Fuel Circles

[Grob Queen]

I am sure many of the old and bold on here will have a view on this, and will probably disagree with me, as I know that some of you disapprove of the way I am taught ;) So this is not a question, more something that I thought would get the Ppruners in discussion; I have now got my head around the working out and use of Fuel Circles for nav planning well enough to start a discussion on their useage.

So, picture your triangular navex route drawn on map. For a trip from base to Duxford and back via Grafham Water I have planned six fuel circles at points just after an "event" to check the fuel levels and diversion fuel. We can fly the trip on minimum 75 litres of fuel adn this is what I planned for (if it were the normal "Club fill" of 60 litres we would be into minus fuel!)

The figures I have (from base back to base) are:
72 62 52 47 39 35
57 47 37 32 24 20

The black figure is the amount of fuel which I still have to use. The bottom red figure is the Diversion fuel including FOG (in the Grob's case minimum FOG 15L.

The way to work out ones red fuel is to work out how many litres you are going to use to get to your destination (or furthest point on the navex). IN this case we would use 15 litres to reach Duxford. Therefore, 15 is taken off the last black figure and there you have the difference (in this case 15). Then you work backwards and take 15 (or whatever the difference is) off your black fuel to get your red fuel at that check point along your route. It has the advantage of being there on your chart and not having to check lots of paperwork.

Personally I think its a great system...would be interested to hear if anyone else is taught/teaches/was taught this method, or it is, as I suspect, a very useful military system; and one which I am very pleased to use...despite the incoming which I suspect will appear......:rolleyes:

[wiggy]

Fuel Circles

Aim: Navigate from A to B to C to A and not Run Out of Fuel

A'Ship: Fuel Awareness, LOOKOUT

Ah that brings back memories of Jet Provost Navigation Exercises and yes, it sound like fuel circles as approved by RAF Central Flying School when Pontious was a pilot and used by yours truely as both a student and as an instructor decades ago.

Black/top = planned fuel remaining.

Red/bottom figure = "Bingo", your minimum to continue the navex as planned.

[Torque Tonight]

Yep, standard RAF technique (except I think your first pair of figures are wrong). Really becomes useful on more complex navexs where you go off-piste or have unexpected injects and need to know where you stand with regards to recovering the plan.

[Grob Queen]

Absolutely Torque, couldn't decipher my own handwriting!!!:O

So, as this system is so useful, I wonder why it is not standard PPL practice to teach it? Makes me glad i'm being taught by the RAF !!

[BEagle]

Rather than doing fuel checks just after a turning point, when you're sorting out post-HAAT checks, or at a navigation check point, do them at a low activity point when you do a normal FREDAL check.

Sort the navigation first, do your fuel checks when things are quiet!

[peterh337]

I have never been in the RAF (tried to join in 1973 but they were convinced I was KGB :) ) but I would guess that modern pilots don't navigate the way people used to, especially compared with the RAF as it was many years ago.

From what I hear and read, RAF missions were characterised by chronically tight fuel margins. If you fly a jet which has 1-2hrs of fuel, and you are navigating visually by dead reckoning, and you are supposed to do this in real weather, then you need a very robust system, comprising of highly selective recruitment, excellent pilot training, and strictly operated procedures. You also need the D&D 121.50 system which modern GA doesn't need.

GA is very different. Pilot training is very basic. Most "spamcan" missions are characterised by a poor knowledge of how much fuel is in the tanks at any point in the flight; this is dealt with by being very conservative on range and thus wasting much of the plane's capability. And there is a small % of GA which has accurate fuel metering, linked to the GPS flight plan, and they don't need these methods to plan diversions.

[gasax]

And what is the purpose of this 'great system'?

If you are going to plan fuel consuption down to the nearest 5 minutes it may have a purpose - except I have towonder what on earth you are flying that justifies such precision.

But bluntly it is completely pointless. To get the necessary levels of accuracy - you need an accurate fuel flow and totaliser - if you have that then all of the rest of it - - - is pointless.

Typically I have about 2.5 hours of fuel reserve - virtually guarantees me another county, countrt or continent........... depending where I am.

Whatever rings your bell, what do you genuinely think this adds any value?

[Grob Queen]

You also need the D&D 121.50 system which modern GA doesn't need.

Really???!!! I'm taught that if you're lost, D&D are there to help anyone who requires it and are only too happy too! 121.50 is a frequency which is etched on my brain!

If in general then, GA "doesn't need" the D&D; I have some questions. What sort of fuel loads do civilian schools teach students to carry? (OK, I know different aircraft have different weights, but generally speaking) How do they teach students to cope in an emergency where I would have no hesitation in using D&D?? I practice planning with a PLOG as well (to pass the skills test when it comes), but on the standard form, there is no where to put the fuel circle info which I put on the chart.

[Squeegee Longtail]

I was introduced to it a couple of years ago when I started flying ex-mil jets.
Bingo rings are good for keeping you on top of your fuel requirement, especially when you depart the original plan.
It is a very useful system to use when "eyes down" time needs to be kept to a minimum (ie. low level fast jet).

Modern GA aircraft with fuel totalisers and gps charts etc etc would have no requirement to use this system, but the technique is always good to know.

[Grob Queen]

It is a very useful system to use when "eyes down" time needs to be kept to a minimum (ie. low level fast jet).

Modern GA aircraft with fuel totalisers and gps charts etc etc would have no requirement to use this system

I would say that "Eyes down" time needs to be kept to a minimum whatever aircraft you are flying, be it FJ or Tiger Moth. I know that my instructor will want me to have my head in the chart as little as possible when navex-ing... aviate, navigate, communicate.

Also, with this manual system is all worked out, the pilot can keep a better personal idea of the fuel situation and does not need to rely on electronic gadgets which could go u/s at any time...


Bingo rings are good for keeping you on top of your fuel requirement, especially when you depart the original plan

Agreed -these are ideal for when you need to divert and are an instant indication of where you can divert to, according to the amount of fuel left. Give me a fuel circle any day.

[Squeegee Longtail]

"Minimum" eyes down at 420 knots is different to "minimum" eyes down at 90 knots though. Take it from me.

[gasax]

Carry an alarm clock - set it at takeoff for whatever the minimum endurance is. Alarm goes off - find runway and land - sorted!

[peterh337]

I'm taught that if you're lost, D&D are there to help anyone who requires it and are only too happy too! 121.50 is a frequency which is etched on my brain!If you are lost, but nowadays that should not happen in the first place.

People who get lost do so almost always because they didn't use a GPS.

It is true that 121.50 is a great service but if a GA pilot needs it, then he has screwed up on multiple fronts. Or more likely just followed his WW1 PPL training ;)

[Grob Queen]

Its the leather flying helmet, coat and gauntlets that really make the difference Peter ;)

Seriously though, I know nothing about GPS, but I thought it was for location and in case of need for diversion...not to tell the pilot what their fuel state is?? Don't get me wrong, I have nothing against a GPS, and I daresay i'll treat myself to one when qualified. Also the aircraft fuel gauge is good; and of course we all do our FEEL cx.... But fuel gauges and GPs systems can go wrong. It is then that you require a manual back up.

[peterh337]

But fuel gauges and GPs systems can go wrong. It is then that you require a manual back up.Sure you want a backup but with any backup system (not just in aviation) you have to ask yourself what the value of it is, relative to the primary system.

To take a silly example but one which illustrates the point: would you drive a Vauxhall Viva, and tow a Toyota behind it in case the Viva breaks down?

In flying, lots of things are inter-related and end up being only as good as the thing they are depending on.

Take the whole concept of MSA for example. This is utterly dependent upon accurate navigation. If you are unsure about position, MSA is out of the window. As many people know; most are dead, but some were very lucky.

