Calibrated Fuel Tubes

[FlyingMonkey]

Last weekend I finally got my fuel tubes calibrated. I drained the tanks completely, and afterwards I shined a light in the tanks and confirmed the bottoms were moist but there was essentially no standing fuel in them. if there is really 0.5g unusable, it's sitting somewhere it can't be seen from the filler neck. I rocked the wings and could not get any to slosh into sight. Lesson: when the tanks are empty in the CT, they are well and truly EMPTY.

 

I put marks at 2.5 (in red), 5, and 10 (in black) gallons. The 2.5g mark is surprisingly high up on the tube, about 25% of the way up. 5g is about halfway, 10g is really at the very top of the tube, I doubt I could see the mark very well in flight. I have to reach up and push the tube forward slightly to see the fuel level at that mark.

 

So my experience mimics what Charlie Tango has told me...each tube is basically two hours of flying when full. My plan is to take on fuel when hitting the 5g mark in each wing, and if I were to hit the 2.5g red marks I would be getting on the ground immediately. I could not envision letting fuel get that low unless I was on a long cross country and was almost at the destination. This should keep me with 2hr reserves in most cases, and 1hr at the bare minimum.

 

I also calibrated my dipstick. It turns out my right side is almost dead nuts on, and the left is WAY off. I made marks on the stick at the 5 gallon level (which was slightly above the factory 7.5g mark) and at 10 gallons (which was above the 13.5g factory mark).

[Jim Meade]

Remember that fuel tank markings are by reg supposed to be usable fuel. If you drained your tanks completely so that there was no ;fuel at all, maybe you are below the usable fuel line. Your markings might be 0.5 gallon too optimistic.

Were you positive your plane was absolutely level when you did your measurements? When I did mine we used a digital level and put jacks under both main axles and tweaked them till they were precisely level. Then, we filled the plane in even increments on each side to avoid the situation of one side full and the other empty, but fuel in some unknown amount transfering. We had pinched off the fuel tubes at the firewall so fuel could not cross level anyway, but we wanted to be sure everything evened out in through the baffles so did fuel additions in a more or less balanced fashion to each side to give time for the baffles to be neutralized.

I agree that 10 gallons on the sight tubes is virtually unreadable. My highest mark is 7 gallons, but whatever makes one happy should be OK. I had to reset the factory decal to be accurate and show zero gallons with no more usable fuel.

To say that there is two hours fuel in each tank when they show full is not strictly accurate. The sight gauge will show "full" from 17 gallons (16.5 usable) down to about 10 gallons. One can say that if the sight tube is full one has at about two hours of fuel per side (assuming 5 gph) but it could be over thee hours per side.

[Ed Cesnalis]

Thinking out loud,

 

Calibrated sight tubes are useful because I can pinpoint a 'level' condition in flight by yawing left and right. In smooth air I can tell 'level'.

 

Calibrating my dip stick means less if it takes jacks and a level to get a precise reading.

[FlyingMonkey]

Remember that fuel tank markings are by reg supposed to be usable fuel. If you drained your tanks completely so that there was no ;fuel at all, maybe you are below the usable fuel line. Your markings might be 0.5 gallon too optimistic.

Were you positive your plane was absolutely level when you did your measurements? When I did mine we used a digital level and put jacks under both main axles and tweaked them till they were precisely level. Then, we filled the plane in even increments on each side to avoid the situation of one side full and the other empty, but fuel in some unknown amount transfering. We had pinched off the fuel tubes at the firewall so fuel could not cross level anyway, but we wanted to be sure everything evened out in through the baffles so did fuel additions in a more or less balanced fashion to each side to give time for the baffles to be neutralized.

I agree that 10 gallons on the sight tubes is virtually unreadable. My highest mark is 7 gallons, but whatever makes one happy should be OK. I had to reset the factory decal to be accurate and show zero gallons with no more usable fuel.

To say that there is two hours fuel in each tank when they show full is not strictly accurate. The sight gauge will show "full" from 17 gallons (16.5 usable) down to about 10 gallons. One can say that if the sight tube is full one has at about two hours of fuel per side (assuming 5 gph) but it could be over thee hours per side.

 

I didn't drain them completely dry per se, but when fuel stopped coming out of the gascolator, there was essentially no fuel I could see in the tank. whatever level of "unusable" fuel there is in level flight, remained in the tanks. My observation was simply that if there is unusable fuel, it seems to be a very small amount.

 

My airplane was as level as it sits. My left and right wing tips are within 1/4" of each other in height, and there is a 0.6° grade in my hangar. I'd rather get the levels reading correctly on the ground as it normally sits, so that when I look on the ground where I normally fuel and pre-flight it will be accurate. It might change slightly in flight, but not enough to change a fuel-related decision to land or stay aloft. Your method is no doubt more accurate, but I'm not convinced the difference will be noticeable in real world operations.

 

I didn't mean that a full tube means *exactly* two hours, I should have said what I meant, which is *at least* two hours per side. That of course assumes operational engine speeds 5200rpm or less.

