Fuel planning

[Ian_Wannabe]

Hello - I was wondering, does anyone know of a website that explains the basics of fuel planning?

I like to read into the basics every now and then to keep it all retained inside my head so just to make sure I dont forget anything I'd like to find such information so I can read over it.

Thanks

[LH2]

For non-commercial operations? Strictly, your aircraft manual has everything you need, but your best bet is to get together with some old (and knowledgeable) hand at your flying club and ask him to explain.

Also if you're actually going somewhere, then always ask someone else to go through your entire flight planning with you, at least until you have built up enough experience.

Like many other things, this is best learn by practise.

[Ian_Wannabe]

Yeah, see this is what im thinking. Basically, to try and push myself so im not doing the same thing over and over im planning on doing a bit of a further land away so I wanna strip everything back and make sure I cover every little basic thing in fuel planning and weight and balance etc.

I was gonna head over to my club to get a photo copy of all those documents but was just wondering if there was anything online that I could mull around the old noggin.

Cheers

[UncleNobby]

Basically, fuel burn is contained on the POH. Fuel burn is based on power settings and time, not distance (e.g 9 Gallons PH for a warrior at 2450 RPM at 6000 FT and 0 degrees celcius). You calculate your duration using these figures, and the distance you can travel once you have all the other factors such as winds, altitude route etc. Enroute you will need to recalculate based on actual groundspeed and see if actual conditions match your plan and take action if necessary (land and refuel, reduce RPMS, etc)
In the States to be VFR legal you need to plan to get to your destination with 30 minutes reserve daytime and 45 minutes night.

[SNS3Guppy]

Ian,

You should really have a copy of the aircraft flight manual on your own...no need to copy a few pages; buy an entire manual and keep it at home.

When considering the fuel burns in the manual, always add an increased margin and never plan for minimum fuel.

Remember, it's always best to make an extra fuel stop or carry extra, than realize a little too late that you should have.

[Ian_Wannabe]

Cheers for the answers guys. I cant help but feel that during my training, this kind of planning wasn't really covered in any huge detail - which makes no sense as its one of the more important things you need to know when flying.

Anyone else feel that this part of their PPL was rushed over?

[IO540]

The way fuel management is taught in the PPL is usually quite poor.

They keep the thing called "tech log" in which each flight is supposed to be written down, and from that one is supposed to work out how much is left in the tanks.

This is dangerous. NEVER fly unless you have checked the fuel physically (visually) and if you cannot then top up to either FULL or to a known level which can be visually checked.

Then one is supposed to make an assumption about the fuel flow at climb, cruise, descent. These figures are rarely known to any accuracy so one has to err very much on the safe side.

This subject was covered here before but the best way to establish cruise consumption is to do two identical flights, with different length cruise segments, and fill up before/after each one.

Then you have a decent yardstick for the fuel flow at a given power setting.

This is before one gets onto the subject of leaning the engine :)

[Ian_Wannabe]

Yeah you see, whenever I go flying Ive never been up with more than one person and ive never been a great distance away from the airfield. So basically, i've always just filled up the tanks and done a calculation to find out my endurance for the book out. (and my piece of mind).

But now i want to go further afield, and I want to take my grandparents on a fly away - only when I really think about it, I was never really properly taught the workings of how many pax you can take "X" Nautical miles with "X" ammount of fuel.

In retrospect its my own fault because I should have hounded my instructor.

Methinks I need to get over to the flying school and sit down with someone!!

[SNS3Guppy]

Ian,

The performance charts in your book are a good place to start. Disregard leaning, use the highest fuel flow numbers, and base your flight on that. Add a healthy margin.

A very old saying it that one can't run out of fuel if one doesn't burn off the bottom half of the tank. What this means is that if you always land with half tanks, you shouldn't run them dry.

Fuel mismanagement, mechanical failure, etc can still leave you starved of fuel in flight, but when the pilot runs out of fuel due to poor planning...well, that's hard to do if you leave a healthy margin. You needn't restrict yourself to a half tank (though it's a good, conservative margin)...but a quarter tank, third tank or any other reference you determine is your bare minimum, is a good rule of thumb.