Fuel reserves are dependent upon various things, all of which can be accurately known if you have the right equipment, but in the typical GA context they are not:

The fuel reserves firstly depend on how much you started off with. You had a chance to physically check that, so that's :ok: (well not always but there is one born every minute and some of them are bound to get a PPL :) ).

Once you get airborne, the fuel reserves depend on various things. Ground speed (not airspeed, which you should know well) is the key. Lateral nav is of course important if you want to get to the destination :) But along the route it is not too vital so long as you are going roughly in the right direction.

If you cannot find the destination then you have a potentially major problem. It could be anywhere.

Most cases of a pilot doing dead reckoning getting lost are ones where he "positively" identified a ground feature but got the wrong one, so he then flew quite a bit further before realising the c0ckup. Or he forgot to start (or stop) the stopwatch. The outcome of such an error is usually highly embarrassing... This is why a cunning choice of visually unambiguous waypoints is vital.

Once airborne, most GA pilots have no idea of the actual fuel state. The fuel gauges are invariably useless. The fuel burn is only taken from the POH, which was prepared about 30 years previously. The pilot has never been taught what the red lever does, and that its correct use can yield an extra 20-30% more MPG.

In GA, the way this is properly addressed is with a GPS, which gives you precise navigation both laterally and along the track (ground speed, time and distance to run to target) and an accurate fuel flowmeter which is initially loaded with the FOB (fuel on board) and which gives both the instantaneous flow rate and the fuel remaining. This data is fed to the GPS (this is panel mounted kit, not handheld) which is programmed with the route and thus knows the distance to run, the ground speed, and it will constantly recalculate the projected fuel at destination based on the current GS (which assumes that the wind etc doesn't change, but that is a reasonable assumption, and pilots doing long trips should be aware of the overall weather pattern anyway).

Here (http://www.peter2000.co.uk/aviation/misc/fuel.pdf) is an article which describes the typical system. It really is far removed from the stuff taught in the PPL, but is not expensive. It is probably also far removed from 1960s-1980s RAF practices, if a book I have just read is anything to go by. I know this will draw ridicule from RAF people here, and I don't suppose the Russians had anything better at any given time, but I think it is a huge piece of good luck that the RAF rarely had to do this stuff for real. For example, IIRC, after the Falklands bombing it was realised that the fuel burn of the Vulcan, under the particular conditions of that flight, was several tens of percent worse than had been assumed for many years beforehand.

[BEagle]

For example, IIRC, after the Falklands bombing it was realised that the fuel burn of the Vulcan, under the particular conditions of that flight, was several tens of percent worse than had been assumed for many years beforehand.

Not so. The Vulcan fuel burn at high weight was entirely in accordance with the Operating Data Manual. The problem was that some complete idiot decided to use training weight rule of thumb figures which were grossly inaccurate at high AUW - nobody had flown the Vulcan at high weight for years as the nuclear bomb weighed considerably less than 21 x 1000lb conventional bombs. Fortunately the AAR planners insisted on ODM calculations after the fool had made such a nonsense of the planning.....

[peterh337]

Thanks for the correction Beagle. However my point was that these people were the very best around; the best selected, best trained, and far more current than anybody in GA.

Today, there is no need to do stuff like this. The equipment and methods exist to plan a flight and execute it accurately and predictably. And if the MPG does drop (e.g. a massive unexpected headwind) then you will be able to divert early.

So much of what we fly with and how we fly is still hanging on 1940s 1950s 1960s practices. I've just done the JAA IR conversion, on which about 90% of the time was spent doing NDB holds and approaches, which almost nobody does (using the ADF) nowadays. Translate that to a typical 55hr ME IR and multiply it by the # of FTO ATPL students and add up the cost... for exactly what purpose?

[A and C]

An interesting thread with the GPS will solve all crowd in one corner and the ex-military in the other corner.

However the thread can only raise awareness of the appalling standard of fuel planning that I find in the flying clubs, keep this one up guys it might just get a few people thinking about the subject.

['India-Mike]

Agree with A&C re fuel planning. I was trained as an FI with fuel circles and that's what I teach my students as all the proprietrary plogs are woeful as fuel planners. Fill a PA28 and you don't need to bother about fuel planning in a UK context. However fill a Chipmunk 22 with 18 and you do.

[Genghis the Engineer]

Problem with using it in light aircraft is that you need an accurate enough fuel gauge - which basically means a sight tube. You'll get that in many microlights, and some vintage aeroplanes - but few spamcans.

Given that, in most light aeroplanes, where it's reasonable to do fuel planning on the basis of predicted performance (plus a bit of a safety margin of-course), I think that the method will work, but using time rather than fuel state.

G

[Genghis the Engineer]

all the proprietrary plogs are woeful as fuel planners

I concluded years ago that "all the proprietary plogs" are woeful in many ways. Eventually I realised what should have been blindingly obvious - which is that like just about everybody else these days, I have a PC with a wordprocessing program and access to a reasonable printer.

So, I designed my own, and tweak it periodically to meet my slightly changing perception of the "perfect PLOG".

Since I've become an instructor, I've just been giving that PLOG as a word file to my students, the good ones have used it, the very good ones have adapted it to suit their own preferences.

G

[A and C]

The computer flight plan that I have will give you the minimum fuel required to do the flight, it then has the minimum fuel on board at each waypoint.

So it is all quite simple, if you don't have the correct fuel quantity at a waypoint then you are going to have to divert.

I can see how this is a problem using the average fuel gauge so for most American aircraft a fuel flow meter is essential.

Fortunately the Robin I fly has four fuel tanks and by running them almost dry (a very accurate tank almost empty light is fitted) you can get a very accurate fuel plot going based on the conditioned for the day rather than filght manual numbers. I have had fuel flow numbers within a ltr after four hours flying in this aircraft however I would not run any aircraft that I did not know well without a much larger margin for error.

[peterh337]

Problem with using it in light aircraft is that you need an accurate enough fuel gauge

You need a) the departure FOB and b) the fuel flow.

a) is easy.

b) is not so easy, but can be established by e.g. doing two identical flights which have different length cruise sections. Fill up before and after each flight and then you can work out your fuel flow in cruise. Assuming of course you lean equally in both cases.

The fuel gauges are actually irrelevant. Mine happen to be very accurate (expensive capacitive type) but I use them only for switching tanks. When flying solo I run down the LHS tank by about 1/4" on the gauge, to keep the plane flying straight.

It is critical to know the progress of the flight in terms of fuel.

[Grob Queen]

All my contacts with other PPLs suggest that fuel management is poorly addressed in PPL training, and my own experience confirms this. .....PPL training practices err on the safe side and most flying is done with the mixture set to fully-rich and few pilots are taught about leaning. Much reliance is placed on using ground based logs of flight times to determine the remaining fuel on board (FOB); this generally works because conservative fuel consumption figures are used and most training flights are short. The downside of this system is that a large part of the aeroplane's real range is not available and a pilot wishing to embark on a long flight is venturing into unfamiliar territory, and quite spectacular fuel planning related incidents do
happen.

Peter, TVM for the link to your article, very interesting, particularly your first paragraph. I think your first sentence says it all. Maybe Civilian FTOs ought to take a look at RAF training (yes, even PPL RAF training as I am doing) and see how we are taught. it may seem archaic and unnecessary, but my instructor really bangs on about fuel planning, so I am incredibly aware of checking it all the time. Indeed, he also points out your point of reliance for Plogs - on the basic form, there is no place for fuel planning - ok, so you have "fuel consumption, total required, fuel on board, reserve and total endurance" but that tells you nothing IMHO. I would rather work it out for each leg or twice for a leg if a long one, so I know when to divert if I need to.

Am I not correct in thinking the aircraft's real range is in the POH? Talking of the POH, yes, fuel consumption is in there, yes, in our case certainly they are about 30 years old, but that is at least a guide. The wise pilot surely also checks the fuel gauge en route...

but using time rather than fuel state.


