Aircraft Design MCQ – Aural Signature

1 - Question

Noise produced by an aircraft is called __________
a) aural signature
b) aurora beam
c) signal beam
d) ir beam
View Answer Answer: a
Explanation: The noise generated by an aircraft is called the aural signature of the aircraft. Aural signature or noise is very important for civil as well as military grade aircraft. Some aircraft suffers retirement due to much higher aural signatures.

2 - Question

Primary cause of aircraft noise is ___________
a) engine exhaust
b) lift
c) fuselage
d) cabin
View Answer Answer: a
Explanation: Aircraft noise is primarily generated due to the engine exhaust. The fuselage, cabin noise are less as compared to the engine exhaust. Lift is an aerodynamic force.

3 - Question

Small diameter and high velocity jet will produce _____________
a) more noise
b) less noise
c) less aural signature
d) independent of diameter and velocity
View Answer Answer: a
Explanation: in a typical aircraft, engine is primary component which generates higher aural signatures. Small diameter and high exhaust will generate more noise due to the effect of air shear layers.

4 - Question

Arrange in the correct order of noise produced by engine type.
a) Turbojet > turbofan > reciprocating engine
b) Turbojet < turbofan < reciprocating engine
c) Turbojet > turbofan = reciprocating engine
d) Turbojet > turbofan < reciprocating engine
View Answer Answer: a
Explanation: Engine exhaust aural signatures will be affected by type of engine used. A large diameter propeller with limited tip speed will generate less noise as compare to high speed turbojets. Turbofan aural signature is less than that of the turbojet but greater than the reciprocating engine. Hence, the correct order will be Turbojet > turbofan > reciprocating engine.

5 - Question

To reduce piston exhaust noise ______________
a) we can use more mufflers
b) mufflers can be used only
c) reduce lift always
d) increase jet speed always
View Answer Answer: a
Explanation: Noise by a piston engine exhaust can be reduced in a number of ways. One of them is by adopting mufflers. Apart from muffler, we can redirect the exhaust in such way that the resulting noise will be much lesser.

6 - Question

Propeller aircraft experiences internal noise.
a) True
b) False
View Answer Answer: a
Explanation: Internal noise will produced if piston engine exhaust impinges upon any part of an aircraft. For example, if exhaust impinges upon cabin, it will generate internal noise. Hence, the correct answer will be true.

7 - Question

Which of the following is correct?
a) Some clearance should be provided between propeller and fuselage
b) Lift will be reduced if only drag is reduced
c) Thrust will be lower than the drag always
d) Engine exhaust does not make any noise
View Answer Answer: a
Explanation: Reduction of lift can be achieved by number of ways such as AOA reduction, drag increment etc. Thrust at cruise will be equal to the drag. Engine exhaust is primary source of aircraft noise. Hence, the correct statement will be ‘Some clearance should be provided between propeller and fuselage’.

8 - Question

To reduce aural signatures of engine exhaust, we can use _____________
a) insulating material
b) lofting
c) drafting
d) non-insulating material
View Answer Answer: a
Explanation: We can use insulating materials to reduce the aural signatures. Lofting is mathematical modeling. Drafting is based on drawing.

9 - Question

Let’s consider a propeller aircraft propeller diameter of 24 feet then, what would be the minimum value of clearance that is required for safe operation of propeller typically?
a) 6ft
b) 8ft
c) 10ft
d) 20ft
View Answer Answer: a
Explanation: Given diameter d = 24ft Typical minimum clearance = d/4 = 24/4 = 6ft.

10 - Question

By directing the exhaust away from the ground we can _____________
a) reduce the aural signature
b) increase the aural signature
c) increase noise
d) noise is not dependent on the direction of exhaust
View Answer Answer: a
Explanation: By redirecting exhaust stacks away from the ground we can reduce the aural signature. We can reduce aural signatures by using mufflers or by providing proper insulation as well.

11 - Question

How to reduce engine noise?
a) By using chevron nozzle
b) By using high velocity jet
c) Using small diameter and high velocity jet
d) Higher exhaust jet with less diameter of exhaust
View Answer Answer: a
Explanation: Chevron nozzle is used to reduce the engine exhaust aural signatures. Chevron nozzle accompanies saw tooth pattern at the trailing edge. High velocity jet will produce more noise due to air shear layer effects.

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