how do you work out the fuel usage?

[machineman9]

interesting question i know... its for a program i am building. i want it to have a guage that displays how much fuel has been used, but i cant think of what the equation would be

i have 40 gallons of fuel, i have 15 miles to the gallon... what could the equation be? (i can work it out from speed, time or distance, i just dont know the equation)

some help?

cheers

[EGNX]

Well for starters you need to know how many gallons it uses per hour. From that you can work out minutes and then seconds....
For example:

Plane uses 8 gallons a hour, thats 0.13 gallons a minute and 0.002 gallons a second. So for your gauge it simply needs to add up how many gallons per second over a certain amount of time giving you how much fuel has been consumed...

The problem is that fuel consumption will not always be the same due to different throttle settings etc....

So really this method is not very useful.... really you want to be using a fuel flow gauge to work this out....

[machineman9]

hmm, i think ive got it actually (after 2 days of thinking about it! i guess D=S/T isnt clever to be working with. darn brain)

miles=(S*1.1)*T

miles/15= gallons used

gallons-gallons used= gallons left.


the speed is in knots, so i need to times it by 1.1 to get into miles and hour. so, would i need to divide the time or anything atall? the time is in minutes and seconds for the meantime

[Brett_Henderson]

Better use 1.15, instead of 1.1 ..

[beaky]

That's good work, but you're missing the point here:

The engine(s) will consume fuel whenever they're running, whether the plane is moving or not, so mpg is not a good starting point.
Pilots track fuel consumption for determining endurance (time), not range. Range is a secondary result of aviation fuel calculations.

So your formula has to be based on the RL average hourly rate of consumption, with some flexibility for taking into account various throttle settings.

[machineman9]

yeh, i havent taken into account the idle fuel usage.

but, for the current moment in time i dont think it is too important, in this very unrealistic yet slighty realistic BETA of it... the engines are set at an X value in the program, and then you can choose to increase or decrease the throttle down or up to 0/100% open/closed

the full thing will have idle usage and things... i just want to use the 2 things which i have (speed and time) because that makes distance, which can be calculated into the usage... tad bit primative but i think it works. later i will be adding a RPM counter, so i guess that could be incorporated?


how could time be used to work it out then? im not so much a trained aviator as more a yr10 student  :-/

[Brett_Henderson]

[quote]how could time be used to work it out then? im not so much a trained aviator as more a yr10 student

[machineman9]

hmm, so it looks like im going to have to get some engine specs then... to get the burning fuel rates?

[Brett_Henderson]

Yes.. that is important data.. but it's still a variable ( different fuel flow for climb, cruise, etc). And it's a given, as in, you'd already know that your C172 burns 8 gallons per hour, and you know how to read your watch. If you have 40 gallons in the tank (40/8=5) you've got an absolute maximum of 5 hours of fuel on board. How many miles the works out to be, depends on other things, like the wind..

[machineman9]

Yes.. that is important data.. but it's still a variable ( different fuel flow for climb, cruise, etc). And it's a given, as in, you'd already know that your C172 burns 8 gallons per hour, and you know how to read your watch. If you have 40 gallons in the tank (40/8=5) you've got an absolute maximum of 5 hours of fuel on board. How many miles the works out to be, depends on other things, like the wind..

and the angle of which you are going and possibly weight too?


damn, this is a tricky one.

[Brett_Henderson]

YES !..  Now you're getting the picture...  

And how high you climb, and how steeply you climb, and how steeply you descend, and whether you go for maximum speed when you're cruising, or whether you go for maximum range (which are both time first and then distance)...

[machineman9]

yeh, but for the meanwhile the program really is far less advanced than that... its in CLI just to proove it  ;D

later im putting it into visual with working and rotating guages, but for now it is very primative

[Brett_Henderson]

Excellent... you'll have fun, and learn stuff too....  

[machineman9]

Excellent... you'll have fun, and learn stuff too....  

such as that strings wont work as variables unless they have speech marks around them. its good fun coding, just a pain in the ass at times... though i do love watching the results

[beaky]

FWIW, as a light-single driver I NEVER look at the gauges, preferring to know how much I have aboard before startup and estimating very conservatively starting with "book" values for fuel burn... and I think even heavy-iron jockeys look at the fuel flow meter more than anything else related to fuel quantity.