Absolutely GtE, Maybe I forgot to mention in my original post that these fuel circles are based, as well as consumption, on the time it takes for the Grob to fly a certain distance and the amount of fuel it uses for that leg. For instance, we burn 25 litres per hour and therefore 2 litres every minutes. Therefore in my example in 25 minutes we have burnt 10 litres, in 18 minutes 8 litres etc. Of course some figures are rounded up or down, and you may use an extra litre per leg or less than planned but you will always have an idea in your mind of how much you are using, and perhaps more importantly, how much you need to return to base.

Are pilots who use GPS so aware of how much fuel they are using? Would you know that you should not do that extra leg because you would not get back to base?

Agree with A&C re fuel planning. I was trained as an FI with fuel circles and that's what I teach my students as all the proprietrary plogs are woeful as fuel planners.


Nice one India-Mike, I agree with you both on that!:ok: How do other FI's instruct their students wrt Fuel planning?

[peterh337]

Most people use a portable GPS, and I don't know how you would best use a portable GPS to assist with fuel planning.

I suppose the biggest contribution is that you know where you are and aren't going to get lost. Getting lost does have a tendency to affect one's fuel plans :)

But you also know your GS and your ETA, and assuming you know the fuel burn you can work out the LFOB (landing fuel on board) from that, manually. If you have 2hrs to run and your burn is 10GPH then you know you will burn another 20 gallons before you get there.

As regards extra legs, my feeling is that the best way is to plan the flight as best as one can, and execute it to the plan. Then (assuming you know the fuel burn) the fuel ought to work out.

I did some (somewhat artificial but required by the FTO) detailed fuel plans in the JAA IR training. One is supposed to maintain a fuel column in the plog. Accounting for every approach, every missed approach, every time around the hold, I managed to get the error down to 1 USG, which was about 3%. The plog form didn't have anywhere enough room so I used a spreadsheet. But paradoxically this is unworkable in "common GA" because the fuel burn is not known anywhere near that accurately. It is know to within about 20%. I was able to make it add up because I know the fuel flow to 1%, but if you know the fuel flow to 1%, and it is GPS linked to compute the LFOB, you don't need to maintain a fuel column in the plog :) In fact you just look at the current FOB reading and decide if another 5 holds or whatever will deplete it too much.

[Grob Queen]

As regards extra legs, my feeling is that the best way is to plan the flight as best as one can, and execute it to the plan. Then (assuming you know the fuel burn) the fuel ought to work out.

Fuel circles are part of that flight planning and which is precisely why Fuel circles on the chart are a good idea...if you need to make extra legs, you know with a quick glance whether you have the fuel to do so....

I did some (somewhat artificial but required by the FTO) detailed fuel plans in the JAA IR training. One is supposed to maintain a fuel column in the plog.....The plog form didn't have anywhere enough room so I used a spreadsheet.

...and did you find this useful? Wouldn't it have been much better on your chart though instead of a spreadsheet?!

But paradoxically this is unworkable in "common GA" because the fuel burn is not known anywhere near that accurately. It is know to within about 20%.

Understood, but my point is, when flying at 90kts, one does not have to be quite so accurate. I have already admitted that I round my fuel figures up or down to make mental arithmetic easier. I would much rather know that I still have the required 15 litres FOG minimum plus some to get home! ;)

[peterh337]

and did you find this useful? Wouldn't it have been much better on your chart though instead of a spreadsheet?!

Not really because I merely need to press the top right button on this

http://www.peter2000.co.uk/aviation/shadin/shadin2.jpg

and I get the "exact" fuel in the tanks, and I know the flow rate because it is on the display. I don't need range circles on the map, and anyway they are not circles if there is any wind ..... and at 90kt IAS the wind could be awfully relevant :)

when flying at 90kts, one does not have to be quite so accurate

I don't think the IAS affects the need for accurate fuel management.- except that a lower speed needs better management if anything because, per hour of endurance, you have fewer airports within range. You are also less likely to escape bad wx if you are flying slower, and wx is by far the most likely reason for diversions (blocked runways that actually close an airport are very rare).

[Cows getting bigger]

Doesn't anyone read the POH any more? For example, the Cessna 172 has a fine (and accurate) cruise performance table. Set an RPM and lean in accordance with the guidance in Normal Operating Prcedrues and you'll get a pretty accurate fuel burn. Add 10% and 45 mins if, like me, you like to adopt IFR criteria and you will never need to stare longingly at notoriously inaccurate fuel gauges.

PS. I agree about the poor standard of training on this during PPL; we appear to have resorted to filling the tanks and assuming a pilot will be bored, out of cash or in need of a pee before the tanks run dry.

[Johnm]

Set an RPM and lean in accordance with the guidance in Normal Operating Prcedrues and you'll get a pretty accurate fuel burn. Add 10% and 45 mins if, like me, you like to adopt IFR criteria and you will never need to stare longingly at notoriously inaccurate fuel gauges.



Which is why the only items I would tolerate "inop" on my Archer were fuel gauges

[RTN11]

in need of a pee before the tanks run dry.That's certainly the case for me :}

Also, I've flown a few vintage aircraft where the oil consumption is more limiting that the fuel - you can carry 5 hours of fuel but only perhaps 3-4 hours oil.

Pilots should always be aware of their remaining endurance and/or range, but most civvie schools air an awful lot on the cautious side. One school I visited offered students a fuel planning sheet with a fuel burn stated of 35 litres/hr for a PA28, when the POH would state something more around 28 for a normal cruise level/leaned, and less if you got higher.

Most training flights don't last much more than an hour, and you would usually have at least 3 hours fuel when you taxi out, so it's not really part of the normal flying training to fly right down to minimum fuel.

[Grob Queen]

I see Peter...I don't recognise that gadget so we obviously don't have one:) But I can see now, why you always know your exact fuel and the flow rate!


Most training flights don't last much more than an hour, and you would usually have at least 3 hours fuel when you taxi out, so it's not really part of the normal flying training to fly right down to minimum fuel.

True. But we only fill our tanks with enough fuel plus a bit for the Sortie. Hence most training trips will only use about 20 litres, leaving 40 in the tank. But if we are flying navexes out of the local area, or the qualified club pilots are taking a club aircraft out, we will fuel up with more. So training with planning using fuel circles ensures that we fill up with enough fuel and that we don't fly down to minimum fuel. This system also ensures that we know (ok, I know as the student) the minimum fuel required to land with.

As it happens, I am planning a trip of 93 miles at the moment, with the aforementioned fuel circles, and I know that I can fuel up with 75 litres and be fine...:)

[FlyingStone]

I know the fuel gauges are notoriously unreliable, but you could always do a simple calibration test here and then - very simple, especially if aircraft flies a lot.

You drain the tanks, put in the unusable fuel - the fuel gauges should read zero. Then you start filling up, let's say in 5 USgal increments - and check what the gauges read and note it down. You end up with a full tank and a nice table showing actual fuel in tanks vs. fuel shown by the fuel gagues. Quite simple or am I missing something here?

Obviously you don't need a fuel totalizer if you're doing one-hour trips, although it's quite handy to have one - or at least an accurate fuel flow gauge.

Doesn't anyone read the POH any more? For example, the Cessna 172 has a fine (and accurate) cruise performance table. Set an RPM and lean in accordance with the guidance in Normal Operating Prcedrues and you'll get a pretty accurate fuel burn. Add 10% and 45 mins if, like me, you like to adopt IFR criteria and you will never need to stare longingly at notoriously inaccurate fuel gauges.

Spot on! If only people weren't afraid of the red knob and follow the leaning procedure in the POH exactly, the fuel flow probably wouldn't be more than 5% off the book value. I think one of the problems is that people who rent aircraft just listen to the owner, who says "this aircraft burns xx USgal/h" and use it for fuel planning. It all depends on the mission profile you have - full throttle/full rich at sea level will definitely burn a bit more than a nice economy full throttle/peak EGT at FL100. It's like saying a car has the same mileage/fuel consumption for driving in a city or on the highway.

