Why is water in the fuel tanks bad?

[Big Pistons Forever]

Once when instructing on a students own aircraft the student sampled the fuel right after fueling and got a clean sample... So after about a 20 min preflight briefing we went back to the aircraft and on a hunch I got him to re-sample the fuel.

Just a thought: What happened between the first sampling, and the second sampling? Was the plane left, unmoved, at the fuel dock? (Aside: If it was, then that was a good time for a lesson on airmanship...)

.

The airplane was fueled at its parking spot off the fuel truck. It was not moved in between the fuel samples.

[triplese7en]

triplese7en are you instructing on an airplane that uses water injection?

No. I fly a turboprop that uses water/methanol injection though.

I don't currently instruct students. From post #1 this has been a hypothetical situation.

But on further reflection I can think of many times ab initio students asks questions where my first reaction was " are you really that stupid ? ".

These questions are usually spontaneously blurted out without the student really giving the question much thought.

I've experienced the exact same thing. However, I've slowly come to the realization that some things are so obvious, for a number of reasons, to one person but may not be obvious to many others. I've also come to the realization that you can't assess someones intellect after a question like this is asked, even though we automatically judge the person who asked the question. I guess it's human nature - we judge people within seconds of meeting them. Generally, our assessment of that person will change (sometimes drastically) over the period of time that we know them.

I also try to be careful about how I respond to these types of questions because there are sometimes where the person asking the question has thought of something that you never bothered considering. You will look very ignorant (among other things) if you insult someone for asking a question and they stump you with a factor you haven't thought of!

Just that little mock discussion that BPF came up with provokes thinking about the matter and can be a process for the student to methodically, and logically, come to the answer to their own question. Developmental teaching, anyone?

The fact that the student has even bothered to ask a question shows that they are thinking about the matter and that's not something you see a lot of to be honest. A lot of students won't ask any questions in class and end up doing poorly throughout their training. They're usually either lazy or scared of asking a "stupid question" so they never do. You can 'scar' students by responding to a question in a belittling or derogatory manner - they will be very reluctant to ask questions in your class ever again and might influence their behaviour in the same way with other instructors.

Water can cause double engine failures...happened to myself and several other crews last summer in Schefferville.

Water can cause octuple engine failures - e.g., B52. I believe better logic to this would be that "water can cause an engine failure"?

I think most of us understand how that statement is true. Even in a jet engine, enough water ingestion can cause a flame-out. If enough water got injected into a cylinder it would cause a flame-out as well. What would happen once all the water has gone through the system (say it was just a little more than enough to cause the engine to flame-out in all cylinders)? Would the engine start up? Would all the water get pushed out of the cylinder? What are the chances of hydrostatic lock? There are many things to discuss from a simple question.

An example from outside the flying world would be; what makes the wheels on the bus go 'round? The sun does. If you start backwards using logic, you'll end up with the answer that the sun does. Believe me, you can have quite the conversation with that one question!

Those are my thoughts on the matter as of now. Hopefully I've influenced some of you to think differently.

[AirFrame]

The airplane was fueled at its parking spot off the fuel truck. It was not moved in between the fuel samples.

Nobody got in to put the fuel tester back in the cockpit, grab a kneeboard for the briefing, drop off a jacket, etc? Was the wind blowing on the ramp for the 20 minutes you were briefing?

I only persist because the laws of physics and fluid dynamics don't support the assertion that waiting 20 minutes made a difference in a completely static system.

[Colonel Sanders]

don't support the assertion that waiting 20 minutes

I've had similar experiences. It can take a while for
the water to settle, so that you can drain it out.

This might be just a result of poor drain design and
a wide flat tank bottom, which would cause the water
to move very sluggishly to the drain, as shown in the
previous photos.

