PaladinX 11 Posted August 13, 2019 Share Posted August 13, 2019 Dear Aerosoft Support Team, a fuel question: Is there a thumbrule, how to increase the amount of fuel, when i fly with a higher cost index? (E.g. when i want to fly faster, i fly with an index of 50, 70 or 90). How much more fuel do i need then compared to the results of the fuel planner? What cost index is taken in the background? Link to comment Share on other sites More sharing options...
Fragged^2 40 Posted August 13, 2019 Share Posted August 13, 2019 This would be in the OFP. You can use a tool like Simbrief to generate one and it will show how flight levels and cost index change the flight time and fuel burn. Below is a paste from my A319 flight from LOWI to EGKK. The fuel planner that comes with the plane is really simple and I only use it to plug in the numbers from Simbrief (ZFW and Block fuel). OPERATIONAL IMPACTS ------------------- WEIGHT CHANGE UP 1.0 TRIP P 0037 KGS TIME P 0000 WEIGHT CHANGE DN 1.0 TRIP M 0033 KGS TIME M 0000 FL CHANGE UP FL1 NOT AVAILABLE FL CHANGE DN FL1 TRIP P 0018 KGS TIME P 0000 FL CHANGE DN FL2 TRIP P 0094 KGS TIME P 0000 SPD CHANGE CI 0 TRIP M 0064 KGS TIME P 0002 SPD CHANGE CI 50 TRIP P 0017 KGS TIME M 0000 Link to comment Share on other sites More sharing options...
PaladinX 11 Posted August 13, 2019 Author Share Posted August 13, 2019 Hmm, interesting. Why does SPD Change CI 0 (which would be slower) use 64 KGS, while CI 50 (which would be faster) use only 17 KGS more? *confused* *Edit: Ok, now i understood: "M" 0064 KGS "minor"? And "P" 0017 KGS "more"?? That would be nearly neclectable, seen on the whole trip. Or do i interprete wrong? Link to comment Share on other sites More sharing options...
Fragged^2 40 Posted August 13, 2019 Share Posted August 13, 2019 58 minutes ago, PaladinX said: Hmm, interesting. Why does SPD Change CI 0 (which would be slower) use 64 KGS, while CI 50 (which would be faster) use only 17 KGS more? *confused* *Edit: Ok, now i understood: "M" 0064 KGS "minor"? And "P" 0017 KGS "more"?? That would be nearly neclectable, seen on the whole trip. Or do i interprete wrong? M = Minus / less, P = Plus / more. This is vs the calculated CI of 21 for the flight. Simbrief has a interactive tutorial/guide for what all the info in an OFP mean: https://www.simbrief.com/system/guide.php#ofpsample Link to comment Share on other sites More sharing options...
Deputy Sheriffs Secondator 643 Posted August 16, 2019 Deputy Sheriffs Share Posted August 16, 2019 On 8/13/2019 at 4:27 PM, PaladinX said: Hmm, interesting. Why does SPD Change CI 0 (which would be slower) use 64 KGS, while CI 50 (which would be faster) use only 17 KGS more? *confused* *Edit: Ok, now i understood: "M" 0064 KGS "minor"? And "P" 0017 KGS "more"?? That would be nearly neclectable, seen on the whole trip. Or do i interprete wrong? To simplify Cost Index: CI = cost of time / cost of fuel With low cost index you are using least possible amount of fuel to complete the flight but at the same time you are also using the most time to complete the flight. With higher cost index you are using less time to complete the flight but in exchange you are using more fuel to complete the flight. This is the very basics of it. Depending on how much different areas cost to operate the Cost Index can be adjusted accordingly. So since CI=0 means that you are using least possible fuel to complete the flight that's why the M for Minus in front. Means that you will save that fuel from trip fuel and therefore can subtract it from the trip fuel is the flight is completed with CI=0 instead of the planned cost index in the flightplan. Link to comment Share on other sites More sharing options...
PaladinX 11 Posted August 18, 2019 Author Share Posted August 18, 2019 Thank you for the additional infos. I am aware about the function of the cost index. But while the speed changes more than expected (e.g. 290 kts with CI=30 to 340 kts with CI=90), i have no feeling about the fuel usage. Thats why i ask for the CI that is used with the Fuel Planner by Aerosoft. Its still unclear for me, because it contains no information. Link to comment Share on other sites More sharing options...
Deputy Sheriffs Secondator 643 Posted August 20, 2019 Deputy Sheriffs Share Posted August 20, 2019 Especially on shorter flights Cost Index doesn't really play that big of a factor on fuel usage. On Longer flights it becomes more important but still the difference isn't that big on single flight. But the cumulative effect when you apply this to whole fleet over the span of a year is already significant. So the difference is so small that when doing fuel calculations the cost index doesn't really matter that much. But with software like simbrief the cost index affects several other things than just fuel usage and that's probably why it asks it to make better predictions (on top of estimating the fuel usage). Link to comment Share on other sites More sharing options...
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