Category: Aircraft Performance Objective Questions

Aircraft Performance Questions and Answers for Freshers on “Vertical Development of Air”.

1. The atmosphere is mainly divided into _______ layers.
a) 2
b) 6
c) 7
d) 5
Answer: d
Clarification: The atmosphere is divided into 5 layers. They are troposphere, stratosphere, mesosphere, thermosphere and exosphere where these layers are sub divided into lower and upper layers.

2. According to ISA atmospheric model what is the value of datum atmospheric temperature?
a) 273K
b) 277K
c) 288.15K
d) 288.15°C
Answer: c
Clarification: According to ISA atmospheric model what is the value of datum atmospheric temperature is 288.15K. It can also be written as 15.15°C. The relation between Kelvin scale and Celsius scale is K=°C+273.

3. The range of temperature in mesosphere is ________
a) below 130K
b) below 140K
c) below 110K
d) below 120K
Answer: a
Clarification: The range of temperature in mesosphere is below 130K. It starts at the top of stratosphere and ends at mesopause. It is the coldest part of earth’s atmosphere. It is usually around 85 to 100 kilometers.

4. The range of temperature in thermosphere is ________
a) 200-500°C
b) 200-1000°C
c) 200-2000°C
d) 200-700°C
Answer: c
Clarification: The range of temperature in thermosphere is 200-2000°C. The temperature varies from day and night, during night its 200°C and during day it’s 200°C. The upper thermosphere extends up to a temperature of 2000°C.

5. The range of temperature in stratosphere is _____________
a) -51°C to -15°C
b) -5°C to -10°C
c) -510°C to -105°C
d) -31°C to -10°C
Answer: a
Clarification: The range of temperature in stratosphere is -51°C to -15°C. The layer closer to tropopause is -51°C and the layer close to mesosphere is -15°C. This temperature change happens depending on seasonal changes.

6. The range of temperature in troposphere is _____________
a) 15°C to -51°C
b) 5°C to -10°C
c) 510°C to -105°C
d) 31°C to -10°C
Answer: a
Clarification: The range of temperature in troposphere is 15°C to -51°C. Troposphere is quite cool compared to other atmospheric layers of earth. Troposphere has higher temperature than stratosphere.

7. The altitude range of thermosphere is ___________
a) 50km to 400km
b) 90km to 500km
c) 100km to 300km
d) 70km to 400km
Answer: b
Clarification: The altitude range of thermosphere is 90km to 500km. Thermosphere is present between mesosphere and exosphere. The range of temperature in thermosphere is 200-2000°C. The temperature varies from day and night, during night its 200°C and during day it’s 200°C. The upper thermosphere extends up to a temperature of 2000°C.

8. The altitude range of troposphere is ___________
a) 10km to 50km
b) 8km to 18km
c) 20km to 60km
d) 10km to 30km
Answer: b
Clarification: The altitude range of troposphere is 8km to 18km. The tropopause is about 18km above the equator. The height of the troposphere varies with seasons, it is highest in summer and lowest in winter.

9. The altitude range of mesosphere is ___________
a) 40km to 80km
b) 30km to 50km
c) 50km to 85km
d) 40km to 70km
Answer: c
Clarification: The altitude range of mesosphere is 50km to 85km. Mesosphere is present between stratosphere and thermosphere. The temperature in this region constantly decreases with increase in altitude.

10. The altitude range of stratosphere is ___________
a) 20km to 70km
b) 18km to 50km
c) 10km to 50km
d) 30km to 40km
Answer: b
Clarification: The altitude range of stratosphere is 18km to 50km. Stratosphere extends to an altitude of about 50km above earth’s surface. Stratosphere is above troposphere.