Similarly, if you had a long tube draining from the bottom
of the system to the quick drain - I've seen that setup -
it will take a while for the water to displace the gasoline
in that long tube. Anyone who has had trouble bleeding
brakes will understand this - even though the fluid is much
denser than air, it can be quite a trick to get all the less-dense
air (think gasoline) at the top of the system, and all the
more-dense brake fluid (think water) down to the bottom
of the system.

And I'm sure the density delta is much greater between
the air and the brake fluid, than it is between the gasoline
and the water.

Edit -- I remember a few years ago. Got the brake fluid down
on one of the Pitts (pads wear) and added fluid a wee bit late -
master was a bit dry, so we probably ended up with fluid on
top of some trapped air in the line down to the caliper. Eric
was grumbling about the brake being mushy - he had to pump
it up. I told the kid to go up and pull +6G's for a while, because
the fluid would figure out which way the caliper was, and the
air would find the master.

He did, and it worked. I should mention that neither of us
have a PhD in Fluid Dynamics, so I can't say whether or not
it should have worked.

[mcrit]

I told the kid to go up and pull +6G's

Only 6? You're getting soft on the kid.

[New_PIC]

I remembered reading, and then found again, this somewhat related website:
http://www.avweb.com/news/maint/182907-1.html
where he talks about old Cessna 210 fuel bladders developing wrinkles that could hold water back from the drain. Scary stuff!

[CpnCrunch]

I remembered reading, and then found again, this somewhat related website:
where he talks about old Cessna 210 fuel bladders developing wrinkles that could hold water back from the drain. Scary stuff!

Fuel bladders are generally a bad idea, and even Cessna has figured that out now.

[pelmet]

A blob of water in fuel tanks is bad. Apparently there usually some water entrained in fuel which is not as bad as long as it flows through and gets burned but if it is cold out, I think the ice crystals can block filters. I know jet fuel guys on some aircraft without some sort of fuel heaters mix some icing inhibitor in the fuel and that there is a special way of doing it but have never flown a plane requiring this.

But, water entrained in avgas can "precipitate" out and cause and engine failure such as in this twin Commander.

http://www.tsb.gc.ca/eng/rapports-repor ... 7c0225.asp

How many of you put fuel icing inhibitor in avgas in the winter. I never did. This accident worries me because it seems like there was not much that the pilot could have done. Does anybody out there in their light aircraft put an icing inhibitor in their avgas or have suggestions or comments to expand on this and what can be done?

On a different aspect of the problems caused by ice in fuel, someone mentioned earlier about water freezing in a fuel line which then expands and ruptures the fuel line. Has anyone actually seen this happen.

The reason I ask is because of my understanding of why pipes burst(which may be wrong). My understanding of a burst water pipe in a house for example is this.......if there is a location that freezes, the pipe will burst not at the location of ice formation but at the weakest point downstream of that point toward the faucet. Why, because as the initial ice location forms, any expansion pushes water back toward the sewer which is the equivalent of a vent so no pressure builds up. Once the ice location is solidly in place across the entire pipe, any water upstream of the blockage that freezes will once again only push water back toward the sewer. However, any freezing that now happens between the blockage and the tap has no room to expand and therefore slowly increases pressure on the pipe. That is why only a small drip is required to prevent a pipe burst as the water slowly freezes and expands.

So.....If an ice blockage happens in a fuel pipe, as long as the tank is vented, the transition from liquid to solid of the H2O will just push the upstream fuel back toward the tank vent while fuel downstream of the blockage doesn't freeze anyways. But I am not particularly knowledgeable about this stuff. Comments anyone.

O.K., I read more posts in the thread and someone did have a pipe burst. Maybe it depends on how the freezing occurs.

[photofly]

Fuel bladders are generally a bad idea, and even Cessna has figured that out now.

Less likely to rupture in a crash though, and (used to be that? still is?) the USAF insists on them in their aircraft. I read that somewhere.

[azimuthaviation]

I got asked once what side of the airplane was the right fuel tank on.

Don't be quite so quick to assume this is a stupid question. Without knowing how long the person asking the question had been around airplanes, it's not that silly.