Some pilots erroneously believe that utilizing an airplane to the last drop of fuel on board is the signof a good aviator, but it's not...it's a signpost of poor planning. Charles Lindberg used to hold contests to see who could come back from a flight with the most fuel; and he certainly knew the value of a strong fuel reserve.

Your airplane flight manual will have charts describing the fuel burn to expect for taxi, takeoff, climb, and cruise. You can use these. You can also use the descent charts if you like, but I prefer to use the highest numbers along the route of flight. If your airplane burns eight gallons of fuel an hour in cruise, for example, but only four per hour on the descent and landing, figure it with eight per hour for the descent and landing.

Leaning is another matter, but if you plan for an unleaned condition with respect to fuel flow and use the higher numbers for your planning, then anything you get leaning is a bonus. Be conservative.

[LH2]

Ian,

it's a good idea to plan progressively more difficult flights, that's exactly how you learn, not burning holes in your local area until you reach 150hrs (assuming you're going commercial).

And yes, there seems to be a consensus that flight planning is not taught properly during the PPL (or CPL, for that matter).

I was gonna head over to my club to get a photo copy of all those documents

As someone said, having your own copy is good to get you familiarised, but beware that the POH is a live document, meaning it can change from time to time, so keep in mind that you always have to refer to the original.

Having said that, do not just lock yourself in your room to do the numbers, as I have suggested above, get someone to go through it with you, if nothing else to double-check you haven't done any mistakes, which are easy to make and always embarrassing, sometimes expensive, and sometimes dangerous.

Re., the comments about carrying a healthy reserve, yes of course, but sometimes you need to be a bit careful with how much fuel you carry. Obvious example is on most light aircraft having full tanks and four people up will put you over MTOW. Taking off or landing on a very short or high or hot strip is another example. Too high a load will also penalise your ceiling and rate of climb, which can be a problem in a mountain area (admittedly not much of a concern in the UK). Sometimes the best route is one which requires you to stretch your endurance, and en-route refuelling opportunities might be limited, so you need to get your numbers exactly right (still leaving of course a legal/sensible reserve). Sometimes it makes sense to leave with a lower load if going somewhere where fuel is much cheaper than where you've just left. Etc., etc. So you see why what you are thinking of doing is an excellent idea indeed.

Couple more points just for the sake of it: 1. What IO said about physically checking your tanks (and if what you see doesn't match what you read on the tech log one way or the other, enquire why), and 2. Assuming your flying the usual spamcan, do not, never, ever trust the gauges. You probably know that already, but if your stated endurance is, say five hours and you've been flying for four hours, it's time to start thinking about getting back on the ground, even if the gauge optimistically shows a half-full tank.

(bit long winded, am I? :))

[SNS3Guppy]

bit long winded, am I?


No...good counsel.

[DFC]

But now i want to go further afield, and I want to take my grandparents on a fly away - only when I really think about it, I was never really properly taught the workings of how many pax you can take "X" Nautical miles with "X" ammount of fuel.



A good place to start is to ask yourself;

Do you want to fly a certain load? or

Can you vary the load to carry the fuel you want?

In the first case, simple total weight calculation gives you the meximum amount of fuel you can carry with the load. This will then determine the maximum length of your leg which will be affected by weather, winds, oats, alternates etc etc

In the second case, if you find that you can not fly the desired leg than you can reduce the load until you can fit in enough fuel.

----------

If you know the load you want to carry then you also know the maximum fuel you can carry.

For rough pre-planning, take 1 hour off the endurance and with what is left see how far you can fly with your chosen power setting and speed.

So if you use 65% and get 100 Kt then with 2.5 hours flight time (after taking your 1 hour off) you can fly 250nm in no wind with no contingency.

make that 225nm with a rough 10% contingency

What if there is a headwind component?

If you have a headwind then the distance covered will be reduced by the amount of the headwind each hour that you fly.

i.e. With 100 Kt TAS

with no wind you cover 100nm each hour

with a 20 knot headwind your progress is reduced by 20 knots to 80nm for each hour

Going back to the 2.5 hours flying time with say a 20 Kt headwind the distance covered is reduced by 2.5 * 20 = 50nm so before contingency you are down to 200nm - call that 180nm with a rough 10% contingency.

A tailwind will of course increase the distance covered and you can apply the same principle.

