Aircraft Performance
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Aircraft Performance
Good morning,
I understand that for two identical turbojet aircrafts flying at the same altitude, at Max autonomy velocity (or Max endurance ? Are both terms synonyms ?) in a holding pattern, if one of the aircraft is heavier than the other, then its Fuel Flow (in kg/h) will be higher.
I believe that an increase in weight ox x% will increase the Fuel Flow by x% too.
Now please have a look at the following JAA ATPL questions :
Question1.
Two identical turbojet aeroplane (whose specific fuel consumptions are considered to be equal) are at holding speed at the same altitude.
The mass of the first aircraft is 130 000 kg and its hourly fuel consumption is 4300 kg/h. The mass of the second aircraft is 115 000 kg and its hourly fuel consumption is:
Answer :
Increase in weight = (115000-13000)/130000 = -0,115
Therefore we will have a decrease in fuel flow = 4300 * 0,115 = 496 kg/h
2nd airplane fuel flow = 4300 - 496 = 3804 kg (Right answer according to FlyAround)
I agree with that.
Question2.
Two identical turbojet aeroplanes (whose specific fuel consumption is assumed to be constant) are in a holding pattern at the same altitude. The mass of the first one is 95 000 kg and its hourly fuel consumption is equal to 3100 kg/h. Since the mass of the second one is 105 000 kg, its hourly fuel consumption is:
If I follow the same logic, I find : 2nd airplane FF = 3 426,3 kg/h
However, according to FlyAround, the right answer is : 3259 kg/h
Do you understand what happened ?
Thanks for your help.
Emmanuel Cordier.
I understand that for two identical turbojet aircrafts flying at the same altitude, at Max autonomy velocity (or Max endurance ? Are both terms synonyms ?) in a holding pattern, if one of the aircraft is heavier than the other, then its Fuel Flow (in kg/h) will be higher.
I believe that an increase in weight ox x% will increase the Fuel Flow by x% too.
Now please have a look at the following JAA ATPL questions :
Question1.
Two identical turbojet aeroplane (whose specific fuel consumptions are considered to be equal) are at holding speed at the same altitude.
The mass of the first aircraft is 130 000 kg and its hourly fuel consumption is 4300 kg/h. The mass of the second aircraft is 115 000 kg and its hourly fuel consumption is:
Answer :
Increase in weight = (115000-13000)/130000 = -0,115
Therefore we will have a decrease in fuel flow = 4300 * 0,115 = 496 kg/h
2nd airplane fuel flow = 4300 - 496 = 3804 kg (Right answer according to FlyAround)
I agree with that.
Question2.
Two identical turbojet aeroplanes (whose specific fuel consumption is assumed to be constant) are in a holding pattern at the same altitude. The mass of the first one is 95 000 kg and its hourly fuel consumption is equal to 3100 kg/h. Since the mass of the second one is 105 000 kg, its hourly fuel consumption is:
If I follow the same logic, I find : 2nd airplane FF = 3 426,3 kg/h
However, according to FlyAround, the right answer is : 3259 kg/h
Do you understand what happened ?
Thanks for your help.
Emmanuel Cordier.
Last edited by manucordier; 21st Sep 2010 at 12:37.
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The problem of these two questions both being in the CQB has existed for a number of years. The fact that a known problem has not been correct is not at all unusual.
The correct method is to use:
FF2 = FF1 x W2/W1
The correct method is to use:
FF2 = FF1 x W2/W1
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I have one more question for you Keith.
Why are Civil Aviation employees so bad professionals ? (At least from what I've seen in Belgium and in Spain). I am not only referring to bad wording in JAA exams but also to all the big mistakes and negligences they make at all levels in their administration. They just do their job carelessly. It's a shame for Europe.
If you have an answer for that one,...
Emmanuel.
Why are Civil Aviation employees so bad professionals ? (At least from what I've seen in Belgium and in Spain). I am not only referring to bad wording in JAA exams but also to all the big mistakes and negligences they make at all levels in their administration. They just do their job carelessly. It's a shame for Europe.
If you have an answer for that one,...
Emmanuel.
Last edited by manucordier; 21st Sep 2010 at 15:12.
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What makes you think that they are professionals?
To be fair, those two questions were not put there by the UK CAA alone.
It took a whole multi-national SUBJECT EXPERT TEAM to do that.
To be fair, those two questions were not put there by the UK CAA alone.
It took a whole multi-national SUBJECT EXPERT TEAM to do that.
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The european CAA authorities competency to serve the citizen
Well, English is not my mother tongue but I think the following adjectives are quite appropriate to describe the situation (you will correct it if I'm wrong) :
worrying, disconcerting, alarming, startling...
Anyone willing to complete this very sad list ?
Have a good night.
Emmanuel.
worrying, disconcerting, alarming, startling...
Anyone willing to complete this very sad list ?
Have a good night.
Emmanuel.
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