[peterh337]

Quite simple or am I missing something here?Many fuel gauges are stuck, or they stick in certain positions.

Often the transmitting mechanism (usually a crude potentiometer, working off a float) is intermittent.

Obviously you don't need a fuel totalizer if you're doing one-hour tripsThat's true if you always fill up and always do 1hr trips.

But the typical UK PPL training scenario is that the school works off a "tech log" e.g.

10/1/2011 Filled up full - endurance 3 hrs
11/1/2011 Flown for 1hr 40 mins - endurance is now 1hr 20 mins
12/1/2011 Flown for 50 mins - endurance is now 30 mins
12/1/2011 55 litres put in (some calc...) endurance is now 1hr 30 mins
12/1/2011 Flown for 30mins (but actually flown for 50 mins) - endurance is now 40 mins but is recorded as 1hr
13/1/2011 Flown for 1hr - OOPS (http://www.aaib.gov.uk/cms_resources.cfm?file=/dft_avsafety_pdf_502314.pdf)

The choice of the final date is intentional :)

When I started my PPL training, I knew s0d all about flying but I was horrified by this procedure, with the obvious potential for cumulative errors and omissions, and I think the same of it now. Anybody with a technical / engineering education or background would think the same of it.

The basic issue is that poorly equipped spamcans don't have much useful range to start with and they tend to get operated either by shrewd people (who don't go anywhere near the limit) or by less than shrewd people (who rely on a lot of luck).

I know I bang on about the TB20 but on that you can fill up at Lydd and fly to Benbecula, with Lydd as your alternate, and (in zero wind) you will still have enough fuel to fly on to roughly Biarritz.

[Mark1234]

Are you serious? That's crazy.

Not really done any touring since returning to the UK, but I always dipped tanks before AND after flight. That way I have a pretty good idea of the starting point AND what it turns out flown my way..

[peterh337]

Yes; the prang I linked to involved prolonged flying (multiple flights) during which the fuel level remained below the visually inspectable level.

This is a trap for many... due to wing dihedral the fuel level is not visible is many/most GA types when below about 50%. This does not usually cause an operational problem in singles but it is an issue with "6-seater" twins operated for charter work, because you never know how many fat people will turn up for the next job, so you have to keep the tanks as low as possible. It's OK if you know exactly what you are doing...

[BEagle]

Using three different units for fuel calculations (litres, Imperial gallons and US gallons) is fraught with risk. Compound this with the useless fuel gauges in most light aircraft and pilots' reluctance to pay for more fuel than is absolutely essential and I'm surprised that there aren't more accidents due to fuel calculation / uplift errors.

When marking Flight Performance and Planning papers for the PPL, I was surprised how many people didn't understand the difference between density and specific gravity, particularly when using US gallons.

We had an aeroplane with a generally accepted 4 hour endurance, but we had an absolute rule concerning minimum in flight fuel indications. A pilot flew it for an hour on an instructional GH flight, then a renter took it on a 90 trip to Wales. He didn't bother refuelling whilst there and despite reaching the minimum indications, pressed on back to base passing a number of available aerdromes en route. At 1+(2 x 1½) = 4 hours, some miles short, it all went quiet and he had to land it in a field....:\ Fortunately without damage.

[peterh337]

pilots' reluctance to pay for more fuel than is absolutely essential

In the case I posted, the FTO reportedly pressed him to not fill up more than necessary, because they used the plane for charter work.

This is inevitable. If you fill a Seneca right up, it will be ~prob90 useless for charter.

[BEagle]

In our case, pilots who uplifted fuel away from base (except where we had an agreement) would only pay the difference between our price and the other price. So uplifting 40 litres, in those days, would have cost him about £4 as he would have been credited the balance from his rental bill.

As for leaning, a private owner with decent CHT, fuel flow and EGT indications should be able to find the best mixture setting. But most of the rental wreckage around at clubs isn't so equipped and excessive leaning (I flew with one pilot who (briefly!) pulled the mixture back to the point of rough running at 1500 ft), can damage engines. We had to change a pot once at the 600 hr point - someone had cooked it through excessive leaning......

With all the advances we've seen in electronics, it surprises me that most of the GA club fleets still rely on ancient carburetted engines with manual mixture controls and the ridiculous need for carburettor heat. Even the cheapest car with a much more complicated engine usually has electronic fuel injection and a reliable EMU these days - but many light aircraft are stuck with some carburettor from a 1950's combine harvester!

[peterh337]

someone had cooked it through excessive leaning

At the risk of starting another thread on this... "excessive" leaning is a danger only at high power settings e.g. 75% or higher, specifically ones which result in high CHTs (perhaps 500F or so).

Excessive leaning alone just gives you a rough engine and a loss of power. No damage is caused.

During taxi, maximum possible leaning is the best thing - keeps the plugs clean.

[Maoraigh1]

I was surprised how many people didn't understand the difference between density and specific gravity, particularly when using US gallons.

What is the difference?

[RTN11]

At the risk of starting another thread on this... "excessive" leaning is a danger only at high power settings e.g. 75% or higher, specifically ones which result in high CHTs (perhaps 500F or so).

Excessive leaning alone just gives you a rough engine and a loss of power. No damage is caused.

During taxi, maximum possible leaning is the best thing - keeps the plugs clean.

Indeed, and is also much worse with a larger engine producing more power. The O-235 seen in most PA38s or C152s can barely produce 75% power, so can pretty well be run lean at most levels or power settings with no ill effect, but once you're onto a higher performance machine you really need to know how to work the red level properly.

[peterh337]

The O-235 seen in most PA38s or C152s can barely produce 75% power

Really.............?

[BEagle]

I was surprised how many people didn't understand the difference between density and specific gravity, particularly when using US gallons.

What is the difference?

Density is the mass of material per unit volume. It has units such as kg per litre or lb per gallon

Specific gravity is a ratio of the mass of a material to the mass of an equal volume of water. As it is a dimensionless ratio, it has no units.

[Big Pistons Forever]

I think pre-planned fuel circles make perfect sense if you are flying a high performance jet on a low level NAVEX where things happen fast and wind has a relatively small effect on flight time. They IMO make no sense in the context of a PPL flying your average Cessna or Piper.

From the very first lesson I teach my students to think about fuel as "time in your tanks". This of course starts with what the dipstick shows on the preflight. Lessons which are flown in the local area use a block fuel burn (ie a conservative average of what is typical for an average training sortie, which is usually about 20 % higher than the leaned cruise fuel flow in the POH), giving the time available in the air for that lesson. This time minus the reserve is the "we have to be on the ground no later than" time.

Navigation exercises are planned in the usual way but I insist that the student be able to tell me how long they can fly from the top of climb point. Have to go somewhere else from any point in the flight ? Well after you figure out how long it is going to take you you can ask yourself "do I have that time in the tanks". This is really useful when you have a GPS (which IMO is mandatory equipment now) because you can get instantaneous ETE information to anywhere (obviously to be double checked early for any GS changes caused by changing your heading)

As for fuel gauges, I intensely dislike the blanket assertion that "fuel gauges are useless".

If you go to the POH for any Cessna there is an equipment list that specifies what equipment is "required". On that list is fuel gauges. If you are flying a Cessna and the fuel gauges are not working then the aircraft is not being operated in accordance with its type certificate.

My experience is that light aircraft fuel gauges particularly the ones in Cessna's are not particularly accurate at the top of the travel but once you get to 1/3 or less quantities they actually are pretty good. If you own an aircraft it would seem foolish to me not to calibrate the gauges by draining the tanks and filling them in 5 gal increments.

