From here
Peter wrote:
It would be great to see you fly to join us at EDNY – we have ~30 for the dinner.
I would have loved to. Unfortunately once again family obligations prevent me from attending as it collides with school vaccations, which are always planned abroad. By the looks of it, I will never again be able to attend. (And even if so, I would not fly as I totally resent their stupid slottery system, which is practically impossible to synchronize with having to observe slots on the origin as well)
Graham wrote:
I have never flown it on a leg longer than 3.5 hours. Whether than constitutes going places or not is a different question, but after 3.5 hours I am thoroughly ready to stretch my legs. Such flights are invariably with 2 on board, so one takes full fuel and then fuel is hardly a consideration – such is the margin.
If you fly with full fuel and will stay within 2 hours of fuel reserve, then of course you don’t need to do exact planning. And obviously that is how a large part of the population flies.
What that does however is give away quite a lot of capability of the airplane.
Graham wrote:
I’m not sure it’s necessary to set ‘precise power’ to have any idea of fuel flow in the absence of a fuel flow indicator or a totaliser.
Totalizer I agree. Fuel flow indicator, I would not want to fly another plane which does not have one, other than really for local flying and circuits. Even cars have FF indicators these days. Without FF you have no idea what really happens other than the quantity indicators.
Peter wrote:
A very significant % of crashes are with empty tanks, and it would be far worse if people flew trips “longer than the bladder” etc.
Absolutely.
You know, I really don’t get it. In the old days, yea, we had to do all the PLOGS by hand, calculate wind for every leg e.t.c. to get an accurate plan. Today, it’s a 5 minute affair, less if you have a pre-planned route, to get an accurate PLOG or OFP out of just about every flight planner with a decent performance model.
Ibra wrote:
To set mixture, one need either 1/ engine monitor that show EGTxCHT (nothing else) or 2/ MPxRPM table on fuel flow (or old school full rich or until roughness)
Leaning to fuel flow is almost always wrong, FF can at best get you into the ball park of where you need to be. To set the mixture correctly, well, yes, your statement stands. Beause FF is the RESULT of MP/RPM/Mixture. It is NOT a target value to set power, but it serves to verify if it’s set correctly.
Doing that properly will e.g. quickly determine errors in either RPM indication or FF if a transducer is off or similar. The same goes for landing fuel on board indications by the GPS. Those are problematic for several reasons: They are the result of several variable figures. Basically, what most GPS based LFOB indicators do is to calculate on the base of the CURRENT FF vs distance remaining. I am not aware of any GPS which will download wind models, some of them allow correction factors however. So, LFOB will change quite a lot in flight. The first time it’s worth looking at it is after TOC, when cruise regime is established. Before that, it will be way too low due to the higher climb FF. In flight, it can change with wind changes.
I recall some A310 operations from Male to Zurich in the 1990ties. Those FMS’s had roughly the capability of our navigators now, with the difference, that you could add wind per leg. Climbing out of MLE, you would get “low fuel” alerts from the FMC all the time, LFOB showing -2 tons or so. On the initial cruise level, this would creep forward to zero. Somewhere half time (after 5 flight hours or so) it would show positive and in the last quarter of the flight it would approach what the OFP predicted.
Graham wrote:
But the point still holds. Unless he’s prepared to go down to LFOB <1hr (and who is, on a flight of non-trivial length?) he doesn’t get any more range using a totaliser than he can get with a rule of thumb.
The main advantage of a totalizer is that you have a 2nd and slightly more stable source of information about FOB than from the fuel gauges, which in many airplanes are not very accurate. So if you do your hourly fuel checks, you can compare the fuel remaining on the gauges vs the totalizer vs the OFP/PLOG. Fuel used also gives you a good indication even if you forget to reset the darn thing before take off, as at least you are supposed to know with what take off fuel you depart.
Sure, rules of thumb work nicely… until they don’t. For me these days, particularly with preciously little experience, I treat every flight like I would plan the airliners I learnt planning from. I do admit I am a number freak when it comes to those things and get a lot of satisfaction out of a flight where EET and AET match and fuel remaining is within pretty close limits to what the OFP proposes.