11. Which of the following is the correct order of atmospheric layers with respect to altitude increase?
a) Exosphere < Thermosphere < Mesosphere < Stratosphere < Troposphere
b) Thermosphere < Stratosphere < Mesosphere < Troposphere < Exosphere
c) Troposphere < Stratosphere < Mesosphere < Thermosphere < Exosphere
d) Troposphere < Stratosphere < Mesosphere < Exosphere < Thermosphere
Answer: c
Clarification: The correct order of atmospheric layers with respect to altitude increase is troposphere < Stratosphere < Mesosphere < Thermosphere < Exosphere. The altitude range of troposphere is 8km to 18km. The altitude range of stratosphere is 18km to 50km. The altitude range of mesosphere is 50km to 85km. The altitude range of thermosphere is 90km to 500km. The altitude range of exosphere is 500km to 10000km.

12. The altitude range of exosphere is ________
a) 400km to 1000km
b) 500km to 1000km
c) 500km to 10000km
d) 500km to 5000km
Answer: c
Clarification: The altitude range of exosphere is 500km to 10000km. The exosphere is the topmost layer of earth and next to this starts the outer space of solar system. This region has a temperature of 1700°C.

Aircraft Performance for Freshers,

Aircraft Performance Questions and Answers for Experienced people on “Thrust Producing Power Plant – 2”.

1. What is thrust drag accounting?
a) Allocation of flow forces to the airframe drag
b) Allocation of flow forces to the wave drag
c) Allocation of flow forces to the induced drag
d) Allocation of flow forces to the parasitic drag
Answer: a
Clarification: The allocation of flow forces to the airframe drag or to the propulsive thrust is known as the thrust drag. It is important to distinguish these force contributions else there results a wrong estimation of the aircraft performance.

2. The net thrust of the powerplant is affected by ____________
a) pressure and temperature
b) altitude andtemperature
c) temperature and mach number
d) mach number and altitude
Answer: d
Clarification: The net thrust of the powerplant is affected by mach number and altitude. As it is not possible to postulate precise function that will relate thrust and mach number and altitude, we develop simple relations that give us the characteristic variation of thrust along with the changes in mach number and altitude.

3. Which of the following is the correct equation for net thrust?
a) F_N=ṁ(V_j+V)
b) F_N=(V_j-V)
c) F_N=ṁ(V_j-V)
d) F_N=ṁ(V-V_j)
Answer: c
Clarification: The equation for net thrust is given by F_N=ṁ(V_j-V) where F_N is net thrust, ṁ is mass flow rate, V_j is exit velocity and V is inlet velocity. In other words the net propulsive force is the difference between the stream force entering and leaving the engine.

4. What is the net thrust of the jet engine if the mass flow rate is 500kg/s, exit velocity is 1000m/s and inlet velocity is 600m/s?
a) 400kN
b) 600kN
c) 500kN
d) 200kN
Answer: d
Clarification: The answer is 200Kn. Given ṁ=500kg/s, V_j=1000m/s and V=600m/s. Substitute the values in the formula, F_N=ṁ(V_j-V).
On substituting F_N=500 (1000– 600)
On solving F_N=20000N.

5. How is thrust related to altitude of an aircraft?
a) Thrust is directly proportional
b) Thrust is indirectly proportional
c) They are independent of each other
d) Thrust increases square of altitude
Answer: b
Clarification: The relation between altitude of an aircraft and thrust is that the thrust is indirectly proportional to the altitude of an aircraft i.e. thrust decreases as there is an increase in the altitude, similarly the thrust increases as there is decrease in the altitude.

6. The velocity of the engine exhaust flow is a function of the temperature of the exhaust gas.
a) True
b) False
Answer: a
Clarification: The velocity of the engine exhaust flow is a function of the temperature of the exhaust gas and this can be determined by the throttle setting. For any given engine thrust setting the exhaust gas velocity can be considered constant.

7. What will be the net thrust when momentum drag is 50N and gross thrust is 400N?
a) 450N
b) 8N
c) 350N
d) 350kN
Answer: c
Clarification: The answer is 350N. Given F_G is 400N and D_m is 50N. From the formula, F_N=F_G-D_m we can find net thrust. Substitute the given values, F_N= 400-50.
On solving F_N=50N.