Unfortunately if you are renting some beater from the flying school you do not have much control over the state of the gauges but you can still get a feel for what they are saying by comparing the dipped amount to what is showing on the gauges. This simple check is almost never taught in flying schools. If you are filling the aircraft with full fuel after your flight, before adding fuel estimate what you think you burned and compare it to the pump meter.

If it is your own aircraft or a rental where you usually fly the same aircraft, with a bit of experience you can get consistently pretty close. :ok:

[NazgulAir]

Our fuel gauges are as accurate as they come, but I wouldn't want to rely on them. Pointers can stick. There are only two gauges with three-way toggle switches, so you don't see all tanks in one glance.

Our plane has six tanks and we switch manually between them using two separate fuel selectors (one for each wing with three positions each). To keep track of our fuel state at any time, we log a detailed record of the contents of each tank, the dip-checked amounts, the fuel used and the fuel remaining before and after each flight, plus the fuel used from each tank between switches, in a separate "fuel log".
NO WAY we wanted to risk getting caught out not knowing *exactly* what our fuel state is or getting in trouble like some unfortunate pilots in the Comanche's long history have. Without keeping some record, it is just too easy too make a bad mistake!

Some Comanche pilots like to avoid trouble by just flying on the main tanks with both switches selected ON, effectively reducing the need to switch. One problem with this is that you don't know from which tank the engine is actually feeding. Another problem is that the mechanical fuel pump's efficiency can lead to fuel crossfeeding from one wing to the other via the central sump. Things like unusual attitudes, turns, and having the electrical fuel pump on further complicate matters, until you end up having no idea at all how much fuel is in which tank while you are flying. Since we don't want to refuel after each flight, which is pretty ridiculous after a one hour flight when you have 10+hours endurance, this way of operating is not suitable for us.

We have a wonderful instrument called the Shadin Miniflo fuel computer. Besides being an invaluable aid in leaning the mixture correctly, it plays an important role in our fuel planning and logging.
Before a flight we plog our expected fuel usage at the planned power settings for the planned legs of our route, expected time to climb, cruise, descend, etc. and we set a procedure for the order in which the tanks are switched and the times to run on a tank given our load balancing needs (This is useful because we have a wide wingspan and 30 minutes flying on a tip tank makes quite a big difference).
We then fly following our planned switches and we note the amounts used at each switch.

This all may sound like a lot of work, but the workload is minimal and just part of our normal operating procedure at the time of the walkaround (dipping and logging) and writing down the amount used at the times a tank is switched. We like the way it automatically adds awareness of our fuel safety. Double-checking the fuel computer against dip-checked amonts and uplifted amounts gives us several opportunities to spot errors in resetting the fuel computer or calculating errors in the log.

In November I got ramp checked. Among other things I was asked to produce proof that I had planned my flight with sufficient range. This was a bit of a laugh because there was about eight hours remaining in the tanks when he asked. When I showed him the fuel log he was so stunned that I wondered if he had ever seen one before. The C414B I have been privileged to get acquainted with had eight tanks to keep track of, so the need for some kind of procedure is not unique to the Comanche.

Most light aircraft have only two tanks, but I know of several types that have long range capacity and extra tanks so for these fuel mismanagement risks might be mitigated by strict procedures as well.

[Grob Queen]

From the very first lesson I teach my students to think about fuel as "time in your tanks". This of course starts with what the dipstick shows on the preflight. Lessons which are flown in the local area use a block fuel burn (ie a conservative average of what is typical for an average training sortie, which is usually about 20 % higher than the leaned cruise fuel flow in the POH), giving the time available in the air for that lesson. This time minus the reserve is the "we have to be on the ground no later than" time.

Navigation exercises are planned in the usual way but I insist that the student be able to tell me how long they can fly from the top of climb point. Have to go somewhere else from any point in the flight ? Well after you figure out how long it is going to take you you can ask yourself "do I have that time in the tanks".

I was very interested in this Big Pistons. Of course I would not dream of arguing with you because from other threads I see that you are vastly experienced and respected on this forum. :) So this is really out of curiosity, nothing else. So ok, the student tells you how long they can fly from top of climb. THis I can do for my instructor by looking at fuel circles seeing we have say 57 litres for our trip and at that point we have enough in teh tank to RTB. It is there on my chart and all the brain work has been done before so I can just concentrate on flying. So I guess what i'm wondering is why form your viewpoint is asking the student to tell you this way when they are probably maxed out with flying, better than our way where my instructor can see from looking at his copy of my planned route, how much fuel I expect us to have?

If we are flying one of the Grobs, we don't use a dipstick, but just check the fuel gauge against the Tech log. However, if we are flying the Firefly we do indeed dip both tanks.

And on the subject of leaning....I am not taught how to, the mixture is ALWAYS rich! ;)

[thing]

HI GQ, I'm not really experienced enough to enter into the technical arguments here but I'm amazed at the difference in training between you 'down the road' as it were and what we do here, which in theory you would think would be broadly similar. I've honestly never heard of a fuel circle, we are taught to lean out at whatever altitude we are at and I personally always take off with full tanks, in fact we always keep the a/c tanks full for condensation prevention. You can never, in my opinion, have too much fuel. Obviously weight and balance considered and bearing in mind I don't fly jumbo jets.

Incidentally I was doing some NDB approaches at your place today, (it's free after all...:-) after ringing your tower mob and being assured they could fit me in at a specific time. I finished up doing four flogs round the holding pattern (in clag with a 30kt wind) before I got clearance. Total time to fly the 8nm to your place and the 8 nm back to mine was 1:30.....it would have been cheaper to go to Donny and pay my £4.50.

[Grob Queen]

Hi Thing,
Maybe 'cos we have the RAF's Ab Initio guys our instructors are used to doing things the RAF way?! ;) Thought there would be talk of fuel circles around your club house!

Anyway, incoming on your PM!

[Big Pistons Forever]

I was very interested in this Big Pistons. Of course I would not dream of arguing with you because from other threads I see that you are vastly experienced and respected on this forum. :) So this is really out of curiosity, nothing else. So ok, the student tells you how long they can fly from top of climb. THis I can do for my instructor by looking at fuel circles seeing we have say 57 litres for our trip and at that point we have enough in teh tank to RTB. It is there on my chart and all the brain work has been done before so I can just concentrate on flying. So I guess what i'm wondering is why form your viewpoint is asking the student to tell you this way when they are probably maxed out with flying, better than our way where my instructor can see from looking at his copy of my planned route, how much fuel I expect us to have?

If we are flying one of the Grobs, we don't use a dipstick, but just check the fuel gauge against the Tech log. However, if we are flying the Firefly we do indeed dip both tanks.

And on the subject of leaning....I am not taught how to, the mixture is ALWAYS rich! ;)


There are few things in aviation that are black and white with "right" and "wrong" ways to do something. Navigation in particular is one where there are numerous acceptable ways to plan and execute a cross country trip. I think most experienced pilot settle on a way that works for them. Being rather lazy I am all for simple procedures where the level of accuracy is proportional to the accuracy requirement. The whole fuel circle thing just doesn't spin my prop......

However what ever method you use it is important that you truly understand what you are doing. From your post this does not appear to be the case. You say you want to RTB and no problem because you are on the 57 litre circle ? Well what about if you are on the crosswind leg or your triangle NAVEX with a 25 knot wind blowing from the direction of your base. Will that 57 litres allow you to fly with a 25 % lower ground speed ? I don't see how. The bottom line is the only thing that matters is the ETE compared to how much time you current fuel state will give you. In slow airplanes this can cause large changes in actual achievable range. When you are in a RAF fast jet doing 350 knots wind is basically irrelevant but it is most certainly relevant at 90 knots.

Finally if you always fly at full rich how do you know your fuel burn ? The POH in every light aircraft I have ever seem only gives you fuel flows with the mixture leaned as per the POH procedure. If you don't know how much you are burning then your circles are meaningless.

