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A little stuck on fuel calculations...


Nealius
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I have been geeking out over the charts in the A-10A -1 and I managed to get through the 3 sheets of the A4-4 and come out with my "specific range" and fuel flow, but how do I actually turn it into fuel needed to fly a certain distance?

 

Let's say I'm flying 200nm and I burn a pound of fuel every 0.10nm according to sheet 3. Is it as simple as 200/0.10 = 2,000lbs of fuel burned, or am I completely wrong?

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Yeah, you've got it.

 

Don't forget to allow for fuel burned before & during take off/departure, in the climb, during combat, as well as approach and landing.

 

Also, if you want to make life a bit easier on yourself and make in flight fuel calculations easier there are a few "rough" values you can use.

 

  • Low Level Cruise - 20 lbs/nm
  • Medium Level Cruise - 15 lbs/nm
  • High Level Cruise - 10 - 12 lbs/nm
  • Single Range Pass/Attack (2 to 2.5 mins) - 200 lbs to 250 lbs
  • Descent & Approach (15 mins) - 500 lbs
  • Instrument Pattern (7 to 10 mins) - 300 lbs to 500 lbs
  • Overhead Pattern (1 to 2 mins) - 150 lbs to 200 lbs

Cruise fuel consumption is based on you flying at best cruise speed, the first white band on the AoA gauge. Around 220 KIAS at normal combat weights.

 

Climb consumption will need to be calculated based on weight, drag, and height of climb. Likewise best cruise altitude will need to be worked out, and is based on weight & drag index.

 

For a general starting point, a 1.5 hour Hi-Hi-Hi mission in a COIN (so mostly low threat & med alt PGM employment), will require about 7000 lbs of fuel. Allow at least an 1100 lb landing reserve, and also plan to allow enough fuel to reach a divert base if you can't land at primary for any reason (normally gives around 2000 lbs total reserve in the current theatre). That means you'd require at least 9100 lbs for that 1.5 hour hi-hi-hi mission.


Edited by Eddie
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Silly question but there's no hidden 'trip computer' like modern day cars that tells you distance or time to empty is there?

 

Or is it all done in one's head with a bit of maths?

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Just a bit of maths.

 

Best bet is to work out a bingo before you go.

 

To see if you can make it home, once you are in the cruise just get your time to destination from the data block at the bottom right of the HUD. Work out what fraction of an hour that is and time it by your fuel flow. That will roughly be your enroute gas.

 

If you are really low on fuel you can use your AoA to work out best range speed (angle of attack).

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You could to a degree look at using a 'Whiz Wheel'.

There a few online print outs you can get; or app's for Ipad/Android, etc.

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I've got a "whiz wheel," still learning all of its functions.

 

One thing I noticed about the charts though, the speed is given in Mach/TAS. I thought fuel calculations were supposed to be done in GS?

 

I haven't gotten to the landing calculations yet, I'm not really sure how to predict aircraft weight /fuel when coming to the landing phase. I usually just do a simple visual approach and fly the AoA indexer.

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Crashed for me when I tried putting in the runway heading :(

 

I have a question about wind speeds. My game settings are set to Imperial, but wind is still given in m/s. Do I need to convert, or is the true value in knots with the wrong unit notation?

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Might be the .net libraries. I have no idea what version I have.

 

Okay, now here are two things that don't make any sense to me:

 

1. Calculating how much fuel you need to get from A to B. The charts require gross weight, thus you already have to know your fuel weight. If you don't know your fuel weight you can't do anything. So how can you load "just enough" fuel to get from A to B? That will change your gross weight and your fuel calculations.

 

2. How do you know your gross weight when you begin your descent? I don't know how much distance/time it takes to descend from my cruise altitude, which means I have no clue at what point to begin my descent and thus no clue how much fuel I have burned up to that point. But the chart wants gross weight to calculate distance/time? It has me caught in a loop.


Edited by Nealius
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One thing I noticed about the charts though, the speed is given in Mach/TAS. I thought fuel calculations were supposed to be done in GS?

 

TAS plus wind velocity is equal to your GS which is why the chart gives you TAS.

 

I haven't gotten to the landing calculations yet, I'm not really sure how to predict aircraft weight /fuel when coming to the landing phase. I usually just do a simple visual approach and fly the AoA indexer.

 

Flying the AoA is the safest bet, I doubt that even the real guys do full on landing computations when they're recovering to large runways at an AFB.

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Wind at altitude? ATIS/ATC only gives local wind doesn't it?

Yep. May have misunderstood what you were asking. Generally you use published forecasts based on radiosonde data to calculate cruise groundspeed before flight. In the USA the forecast is available four times per day.

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Well this is cool. I didn't get my fuel calculations quite right because I wanted to fly 250KIAS at FL250 which wasn't possible (only made it up to 230KIAS) but I checked the charts and the charts said I should be using about ~3600lbs/hour. Checked my engine instruments and what do you know, 3600lbs/hour :D

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Well this is cool. I didn't get my fuel calculations quite right because I wanted to fly 250KIAS at FL250 which wasn't possible (only made it up to 230KIAS) but I checked the charts and the charts said I should be using about ~3600lbs/hour. Checked my engine instruments and what do you know, 3600lbs/hour :D

 

Have any luck with the fuel calculator?

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