Calculate fuel with D.S.T

(Because some people are uno…)This is for flight sim use, and does not take into account actual aircraft figures and legal fuel reserves!

With that being said, I’m going to explain how to calculate trip fuel, so you don’t drag the fuel slider over to “full tank” on a 25min flight, or worse, think you have enough fuel in your C172 to fly from KLAX to PHNL!

Now, for those of you who have read my last post on dst, this should be fairly straight forward.

  • if we want to calculate our max range, we need to find (S and T) our speed (GS) and the time that we can fly for (not taking into account reserves) to find distance right?
    (S X T = D)

“ I know the speed but how do I find time?!”

Simple! It’s yet again DST! (we use the formula twice) If we know our fuel on board (LTRs, USG, Kg, LBs…whatever you use!) and the rate that it’s being used, we can work out time! I’ll use the whiteboard to explain.

Remember how we can change the “D” in the triangle to whatever we want? This time we change it to “L” for litres, and the “S” to “R” (Rate) to get the endurance in HRS (X60 to get mins)

  • I’ll put a table below so you can convert between units if you use the imperial system. now with that time figure we can find max DIST by again, covering the item we want to work out. Let’s do a worked example.
    Out speed is 110kts in our C172 and we are burning 36 LTRs per hour with 200 LTRs (AVgas) in out tanks. Find max Range:

Ans: 610nm

So first we had to work out the time, then we could work out our dist by multiplying our speed and time.

Now let’s find the fuel we need to complete a trip!
Say we had a 200mile long trip planned when we’re waiting for our taxi clearance. Ignoring winds, we have estimated a ground speed of 110kts. We know in order to find LTRs we need R and T. But first we need a time. So we hit the DST, Distance / Speed should give us a time right? So we / 200 by 110 to get 1.8 hrs. Now we can do DST number 2 to find our fuel.
So we are yet again burning 36LPH, and R X T will get us our ”L” value. So, 36 X 1.8 will = 65 ltrs that you need to carry to make the airport at the absolute MINIMUM!
I’ll draw up what we just did.

Now, since infinite flight uses KGS for fuel here’s how to convert:
X ltrs of AVgas by .72 to get kg (Use .81 if using Jet-A instead)

US Gallons to ltrs X 3.8

US Gallons to LBS X 1.58 (if using jetA-1, X1.76 instead)

  • you can revert these by dividing

Yet again, these are estimated figure. Don’t use them in the real world!

Did I miss anything, get something wrong, or not explain anything clear enough? Please let me know.
hope this helped!✈️
(Ignore the spelling mistakes😆)


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