Graham wrote:
With 86.2 USG useable and a planned LFOB of 20 USG, you are planning max fuel burn of 76% of capacity.
Well, with our airplanes and the regions people fly, that corresponds pretty much to my calculation of what you need at your destination, given that usable alternates are not just 10 NM away and you need final reserve anyhow. A TB20 has a final reserve of about 10 USG already (45 mins at cruise speed) and if you need an alternate plus some contingency, 20 USG is pretty spot on for most destinations. That is one reason that big fuel tanks are such a great thing.
However, what you do with the 66.2 USG makes the difference. If you just go by guestimate and set some sort of power between 65 and 75% with a “squared” setting or similar, you might get a lot less range out of this than if you are aiming for the range sweet spot. Peter has plenty of experience with those long flights and I think the approach with 20 USG minimum fuel remaining going into places like Croatia and the likes is pretty sensible and will in 90% of cases be just about correspond to the actual requirements.
Having seen how airliners plan, often with less than 30 mins remaining over final reserve and get there practically every time after a 15 hour flight has left me with the knowledge that you can achive precision if you aim for it. Whether you want to is totally up to you.
THe OP’s Arrow 3 has got a over all product with 77 USG capacity. Used well, it should yeald a pretty impressive range.
Things get interesting however in family-vacation-on-Corsica mode. And the family does want to do this trip again! (… on condition I take a set of spare tubes). At 120 kt, EPKM to LFKO are minimum 5h30’ apart, no routing, no wind, no approach taken into account. No way to fly it without a stop if the dog is on board. A logical stop half way would be the beloved Portorož LJPZ, which in practice I should be able to reach in 3h30’. But then, in this trip mode, I can’t take off with full tanks! If we want to take any luggage, I need to start the whole trip with 45 … 50 … 55 gal. I prefer 55, but the less fuel I take, the more stuff can fit in.
I am not sure, but it seems you are missing how easy it is. Want to depart with 55 gallons? Refuel both tanks to tabs, then note the counter on the fuel pump, then add another 5 gallons / 19 litres. Done.
What get‘s a little bit more tricky is if you want say 45 gallons total. But that is usually only necessary with 4 POB.
boscomantico wrote:
Refuel both tanks to tabs, then note the counter on the fuel pump, then add another 5 gallons / 19 litres. Done.
Yes, I think the tabs are a very good tool in the Pipers.
I’d add, get a calibrated dip stick. Easiest way to reful to the pretty exact quantity you want to be at.
Leaning to fuel flow is almost always wrong
It is fine for a given MP and rpm. Low level, I set 23" 2400 and 11.7 USG/HR and job done.
The main advantage of a totalizer is that you have a 2nd and slightly more stable source of information about FOB than from the fuel gauges
Sorry but you have completely missed the point here. Normal fuel gauges are about 20-30% accuracy and often much worse. Capacitive ones (rare in GA) are around 5% of FSD. A totaliser is accurate to 1-2% and the system recalculates the LFOB every second or so. It’s a completely different concept.
Peter wrote:
A totaliser is accurate to 1-2% and the system recalculates the LFOB every second or so.
Yes, but it depends 100% on the right amount of fuel given to it before you start. Which if you are not filling up to capacity and reset the totalizer to 100% fuel (and on top of that really have fuelled to capacity) is not always an easy thing. It also won’t account for fuel leaks or other irreguliarities.
So you still need to crosscheck with the gauges. If there is a notable difference, the lower of the two remaining should be taken as “true”.
Normal fuel gauges should read reasonably while in level flight. If they don’t then something has to be done about it.
The most prominent example would have to be the Air Transat A330 which ran out of fuel due to a fuel leak, partially because the pilots did not believe the gauges but the fuel used figures more. The same would happen if a GA plane has a leak, be it a not properly sealed fuel cap or something else.
My fuel monitoring would consist of doing a regular check (in GA let’s say each half hour at a convenient waypoint).
Fuel remaining according to Totalizer
Fuel remaining according to gauges
Predicted fuel remaining according to OFP/PLOG
Those 3 figures need to be in sync to a large extent, with a small tolerance.