Aircraft Performance for Experienced people,

Aircraft Performance Multiple Choice Questions on “Standard Atmospheric Model”.

1. International Standard Atmosphere is based on the assumption that air is a perfect gas and obeys gas law.
a) True
b) False
Answer: a
Clarification: International Standard Atmosphere is based on the assumption that air is a perfect gas and obeys gas law. It also neglects the effects of dust, water vapour and moisture.

2. According to ISA atmospheric model what is the value of datum atmospheric air density kg/m³?
a) 1.225
b) 12.225
c) 1.23
d) 1.000
Answer: a
Clarification: According to ISA atmospheric model what is the value of datum atmospheric air density is 1.225 kg/m³. It can also be written as 1225 g/m³ else 1.225 x 10^-9 kg/mm³.

3. The temperature-height profile is given by ___________
a) T=Ti+Li (H-Hi)
b) T=Ti+Li (H+Hi)
c) T=Ti-Li (H-Hi)
d) T=Ti-Li (H+Hi)
Answer: a
Clarification: The temperature-height profile is given by T=Ti+Li (H-Hi), where
T= temperature
Ti=temperature at lower boundary layer at that height
Li=lapse rate
H=height
Hi=height at lower boundary layer at that height.

4. What is lapse rate?
a) Change of temperature with respect to altitude
b) Change of temperature with respect to pressure
c) Change of pressure with respect to altitude
d) Change of temperature with respect to density
Answer: a
Clarification: Lapse rate is the change of temperature with respect to altitude. The temperature lapse rate is linear at tropopause to stratosphere. The lapse rate is zero in from the altitude 11km to 20km. The temperature lapse rate becomes positive at the middle of stratosphere.

5. What is true height?
a) The vertical geometrical distance between an object and a datum level
b) The vertical geometrical distance between a certain height and a datum level
c) The horizontal geometrical distance between an object and a datum level
d) The horizontal geometrical distance between a certain height and a datum level
Answer: a
Clarification: True height is the vertical geometrical distance between an object and a datum level. It is denoted by –z. Unit of true height is meter.

6. What is the hydrostatic equation?
a) ΔP=-ρg∆h
b) ΔP=-ρgh
c) P=-ρgΔh
d) ΔP=ρgΔh
Answer: a
Clarification: The hydrostatic equation is given by ΔP=-ρg∆h. This equation is derived from equating force acting on a cylindrical flow. The unit of pressure is N/m². It can also be represented in atm, bar, Pascal.

7. What is the pressure difference across a cylinder which consists of water and has a height difference of 20m?
a) -196.2 kN/m²
b) -1.962×10^-5 bar
c) -196.2 kN/m²
d) -1.962×10^-5 bar
Answer: a
Clarification: The answer is -196.2 kN/m².
Given Δh=20m, g=9.81m/s², ρ=1000kg/m³.
From ΔP=-ρg∆h,
ΔP=-1000*9.81*20
ΔP=-196200 N/m² or ∆P=-196.2 kN/m².

8. The difference between true height and geopotential height is relatively small.
a) True
b) False
Answer: a
Clarification: True height is the vertical geometrical distance between an object and a datum level whereas the geopotential height is the vertical coordinate referenced to earth’s mean sea level and the difference between true height and geopotential height is relatively small.

9. The pressure-height relationship in troposphere is given by _______
a) (frac{p}{p_0})=[1 + (frac{L_0}{T_0})H]^{(frac{-g_0}{RL_0})}
b) (frac{p}{p_0})=[1 + (frac{L_0}{T_0})H]^{(frac{-T_0}{RL_0})}
c) (frac{p}{p_0})=[1 + (frac{g_0}{T_0})H]^{(frac{-g_0}{RL_0})}
d) (frac{p}{p_0})=[1 + (frac{L_0}{g_0})H]^{(frac{-g_0}{RL_0})}
Answer: a
Clarification: The pressure-height relationship in troposphere is given by (frac{p}{p_0})=[1 + (frac{L_0}{T_0})H]^{(frac{-g_0}{RL_0})}
, where
p=pressure
p₀=datum pressure
L₀=lapse rate
T₀=datum temperature
g₀=acceleration due to gravity
H=height.

