Fuel planning
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The only time you should believe in the fuel gauges is when they worked fine at first but indicate less fuel than you believe you should have some time into your trip.
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More on fuel
I'm not an instructor, so these are my personal thoughts only, but if they're helpful....
I think the old saw about not trusting your gauges has the potential to be quite dangerous, and is worth re-emphasising. Yes, for certification purposes, it's true that the only time they're required to be accurate is when empty. This doesn't mean they're still accurate, 30 years after the aircraft was built, of course. I suspect the main reason for gauge inaccuracy is cos of the physics involved with a long, flat, shallow tank (typical wing tank in aircraft) as opposed to a more cube-shaped tank, which is why heli tanks tend to be more accurate, and also tanks in front of cockpit, a la Cub with wire sticking out. Anyway, point is, I DON'T "ignore the gauges" - I take them with a big grain of salt, but I make sure to include them in my engine instruments scan. The thing is, every now and then a fuel drain can get stuck, for instance (hence always being sure to reseat them when draining) or, yes, it happens to people, you can forget to put a cap on, or just have a plain old leak. In which case gauge indications are all you'll have to indicate a problem. So if one of those gauges is showing close to "E" when I reckon I've got 3/4s of a tank, I DON'T ignore it - generally, I'd rely on the lowest of the two. So treat it at a tank that really is close to "E", unless you know the particular aircraft's gauging system really well and are sure it's a false indication.
To add to a previous poster's comment, the "post flight wash-up" is a good idea, and feeds into a habit that I think is helpful, which is using ALL AVAILABLE sources of information re fuel planning and useage. So manual-predicted burn rates, real burn rates, fuel gauges, etc - all worth paying attention to - then use the ***most pessimistic*** of them all, plus a hefty reserve. Not all aircraft can be operated with Guppy's approach - never burning into the bottom half, or whatever - but it's certainly a wise default position. It's a question of attitude - you either start with the question "how much fuel do I need to do X", or you start with the question "how much can I carry/how far can I go if I never let the fuel get below Y". I think The second question is a better approach, and I fly that way myself. Except on rare occasions (local flights on nice days, basically) I use a 60 minute reserve, but am happier if I have a good 90 minutes when I land. Just in case. Which leads to an awful lot of "duh" moments as I stop and fuel up and discover I still had 100 litres on board....but is a whole lot better than everything going quiet. As we all know, fuel exhaustion is a very common cause of engine failures, and avoiding it justifies a fair amount of inconvenience. Especially if you're doing real X/Cs, dealing with real weather and so on, as opposed to blue sky local hops, where you can be a little less conservative.
Three other things I like to do, that relate to fuel management, the latter two of which don't apply to aircraft with BOTH positions on the fuel selector (many Cessnas) but certainly do apply to aircraft that only have L & R positions (many Pipers):
1. Be sure both electric pump & engine pump are working (where applicable - no pumps on many gravity fed high wing aircraft, although some do have pumps)
2. Be sure you have at least one tank feeding BEFORE takeoff, and don't mess with it once you've proved good fuel flow, and
3. Do an early tank swap (but well after takeoff) to ensure fuel will feed from both under normal running conditions, as opposed to idle.
(1) and (2)
I check electric pump works (aural AND fuel pressure) before start up, then switch it off at some point, either just before start or just after, depending on aircraft, to check the engine pump's operation. Some POH's don't include this step, or explain what it's for, but I think it's worth doing anyway, just to be sure. It's otherwise quite possible that using both pumps could mask a failure of one.
