Originally Posted by
Doors to Automatic
On an A320 carrying an extra 45 mins of fuel would add around 2% to take-off weight. What effect would this have on fuel burn?
As mentioned by CaptainProp, the extra fuel burn caused by additional weight is computed using the weight factor.
The weight factor for modern aircrafts is typically between 3.1% per hour and 3.5% per hour. Historical values have ranged from 2.5% per hour to 5% per hour.
In practical terms, uploading an additional 1000 kg of jet A1 will burn an additional 31 to 35 kg of fuel with every hour of the flight.
Or, if your aircraft needs 1200 kg of fuel for flying 30 minutes at 1500 ft as the final reserve and if your planned flight time is 2h, you need to upload 1285 kg of fuel.
Weight factor increase with longer flight time because its effect is cumulative.
The weight factor for a 5h flight is not (1 + 5 * 0.035 ) = 1.175 (or a 17.5% factor),
but it is 1.035 ^ 5 = 1.188 (or a 18.7% factor).
It also increases (slightly) with very short flights because of climb and approach burn.
If you want to read about the theory behind weight factor, google on "Breguet Range Equation"
or read this page
https://www.aircraftit.com/articles/...of-weight-cow/