

lift curve

B)

drag polar

C)

bhp variation with altitude

D)

power required vs thrust required

Correct Answer : bhp variation with altitude

Explaination : Typical bhp variation with altitude is presented in this diagram. Above diagram is illustrating the relationship between bhp and the altitude. Drag polar is used to provide information about drag characteristics. Lift curve is used to provide relationship between lift and angle of attack.

27 .

Following diagram represents _______

A)

thrust reversal

B)

vortex generator

C)

lift augmentation

D)

static propeller thrust

Correct Answer : static propeller thrust

Explaination : Above diagram is representing typical static propeller thrust concept. Lift augmentation is used to increase the amount of lift produced. Thrust augmentation is used to increase the amount of thrust produced by engine. Thrust augmentation is used to increase thrust during short takeoff distance.

28 .

Activity factor is a measure of ________

A)

parasite drag

B)

lift induced drag

C)

power generated by propeller

D)

the amount of power which is being absorbed by propeller

Correct Answer : the amount of power which is being absorbed by propeller

Explanation : How much power is being absorbed by propeller can be measured by using activity factor. Activity factor varies from 90-200. A typical large turboprop will have an activity factor of 140. Lighter aircraft can have activity factor as 100 typically.

29 .

Inflow ratio is defined as _______

A)

drag to lift ratio

B)

total inflow velocity to tip speed

C)

propulsive efficiency

D)

total lift by rotor to the total drag

Correct Answer : total inflow velocity to tip speed

Explanation : Inflow ratio can be defined as the ratio of total inflow velocity to the tip speed. Drag to lift ratio is inverse of Aerodynamic efficiency. Higher Aerodynamic efficiency indicates that the aircraft will have higher lift.

30 .

A propeller is rotating with 20 rps has diameter of 2.5m. Calculate thrust produced by the propeller if thrust coefficient is 0.01.

A)

1.2MN

B)

190KN

C)

191.40N

D)

2000kN

Correct Answer : 191.40N

Explanation : Thrust = Thrust coefficient*density*diameter⁴*rps² = 0.01*1.225*2.5⁴*20² = 191.40 N.

31 .

Determine thrust of propeller if propeller efficiency is 85%. Propeller is assumed to be operated with 1200 bhp and 350ft/s of velocity.

A)

1602.85 lb

B)

8902lb

C)

16789lb

D)

12kN

Correct Answer : 1602.85 lb

Explanation : Thrust = 550*bhp*propeller efficiency/velocity = 550*1200*0.85/350 = 1602.85 lb of force.

32 .

If a propeller has bhp of 700 and diameter as 1.2 ft. and rotating with 20 rps then, determine power coefficient. Consider sea level density.

A)

1.8

B)

15.8

C)

30.2

D)

40

Correct Answer : 15.8

Explanation : Power coefficient = 550*bhp / (density*diameter⁵*rps³)
= 550*700 / (1.225*1.2⁵*20³) = 15.8.

33 .

Determine the required thrust coefficient to produce thrust of 1000N. Given diameter is 1.2m and n=22 rps.

A)

0.1

B)

0.32

C)

0.489

D)

0.813

Correct Answer : 0.813

Explanation : Thrust coefficient = Thrust / (density*diameter⁴*rps²) = 1000 / (1.225*1.2⁴*22²) = 0.813.

34 .

Determine the propeller efficiency if propeller velocity is 300ft/s and thrust of 1320 lb. Given bhp is 800.

A)

0.03%

B)

0.09%

C)

0.895%

D)

90%

Correct Answer : 90%

Explanation : Propeller efficiency = (thrust*velocity) / (bhp*550) = 1320*300/ (550*800) = 0.9 = 0.9*100 % = 90%.