What is the 1 hour cruise fuel used for? - 45 minutes at best endurance / holding speed and the start / taxi / take-off / circuit / landing fuel plus the excess you will burn while climbing as opposed to cruising

Note that this is an example and not to be used without checking correct figures first

Lots of playing with the numbers at home will help you including getting some general figures worked out to make rough planning easy eg One aircraft I fly burns 10 USG per hour in the cruise and each 1000ft climbed costs an extra 0.5 USG.........all very much rounded figures and all including contingency etc etc..........but very easy to work out how much fuel is required for a 2 hour flight cruising at FL80.

Finally the most important thing you can have is the minimum fuel required noted at waypoints enroute - not every single one but every 30 miutes or so is good don't forget that the minimum fuel overhead destination is the final reserve plus diversion fuel (if any).

The alternative especially for those with crap fuel gauges is to note eta's at each major point as soon as settled in the cruise and use being late at these points as an indication that you are going to have less fuel overhead destination.

Another good thing to note on your plog is the endurance and beside this when settled in the cruise, you add this to your take-off time to find the time that the engine will stop. If you get it seriously wrong then 30 minutes prior to this time pick a precautionary landing field and do the procedure.

Don't forget that to get the book figures you have to set the correct power and use the mixture. It pays to fly faster into a headwind and slower with a tailwind (IAS / TAS).

Finally

Fuel required is

A to B

Divert to C if an alternate is necessary

Contingency

start taxi etc

Final Reserve

Extra Fuel - for diverting round CBs if forecast or holding at busy airfields etc

This gives you your minimum departure fuel.

Hopefuly at your experience level there will be a gap between the minimum departure fuel and the maximum you can take. This is simply bonus fuel which you should take and use as an extra reserve.

Every trip don't forget to debrief yourself and see if your calculations worked and if refinement is necessary - it is a constant learning process.

Regards,

DFC

[Ian_Wannabe]

Nah great advice from all.

Can I get a generic flight manual from shops like transair?

[fireflybob]

Another tip having done quite a few "long range" trips in light singles (and twins) is to do a post flight wash up on the achieved fuel usage.

i.e. after landing refuel to full tanks and work out the gallons or litres consumed per hour of flight time. It's important to work on the theoretical figures from the POH but you can't beat actual experience. I have found the actual figures to be quite consistent and can be useful for future trips.

[Radix]

............

[Fright Level]

Ian, it's fairly straightforward as is based on the plan for your trip. Say you plan for a flight from A to B. You should also plan an alternate in case of weather, airfield closed due preceding aircraft stopping on runway etc. Your "alternate" could even be back home again if it's close or is your preference.

You should have enough fuel then to get from your departure to destination, not land then carry on to your alternate. Add to that some reserve fuel (commercial flights must have a minimum of 30 minutes) and contingency of, say, 10-20%. That's the fuel you should depart with. I make a mental note of the time the tanks will be dry when I take off (sometimes note it on the plog) so that whatever happens, I know when it's all going to go very quiet around me.

So, as an example for a 35 litre an hour plane:

Trip fuel (2.0 hour flight) A-B = 70 litres
Contingency 10% of trip fuel = 7 litres (12 mins flight time)
Diversion B-C (20 mins) = 12 litres
Reserve (45 mins) = 27 litres

Total fuel required = 116 litres (3 hours 18 mins endurance)

Obviously substitute your own numbers here. Contingency can depend on all sorts of things like how good the weather is, how many airfields there are between you and your destination, the likelihood of you having to alter your planned route (weather build ups, ATC or controlled airspace permissions etc).

The tip about checking post flight fuel for your specific a/c is a good one, it will give you confidence in the book figures (provided you lean the mixture according to the book too, cue Peter here).

[Ian_Wannabe]

Cheers for all your imput guys - and thanks for the link.

One more question, the manuals have part numbers - do I need a specific one?