I like to make sure the engine's running well on any one tank, before take off, which means no swapping of tanks immediately prior to take off. (Just in case you take off on the fuel from the tank you just swapped from, and then the tank you swapped TO won't feed, typically at or shortly after rotation, and also minimises the chance for accidentally selecting OFF, which DOES happen)
I start on whatever the aircraft was flown in on, (say, L) but once the engine's been running for a couple of minutes, and definitely pre-run up, I'll swap to the other tank (R), or MAIN, or whatever the POH says is OK for takeoff. The timing is a balance between checking the feeding from the tank you just started up on (not so important) and the feeding of the tank you're going to take off on (ultra important). So you gotta make sure the tank you take off with is the same one you ran up on. Turn the electric boost pump OFF, to be sure that the engine pump works, and run up on R, MAIN or whatever, without electric boost pump. Then electric boost pump on, unless POH says otherwise, for takeoff, and don't change tank again until safely airborne and high enough that any failure to feed from one tank would not be a major problem.
(3)
Passing through, say, three thousand feet, or some time 5 mins or so after takeoff, swap tanks as per manual, to be sure they're all feeding now you're airborne. You don't want to find out, say, 45 mins into a flight, or later if you forget to swap tanks as per schedule, that you have half the fuel you thought you did.
An alternative to (2) would be to not change tanks at all on the ground, which means you'll really minimise a feeding problem - but don't have a chance to check the feeding of the other tank. Personally, I'd prefer to find out about problems like this on the ground - but I think the principles stand, whichever way you do it.
Last thought - a lot of fuel management really comes down to currency with the aircraft. When you're just learning, it's easy enough to totally forget to lean, for instance, which can make the fuel figures in the manual very innacurate. So use those checklists, all the time, use a written cross country log, and carry a very hefty reserve, particularly in aircraft you don't fly all the time. Once you're more current in any particular machine, and if you make cross checking fuel burn when fueling up with your power settings/leaning/flight time, then you have a better idea of what to expect. It's all about being conservative, and recognising that running out of fuel is a very, very big deal.
I think the old saw about not trusting your gauges has the potential to be quite dangerous, and is worth re-emphasising. Yes, for certification purposes, it's true that the only time they're required to be accurate is when empty. This doesn't mean they're still accurate, 30 years after the aircraft was built, of course. I suspect the main reason for gauge inaccuracy is cos of the physics involved with a long, flat, shallow tank (typical wing tank in aircraft) as opposed to a more cube-shaped tank, which is why heli tanks tend to be more accurate, and also tanks in front of cockpit, a la Cub with wire sticking out. Anyway, point is, I DON'T "ignore the gauges" - I take them with a big grain of salt, but I make sure to include them in my engine instruments scan. The thing is, every now and then a fuel drain can get stuck, for instance (hence always being sure to reseat them when draining) or, yes, it happens to people, you can forget to put a cap on, or just have a plain old leak. In which case gauge indications are all you'll have to indicate a problem. So if one of those gauges is showing close to "E" when I reckon I've got 3/4s of a tank, I DON'T ignore it - generally, I'd rely on the lowest of the two. So treat it at a tank that really is close to "E", unless you know the particular aircraft's gauging system really well and are sure it's a false indication.
To add to a previous poster's comment, the "post flight wash-up" is a good idea, and feeds into a habit that I think is helpful, which is using ALL AVAILABLE sources of information re fuel planning and useage. So manual-predicted burn rates, real burn rates, fuel gauges, etc - all worth paying attention to - then use the ***most pessimistic*** of them all, plus a hefty reserve. Not all aircraft can be operated with Guppy's approach - never burning into the bottom half, or whatever - but it's certainly a wise default position. It's a question of attitude - you either start with the question "how much fuel do I need to do X", or you start with the question "how much can I carry/how far can I go if I never let the fuel get below Y". I think The second question is a better approach, and I fly that way myself. Except on rare occasions (local flights on nice days, basically) I use a 60 minute reserve, but am happier if I have a good 90 minutes when I land. Just in case. Which leads to an awful lot of "duh" moments as I stop and fuel up and discover I still had 100 litres on board....but is a whole lot better than everything going quiet. As we all know, fuel exhaustion is a very common cause of engine failures, and avoiding it justifies a fair amount of inconvenience. Especially if you're doing real X/Cs, dealing with real weather and so on, as opposed to blue sky local hops, where you can be a little less conservative.
