1. A prop-driven aircraft having fuel weight of 650kg. Now, aircraft is taxing on runway, after which it has fuel fraction of 0.975. Determine fuel used during taxing of aircraft, if W0 = 5000kg.
a) 225kg
b) 125kg
c) 221kg
d) 125.65lb
Explanation: Given,
Aircraft take-off gross weight W0 = 5000kg,
Fuel weight fraction after taxi = Wtaxi/W0 = 0.975
Here, there is no provision of reserved fuel is mentioned. So, we are neglecting reserve fuel fraction.
Now, from fuel fraction method,
Used fuel weight fraction is Wf /W0 = 1 – (Wtaxi/W0)
= 1 – 0.975 = 0.025
Hence, fuel used during taxing mission = Wf = W0 * 0.025 = 125kg.
2. A jet transport aircraft has fuel storage of 1200kg. It has completed taxi phase and preparing for take-off. At the end of the taxing, it has fuel fraction of 0.98. Determine how much fuel is available after taxing. Given take-off gross weight is 9000kg.
a) 1020kg
b) 180kg
c) 1800kg
d) 2240lb
Explanation: Given,
Aircraft take-off gross weight W0 = 9000kg, Fuel storage = 1200kg
Fuel weight fraction after taxi = Wtaxi/W0 = 0.98
Here, there is no provision of reserved fuel is mentioned so, we are neglecting reserve fuel fraction.
Now, from fuel fraction method,
Used fuel weight fraction is Wf / W0 = 1 – (Wtaxi/W0)
= 1 – 0.98 = 0.02
Hence, fuel used during taxing mission = Wf = W0 * 0.02 = 180kg.
Now, remaining fuel weight = fuel storage – fuel used during taxi
= 1200 – 180 = 1020kg.
3. Determine the corrections or otherwise of the following assertion [A] and reason [R]:
Assertion [A]: Fuel consumption is more for low level, high speed flight mission.
Reason[R]: At low altitude, the aerodynamic efficiency decreases drastically which affects the engine efficiency and range as well. To maintain cruise flight more fuel consumption is required.
a) Both [A] and [R] are true and [R] is the correct reason for [A]
b) Both [A] and [R] are true but [R] is not the correct reason for [A]
c) [A] is true but [R] is false
d) [A] is false but [R] is true
Explanation: The low-level strike mission has to fly at just few km off the ground. During such flight the L/D ratio – aerodynamic efficiency is reduced in drastic manner. Since flight needs to be at higher velocity more thrust will be required. This will increase fuel consumption as compare to high altitude flight. Hence, both [A] and [R] are true and [R] is the correct reason for [A].
4. Mission leg fuel fraction is defined by _____
a) weight at end of the phase to that of at the begin
b) weight at end of the phase
c) weight of phase at the begin
d) None of the above
Explanation: Mission leg is nothing but the individual mission segment or phase. Mission leg fuel fraction is weight of the fuel at end of the phase to that of at beginning of that mission leg.
5. Which of the following is part of the fuel-fraction method?
a) Developing lofting
b) Empty weight fraction
c) Calculating individual mission segment weight fraction
d) Finding volume ratio
Explanation: Lofting is a vital part of preliminary design phase. The fuel fraction method is very simple and basic approximation method. Here, mission profile is divided and then for every individual phase we calculate mission segment weight fraction
6. An Aircraft has gross weight of 10000lb. At the end of the mission segment it has weight fraction as 0.985. Determine fuel consumed for this mission.
a) 150lb
b) 150kg
c) 60kg
d) 60lb
Explanation: Given,
Aircraft gross weight W0 = 10000lb
Fuel weight fraction at the end of mission = Wx/W0 = 0.985
Here, there is no provision of reserved fuel is mentioned. So, we are neglecting reserve fuel fraction.
Now, from fuel fraction method,
Used fuel weight fraction is Wf / W0 = 1 – (Wx / W0)
= 1 – 0.985 = 0.015
Hence, fuel consumed during this mission = Wf = W0 * 0.015 = 10000 * 0.015 = 150lb.
7. Choose appropriate option for cruise mission leg weight fraction.
a) Breguet endurance formula
b) Breguet range formula
c) Cruise invert method
d) Breguet approximation
Explanation: Breguet endurance formula is used to determine the endurance of aircraft. Range formula is used to calculate range for respective mission. In simple sizing method we consider that the cruise is ending with descent. Also, we assume that cruise range has accounted for descent as well. Hence, we use range formula to determine fuel fraction.
8. A jet aircraft is cruising at 12000ft. What will be the cruise leg (mission phase ‘n’) weight fraction?
a) Wn/Wn-1 = \(e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}\)
b) Wn/Wn+1 = \(e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}\)
c) Wn/Wn-2 = \(e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}\)
d) Wn/Wn-1 = \(e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}\)
Explanation: Aircraft is cruising at 12000ft and the cruise mission leg is nth mission phase of whole mission profile. Here, we will use Breguet range formula to find Weight fraction. Breguet range formula,
R = (V/C) * (L/D) * ln (Wn-1/ Wn)
Now by re-arranging, cruise mission leg weight fraction is,
Wn/Wn-1 = \(e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}\)
9. What will be the total fuel weight fraction for x-number of mission phases?
a) Wf / W0 = 1 – (Wx / W0)
b) Wf / W0 = 1 + (Wx / W0)
c) Wf / W0 = 1 / (Wx / W0)
d) Wf / W0 = 1 + (Wx / W0)
Explanation: The fuel-fraction method is used to determine total fuel weight fraction.
According to which if there are x – number of mission phases in mission profile then the total fuel weight fraction is given by,
Wf / W0 = 1 – (Wx / W0)
Since, reserved fuel is not mentioned we can neglect it.
10. What will be the weight fraction of the aircraft at final mission segment w.r.t. W0?
a) Multiplication of individual weight fraction
b) Division of individual weight fraction
c) Addition of individual weight fraction
d) Subtraction of individual weight fraction
Explanation: We can divide whole mission profile of aircraft into number of mission phases or legs. Fuel fraction at each mission segment will be fuel weight at end of phase to that of beginning. Hence, if there are z – number of mission phase then, final mission phase fraction will be multiplication of individual weight fraction which will give weight fraction w.r.t. take-off gross weight W0