[Roger Lee]

A 2.5 and 5 gal mark is all anyone should need. When it gets to 2.5 gals it's time to be on the ground. Or on the ground sooner depending on the flight.

[Roger Lee]

A little experience and you can get really close with the sight tubes. Play with it a while, you'll see what I mean.

[Jim Meade]

BTW, I think I would be sure to keep the factory placard for fuel sight gauge levels. Mine is an ELSA and I kept the placard but moved it to read correctly. I assume this placard is required per the AOI, but maybe someone who knows the legal aspect can comment and cite the reference.

[FlyingMonkey]

 

 

Burned once is enough for me. I ignore the tubes entirely now. The 315nm trip my wife and I did this morning was done by dipping, adding 6 gallons per side (est 26 gallons in wing tanks, 1.5 in header tank), entering the fuel in the Dynon with a 3.8gph est burn rate. Setting the flight plan in the Garmin. Activating the plan entered on DUATS after leaving the airfield. Flying the plan. Landing with 11.9 gallons burned, or about 3.9 gph. Wind was double what WXBRIEF said would be out there, but we still landed five minutes of est time, and 1 gallon over est fuel use. 16 gallons left, and ready to fuel for tomm. flight.

 

Your fuel issue had nothing to do with the sight tubes.

[Ed Cesnalis]

Bigs,

 

Don't ignore your sight tubes. If things go wrong you will see it in the sight tubes.

 

If your slip skid ball is lying to you because of a technical issue and you are about to starve your engine you will see it in the sight tubes because the visible fuel will have dropped to zero.

 

If your fuel cap departs and the fuel follows in one wing you will see it in the sight tube.

 

The sight tubes are capable of telling you that a fuel emergency is developing or if one exists, why would you entirely ignore that?

 

BTW your fuel and speed numbers sound more realistic, good report.

[Roger Lee]

And so how do your gauges detect a fuel leak that may only show up in the sight tube? Using just instruments you have on-board works for normal activity, but can lead you astray under the right circumstances. The tubes were put there for visual reference because gauges don't always tell the story. The tubes and gauges are each a single tool to be used as a group and should never be a single point of total trust.

[Ed Cesnalis]

Burned once is enough for me. I ignore the tubes entirely now. ...

 

But bigs, you have that highly advanced, CTLSi only fuel valve with left right on and off settings!!!!!!!!!!!!!!!!

 

CTs are notorious for burning from one side and your advanced plane can control that misbehavior but your have to look at the tubes to see which tank has the larger quantity of fuel to fix the imbalance.

 

Try it, seeing is believing.

[Ed Cesnalis]

Oh you have gauges? You need the tubes to confirm the gauges are working correctly.

 

The tanks are low and flat and the nose on a CT is invisible and the CT's fuselage allows wind to pass through easily. This all ads up to easy to slip enough to transfer fuel and imprecise readings by gauges or sight tubes so another confirming method shouldn't be ignored.

 

I like to watch the TV flight emergency shows on youtube and I notice that often the crew has to walk aft with flashlights trying to get a visual on various components. Seeing is another crosscheck and a highly reliable one.

[Jim Meade]

Understanding that LSA are not subject to FAR Part 23, at least not as standard certificated airplanes are, still it is illuminating to note:

 

23:1337

 

( Fuel quantity indication. There must be a means to indicate to the flightcrew members the quantity of usable fuel in each tank during flight. An indicator calibrated in appropriate units and clearly marked to indicate those units must be used. In addition:

 

(1) Each fuel quantity indicator must be calibrated to read “zero” during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined under § 23.959(a);

 

(2) Each exposed sight gauge used as a fuel quantity indicator must be protected against damage;

 

(3) Each sight gauge that forms a trap in which water can collect and freeze must have means to allow drainage on the ground;

 

(4) There must be a means to indicate the amount of usable fuel in each tank when the airplane is on the ground (such as by a stick gauge);

 

The sight gauges meet any requirement for a fuel quantity indicator as far as FAR 23 is concerned. Now, if only ASTM were free and published where we could all read them.

[Tom Baker]

Jim, not all standard category airplanes were certified under part 23 rules, so you may see a certified aircraft with fuel tanks that have no fuel quantity indicator.

[Jim Meade]

Tom,

Are there some with no fuel quantity indicator at all? I assume you mean CAR 3 planes?

[Tom Baker]

Jim,

One that I know is Taylorcraft. A BC-12D can have two 6 gallon wing tanks in addition to the 12 gallon nose tank. The wing tanks have no way of telling quantity in flight. Only the nose tank has an indicator. It was certified under CAR 4.

[Doug G.]

You can't detect a fuel leak watching the sight tubes...

 

If the source of the leak is a missing fuel cap you would certainly be able to tell. One side would drop much quicker than the other.

 

I always over plan my fuel. I work with a larger burn than I know the plane has, I always plan an hour of extra fuel at my destination or waypoint stop.

 

I ran out of gas in our pickup while pulling out travel trailer this summer because I trusted the fuel computer. The truck died on the interstate, in a construction zone, within sight of the next town. It took two hours to get someone there with a $100 five gallons of gas.