Three other things I like to do, that relate to fuel management, the latter two of which don't apply to aircraft with BOTH positions on the fuel selector (many Cessnas) but certainly do apply to aircraft that only have L & R positions (many Pipers):
1. Be sure both electric pump & engine pump are working (where applicable - no pumps on many gravity fed high wing aircraft, although some do have pumps)
2. Be sure you have at least one tank feeding BEFORE takeoff, and don't mess with it once you've proved good fuel flow, and
3. Do an early tank swap (but well after takeoff) to ensure fuel will feed from both under normal running conditions, as opposed to idle.
(1) and (2)
I check electric pump works (aural AND fuel pressure) before start up, then switch it off at some point, either just before start or just after, depending on aircraft, to check the engine pump's operation. Some POH's don't include this step, or explain what it's for, but I think it's worth doing anyway, just to be sure. It's otherwise quite possible that using both pumps could mask a failure of one.
I like to make sure the engine's running well on any one tank, before take off, which means no swapping of tanks immediately prior to take off. (Just in case you take off on the fuel from the tank you just swapped from, and then the tank you swapped TO won't feed, typically at or shortly after rotation, and also minimises the chance for accidentally selecting OFF, which DOES happen)
I start on whatever the aircraft was flown in on, (say, L) but once the engine's been running for a couple of minutes, and definitely pre-run up, I'll swap to the other tank (R), or MAIN, or whatever the POH says is OK for takeoff. The timing is a balance between checking the feeding from the tank you just started up on (not so important) and the feeding of the tank you're going to take off on (ultra important). So you gotta make sure the tank you take off with is the same one you ran up on. Turn the electric boost pump OFF, to be sure that the engine pump works, and run up on R, MAIN or whatever, without electric boost pump. Then electric boost pump on, unless POH says otherwise, for takeoff, and don't change tank again until safely airborne and high enough that any failure to feed from one tank would not be a major problem.
(3)
Passing through, say, three thousand feet, or some time 5 mins or so after takeoff, swap tanks as per manual, to be sure they're all feeding now you're airborne. You don't want to find out, say, 45 mins into a flight, or later if you forget to swap tanks as per schedule, that you have half the fuel you thought you did.
An alternative to (2) would be to not change tanks at all on the ground, which means you'll really minimise a feeding problem - but don't have a chance to check the feeding of the other tank. Personally, I'd prefer to find out about problems like this on the ground - but I think the principles stand, whichever way you do it.
Last thought - a lot of fuel management really comes down to currency with the aircraft. When you're just learning, it's easy enough to totally forget to lean, for instance, which can make the fuel figures in the manual very innacurate. So use those checklists, all the time, use a written cross country log, and carry a very hefty reserve, particularly in aircraft you don't fly all the time. Once you're more current in any particular machine, and if you make cross checking fuel burn when fueling up with your power settings/leaning/flight time, then you have a better idea of what to expect. It's all about being conservative, and recognising that running out of fuel is a very, very big deal.
Last edited by lostpianoplayer; 19th May 2008 at 12:01. Reason: accuracy
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Anybody intelligent enough to pass the PPL exams can be taught how to lean the engine to set up a specific operating point e.g. 65% power, peak EGT.
Or (if not paying for the fuel) just fly full rich everywhere but accept a range reduced to around 60-70% of what it could be.
Then do the two flights to establish cruise fuel flow.
Then you can do proper fuel planning.
Everything else is guessing, which is OK in the school scenario where one never goes anywhere far.
Or (if not paying for the fuel) just fly full rich everywhere but accept a range reduced to around 60-70% of what it could be.
Then do the two flights to establish cruise fuel flow.
Then you can do proper fuel planning.
Everything else is guessing, which is OK in the school scenario where one never goes anywhere far.
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Some stuff just isn't covered in the PPL exams (at least not the Canadian one) and the particular instructor might miss them. Besides, tiny little airplanes don't have EGT gauges. I had to tune mine entirely by ear. Getting peak power is a bit of an art in such a case.
