Is there any roughly accurate way at determining the fuel expenditure in gallons for an aircraft based either on minutes flown or flight miles for a given aircraft?
Example of what I am asking:
Assume the following:
1) A flight between DTW and DFW
2) Aircraft Type: A320, B757, or Embraer 170
3) Flight Miles: 995
4) Flight Time (actual time flying): 135 minutes
Are the four parameters listed above sufficient to gauge a rough estimate of how much fuel would be burned? Is there a formula given by any of the aircraft manufacturers which help estimate fuel consumption?
Also, a secondary question: I assume that airlines don't fill the tanks to maximum capacity when a flight is known to only need, say 30 or 35% of a full tank. I assume the airlines save the cost of hauling the extra fuel, and would just re-fuel the needed amount at the destination. Question is, and this is purely speculative, if a flight from Detroit to Dallas is known to consume 35% of a full tank, then how much extra fuel do airlines normally allow as a buffer, for instances like circling over a storm, circiling for some miscellaneous airport delays, or unforseen extra flying which may be required? Do they allot a given percentage of fuel to buffer the occasions I just mentioned? And how much?
Thanks in advance, and I appreciate any help any of you could be.