# Aircraft Design Questions and Answers – Conceptual Sketch Sizing – Takeoff-Weight Calculation

This set of Aircraft Design Multiple Choice Questions & Answers (MCQs) focuses on “Conceptual Sketch Sizing – Takeoff-Weight Calculation”.

1. Estimation of take-off weight is an iterative method.
a) True
b) False

Explanation: Take-off gross weight estimation is an iterative process. Here, we guess the take-off gross weight. According to which we calculate the actual weight. This is a step by step method.

2. Which of the following is part of take-off weight estimation?
a) Lofting
b) Drafting
c) Initial guess of take-off gross weight based on mission specifications
d) Manufacturing part is first step

Explanation: Lofting is definition of skin. Drafting is related to drawing. Based mission specification, crew and payload weight is determined. After which next step is to make an initial guess of take-off gross weight.

3. What is the first step to estimate the gross weight W0?
a) To find crew and payload weight so initial W0 can be guess
b) To find proper lofting
c) Drafting
d) Directly finding take-off distance

Explanation: Take-off gross weight is determined in stepwise manner. It is an iterative process in which we first find weight of crew, passenger, payloads etc. After which next step is to guess gross weight based on crew and payload weight.

4. An aircraft with crew and payload of 180kg is flying. If fuel weight fraction is 0.353 and empty weight fraction 0.481 then, what will be the gross weight of aircraft?
a) 2391kg
b) 2391lb
c) 1000kg
d) 1000lb

Explanation: Given crew and payload = 180kg,
Fuel weight fraction Wf / W0 = 0.353, empty weight fraction We / W0 = 0.481
Gross weight of aircraft is,
W0 = Wcrew + Wpayload + Wfuel + Wempty
By re-arranging,
W0 = Wcrew + Wpayload / [1 – (Wf / W0) – (We / W0)]
= 180 / [1-0.353-0.481] = 1084.33 kg = 2390.96lb

5. Initial guess of gross weight will be same for every aircraft.
a) True
b) False

Explanation: Initial guess of aircraft partially based on crew and payload weight. Crew and payload weight will be based on specification of particular aircraft. Hence, initial guess is not same for each aircraft.
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6. Following diagram is showing mission profile with different phases with mission segment fuel fraction as shown. If crew weight is 150kg, payload of 600kg and empty fraction of 0.495. Determine gross weight of the aircraft.

a) 4430kg
b) 39810kg
c) 4431lb
d) 38910lb

Explanation: Given crew weight = 150kg, payload weight = 600kg
Fuel weight fraction Wf / W0 = 1.06[1 – Wx/W0],
Now from fuel fraction method,
Wx / W0 = multiplication of each phase fraction
= 0.975*0.98*0.96*0.8*0.96*0.97
= 0.6833
Now,
Wf / W0 = 1.06 * [1 – (Wx / W0)] = 0.3357
Empty weight fraction We / W0 = 0.481
Gross weight of aircraft is,
W0 = Wcrew + Wpayload + Wfuel + Wempty
By re-arranging,
W0 = Wcrew + Wpayload / [1 – (Wf/ W0) – (We / W0)]
= 150 + 600 / [1-0.3357-0.495] = 4430kg

7. An aircraft has cruise range of 1500NM and SFC C = 0.5 1/hr. Cruise velocity of jet aircraft is 570ft/s with L/D as 13.2. Aircraft is supposed to do loiter of 2 hrs then what should be the gross weight of aircraft? Given, empty weight fraction of 0.55, crew and payload OF 6500kg with 0.98 as mission segment fuel fraction for climb, take-off and landing.
a) 37000 kg
b) 37.8 ton
c) 37880lb
d) 3780 kg

Explanation: Given, a jet aircraft, crew and payload = 6500 kg.
Since, mission profiles are given we need to find mission segment fuel weight fraction for each.
For take-off, climb and landing it is given as 0.98.
For cruise,
Range R 1500 nm= 9114000ft, C =0.5 1/hr. =0.0001389 1/s, L/D =13.2, velocity V=570 ft/s
Now cruise weight fraction is given by Range formula. For, prop-driven aircraft it is given by,
Wcruise / W0 = $$e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}$$ = $$e^{(-\frac{9114000*0.0001389}{570*13.2})}$$ = 0.8451
Loiter: loiter of 2 hour is given hence,
Endurance E = 2*3600 = 7200 s
Now, loiter fuel fraction
Wloiter / W0 = $$e^{\left(-\frac{E*C}{\frac{L}{D}}\right)}$$ = $$e^{(-\frac{7200*0.0001389}{13.2})}$$ = 0.9270
Now from fuel fraction method,
Wx / W0 = multiplication of each phase fraction
= 0.98*0.98*0.8451*0.9270*0.98
= 0.7373
Now,
Wf / W0 = 1.06 * [1 – (Wx / W0)] = 1.06 * [1-0.7373] = 0.2784
Empty weight fraction We / W0 = 0.55
Gross weight of aircraft is,
W0 = Wcrew + Wpayload + Wfuel + Wempty
By re-arranging,
W0 = Wcrew + Wpayload / [1 – (Wf / W0) – (We / W0)]
= 6500 / [1-0.2784-0.55] = 37880 kg = 37.8 ton

8. Total take-off gross weight depends on _____
a) fuel consumption only
b) only on aerodynamic efficiency
c) fuel, crew, payload and empty weight
d) independent

Explanation: Total take-off gross weight is nothing but the sum of all the possible aspects of an aircraft. Hence, it will depend on fuel weight, crew and payload weight and also on empty weight.

9. Which of the following is correct?
a) Fuel weight fraction is based on mission profile only
b) Take-off gross weight is sum of all possible weight of aircraft
c) Empty weight fraction is always 0.55

Explanation: Fuel weight fraction is affected by mission profile, aerodynamics of aircraft, engine type etc. Empty weight fraction will be different for different type of aircraft. Crew load and payload will be based on mission specifications.

10. An aircraft has Crew and payload of 180kg. It has empty weight fraction of 0.48 and fuel weight is 0.7 times empty weight. What will be the gross weight of aircraft?
a) 2157lb
b) 215kg
c) 950kg
d) 1000lb

Explanation: Given crew and payload = 180kg,
Empty weight fraction We / W0 = 0.48
Fuel weight is 0.7 times empty weight.
Hence, Wf = 0.7*We
Hence, Wf / W0 = 0.7*We / W0 = 0.7*0.48 = 0.336
Gross weight of aircraft is,
W0 = Wcrew + Wpayload + Wfuel + Wempty
By re-arranging,
W0 = Wcrew + Wpayload / [1 – (Wf/ W0) – (We / W0)]
= 180 / [1-0.336-0.48] = 978.26kg = 2157.06lb.

11. Keeping all other factors constant if only range of aircraft is increased then, what will be effect on the gross weight of aircraft?
a) Gross weight will increase
b) Will decrease
c) Unchanged
d) Not depended on range

Explanation: Cruise range will directly affect the fuel fraction of the aircraft. If range is increased then the fuel weight will also increase. Hence, as per W0 = Wcrew + Wpayload + Wfuel + Wempty gross weight will increase.

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