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Exercise A1 question 3

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jukzizy created the topic: Exercise A1 question 3

For an aircraft in level flight to cover the greatest possible time per litre of fuel consumed, it must be flown at a speed which requires
A) The least amount of drag
B) The smallest angle of attack
C) The least amount of power
D) The best lift/drag ratio

The answer in the book is "A"

Just want to know if anyone can explain to me why the answer cannot be D) The lowest possible fuel flow.
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  • Stuart Tait

Stuart Tait replied the topic: Exercise A1 question 3

At the lowest possible fuel flow the power levels would very low as such your airspeed would be low, so induced drag would become a factor as you would need a larger angle of attack, so you would travel less distance per litre of fuel burnt. (ie: maximum endurance)
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jukzizy replied the topic: Exercise A1 question 3

thank you sir
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  • Carello

Carello replied the topic: Exercise A1 question 3

The question asks for a speed to "cover the greatest possible time per liter of fuel consumed". In other words, the question is asking for the best endurance speed. It is a time question.

For any aircraft, best endurance occurs when the fuel flow is at a minimum for level flight. For a piston engine aircraft this will occur when the power required for level flight is at a minimum. You may recall that FF is proportional to power in a piston engine aircraft - the lower the power setting, the lower the fuel flow, the greater the endurance.

With the above in mind, the correct answer is "C" not "B"
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jukzizy replied the topic: Exercise A1 question 3

Thanks alot sir
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  • baddles

baddles replied the topic: Exercise A1 question 3

In the current version of the CADA book, this is Question 4, with correct answer (c).
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