If they're quite new, what direction are they facing when checking the tanks? Typically towards the tail. If they haven't been around enough to know that the reference left or right is always facing towards the front of the airplane it's easy to see why they would be confused by a reference to the right tank. After all, in their limited experience when looking at the tanks, it's not intuitive that the right one is the one on the left.

And when checking the tanks the tail is also forward and the prop aft. That can cause a lot of confusion if someone hasnt been around airplanes much.

[trey kule]

I have been around planes since I was a small child..flying for nearly Fifty years. Thought I pretty well had it figured out where parts of the plane are located....but your statement confused me

Perhaps I need an hour of ground briefing on the location of the tail and prop....or maybe instructor nonclemature Do you have a power point presentation explaining all this ?

[Colonel Sanders]

the tail is also forward and the prop aft

That's quite true during a tailslide or a torque roll.

[trey kule]

Ah,I see. Totally relevant,

[Colonel Sanders]

Well, it's probably more relevant than asking,

"If you fly an ILS inverted, will the LOC needle
sense properly or reversed like a BC? Does
this change with an HSI?"

[azimuthaviation]

"If you fly an ILS inverted, will the LOC needle
sense properly or reversed like a BC? Does
this change with an HSI?"

No it wont be because it is picking up a preponderance of either 150 or 90Hz dedending how far you are from centre line. If it did then you could just rotate the hsi and fly the needle normally. Another cool experiment suggested here. Let me know how the landing goes.

[Colonel Sanders]

They're a little tricky, but getting better.



The good news is that I can drain the water
out of the tanks after landing by just opening
the caps.

[Shiny Side Up]

Don't be quite so quick to assume this is a stupid question. Without knowing how long the person asking the question had been around airplanes, it's not that silly.

If they're quite new, what direction are they facing when checking the tanks? Typically towards the tail. If they haven't been around enough to know that the reference left or right is always facing towards the front of the airplane it's easy to see why they would be confused by a reference to the right tank. After all, in their limited experience when looking at the tanks, it's not intuitive that the right one is the one on the left.

And when checking the tanks the tail is also forward and the prop aft. That can cause a lot of confusion if someone hasnt been around airplanes much.

I suppose if one is used to operating from an excessively self centered view of the world, using the terms right and left in reference to something besides their current point of view might be very confusing. But before all you guys get too indignant, I'll have to say that BPF has the same sort of view on this as I do.

Unfortunately this thread seems to have come off the rails so I would like to return to the original question. What do you as the instructor say when the student asks " Why is water in the fuel tanks bad ?" . My first reaction was to blow off the original poster as just a troll who wants to be a smart ass. But on further reflection I can think of many times ab initio students asks questions where my first reaction was " are you really that stupid ? ".

These questions are usually spontaneously blurted out without the student really giving the question much thought. IMO the best way to deal with these is to redirect the question to a more usefull discussion but remain on topic. So this is how I would answer this question

While every unpondered question shaves a small bit off of the reserves of patience I have left for this lifetime, I can still weather through these sort of things without hurting feelings of students, the most important aspect of flight training...

In all seriousness though, while I always encourage students to ask questions, I also encourage them to think before they ask. You get a student who has a tendancy to blurt this sort of stuff out (and I'll say that this "student" actually had a PPL and owned his own airplane, and this stuff still threw him for a loop) always take longer to complete stuff. They have a tendancy for not thinking for themselves, their first notion is always to ask anything that stalls up their thought process. I'll say that it was this sort of student that made me stop giving my phone number out. This sort of student seeks to be spoonfed. I know its not PC around here to assert that students themselves might have problems that hinder their ability to learn, its only instructors, but that's been my experience. The biggest thing that affects how fast people learn things is how their own thought process has matured.

The world is not that complex of a place. The KISS principle applies in most circumstances. Occam's razor can be used to figure out the "why" in most circumstances. Contrary to popular belief, they didn't make airplanes that complex either.