Mithras

How Do I Calculate Fuel Burn?

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Hi,

 

I'm stuck with flight planning because I cannot see any fuel burn numbers in any of the aircraft I have! Am I missing something in the Nav Log or something? I generally fly A2A GA planes, plus the Twin Otter and Flight 1 Islander, as well as a few Carenados and the default airliners. I know how far I want to fly, and I want to carry enough fuel to cover that plus reserves, but nowhere can I find the fuel consumption numbers I need. Do you think referring to real eorld figures would be reliable ...?

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I'm fairly certain for A2A fuel consumption is provided in the manuals, and I would imagine their model is good enough that it would be fairly accurate. 
AFAIK the Nav Log does include estimated fuel consumption in the top left (?) corner but it is notoriously unreliable for pretty much anything apart from default aircraft (and even then can be iffy).

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Fuel burn depends on a lot of parameters (altitude, throttle settings, temperature, mixture settings, ..) so that it is necessary to look at published material for a specific plane for accurate fuel burn estimates. However, if you just want to have enough fuel to get through your flight with enough reserves left, then a rule of thumb for each plane is usually sufficient.

 

I found that the best way to estimate fuel burn is to hop in the plane, fly a little bit at a typical altitude and read off the fuel flow from the plane's instruments. If for some reason your plane doesn't have that, you can probably find a fuel flow gauge on the web or use Aivlasoft's EFB.

 

Peter

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Hi,

 

For VFR, non-commercial flights, this is easy. You don't need to calculate fuel very accurately.

Exception is when you want to save fuel for longer cross-country, you take a look at POH and read accurate fuel burn for given power settings and altitude.

 

Let's focus on some example for C152.

We use average fuel burn per hour as 25 liters.

 

Here is screenshot from my flight planner:

20.jpg

 

 

Fuel calculations are in the table at lower right

 

Qmax - fuel tanks capacity (100l for C152)
Qm - unusable fuel (you get this value from POH, this is the fuel reserve you never use - 7l for C152)
Qnav - navigational fuel reserve - fuel reserve for 45 minutes - you include this as a backup for every flight
Qfl - fuel used for flight - flight duration in hours (2:05) times average fuel burn (25lph)
Qlft - fuel left after flight = Qmax - Qm - Qnav - Qfl
 
VfrFlight has a 'Ruler' feature which lets you to measure distance on map and fuel burn for given distance (below is example - distance 15.5 nm, 12 minutes of flight, 4.8l fuel burn):
 
23.jpg
 
If you want to use US or imperial gallons, you can change it in the settings  :rolleyes: .
 
Lukasz

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Back in the day, when I was flying Islanders for Mount Cook Airlines in New Zealand, as I recall we used a fixed fuel burn rate for flight planning. I don't remember what it was but you could figure it out yourself in the same way you can find out MPG in your car - start up with full fuel, do a flight and then see how much it takes to fill the tanks again. As I recall, what we did have to be careful about was CofG and Total All-Up Weight with pax, bags and fuel. We had a circular slide rule thing that we used...

This is an issue that some developers have addressed and others ignored. One of the best utilities offered by a developer that I've seen is iFly.

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