Aircraft Design Questions and Answers – Configuration Layout Considerations – Infrared Detectability

This set of Aircraft Design Multiple Choice Questions & Answers (MCQs) focuses on “Configuration Layout Considerations – Infrared Detectability”.

1. An aircraft does not emit any IR radiation.
a) True
b) False
View Answer

Answer: b
Explanation: IR is an electromagnetic wave. An infrared radiation is not visible to a human named eye. Any bay which has warmth will generate infrared radiation. Aircraft will emit infrared radiation.

2. In general, an IR detector will respond to?
a) Irradiance
b) Rotational fluid
c) Rotational force
d) RCS
View Answer

Answer: a
Explanation: Typically, all it detector will respond to irradiance. Irradiance is area density of the power. Hence, an infrared detector will respond to the density of the radiant power. RCS is measure of radar detection.

3. Calculate the irradiance E in W/cm2 if, radiant intensity I is 10 W/sr and range R is 10cm.
a) 0.1
b) 0.001
c) 0.45
d) 10
View Answer

Answer: a
Explanation: Given, radiant intensity I = 10 W/sr, range R = 10 cm.
Irradiance E is given by,
E = I/R2 = 10/102 = 10/100 = 0.1 W/cm2.

4. What is an IR signature of an aircraft?
a) Total of detectable emissions and reflections
b) Sum of some emissions only
c) Only reflections
d) Only refraction
View Answer

Answer: a
Explanation: Total of detectable and reflections can be called as an IR signature. This signature is used for tracking and detecting the aircraft. An aircraft’s IR signature is complex mixture of reflections and emission of various components.

5. Which of the following is primarily responsible for an IR signature?
a) Engine exhaust
b) Passenger
c) Fuel tank
d) Cabin crew
View Answer

Answer: a
Explanation: Primary sources for IR detection in an aircraft is engine exhaust. Passenger, cabin crew and fuel tank will play minor role as compared to the engine exhaust. Engine exhaust consists of hot gases and emissions.
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6. An aircraft is flying with Mach 2.0. Calculate recovery temperature if ambient temperature is 305K. Assume recovery factor is 0.85.
a) 512.4K
b) 253.2K
c) 100°C
d) 400°C
View Answer

Answer: a
Explanation: Given, Mach number = 2.0, ambient temperature T1 = 305K
Assuming the recover factor as 0.85 and for such case,
Recovery temperature T2 = T1*(1+0.17*M2)
T2 = 305*(1+0.17*2*2) = 305*1.68 = 512.4K.

7. A military aircraft can use _____ as a countermeasure for IR detection.
a) flares
b) lift
c) glares
d) engine temperature increase
View Answer

Answer: a
Explanation: If we increase engine exhaust temperature then, it will increase the IR detection. As a countermeasure for IR detection, most of military a/c are using flares. Flares are used to generate fake IR signatures.


8. Plume emissions can be reduced by ___________
a) quickly mixing exhaust with outside air
b) increasing exhaust temperature
c) increasing engine outlet temperature
d) increasing plume temperature
View Answer

Answer: a
Explanation: Plume emissions can be reduced by quickly mixing the exhaust of engine with outside air. Emissions from hot parts are reduced by cooling them. Increase in temperature will increase emissions and as a result, it will increase IR detection as well.

9. Which of the following is one of the countermeasures for IR detection?
a) Decoy
b) Temperature increase
c) Engine exhaust temperature increase
d) Not mixing plume with outside air
View Answer

Answer: a
Explanation: A decoy is an off-board system. Decoy is a countermeasure that is ejected from and separated away from the aircraft. Decoy will try to lure the missile track away from the aircraft.

10. Sun glint affects the IR detection of an aircraft.
a) True
b) False
View Answer

Answer: a
Explanation: Sun glint will affect the reflections and hence, will affect the IR detection. Sun glint can be reduced by using special paints. These paints will have low IR reflectivity which can improve the IR detection.

11. To improve IR detection of engine, we can ____________
a) hide the nozzle from expected location of an IR sensor
b) use higher exhaust temperature
c) show nozzle at IR sensor
d) nozzle does not affect the IR detection
View Answer

Answer: a
Explanation: Emissions of hot parts can be reduced by lowering their temperature. We can hide nozzle from the IR detector itself. As a result we can improve the IR detectability.

Sanfoundry Global Education & Learning Series – Aircraft Design.

To practice all areas of Aircraft Design, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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