Calculating fuel burn in your nav logs. (method)
I am a student pilot and filled out a nav log for my first cross country. I measured fuel burn by time remaining not gallons. To me it makes more sense. I have seen measured fuel burn by gallons remaining which requires one more look at the whiz wheel to determine actual gallons used. Is there a right or wrong way? Why throw in the extra calculation when you can just deduct minutes?
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Replies to This Discussion
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Permalink Reply by Scott Coyle on
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My instructor says to track gallons used like you say, but to me it makes less sense. In fact, look at this AOPA training tip. It says to track fuel use by "time".
http://www.aopa.org/members/files/pilot/epilot/ft/2011/110819epilot...
"En route, think of fuel consumption in terms of hours and minutes, rather than gallons, and keep careful track of time remaining (allowing for reserves)."
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Permalink Reply by Matthew Everett on
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Yes, that's all well and good, but you still need to know the rate of burn and the quantity remaining in order to keep track of how long it will burn. For proper planning and safe flying, you need to know all three.
For example, in a Cessna 172SP with 53 gallons usable, I can burn 13 GPH at full throttle on take off. If I maintain that rate of fuel burn, I will have 4.07 hours until the engine quits. If I drop back to 8.5 GPH for cruise, I'm now looking at 6.23 hours until the engine quits. If I base everything off that 6 hour figure, but I'm running full throttle, I'm out of gas 2 hours sooner than I thought.
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Permalink Reply by Joe Hopwood on
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Regulations do state time remaining not gallons remaining. Of course you must know fuel consumption rate to get the minutes.
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Yep! No mention of gallons, quarts, litres, etc.
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Permalink Reply by Mamma Mia on
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I respect that you want to see things as black&white. Grey areas tends to confuse all pilots.
Cruise power, from what I know, is whatever power setting that allows the aircraft to fly unaccelerated straight & level flight. Recommeneded power settings are defined by the aircraft operator and ought to be taken out of the respective flight manual. Some companies fly at maximum continious power as their cruise profile. Others use a variety of power settings defined by a cost coeffient. For general avaition without specific operating manual, the aircraft flight manual with performance charts is the true bible.
To summarize, calculating a fuel burn in either time, weight, volume or a combination hereof is irrelevant if the pilot has a profound understanding of their relations. I like to do all the above calculations because it elevates my situational awareness. In my company we fuel in: pounds, US gallons, litres, kgs, minutes, hours, and drums.
"The only time you have too much fuel is when you are on fire!" :)
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Permalink Reply by David Vandenbroeck on
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Before you can compute time remaining, you need to know how many gallons you have remaining and your burn rate. The clock will not tell you this info! Then when you know how much time you have left and your speed, you can calculate how far you can fly which is what it is all about in the first place. While it takes both time and fuel to get somewhere, I have never heard of a plane crashing due to time starvation. ; -)
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Got it.
Using time would only make sense if you had a constant burn rate. Since that is not the case then when you calculate fuel use over a certain leg of the flight, do you make a rough estimate on your power setting over that leg and use that in your calculation? There is no column in any nav log that I have seen where you can jot your power setting for that leg.
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David, While what you say of course is true, clocks are much more accurate than fuel guages. They are only required to be accurate when empty and that is too late. The only really safe way is to have plenty of reserve, know your burn rate and know how much fuel you have when you started. I would not be surprised if many out of fuel situations are due to relying on fuel guage.
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Permalink Reply by Robert J. McCormick on
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Whatever method you use, consider your fuel reserves as SACRED and make absolutely certain you know how much useable fuel is onboard the aircraft before it leaves the ground. Individual burn rates are, at best, a guess because of the varying conditions under which you operate the aircraft. Unless you have some very accurate measuring devices in the aircraft, and most light single-engine aircraft do not, be very conservative in your time or gallon estimates. I am not certain if the numbers have changed; but, the last statistics I saw revealed that an aircraft experiences "fuel starvation" every 4th day in the United States. There are many reasons for this starvation; but, far too many of them are from total useable fuel exhaustion. Be aware that many aircraft leave the ground on cross-country flights and they have already left their legal reserves behind because of the fueling methods employed. Good luck.
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Permalink Reply by Rick Bernskoetter on
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Oh what the heck, I'll throw my two cents in here as well! I'm going to start out by telling on myself here. I don't spend much time contemplating fuel numbers and I fly an airliner! Here's what I mean:
When you're cruising from your orignating airport to your destination, you should have already figured out how much fuel it was going to take. When you calculated or estimated this, you based it on time, whether you think you did or not. You knew how many miles you were going to fly; you looked at winds aloft and came up with a pretty good idea of how long it was going to take you to fly that distance, and you calculated a fuel burn based on those assumptions. Oh, and because you're smart and you were well trained, you added a requisite amount of either VFR or IFR reserve fuel - or contingency fuel if you want to call it that. Having done all this, you could fly your entire route and never once look at those fuel gages. Nothing would happen. You'd arrive at your destination and your reserve fuel would still be on board, right where you planned it to be - unless you developed a leak, then all bets are off anyway.
Things get interesting when the unexpected happens. I said at the top I don't pay much attention to fuel numbers en route because I know how much my airplane consumes, and it's been fueled accordingly (I confess, I have the cool gages that display fuel flows, and they tell me at a glance how we're doing). But when we get that dreaded alert from ATC. "Stand by to copy holding instructions..." that's when my brain shifts from gallons (or pounds) to endurance.
My thought process works kind of like this: "Okay, we're going to be holding at this point on the map. It's so many miles from where I want to end up. When I slow to my holding speed, we will burn this much fuel each hour. Time to my destination at a reduced speed will be this many minutes. Time to my alternate at that speed will be this many minutes. That translates into x amount of fuel." Once we do the math, the one question I want an answer to is: "When I land - either at my destination or my alternate - how much gas do I want sloshing around in those tanks so that I'm not sweating bullets with the realization that I nearly flew myself out of options." Once I have a firm grasp of that number, I can work backward from there.
I guess the bottom line is, fuel in your tanks equals time in the air. How you do the math really doesn't matter.
Sorry for the long rant. Too much caffeine I suspect...
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Permalink Reply by Michael Foster on
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Good thread.
Whatever method you use always use endurance/hours not miles and be conservative.
Do yourself a favor, always add 1 hour for reserves.... I know the FAR's call for 30 minutes VFR day, 45 minutes VFR night, but use at least 1 hour for reserves and you should never be one of those "fuel starvation" statistics we read about. Nobody ever thinks that could happen to them (I'd never be that dumb) but it happens and way too often.
A tip I'd add, you probably don't pay any attention to how much fuel was actually used during your lesson or dual cross-country, most student s don't.... but start seeing how much the line guy puts in when your done. Get a handle on how much fuel the aircraft you fly actually burns.
Another tip, don't trust fuel guages.
The Arrow I fly has a fuel flow instrument that shows how much I'm burning at any given time, but the others I fly don't. I've found this Arrow actually uses about 10.1 gal./hr. on cross-countries even though the book calls for slightly more.... I fuel plan it at 10.5 gals./hr. anyway.... and always allow for an hour in reserve.
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