Accurate fuel flow

[gkey]

Just a question I need some advice on.

I learned a very valuable lesson yesterday when I re-fueled my 148 US GAL tanks. Calculations showed that prior to fill-up I had only 6 GAL left in the tanks, but the gauges showed "1/2 full". So, even the preceived belief that these needles will at least show when it is empty, is false.

I need to get a much more accurate read on the true status of my residual fuel volume. I have an EDM-800 in my 172, and it works great. I know JPI makes similar units for twins, and will investigate this, but are there any other options?

[Ernie Martin]

I'm on my second Skymaster. Given their age, fuel guages are not accurate. Don't trust them. Here's what I recommend:

1. Buy a plastic/glass hollow tube with gradations (sold at most aviation eqpt. stores) and calibrate it per the instructions that come with it.

2. Never, ever, take off unless you have visually determined fuel quantity with the tube.

3. Determine the fuel consumption per hour for your airplane at the typical cruising conditions you most use (don't forget that climb consumption will be higher).

Ernie

[Ed Coffman]

Ernie,

There is no way to accurately stick a skymaster. The slightest uneveness in the parking area will make one take seem full and the other 40 gallons low. There are only two times when you know how much fuel is in your tanks, full and empty. As you recommend, get a fuel totalizer and calibrate it over several flights and you will be as close to accurate as you will ever get.

Ed Coffman
________
No2 Vaporizer

[Jim Rainer]

WOW! You were 10 minutes from a deadstick landing! But here's a few thoughts.

1. Your fuel gauges are illegal. They must read empty when your tanks are empty - beyond that you can't trust them even though they are legal. I ignore mine unless they hit bottom and won't wiggle when I step on a rudder pedal.

2. Not every lineman knows how to fill your tanks. Assuming you are on level ground, once they are full, rock the wings then refill. You may get another 5 gallons a side (would not have helped you much.)

3. I have a normal 1976 337G like you and I use 20 gph (using the hour meter hooked to the battery.) In 9 years and almost 700 hours this has been accurate within 5 gallons.) Your plane should go 7.5 hours to dry tanks at 60% or so. After 5 to 5.5 hrs, stop for fuel. If you make several T.O.s ,climbs and landings in the 5 hrs, use a higher number - 23 gph. In short, we used the clock to compute fuel used/remaining.

[Roger]

I recently installed a Shadin on my PushPull (for those of you soon off the the Bahamas, get used to that name). But recently had all of the fuel leak out of my left wing due to a leaking gasket, and it did not register on the Shadin obviously, but did show on the fuel guage. Likewise it would have made no difference to know how much I burned per average house, nor how much was in the tank when I departed. As such, and while those other ideas are good, as is the Shadin, it is still worth it to try and get the fuel guages calibrated and operational.

[gkey]

Very good advice, all of you. Thanks.

I too believe that - on paper, at least - my fuel gauges are illegal. They need to be serviced or replaced, but more so, I believe that I might need new senders from the tanks too. They need to be much more accurate, especially towards the "empty" side of affairs. Any advice on good senders?

I too have now adopted the habit of filling up the tanks whenever I have done 3-4 hours of flying - it brings the anxiety levels down a bit. I fly EXACTLY by the POH numbers on cruise performance, because right now that is my best indicator of in-flight fuel consumption. It checks out pretty similar with calculations later at the pump.

But I was also wondering about a fuel flow/totalizer. Right or wrong, I am a J P Instruments fan, and was wondering about which of the following products to go for: Fuel Scan 450 vs EDM-760. Both will give me pretty much the same answers I want regarding fuel, but then, do I really need the rest of the 760? I already have a digital EGT gauge for each engine.

OTOH, the 760 would make leaning a lot easier and accurate, which might pay for itself in the long run in cheaper maintenance issues...Should I just dump the current EGT gauge, and in it's place install the EDM-760 instead?

[Dave Underwood]

My two cents worth.

I installed a 760 with fuel flow shortly after I bought the plane.

With the exception of a couple of problems I have had with the fuel flow side of things, the 760 is great and I would not fly without it. Leaning is a snap and it is always great to know what is happening in each engine in detail. The logging is also great as well.

The only short coming on the 760 is that I was hoping to be able to alarm the OAT and use it as an ice alert. The second suggestion would be to get the bayonet piggyback adapters and use those in place of the gasket CHT probes with the existing CHT equipppment. You then will not see the higher temps & alarms from the gasket probes as they run up to 80 +/-degrees hotter than the others.

On fuel and gauges, mine have gone from being pretty accurate to not so. I top the tanks on a regular basis - every second flight or so. OK, I end up tankering fuel, but I won't run out at the wrong time. I have added debugging the fuel display to the list of projects.

I figure the next step is Gami Injectors and LOP ops to save another couple of gals per hour. I don't mean to reopen the LOP debate, but I am currently paying over $10 US a gallon for 100LL here in the UK so even a couple of gallons an hour saving is worthwhile.

That is on top of landing fees & manditory handling fees that make the $100 hamburger more like $300 to $400 and that only on a good day.

Summary of the above is to fight the FAA user fees as it is killing GA here in the UK.