Don't get me wrong if this method appeals to you fill your boots but make sure you know what you are actually planning.

I am a big believer in the intelligent use of technology. The GPS is a very valuable aid and its nearest airport function can literally be a lifesaver. Knowing your exact GPS derived ETE is extremely helpfull and that combined with knowing how much time you can fly with the fuel in your tanks an easy calculation that is simply the total time in your tanks minus how long you have flown since top of climb, makes a diversion pretty straighforward.

Its even easier with a fuel totalizer with a GPS input, but a couple of hundred pound portable GPS and a watch are almost as good and can be used on any club rental.........

[Grob Queen]

Hmmm, i'm feeling this is starting to get a little out of my depth - still have lots to learn and don't mind admitting so! ;)

However, in answer to Big Pistons (and I say again, I am not trying to argue with those more experienced, just stating what I am taught):

However what ever method you use it is important that you truly understand what you are doing. From your post this does not appear to be the case. You say you want to RTB and no problem because you are on the 57 litre circle ?

I have to disagree with this statement I am afraid as I believe I do indeed understand fuel circles..a fact on which my instructor agrees! RTB on say in this example I quoted a 72 litre circle. The 72 litre circle is the first circle where we have used 3 litres in taxi and climb to the RVP. if the engine was to go bang at this point, we would only require three more litres to RTB. If however, the engine went bang at the furthest point on the trip outlined, we would have 66 litres to RTB and the minimum red fuel is 56 litres. PLanned fuel useage on the return leg is about 9 litres, so we are well in board.

This of course is indeed in still air, and one would have to recalculate in flight if there was a 25kt headwind, or for diversion etc. Fuel burn? Grob uses 25 litres in 1 hour. I would need to check if this was fully rich or leaned. But as this is the figure I am taught to use, and my teaching is not to lean, it must be the fully rich figure.

I do stress though, I am not trying to pretend I know more than I do...just interested to see how others are taught and if the military/ex military pilots out there agree that this is a worthwhile system or whether they when flying privately use GPS! :)

[thing]

Still can't see why you're taught to fly full rich all the time unless you never get above 100 ft. I don't know the Grob so there may well be a perfectly valid technical reason.

[gasax]

I'm not sure that you really do understand fuel circles.

What is the point of a technique which ignores wind and where the largest single input - fuel burn - is a gross approximation?

Last Saturday I flew a point to point flight of about 30 miles - it took me 2 hours because I took a pretty scenic route!

I took off with a wind of about 260/3kts. Midway the wind was about 210/12kts and when I landed it was 270/5kts. The bit in the middle would make the 'fuel circle' method hopelessly inaccurate. So too would the fact that I was so enjoying the view that I throttled back and used the wind to slope soar and loiter around the hills.

The critical aspect for light aircraft is that wind has a massive impact at 90kts. Last year I flew from my engineers back to my home base - ground speed for much of the flight - 45kts. On the ground it was about 260/25kts at 1000 foot very very much more - as shown by the GPS!

Calculating a set of range rings which are highly inaccurate simply does not seem to be a smart technique. Flying at 360 or 420 kts - ok I can ignore the wind flying at 90 kts it is one of the most significant inputs. Oh, along with the 'loud pedal'.

[Grob Queen]

I think that may be the case Thing...as we've seen from other posts, there aren't that many other Grob "drivers" out there.....

One thought has just occurred though...maybe we just haven't cruised enough for me to be introduced to leaning? So far we have really only bimbled around the local area on GH trips. The Grob cruises at 2400RPM is that maybe too slow to lean? :hmm:

Oh well, maybe I do, maybe I don't. :rolleyes: Bottom line is I need to understand the circle method cos thats the way i'm taught; and I daresay theres a reason for it. But i'm glad this thread is doing what I hoped it would - bring a little dicussion and controversy to PPruNE ;)

[peterh337]

The fuel circles are not circles.

They are probably elliptical, with the elongation stronger as the wind becomes a higher % of the TAS.

[BEagle]

The problem is that the RAF is trying to apply a system which works for still/air low level high speed navigation, where W/V is of little consequence, to medium level navigation at low speed in the Plastic Pig, where W/V is highly significant.....:rolleyes:

The same logic which uses MDR for pre-flight planning purposes, resulting in inaccurate GS values. It is actually OK to plan a low level navigation trip at 240 KIAS+ using still air, but to use MDR for pre-flight planning at 120KIAS is inadequate for GS calculations.

This is the 'running before you've learned to walk' approach, using elementary training aeroplanes for purposes for which they are quite unsuitable. Why? Because they can't afford to operate proper basic trainers such as the Jet Provost these days....:mad:

[thing]

Did the JP manage more than 120 kts....? :} I remember back in my day they were known as the variable noise constant speed machine.

[BEagle]

'Constant thrust, variable noise'!

We did some LL at 300KIAS, but that meant that you couldn't use the standard technique for regaining ETA without exceeding the engine limits. It was also a rock-hard ride and any significant turns at 60º AoB bled speed off considerably. It used a LOT of fuel and the controls were quite heavy, particularly in roll.

Whereas 240KIAS at 250 ft was a much better regime - and gave greater time at LL.

[sycamore]

Guys,several of you have misunderstood what GQ calls `fuel circles`.. more properly they are `fuel check circles`,,,
At the end of each `leg` of the navex ,in planning, a small circle,about 1" diam. is drawn,with a horizontal line across the circle.
In the top half of the circle is drawn the amount of `fuel remaining `expected`.
In the lower half of the circle(probably in `red`,is the `minimum fuel required` to complete the sortie,flying the rest of the route..
Therefore,at all times the fuel in the `top` segment should always be greater than in the lower half....Irrespective of whether you lean or not..
It is a simple `Howgozit`,so that one can check easily if fuel is sufficient.
For those that have drifted into `range circles`,fuel flowmeters and GPS,the OP is just learning his trade with the simple Grob... RTFQ..

[thing]

I remember the civvie pilots at Shawbury getting an award for saving x amount of fuel simply by retracting the undercarriage on ccts. (For the unknowing Shawbury is where they used to hack around the cct all day in JP3's training newbie ATC chaps and chappesses.)

[Grob Queen]

Eureka!! Sycamore, you're brilliant!!:ok: Thank you for your post, that is PRECISELY what a fuel circle is....and the lower half of the circle (minimum fuel required) is indeed in red.

Thing...I thought the trainee wokka boys and girls were there to provide enough sport for the trainee air traffickers??!! ;)

[thing]

Ah this was a looong time ago, probably before you were a twinkle.

[Grob Queen]

JPs...what like the sort HRH flew at our place (with varying success ;)) in 71-72?

If so, yes, that was before I was around...but not by much! :p

[GeeWhizz]

Interesting topic.

These fuel circles seem to do exactly what most of us probably have in the fuel column of our plog. These fuel circles are drawn on the chart(?). My plog for example has a fuel column at the end of each leg with how much I expect to use, and what I expect to have in the tanks. Both written in a box with a horizontal line as opposed to a circle. Now whether these 'estimations' are for the leaned engine or otherwise they work and will do just fine for my flying. Furthermore in the planning phase of the flight 45 mins extra fuel is added plus 10% of that again. So with that in mind I suggest the leaned/full rich figures wouldn't be too dissimilar for the GA hops we see around the UK, and if so the contingency will cover it.

On using the circles method: the red half of the circle seems to be drawn in red to be conspicuous. I would consider drawing the whole circle in black or blue regardless, as red wont be easily read in red light (night flying?). I'll also mention that if flying IFR then fuel circles may not be the easiest way to check fuel calculations. IFR flight = higher workload and tends to be more accurate due to the navigation aids, ATC, etc, and I personally believe the chances of getting lost whilst IFR are close to zero. The latter reason is my preference for not using circles drawn on the chart (as well as preferring as clearer chart as possible).