Also check remaining EET according to GPS vs OFP.
And of course, before departure, verify the correct amount of fuel in tanks vs what the totalizer sais. In some models that is easy, in others it’s not trivial.
With proper planning and a good wind model as well as properly set power and altitude being the same as on plan, there should be hardly any difference. If there is, inflight replanning will become necessary.
Clearly a totalizer helps and I would not wish to fly without one.
Mooney_Driver wrote:
So you still need to crosscheck with the gauges. If there is a notable difference, the lower of the two remaining should be taken as “true”.
Normal fuel gauges should read reasonably while in level flight. If they don’t then something has to be done about it.
On a recent flight I had to carry less fuel because I had a two adults and two teenage boys (basically adult weight) plus bags. The trip time was 3 hours, and I had 160L on board. While I plan for a 40 lph flow in reality I get more like 32-35 in economy cruise. My old Socata gauges were generally bad enough that I only really relied on my calculations and measurements, but this time I had the GI275 measuring flow, LFOB, and of course a beautiful digital readout of the fuel quantity.
Problem is the flow-based data showed what I expected and the now-more-precise quantity gauges showed all kinds of fluctuations, none of which were confidence inspiring—especially when I started getting low fuel warnings about 15 min out (not great for the passengers). The quantity readings on final (which were carefully calibrated in my presence while installing the GI-275) were showing about 30L remaining, while I expected >60. When I landed I filled the tanks, and the FF (and my fuel calculations) were correct, whereas the gauges were off by 50% of the remaining fuel.
I’m still not sure what the right answer is with this. Should I disable the low fuel warnings (they are user configurable) and generally distrust the fuel gauges unless they are grossly out of whack?
Primary fuel gauges are required to show empty accurately and nothing else, so you should ensure that is the case. With that being the case, when at levels above say 1/4 full ignore them and use the totalizer data.
My old float style gauges are accurate below 1/4 because I calibrated them with a stick until that was the case. Above 1/4 full they read all kinds of nonsense, for example reading full for a long time then plummeting quickly downward.
Primary engine monitors like my EDM930 allow to calibrate the fuel gauges for the values returned by the sender. There are 5 points: empty, 1/4, 1/2, 3/4 and 4/4 in the case of the EDM930. Therefore I’d assume it is relatively accurate, however I still treat it as inaccurate and double check with the result of the totalizer.
The most annoying thing with that EDM930 is that it shows “INOP” (and no indication) whenever the fuel sender value exceeds the calibrated value for full. This happens whenever I fill it with “a little bit more” fuel than whatever the EDM thinks is full. I am thinking about modifying the 4/4 calibration value to avoid this…
dutch_flyer wrote:
When I landed I filled the tanks, and the FF (and my fuel calculations) were correct, whereas the gauges were off by 50% of the remaining fuel.
Well, this installation is faulty. Such a behaviour is not acceptable at all.
What did the Socata gauges show throughout all this?
Last time we weighed our airplane, I did a controlled refuelling afterwards. Fuel each tank until the gauge shows a particular value and crosscheck with what has been fuelled, continue to each marking and write down the result. This can be done whenever you have a tank dry, also after a flight for one side, then for the other.
The C model Mooney stands pretty horizontal when on a concrete surface, unlike later models which have a pretty pronounced pitch up. I found that my gauges are fairly accurate when the plane is in a level condition. The only thing I have a “problem” with with those gauges is that they show LB while the tanks are labled in USG and the totalizer and GNS430W in Liters. My OFP shows it’s figures in USG as the performance manual is thus. So it needs a bit of calculations to correspond the figures. My performance tables take this babylonic mess in account.
Mooney_Driver wrote:
Well, this installation is faulty. Such a behaviour is not acceptable at all.
I don’t know. I was there during the calibration with the GI-275, and it was done in 5 liter increments with a leveled airplane. I’m not sure what more could be done to improve the accuracy. It seems less accurate the lower the level gets, which I guess is logical given that there’s less volume in the tank.
Mooney_Driver wrote:
What did the Socata gauges show throughout all this?
The Socata gauges were removed.