I fly an Archer II

[bookworm]

So, as an example for a 35 litre an hour plane:

Trip fuel (2.0 hour flight) A-B = 70 litres
Contingency 10% of trip fuel = 7 litres (12 mins flight time)
Diversion B-C (20 mins) = 12 litres
Reserve (45 mins) = 27 litres

Total fuel required = 116 litres (3 hours 18 mins endurance)

Nothing wrong with this for a low level VFR trip on a good weather day in uncongested airspace. For IFR, typically at a higher level:

* Need to add something for the taxi, take-off and climb. In my aircraft I use a 4 gallon excess over the cruise fuel burn for a taxi, take-ff and climb to FL100 ish.

* Need to add an allowance for an approach and go-around at B, rather than just assume you've got there when you reach the overhead. For VFR equivalent, don't forget about the procedures ATC may need you to follow at destination.

* If the weather (e.g. showers) makes it possible that you'll need to deviate from track a lot, add more contingency. Such dog-legs can add up.

* Again, if there's the possibility of TEMPO bad weather at the destination, you may want to add a little more holding fuel to allow time for the weather to pass through. In convective weather, 10 mins is a long time, and it's a pity to head for your alternate immediately.

[SNS3Guppy]

Try this:

http://www.glasscockpitaviation.com/MainPages/documents/PA-28-181-POH.pdf

[slam525i]

I'll admit it. I haven't flown for several years after getting my PPL. Ran out of money :*, but I can't help but chime in.

The numbers on the books apply to the airplane when it came out of the shop with a shiny new engine, no speed tape on the cracked fiberglass, no dings on the propeller, and no squished bugs on the wings. Assume you won't actually get those performance numbers.

Like IO540 said, dip-stick the fuel tanks. I'll add that tanks in some planes aren't perfectly shaped, so height in the dip-stick may not correspond perfectly to fuel in the tank.

Fuel burn per hour as listed assume proper/perfect lean to max. economy. Most trainers don't even have an EGT gauge, so add margin for that too. Don't forget fuel consumed during run-up, taxi and climb out.

Carry extra fuel provided you don't exceed max weight. Carry about an extra 90 minutes. (I got stuck for an hour once in actual-IMC while I was under the hood with a new instructor. All the area airports were "no-special VFR". I nearly smacked him afterwards.) I'm not familiar with Pipers to be honest, but on a Cessna, 2 bodies and full fuel isn't a problem, but any more and you better look into your weight & balance. That's something you likely never had to worry flying dual/solo-without-pax. Your plane probably gained weight over the years too, so you'll want to look for the latest weight & balance for the empty plane, not the one the POH has.

On our little airplanes, the fuel weight penalty on performance isn't going to be that great (max weight permitting of course). If you're worried about performance, plan another route. You don't want to be flying single engine VFR in terrain where the reduction in climb performance becomes an issue unless your base and destination demands it. Since you're from the UK, watch for flying over water too. Make sure you're within gliding/crashing distance of dry land.

Plan several alternates along the flight path. If your fuel is going to be anywhere close to eating into your reserves, plan a fuel stop. Have all the charts ready. Alternates are useful, not just in case of mechanical failure, weather, but also for puke and bathroom emergencies.

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. You'll feel awfully stupid if you ran out of fuel with the gauges on empty because you were "taught never to trust them".

Fully brief your passengers on the operation of the doors, seat belts, etc. Point out any controls they may accidentally knock. Include the obvious, such as stay away from the noisy wind generator up front. Bring a few air-sick bags with you.

Before you do all of this, smack your instructor for not having made you go through this with him several times, including doing actual, dual and solo "cross-country" flights. And find someone who's familiar with the airplane to go through your flight plan with you and walk them through your plan step-by-step.

Anyone in southwestern Ontario (Canada) want to lend me an airplane? I miss flying. :{

[SNS3Guppy]

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.


The only time the fuel gauge is technically required to read correctly is when it's empty; down to unuseable fuel.

[lostpianoplayer]

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.

[IO540]

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.

[slam525i]

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.)

[gfunc]

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.

[IO540]

Aircraft endurance (4-5hrs) > Bladder endurance (3hrs tops!).


I guess the above is partly tongue in cheek, but it isn't that simple.

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.

[slam525i]

Just make sure they're not apple juice bottles.

There are solutions available http://www.sportys.com/acb/showprod.cfm?&DID=19&CATID=178&ObjectGroup_ID=1284

Interestingly, they consider it "Safety & Survival"

[lostpianoplayer]

...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.