# Aircraft Design Questions and Answers – Conceptual Sketch Sizing – Fuel-Fraction Estimation-1

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This set of Aircraft Design Multiple Choice Questions & Answers (MCQs) focuses on “Conceptual Sketch Sizing – Fuel-Fraction Estimation-1”.

1. Aircraft fuel weight does not include reserved fuel fraction.
a) True
b) False

Explanation: The total fuel carried by aircraft consists of usable fuel and reserved fuel. Useable fuel is provided for completing a particular mission. Reserved fuel is for an emergency.

2. Total fuel weight of aircraft is ______
a) mission fuel only
b) sum of mission fuel, reserve fuel and trapped fuel
c) sum of trapped and mission fuel
d) reserved fuel only

Explanation: The fuel weight of aircraft is sum of useable mission fuel, reserved fuel and trapped fuel. Mission fuel is the actual useable fuel for the respective mission. Trapped fuel is unusable fuel which has been trapped in supply lines or which cannot be used.

3. Choose the correct statement based on fuel weight.
a) Fuel required is solely based on mission profile
b) Fuel weight is independent of SFC of engine
c) The required amount of the fuel for mission depends on aerodynamics, SFC, mission itself etc
d) Fuel requirement is not affected by any factors

Explanation: Total aircraft fuel requirement does not solely depend on mission profile. Fuel weight for mission depends on number of factors such as mission profile, aerodynamics, SFC of engine etc.

4. Is it mandatory for Aircraft to carry reserved fuel?
a) Yes
b) No
c) Depends upon the type of aircraft
d) Depends upon manufacture

Explanation: Every aircraft has to carry reserved fuel as an additional weight. Reserved fuel is provided in case of an emergency. During rejected take-off reserved fuel can be used to perform loiter as well.

5. The typical method for determining fuel weight used is called as _____
a) fuel-fraction method
b) fuel-invert method
c) fuel interpolation
d) fuel fraction mining

Explanation: Fuel- fraction method is a simple method for estimating fuel fraction of the aircraft. It is the most commonly used method due to the simplicity of calculations.

6. What is the working principle of ‘fuel-fraction’ method?
a) Division of mission profile into number of phases and finding individual phase fuel fraction
b) Division of mission profile into 3 phases only
c) Calculating fuel fraction for each stage
d) Assuming any value for fuel fraction

Explanation: The fuel fraction method is mostly used method for fuel weight fraction. This is very simple method in which we divide whole mission profile into number of mission phases. After that we calculate individual mission segment weight fraction. And based on which we determine approximated fuel weight.

7. In A/C, we provide reserve fuel for _____
a) loiter maneuver
b) weight reduction
c) to increase weight
d) there is no provision for it

Explanation: Every aircraft has a particular mission profile to follow. Fuel requirement are based on it. In some cases, aircraft need to loiter for more time. If some additional fuel is nor provided then, in such cases aircraft will not be able to perform any additional loiter. Hence, for such cases and also for emergencies we provide reserved fuel.

8. According to FAA, general aviation aircraft requires reserved fuel in terms of _____
a) additional cruise fuel of half hour
c) no provision is mentioned in FAA
d) additional taxi-way fuel of three hours

Explanation: For a typical aircraft, it is mandatory to carry reserved fuel. This reserved fuel can be utilized at the time of emergency. According to FAA regulation, for general aviation category we need to provide additional cruise fuel so that it can be used to improve endurance by half hour.

9. Determine the corrections or otherwise of the following Assertion [A] and reason [R]:
Assertion [A]: Total fuel volume of aircraft is divided into mission or used fuel, reserve fuel and trapped fuel.
Reason[R]: Depending on type of aircraft, fuel fraction for each category will be different.
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 total fuel of aircraft can be seen as sum of mission fuel, reserved fuel and trapped fuel. Each fuel has specific definition. Mission fuel or useable fuel is actual available fuel to complete mission profile. Trapped fuel is that fuel that cannot be used. Fuel fraction for each category will be different for different aircrafts as their mission profile, aerodynamics etc. will be different.

10. An airliner with take-off gross weight of 2100kg is cruising with fuel weight fraction of 0.280. Then, what will be the weight of fuel (Wf)?
a) 588kg
b) 588lb
c) 90kg
d) 28lb

Explanation: Given,
Aircraft take-off gross weight W0 = 2100kg,
Fuel weight fraction = Wf/W0 = 0.28
Hence, fuel weight Wf = (Wf/W0) * W0 = 0.28*2100 = 588kg.

11. 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.

12. 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.

13. 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].

14. 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 to that of at the begin
c) weight of phase at the begin
d) weight at end of the phase 