Will a small engine stay happy at altitude running on full rich? Of course there will be power loss and increased fuel consumption, but I don't know how unhappy the engine will get. (I assume with a nick like IO540, you know them a lot better than I do.)
Will a small engine stay happy at altitude running on full rich? Of course there will be power loss and increased fuel consumption, but I don't know how unhappy the engine will get. (I assume with a nick like IO540, you know them a lot better than I do.)
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Although I do go through the rigmorale of flight planning when I need to, I have devised a very simple formula for the 172 I fly:
(At full tanks):
Aircraft endurance (4-5hrs) > Bladder endurance (3hrs tops!).
Gareth.
(At full tanks):
Aircraft endurance (4-5hrs) > Bladder endurance (3hrs tops!).
Gareth.
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Aircraft endurance (4-5hrs) > Bladder endurance (3hrs tops!).
In the summer, one can go for say 5hrs without a pee. Try that on a freezing cold winter evening!
I fly with the little plastic Tropicana juice bottles (empty of course). Screw tops. Excellent, and go in the bin after a single use.
There is no point in being desperate for a leak, when in the air.
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Just make sure they're not apple juice bottles.
There are solutions available http://www.sportys.com/acb/showprod....tGroup_ID=1284
Interestingly, they consider it "Safety & Survival"
There are solutions available http://www.sportys.com/acb/showprod....tGroup_ID=1284
Interestingly, they consider it "Safety & Survival"
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Full rich running at altitude
...is SOP in the Robinson (piston) helicopter world. Unlike fixed wing, no flywheel effect to keep the motor running if you accidentally overlean, or descend without releaning. Engine is more likely to just stop stone dead, than "run rough" but keep turning, which can be a big deal in a heli, so we're told not to lean at all. Doesn't seem to cause any harm, despite my own very real experiences of plugs fouling in aircraft engines that have been run too rich. And it's moderately easy to forget, thus upping fuel burns, when you're just learning.
Re 10540, I couldn't agree more. Why suffer? Course, your passengers need to be close friends not business clients you're trying to impress, and it's far more complicated for women...but yeah, I treat fuel management & bladder management as separate issues
One final thought, on fuel reserves. The other reason I think it's unwise to use a 30 minute reserve, apart from simply giving yourself more options at the other end, is that of calibration. Until one REALLY knows one's aircraft, it's hard to know exactly how much fuel you're burning. You have to be very accurate on fuel burns, if, say, you've got a 5 hours-to-dry-tanks endurance, and you're trying to land with exactly 30 minutes in your tanks. I think it requires quite a few flights in any given aircraft, at different altitudes & power settings, doing the 'post-flight wash-up', to be really accurate. I'd guess that a lot of the fuel exhaustion accidents happen when people thought they, had, say "30 minutes to go", (30 minutes? Too short. Just cos it's legal don't mean it's safe!) or were just cutting into it a little bit, so still had a safe "20 minutes" to go. Fat reserves = no sudden silences.
Re 10540, I couldn't agree more. Why suffer? Course, your passengers need to be close friends not business clients you're trying to impress, and it's far more complicated for women...but yeah, I treat fuel management & bladder management as separate issues
One final thought, on fuel reserves. The other reason I think it's unwise to use a 30 minute reserve, apart from simply giving yourself more options at the other end, is that of calibration. Until one REALLY knows one's aircraft, it's hard to know exactly how much fuel you're burning. You have to be very accurate on fuel burns, if, say, you've got a 5 hours-to-dry-tanks endurance, and you're trying to land with exactly 30 minutes in your tanks. I think it requires quite a few flights in any given aircraft, at different altitudes & power settings, doing the 'post-flight wash-up', to be really accurate. I'd guess that a lot of the fuel exhaustion accidents happen when people thought they, had, say "30 minutes to go", (30 minutes? Too short. Just cos it's legal don't mean it's safe!) or were just cutting into it a little bit, so still had a safe "20 minutes" to go. Fat reserves = no sudden silences.
Last edited by lostpianoplayer; 19th May 2008 at 21:41. Reason: spelling
