# Aircraft Design MCQ – Configuration Layout Considerations – Infrared Detectability

1 - Question

An aircraft does not emit any IR radiation.
a) True
b) False
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 - Question

In general, an IR detector will respond to?
b) Rotational fluid
c) Rotational force
d) RCS
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 - Question

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
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 - Question

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
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 - Question

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

6 - Question

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
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 - Question

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

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
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 - Question

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
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 - Question

Sun glint affects the IR detection of an aircraft.
a) True
b) False
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 - Question

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