 

That was aggravating and inconvenient but it taught me I cannot trust what the truck tells me. If I had this situation in my plane my life (and possibly another) would be in jeopardy. I don't intend to let that happen.

[Ed Cesnalis]

You can't detect a fuel leak watching the sight tubes anymore than you can tell how fast your fuel burn is using those tubes. In the CTLSi the tubes become even more redundant and ignorable as there is a large red enunicator light on the panel that flashes low fuel indicating the only fuel left is in the header tank. About 1.2 gallons.

 

We all argue over this problem for the FD because they offer no reliable way to manage fuel other than to load too much of it with a larger margin for error and stop frequently enough to keep that margin of error established. If you get a fuel leak thats large enough to take you out of the air before a fuel stop then you have much bigger problems than watching a plastic tube drop fuel level.

 

All the more reason to have the backup header tank there.

 

Your attitude is a bit scary, think this over carefully. You keep crediting the header tank for providing extra margin. If you wait for your red enuciator to tell you that you have only minutes left then you blew it already.

 

Use your Vegas commute for an example and think in terms of points of no return. Once you are beyond Tonopah's point of no return you are committed to making North Las Vegas or at least Mercury so you better have enough fuel or not go beyond that point.

 

Take your fuel emergency flight, as you passed Tonopah your ETE was 1 1/2 hours and your sight gauges showed 1 1/2 hours, that leaves zero for VFR reserves and less than zero for your personal minimums that need to be higher yet for this type of flight. You claim that you can ignore them because they are redundant yet you got yourself in big trouble already relying on your other technology. You are not going to be so lucky the next time.

 

You can learn to view your sight tubes and have a visual on how your remaining fuel compares with your remaining flight time plus reserves.

[Roger Lee]

CK,

"You can't detect a fuel leak watching the sight tubes anymore than you can tell how fast your fuel burn is using those tubes. In the CTLSi the tubes become even more redundant and ignorable as there is a large red enunicator light on the panel that flashes low fuel indicating the only fuel left is in the header tank. About 1.2 gallons."

That's not true. The gauges only show what passes through the transducer. If you have a leak else where it won't show. Looking at the sight tubes will show when the fuel drains out and way faster than your intended fuel burn for the trip at hand. Any number of things could cause a significant leak.
If you fail to look at the tubes and your first indication of an out of fuel scenario is when the alarm goes off for low fuel level in the header tank you have done something seriously wrong by ignoring one of your tools. The instruments, the fuel dip stick and the sight tubes are each a single tool to be used to assertain a total picture. If you run out of fuel and have to face the FAA they will ask about you checking each one. If you say you never look at the sight tubes and don't trust the fuel dip stick and only rely on the gauges you'll have some remedial training required by the FAA. Right now you don't trust things, but with more time and experience on what to look for they are invaluable tools to be used together. Use all the tools at hand and don't limit yourself.

Remember how uncomfortable it was when you almost ran out of fuel? Why revisit that. Your pretty new to the CT world so the guys with 7+ years have a pretty good handle on this. Might as well learn the easy way and not cause any damage. Your sight tubes our just like ours as far as function.

[FredG]

Shockingly enough, no fuel management tool or measure is perfect. All fuel management tools available to CT pilots are useful, however, once their limitations are understood. Declaring that any one of them is useless is simply throwing information away.

 

Just my personal opinion, not flight instruction.

[Roger Lee]

Hi Fred,

 

You've got my vote.

[Ed Cesnalis]

How do the gauges work? If they only show what is passing though the transducer then they don't even know that you ran one tank dry while the other has lots of fuel? Don't you need to know this to manage the fuel, wouldn't you have to look at the sight tubes?

[FlyingMonkey]

You can't detect a fuel leak watching the sight tubes anymore than you can tell how fast your fuel burn is using those tubes. In the CTLSi the tubes become even more redundant and ignorable as there is a large red enunicator light on the panel that flashes low fuel indicating the only fuel left is in the header tank. About 1.2 gallons.

 

 

You have just stated your intention to ignore one of the fuel management devices in your aircraft, how do you think that would play out with the FAA? Relying on a 1.2 gallon header tank's annunciator light to reveal your fuel state is seriously flawed. Even if it works, that's about 20 minutes of flight at best...what if you are over hostile terrain that will take more time than that to clear?

 

What if the light bulb is burned out? Then your low fuel warning is when the engine stops.

[Doug G.]

Too bad we don't have a "like" button on this forum!

[Ed Cesnalis]

The sight tubes wouldn't have helped ... Once the fuel disappears in the tubes it's impossible to tell how much is actually still in the wings.

 

 

If you see the fuel in the tubes disappearing it means you are out of gas. If you think you have some fuel in a wing then use your rudder to yaw left and right. If there is some fuel sloshed outboard you will see it when you yaw. But that's missing the point you should already be on the ground not looking for a gallon that is sloshed outboard.

 

You have to look at them in flight and if you would have you would have stopped for gas. Stop defending the indefensible before you get yourself or someone listening to this nonsense killed.

 

Your beloved header tank is too small to save you.