manucordier
21st Sep 2010, 12:26
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.