10. Any atmosphere that does not conform to the ISA profile is referred to as an off-standard atmosphere.
a) True
b) False
Answer: a
Clarification: Any atmosphere that does not conform to the ISA profile is referred to as an off-standard atmosphere. In this atmosphere there are no assumptions taken as in that of ISA tables.

11. What is relative pressure at 101325 N/m²?
a) 1
b) 2
c) 3
d) 4
Answer: a
Clarification: The answer is 1.
Given p=101325 N/m²,
From relative pressure (δ)=(frac{p}{p_0})
δ=(frac{101325}{101325})=1.

12. What is relative temperature at 241.45K?
a) 1
b) 0.8379
c) 0.8774
d) 0.8756
Answer: b
Clarification: The answer is 0.8379.
Given T=241.45K,
From relative temperature (θ)=(frac{T}{T_0})
θ=(frac{241.45}{288.15})=0.8379.

13. What is relative temperature at 1600ft? (T₁₆₀₀=284.98 K)
a) 0.989
b) 0.838
c) 0.877
d) 0.999
Answer: a
Clarification: The answer is 0.989.
Given T₁₆₀₀=241.45K,
From relative temperature (θ)=(frac{T_{1600}}{T_0})
θ=(frac{284.98}{288.15})=0.989.

14. What is relative pressure at 1600ft? (P₁₆₀₀=95602 N/m²)
a) 0.9453
b) 0.9858
c) 0.9435
d) 0.9595
Answer: c
Clarification: The answer is 0.9435.
Given P₁₆₀₀=101325 N/m²,
From relative pressure (δ)=(frac{P_{1600}}{p_0})
δ=(frac{95602}{101325})=0.9435.

15. What will be the pressure-height ratio of air at an altitude of 9144m? (L₀=-0.0065 K/m, T₀=288.15K, P₀=101325 N/m²)
a) 0.297
b) 0.596
c) 0.359
d) 0.458
Answer: a
Clarification: The answer is 0.297.
Given L₀=-0.0065 K/m, T₀=288.15K, P₀=101325 N/m², H=9144m, we know g₀=9.81m/s², R=287 J/kg-K
From (frac{p}{p_0})=[1 + (frac{L_0}{T_0})H]^{(frac{-g_0}{RL_0})}
(frac{P}{P_0})=[1 + (frac{-0.0065}{288.15})9144]^{(frac{-9.81}{287*-0.0065})}
(frac{P}{P_0})=0.297.

Aircraft Performance Multiple Choice Questions on “Power Producing Power Plant”.

1. What is power producing powerplant?
a) Propulsive force that is directed by increasing momentum of the airflow
b) Propulsive force that is obtained from shaft power by propeller
c) Propulsive force that is directed by decreasing momentum of the airflow
d) Propulsive force that is obtained from engine power by propeller
Answer: b
Clarification: The two forms of powerplant used in aircraft propulsion are thrust-producing and power producing. A power-producing powerplant is the one whose propulsive force is obtained from shaft power by propeller.

2. Which of the following is a power-producing powerplant?
a) Turbojet
b) Turbofan
c) Rocket
d) Piston engine
Answer: d
Clarification: The two forms of powerplant used in aircraft propulsion are thrust-producing and power producing. A thrust-producing powerplant is the one whose propulsive force is obtained by increasing momentum of the airflow through the engine. A power-producing powerplant is the one whose propulsive force is obtained from shaft power by propeller. Examples of thrust-producing powerplant are turbojet, turbofan and rocket. Examples of power-producing powerplant are gas turbine and piston engine.

