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Stuart

× Welcome to the CPL Aerodynamics question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

Exercise A1 question 3

• Posts: 92

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
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.

• Posts: 412

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)

• Posts: 92

thank you sir

• Posts: 111

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"

• Posts: 92

Thanks alot sir