Just my thoughts :)

GW

[Grob Queen]

Hi GW,

Yep, I draw my fuel circles on the chart, next to the heading line and the figures are in the direction of travel. They do of course make the chart busier but I draw them in an area I am not going to use. But thats the beauty of circles on the chart, they are there, to check as you are checking your route.

The ystem of the plog fuel column sounds exactly like my circles. In fact, to satisfy the CAA I write these estimations in both the plog as you do AND the chart. That way I am practising for my QXC and Skills test but also learning the "everything on chart way" so when i'm let loose in the sky with my licence, I can use this as it is my preferred method (not so much paper to lose in the cockpit).

So, your 45min extra fuel, that sounds as though its the same as my 15 litres minimum FOG, as that would give me about 30 mins airborne...

Yes, the minimum fuel is in red so to be conspicuous. Thats an interesting point about its use in night flying and IFR. Hadn't considered it before. I will have to ask my instructor whether in that case the entire circle and figures are in black...and bear it in mind when I can graduate onto those ratings! :)

GQ

[BroomstickPilot]

Hi GC,

I have been reading this thread with interest. I note that you have been taught to put everything on your chart, rather than on a plog form. I was told off for doing precisely this by an instructor who was an ex RAF Group Captain, ex fast jet pilot, and a very senior test pilot. My point is that what the RAF does today will be anathema tomorrow. So don't regard it as gospell. It is only how things are done today in one organisation. Do listen to pilots from other spheres; they all have good things to teach.

As to the fuel check circles. As has already been said, these seem to fit the bill fine for fast jets and also for you - as long as you are only flying 50nm legs between quiet aerodromes with only a simple aeroplane and only you and perhaps your instructor aboard.

However, if you were to fly a four or six seater, with several tanks, over legs of 200nm or more and with three or four passengers and luggage aboard, I suspect this method of fuel management might soon prove inadequate.

May I suggest that you ask around at the club and see if there are any pilots there who have flown a Hercules or a Galaxy a Tristar or a Nimrod and ask them how they manage their fuel burn. Let us know what you discover.

I did ATPL groundschool about ten years ago, and the method of fuel management I was taught was based on airline practice, i.e. calculate taxi fuel, trip fuel to destination, fuel from destination to alternate, half an hour's fuel for remaining in the hold at the alternate, and then landing and taxi-in fuel; (not to mention any allowance for 'unusable fuel' and maximum permissable fuel load to remain under max landing weight). Obviously, you can't use this method on a Pa28, but it does at least provide the mental backgound for my fuel planning. Even in a small aeroplane I allow for taxi fuel and I do calculate my fuel from destination to alternate (just in case the aircraft ahead of me does a wheels-up landing on the only runway at my destination). I plan each leg of a multi-stage trip as though each was a separate trip. Yes it takes time, but it gives me confidence.

Regards,

Broomstick.

[GeeWhizz]

As Broomstick above, fuel planning can be as intricate or simplified as you like. For me the A to B flight is calculate something like the following:

- taxi, take off, climb
- total route level (incl. descent)
- diversion
- contingency
- 10% of contingency

If it were a local flight for an hour or so, take off to landing, the aeroplane burns about 8USG/ph so as long as there are about 12-ish USGs in the tanks I'll fly and not worry about the in flight figures, only the time. OK so this relies on time keeping and knowing many local places to divert to should something happen, but I'm confident I know the area well enough ;)

How you monitor fuel is a personal preference ultimately, and another of aviations great 'ifs' :)

[peterh337]

I did ATPL groundschool about ten years ago, and the method of fuel management I was taught was based on airline practice, i.e. calculate taxi fuel, trip fuel to destination, fuel from destination to alternate, half an hour's fuel for remaining in the hold at the alternate, and then landing and taxi-in fuel; (not to mention any allowance for 'unusable fuel' and maximum permissable fuel load to remain under max landing weight). Obviously, you can't use this method on a Pa28, but it does at least provide the mental backgound for my fuel planning.

I don't have an issue with somebody doing fuel planning one way or another way, so long as it is realistic for the situation. (The "fuel circles" method is not good for "slow GA" because the wind is likely to be very significant, so the circles are not circles anyway).

What I think is the biggest issue is that in GA most people don't know their fuel flow accurately.

I know nuffing about big jets but I am pretty sure they have accurate fuel metering (totalising) systems. They probably also have accurate fuel gauges.

But they are also hugely capable weather-wise (anti ice, FL350+ ceiling, autoland, etc) so a "30 minute" (or whatever) reserve for something is actually meaningful whereas in GA it is all but meaningless because 30 mins' flight is unlikely to get you out of a bad wx area.

Piston GA needs bigger reserves.

[GeeWhizz]

Good point Peter, but piston GA vanilla PPLs ain't flying in bad weather to begin with :}

[peterh337]

Not usually :) It is when they end up in it that they need to exercise their diversion options :)

But "bad wx" is relative to your capability (aircraft and pilot).

[Maoraigh1]

Good point Peter, but piston GA vanilla PPLs ain't flying in bad weather to begin with
Last weekend was calm, clear, with high cloud. Perfect for a nice flight. But also likely to produce low fog - leading to a diversion. And in summer there's the haar risk near the coast.

[ShyTorque]

Fuel circles are, as explained above, a circle with two fuel figures written in them.

Nothing to do with range rings on a chart!

When the sortie is being planned, the circles are left blank until just before the flight when the expected wind is applied to the flight plan. The figures are calculated and the circles filled in, working backwards, from the intended destination.

The top figure is the expected figure remaining, depending on how much was in the tanks at start up. The lower figure is the figure needed for the completion of the sortie as planned. The difference is (or was in my time) known by the RAF as "combat fuel".

The RAF taught it this way because when en route to a destination it often won't be refuelling (e.g. it will be carrying out a task such as dropping a bomb, or disembarking troops and then return to base or carry on to another destination). An easily assessed "running fuel plan" needs to be kept because if the aircraft was "bounced" i.e. attacked by an enemy, after the pilot had regained his composure, he would know if he could continue on his mission as planned, or not. In combat you can forget all ideas of economical cruise - it's throttles fully forward and mixture fully rich, not necessarily in that order. So, as soon as the position by the next fuel circle is regained, a rapid go/no-go decision could be made.

In the worst case the two figures would be the same, i.e. no "combat reserve" before start up. Having done much of my military service in a helicopter with a shabby 1 hour 25 minute endurance, fuel planning was always a major consideration.

[Grob Queen]

Ok guys, looks like I need to clarify a few things...! Have just spent the morning at the Club as it happens and as gusts of 40kts meant that flying was out, we have been chatting Navexes and Sector Recces (hmmm, i'm sure that one will get you all going too ;)) which we'll fly next time.

Broomstick - many thanks for your thoughts. I will certainly ask around at work as I know there is at least one Herc pilot. We also have ex-E3-D pilots on Station and a good friend of mine is ex-Vc10s so there are plenty of the Multi drivers around to ask! So in your opinion then, why are fuel management circles not good for legs of more than 50nm? I would ahev thought thaat, so long as all the figures were accurate, any length of leg was OK. The Grob is a twin seater with very little luggage space, so quite light really

Even in a small aeroplane I allow for taxi fuel and I do calculate my fuel from destination to alternate (just in case the aircraft ahead of me does a wheels-up landing on the only runway at my destination). I plan each leg of a multi-stage trip as though each was a separate trip.

Div fuel, this was one of the things I was discussing with my QFI today. The circles show planned fuel at all points. Div Fuel is red fuel and in our case we need to RTB with 18 litres FOG, 20 litres Div fuel (to get us easily to the other two local RAF airfields). Therefore the red fuel on the last point needs to be a minimum of 38 litres.

I don't have an issue with somebody doing fuel planning one way or another way, so long as it is realistic for the situation. (The "fuel circles" method is not good for "slow GA" because the wind is likely to be very significant, so the circles are not circles anyway).

