This set of Aircraft Design Multiple Choice Questions & Answers (MCQs) focuses on “Thrust Weight Ratio-1”.
1. A/C with higher thrust to weight ratio can accelerate more quickly.
Explanation: Thrust to weight ratio is an important parameter. This ratio can affect the performance of an aircraft. Higher thrust to weight ratio represents more thrust for given weight. Hence, more quick acceleration, more maximum speed etc. can be achieved through higher values of thrust to weight ratio.
2. Can we estimate thrust loading based on Wing loading?
c) Both are same
d) Are not related to each other
Explanation: Thrust loading and wing loading are one of the crucial parameter of an aircraft design. A designer can find both of them either by estimating thrust loading and then evaluating the wing loading or vice-versa.
3. Higher value of thrust loading indicates ____
a) higher maximum speed
b) lowest maximum speed
c) lowest climb
d) lowest acceleration
Explanation: Thrust loading is nothing but a ratio. It is the ratio of aircraft thrust to the weight of the aircraft. Higher thrust loading means higher thrust for given weight. This will improve maximum speed of an aircraft.
4. Thrust to weight ratio of all the aircrafts is same.
Explanation: Different type of aircrafts will have different requirements. Weight of different aircraft will be based on mission requirements. Thrust produced by engine will be different for all aircraft. Hence, thrust loading is not same for all the aircraft.
5. Thrust loading during flight does not remain constant as _____
a) fuel burns with each mission phase
b) fuel is not burned at all
c) will not change
d) lofting is changed
Explanation: Thrust loading is generally measured based on take-off conditions. At each phase of mission profile weight will vary. Fuel burns throughout the flight which varies aircraft weight and which changes thrust loading as well.
6. Power loading of prop driven aircraft is ______
a) greater or equal to one
b) same as lift of propeller
c) always be zero
d) equal to drag always
Explanation: Power loading for propeller driven aircraft is an important parameter representing the relation between power and weight. Power loading will always be greater than one and in much idle case it will be one. It cannot be zero. Lift and drag are forces.
7. Power loading of a prop driven aircraft is defined as _________
a) weight of aircraft to the horsepower by prop engine
b) weight of aircraft into the horsepower by prop engine
c) horsepower by prop engine
d) weight of aircraft
Explanation: Power loading will be defined as the ratio of weight of the aircraft to the power; typically horsepower produced by prop engine. It will impact on acceleration, climb, maximum speed etc. In general, it varies from 10-20.
8. Determine the corrections or otherwise of the following assertion [A] and reason [R]:
Assertion [A]: Aerobatic prop aircraft has much higher power loading.
Reason[R]: Power loading of prop aircraft is ratio of power to the weight of the aircraft.
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) Both [A] and [R] are false
d) [A] is false but [R] is true
Explanation: Power loading of prop aircraft is the ratio of weight of aircraft to the power produced by engine. Hence, [R] is false. Aerobatic aircrafts will require more power to perform different maneuvers. Hence, typical value of power loading will be around 4-7. Hence, [A] is also false.
9. Which of the following is correct for horsepower (hp) to the weight ratio?
a) T/W = (550*η / V) * (hp/W)
b) T/W = (550*η / V)
c) T/W = (550*η / V) + (hp/W)
d) T/W = (550*η / V) – (hp/W)
Explanation: Power is defined as thrust into velocity. Propeller will be operating with some finite value of propeller efficiency ƞ. 550 we multiply as to make units similar both the side.
In general, for prop aircraft thrust loading and power loading is given as,
T/W = (550*η / V)*(hp/W)
10. Typically, designer designs thrust loading based on ________
a) static sea-level conditions, take-off requirement etc
b) only Lift
c) only static sea-level conditions
d) only landing conditions
Explanation: When designer speaks for a thrust loading it generally refers to the value which has been calculated for standard day conditions, static sea-level conditions, take-off performance etc. Different phases incorporate different values of thrust loading. Hence, a designer typically converts them to take-off conditions.
11. A jet fighter aircraft is flying with maximum Mach number of 2.0. What will be the thrust loading of the fighter?
Explanation: Given, Jet fighter with max Mach number M = 2.0
Now for jet fighter thrust loading is given by,
T/W0 = a*Mc
For a jet fighter a=0.514, c=0.141
Hence, T/W0 = 0.514*2.00.141 = 0.566 = 0.57.
12. If thrust loading is 0.65 then, find the power loading of a prop aircraft. Consider propeller is idle.
Explanation: Given, prop aircraft, thrust loading T.L. = 0.65
Since propeller is idle, propeller efficiency ƞ=1. Here, velocity is not mentioned so we will substitute it as V.
Now, thrust loading is given as,
T.L. = T/W = (550*η / V)*(hp/W)
Hence, power loading W/hp = PL = 550*η / (T.L.*V) = 550/(V*0.65) = 846.15/V.
13. If a turboprop is cruising with 2275kg of weight, then determine power loading. Given power = 190hp.
Explanation: Given, weight at cruise W = 2275kg, power = 190hp.
Hence, power loading = W/hp = 2275/190 = 11.97 = 12.
14. An aircraft is cruising with lift coefficient of 2.5 and thrust loading of 0.6. Find drag coefficient of the aircraft.
Explanation: Given, lift coefficient CL = 2.5, thrust loading T/W = 0.6.
Now, thrust loading at cruise is given by,
T/W = CD / CL
0.6 = CD / 2.5
CD = 0.6*2.5 = 1.5.
Explanation: Above diagram is showing thrust lapse at cruise. It is the variation of maximum thrust at cruise and take-off with altitude. Temperature lapse rate shows how temperature is changing with the altitude.
Sanfoundry Global Education & Learning Series – Aircraft Design.
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