Regards - Dave

[Jim Rainer]

If you can afford it, Shadin is the way to go. In addition, it is a legal replacement for the OEM fuel flow meter which gives you more panel space for other gear.

But, as said, fuel can get lost, stolen, leak out or never be put in so Shadin isn't without problems of it's own. Regular fill-up and a handy ladder for visually inspecting the tanks along with counting hours vs gph fuel flow are mandatory.

A plastic tube doesn't work in the 337s with 148 gallon tanks because the filler cap is so far out on the wing that you can't measure with a tube after burning 60-70 gallons total.

[Dale Campbell]

I have a 337H that I installed a Shadin and love it. I always fill tanks myself to the filler neck and plug in 148 gal in the Shadin. My tanks hold 155 gal. I do notice that the right tank always drops first and continues until the 1/2 point. Than the other tank catches up. I never let the tanks get under 35 gal total on Shadin, so I know I have reserve. I also watch old tank gauges when they get to 1/4, so I know they are not off by to much. Some day I might drain all fuel by hand to see if gauges go to empty. My old instructor had a 337F with separate Aux. tanks. We use to fly until the aux. went totally empty and engine sputtered. I was not to fond of that. We always had to jump on fuel pumps to keep engine running while switching tanks. Dale Campbell

[Paul Sharp]

I have a '67 T337B. It holds 118 gals. total, with 92 in the mains and the rest in the aux. tanks.

I fly between 70% and 75% almost all of the time, which is between 23-25 GPH.

When I'm not making a long flight my usual practice is to leave 7 gals. in each aux. tank. That means if I do something really dumb I can throttle back and still get a half hour of flying. (Rarely would I ever be in a situation where I couldn't find some place to set down in half an hour.)

If I top all tanks off I should theoretically be able to get just under 5 hours before something stops spinning. Of course I never go anywhere near that. After 3 - 3 1/2 hours I usually am ready for a stop anyway.

I always fill up when the plane is level, check the "top off" with a ladder, and if I've filled up the aux. tanks for a longer flight, I'll run down [when an engine starts missing I switch back to the main - warning any passenger(s) just in case they might otherwise be nervous - and woth my model's fuel system it's perfectly safe to do this] so that when I land I can have them measure 7 gals into each aux. again with their fuel truck meter set to zero.

After I flew the plane a few times with all the tanks full, it didn't take long to see how much fuel it took when I topped them off again. Then I could make fairly accurate estimates of what kind of flying time I have. If a 3 hour flight (since I always use pretty much the same settings) means I consistently fill up with 75 gals. and the aux tanks had 14 total in them when I started, then I know I had 31 gals. left. That's over an hour, and for me that's a good comfort level.

I just make it a practice not to start a trip, generally even a very short one, without having the mains topped off, so that I have a reasonable guide as to the endurance available.

If you've done this time after time and you otherwise watch the settings (and if your fuel gages are good enough to give you at least a ballpark backup indication), then relying on the time you fly can provide a reasonable margin - even without the more expensive fuel computers/gages.

I did almost screw up once - I was doing a lot of practicing and short flights and didn't refill when I should have: the rear engine quit just on the landing rollout and it was a real surprise. I could have switched to the aux. tank earlier and then there would have been fuel in the main for the landing, but I don't like ever getting that close anyway. If you do use the aux tanks (I guess some models don't have aux. tanks?) then you need to use them in the earlier portion of a flight so that your mains are available for landing, of course.

[stackj]

Wow David! $10 USD per gallon! - 6 pounds per gallon has a double meaning for you, doesn't it?

[Ernie Martin]

Because of the possibility of a tank leak and fuel theft overnight, I never take off without a visual check. While I have and use the plastic/glass calibrated tube, after a while you hardly need it. On my 337G with the extended tanks, if I see just a bit of fuel in a tank, I've got 30 gallons. Full it's 64 gallons. And you get pretty good at estimating in between. Plus, repeating what I said above, I never take off unless I see and can measure (or estimate) fuel. That means that my flight planning includes putting enough fuel so that when I get to an airport without fuel (the norm in the Bahamas) there is at least 30 gallons per tank (so I can see fuel).

One other thing. I don't think the issue of non-horizontal surfaces renders the tube ineffective. In virtually all airports or air strips, I think you can find at least one 12-foot diameter area that's horizontal.

Ernie

[gkey]

In my still-not-ending quest to find the most accurate and reliable way of knowing at most times what my fuel quantities are, I found this site http://xerionavionix.com/auracle2.html that was quite interesting.

Maybe I'm naive, but am I to believe that this unit can replace almost everything in my right panel? I mean, REPLACE? Outta here? If that is true (and I sure hope so), not only will it bring the right panel into the new century, but also free up the rest of the panel for - oh, I dunno - a FLIR and radar, perhaps?

Furthermore, the same manufacturer advertizes a solution for multiple fuel tanks, such as in our 337's. I was drawn to that idea like a moth to fire. This way, I can monitor every induvidual tank (read: OCD kicking in...)

I did notice that they have an AuRACLE II TWIN as well, but could not find more information on it. Apparently these units are TSO'd, but I am wondering about STC's as well. My estimate is that the AuRACLE II TWIN might cost about $9,000, but look at what it can do!