3. Which of the following statement is correct?
a) Thrust power delivered by an aircraft engine is always less than shaft power delivered
b) Thrust power delivered by an aircraft engine is always more than shaft power delivered
c) Thrust power delivered by an aircraft engine is directly proportional to shaft power delivered
d) Thrust power delivered by an aircraft engine is inversly proportional to shaft power delivered
Answer: a
Clarification: The thrust power delivered by an aircraft engine is always less than shaft power delivered. This is because in a power-producing engine the shaft power have to be converted into thrust during which there occur losses and hence the thrust power delivered by an aircraft engine is always less than shaft power delivered.

4. Which of the following represents the correct formula for propeller efficiency?
a) η=(frac{T}{P})
b) η=(frac{P}{TV})
c) η=(frac{T}{PV})
d) η=(frac{TV}{P})
Answer: d
Clarification: The correct formula for propeller efficiency is η=(frac{TV}{P}) where η is propeller efficiency T is thrust and V is true airspeed and P is shaft power. The propeller efficiency is the ratio of thrust-power output by the shaft power input of a powerplant engine.

5. The propeller efficiency depends on the advance ratio and power coefficient.
a) True
b) False
Answer: a
Clarification: The propeller efficiency depends on the propeller advance ratio and power coefficient. Propeller advance ratio is given by J=(frac{V}{nD}) where J is propeller advance ratio, V is true airspeed, n is rotational speed and D is propeller diameter. Also the pressure coefficient is given by C_P=(frac{P}{frac{rho n^3D^5}{2}}) where C_P is pressure coefficient, ρ is density, P is shaft power, n is rotational speed and D is propeller diameter.

6. Which of the following relations are correct for pressure coefficient?
a) C_P=(frac{P}{frac{rho n^3D^4}{2}})
b) C_P=(frac{P}{frac{rho n^2D^5}{2}})
c) C_P=(frac{TV}{frac{rho n^3D^5}{2}})
d) C_P=(frac{P}{frac{rho n^3D^5}{2}})
Answer: d
Clarification: The propeller efficiency depends on the propeller advance ratio and power coefficient. The pressure coefficient is given by C_P=(frac{P}{frac{rho n^3D^5}{2}}) where C_P is pressure coefficient, ρ is density, P is shaft power, n is rotational speed and D is propeller diameter. Also propeller advance ratio is given by J= (frac{V}{nD}) where J is propeller advance ratio, V is true airspeed, n is rotational speed and D is propeller diameter.

7. Which of the following relations are correct for propeller advance ratio?
a) J=(frac{TV}{nD})
b) J=(frac{P}{nD})
c) J=(frac{V}{nD})
d) J=(frac{PV}{nD})
Answer: c
Clarification: The propeller efficiency depends on the propeller advance ratio and power coefficient. Propeller advance ratio is given by J=(frac{V}{nD}) where J is propeller advance ratio, V is true airspeed, n is rotational speed and D is propeller diameter. Also the pressure coefficient is given by C_P=(frac{P}{frac{rho n^3D^5}{2}}) where C_P is pressure coefficient, ρ is density, P is shaft power, n is rotational speed and D is propeller diameter.

8. What is the propeller advance ratio for the power-producing powerplant when the true airspeed is 300m/s and the diameter of propeller is 0.5 m with rotational speed of 117.81rad/sec?
a) 7.01
b) 9.02
c) 5.09
d) 5.89
Answer: c
Clarification: The answer is 5.09 radian. Given advance ratio V=300m/s , n=117.81rad/sec, D=0.5 m. From the equation J=(frac{V}{nD}) we can find propeller advance ratio. Substitute the given values in the equation J=(frac{300}{117.81*0.5})
On solving J=5.09 radian.

9. What is meant by static thrust?
a) thrust at maximum airspeed
b) power at zero airspeed
c) thrust at zero airspeed
d) power at maximum airspeed
Answer: c
Clarification: Static thrust is the thrust at that is produced at zero airspeed. This static thrust decreases with the increase in airspeed of a power-producing engine. This condition arises when propulsive increases with decrease in airspeed.