Peter, as other have said, these are indeed not range circles, but a quick and simple way of seeing roughly how much fuel you expect to have and therefore whether you need to divert.

pick up a tailwind on leg 1 you might then find your RTB fuel was no longer sufficient when you turn around to fight the headwind. I think we need to check back with GQ whether the fuel calculation allows for wind figures and Groundspeed?

As to the wind...well, asked my QFI that too and the answer was straightforward...its not an issue because you will even out fuel useage during the navex...ie on the southward leg we may have a tailwind...therefore use less fuel...so use more fuel on northward leg back home due to the headwind but we have more anyway because we used less than calculated because of the tailwind on the outward leg - seems logical to me! Groundspeed? I'll have to ask about that one!

Bad wx Divs? very true GW, we don't fly in bad wx..todays a case in point ;) But true, we could end up in bad wx, thats where common sense and training come in. If I was solo, saw a massive great CuNim in my way I would see where I could divert to with the fuel I had, or decide maybe if its just one cell I could skirt round it..surely flying is all down to common sense, training and the pilot deciding the best course of action for a situation with div, fuel, wx all taken into consideration! Also, take Maorigh's point about ice...Last Weekend was a lovely winters day and we were flying...but were still concerned about ice! :)

Well, better get on with my navex planning with fuel circles to Wyton ;)

GQ

[keith williams]

As to the wind...well, asked my QFI that too and the answer was straightforward...its not an issue because you will even out fuel useage during the navex...ie on the southward leg we may have a tailwind...therefore use less fuel...so use more fuel on northward leg back home due to the headwind but we have more anyway because we used less than calculated because of the tailwind on the outward leg - seems logical to me! Groundspeed? I'll have to ask about that one!



I suggest that you be very careful with this assumption.

For example:

TAS 100 kts
Distance A – B 100 NM

40 kt headwind out
40 kt tailwind home.

IN STILL AIR CONDITIONS

Outbound time A-B is 100NM / 100 Kt = 1 hour.

Homebound time B-A is 100NM / 100 Kt = 1 hour.

Total time is 2 hours.

IN 40 KT WIND

Groundspeed out = 100 – 40 = 60 kts.
Outbound time A-B = 100Nm / 60 kts = 1.667 hours.

Groundspeed home = 100 + 40 = 140 kts
Homebound time B-A = 100Nm / 140 kts = 0.714 hours.

Total time = 1.667 + 0.714 = 2.381 hours.

Multiplying the extra 0.381 hours by 60 converts it into 22.88 minutes.

That’s an increase of 19% in flight time and fuel used.

[BEagle]

As to the wind...well, asked my QFI that too and the answer was straightforward...its not an issue because you will even out fuel useage during the navex...ie on the southward leg we may have a tailwind...therefore use less fuel...so use more fuel on northward leg back home due to the headwind but we have more anyway because we used less than calculated because of the tailwind on the outward leg - seems logical to me! Groundspeed? I'll have to ask about that one!

Is nonsense as keith williams has said!

Think of the extreme case of a 100 kt wind....:hmm:

[peterh337]

The funny thing is that, on average, wind is always against you :)

Even a pure crosswind means you have further to fly.

I take the point about the "fuel circles". In that case, the figure inside the circle could be the endurance.

[Grob Queen]

Fair enough, but who in GA actually flies in a wind of more than about 35kts? I certainly d0n't and wouldn't when qualified either!

PPruNe never ceases to amaze me...."Ask your instructor" they all shout...yet when I do...he's obviously wrong...... ;) :p

[gasax]

As I posted earlier, many people fly in 20 kts plus. At height that is frequently very much more - so there is every chance you will maybe inadvertently be flying in those winds.

As for covering the chart in chinagraph close to the turning points? Worst place to do it. These are the areas where you may need the detail. Best practice is to leave that entire area up to 10 miles or so completely clear - no lines nothing.

As for out and back equalling things up........... nicely put a little earlier.

Sector recce? All this pseudo 'top gun' stuff is all great fun I'm sure - but it does not seem to be a particularly good learning environment when fundementals such as an inaccurate guess about actual fuel consumption and ground speed are then detailed the the 'n'th degree.

[Grob Queen]

Sector recce? All this pseudo 'top gun' stuff is all great fun I'm sure -

Thought that would get you all going :) ....I haven't quite progressed to Carrier landings yet ;)

Seriously though, the terminology may sound bravado, and no, agreed, its not in the PPL syllabus. However.... I am particularly bad at knowing where I am in the local area, even after all this time. My usual response to the "Lookout" part of any cx is "err...thats the A1...Err..." But towns, orientation of our airfield etc etc, I am hopeless. Hence the reason for a need to fly an, ok, in more "normal" terms, a local area familiarisation trip...personally I prefer the more snappy "Sector Recce"!

I tried to insert a pic of my current navex to prove that the chart is still quite clear and understandable, but couldn't work out how!

...its not an "inaccurate guess", its worked out on fuel consumption and timing.

[keith williams]

Grob Queen,

It was not my intention to "shout you down" but the idea that the tailwind will cancel out the effects of the headwind is potentially very dangerous. I have met many pilot who have clung to this mistaken belief right up to the start of their ATPL General Navigation studies.

My reason for providing my arguments in the form of a step-by-step calculation was to encourage you to try this for yourself. If you adopt this as a general principle you will probably find that you understand things much better. You might like to try it using the same scenario, but with a 35 kt wind. You will still find yourself about 17 minutes short of fuel. Can the aircraft that you fly, glide for 17 minutes from the altitudes at which you fly it?

If you now go back to your CFI and show him/her this thread, his/her reaction will probably be something along the lines of "but that isn't the question you asked me" or "I didn't say that", or possibly simply "Oh bugger, you caught me at a bad time, sorry".

[gasax]

Grob you've got two ears and one mouth.

Your fuel consumption is a guess because you have no direct measurement - you have an guess based upon whatever the usual use of the aircraft is.

Generally that will be circuits at a flying school. It sounds like your instrutors either have little understanding of flying cross country - or you have an interesting way of eliciting information - neither seem a good way of behaving.

Cross country the consumption can vary by well over 50% - flying rich - who knows - the numbers are not in the POH. How accurate are they?

Sector recce??? - if you can only fly yourself around areas you already 'know' then you are not navigating at all! Which will make fuel circles pretty much irrelevent.

Yes the terminolgy is full of bravado - why? It is far better to actually know what you are talking about.

[Grob Queen]

I say again Gasax, Fuel consumption is based on the POH which I rechecked today as it happens. :rolleyes:

The idea of the sector recce/locals area famil (call it what you will - we do know exactly what we're talking about, sure other clubs have jargon?! ) Is not instead of navexes, it is so that when I am flying solo GH exercises, such as stalls and steep turns, I know exactly where I am and the "lookout" part of the cx has more meaning. You may consider it unnecessary, but I know i'll find it useful.

Keith - Thanks, it looks rather complicated. But I think I get the gist. But with my fuel calculations with the Grob, 22 mins should use up an extra roughly 9 litres of fuel; with a margin of "red" fuel at say 40 in the last fuel circle, this can be covered.

Hmmm, food for thought there. I suppose what we're really all saying (and I think what another poster said) is that we all have our own ways of working this out, and the instructors out there have their own ways of teaching. Doesn't mean that anyone is right or wrong, just different. :)

[BroomstickPilot]

Hi GQ,

Check your PMs.

BroomstickPilot

[gasax]

I say again Gasax, Fuel consumption is based on the POH which I rechecked today as it happens.

And on the subject of leaning....I am not taught how to, the mixture is ALWAYS rich!

Which means you are planning fuel consumption using leaned figures whilst burning significantly more fuel because you are not leaning .........

So you planning all this based on guesswork.