10. Which of the following is the correct equation for longitudinal performance equation of motion?
a) (frac{eta P}{V})=D-Wsinγ₂+mV
b) (frac{eta P}{V})=D+Wsinγ₂-mV
c) (frac{eta T}{V})=D+Wsinγ₂+mV
d) (frac{eta P}{V})=D+Wsinγ₂+mV
Answer: d
Clarification: The correct equation for longitudinal performance equation of motion is (frac{eta P}{V})=D+Wsinγ₂+mV where η is propeller efficiency, V is true airspeed, P is shaft power, D is propeller diameter, m is mass flow rate, W is weight.

Aircraft Performance Multiple Choice Questions on “Climb Rate”.

1. Which of the following is the correct safe height of an aircraft?
a) 20000m
b) 15000m
c) 30000m
d) 40000m
Answer: b
Clarification: The safe height of an aircraft for take-off above the airfield is 15000m. The use of safe height is to avoid ground based obstacles and make a clear flight path to avoid aircraft collision and loss of life and property.

2. The operating height is achieved by maximum rate climb.
a) True
b) False
Answer: a
Clarification: The operating height is achieved by maximum rate climb. The safe height of an aircraft for take-off above the airfield is 15000m. The use of safe height is to avoid ground based obstacles and make a clear flight path to avoid aircraft collision and loss of life and property.

3. The best economic flight is achieved by _________
a) maximum drag
b) minimum speed
c) minimum drag
d) maximum fuel consumption
Answer: c
Clarification: The best economic flight is achieved by minimum drag speed and take minimum time to climb. It is must that the flight path is obstruction free and need to continue flight without any stop before take-off.

4. The airspeed best for rate of climb to close to that of their minimum drag speed.
a) True
b) False
Answer: a
Clarification: The airspeed best for rate of climb to close to that of their minimum drag speed. The operating height is achieved by maximum rate climb. The safe height of an aircraft for take-off above the airfield is 15000m. The use of safe height is to avoid ground based obstacles and make a clear flight path to avoid aircraft collision and loss of life and property.

5. Thrust is directly proportional to airspeed.
a) True
b) False
Answer: a
Clarification: Thrust is directly proportional to airspeed. This means the thrust increases with increase in airspeed and decrease with decrease in decrease in airspeed. The airspeed best for rate of climb to close to that of their minimum drag speed.

6. What is climb rate?
a) The rate at which the flight take-off the ground
b) Speed at which the flight takes-off
c) Distance required for flight to take-off
d) Fuel required for the take-off of flight
Answer: a
Clarification: The climb rate is the rate at which the flight take-off the ground. The airspeed best for rate of climb to close to that of their minimum drag speed. The operating height is achieved by maximum rate climb. The safe height of an aircraft for take-off above the airfield is 15000m.

7. The thrust required during the take-off is a function of ________
a) time
b) fuel
c) weight
d) lift
Answer: c
Clarification: The thrust required during the take-off is a function of weight, altitude and temperature i.e. WAT. Thrust is directly proportional to airspeed. This means the thrust increases with increase in airspeed and decrease with decrease in decrease in airspeed. The airspeed best for rate of climb to close to that of their minimum drag speed.

8. The flight mach number is inversely proportional to relative pressure.
a) True
b) False
Answer: a
Clarification: The flight mach number is inversely proportional to relative pressure. This states that the flight mach number increases with decrease in relative pressure and decreases wit increase in relative pressure.

9. Drag raise is avoided by maintaining constant mach number.
a) True
b) False
Answer: a
Clarification: Drag raise is avoided by maintaining constant mach number. The best economic flight is achieved by minimum drag speed and take minimum time to climb. The best rate of climb is achieved by less drag raise.

10. WAT anticipated changes result in better climb performance.
a) True
b) False
Answer: a
Clarification: WAT anticipated changes result in better climb performance. The thrust required during the take-off is a function of weight, altitude and temperature i.e. WAT. Thrust is directly proportional to airspeed.