How long before water settles to the bottom of the tanks?

Discussion in 'Pilot Training' started by LongRoadBob, Nov 2, 2018.

  1. LongRoadBob

    LongRoadBob Line Up and Wait

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    First, pet peeves, then I'll get to the question...

    A number of things bug me about my clubs' checklists.
    When the CFI is telling me "just follow the checklists!" and yet the list has one setting the parking brake before start, but then before taxi, not releasing it, etc. it bugs the programmer in me.

    Also have to mention, I really get irritated with the Cessna "set fuel shutoff valve to ON" as fuel shutoff "on" to a programmer, or logical person, would mean the fuel is shut off after that step.
    They ought to call it "fuel enable" or "fuel flow" which would make sense being "on" meaning fuel is flowing. A shut-off is a negative thing, if "on" it shuts it off!

    But okay. These are nuance and "we know what they mean" but We have another point, about checking fuel (12 places on Cessna 172) for contaminant, water. I was "sure" (but wrong) that this was a Daily Inspection point. Meaning, as I understand it, the first flight of the day pilot has to do this, check it off in the log, and thereafter it is skipped in preflight. Checking now, I don't see the asterisk that is indicative of DI.

    But it does say you shouldn't move or disrupt the airplane before taking fuel samples "for a while".
    No time frame is given.

    So the main question to all of you experienced pilots is, HOW long is long enough? Say my rented plane comes in and lands, it's my turn to fly it, and I have to top up the tank for my flight. How long do I have to wait to check fuel at the 12 points to be sure I would see water if it was present?

    An aside, they also have you checking the elevator trim travel, in preflight, but then again in warm up too. Same thing with flight controls. I'm a stickler for checks, but even I think the chance of the flight controls to fail, or elevator to change between preflight and warm up is minimal. I'm only a dumbs student, so I don't dare question this logic.

    I would think this was a club that was doing extra good vigilance in their procedures, but the C172 I have been flying has had one of two landing lights out, even after the 100 hr. Check, and a door that doesn't lock, as well as vacuum system failure (just after 100 hr. Inspection). "Since we are VFR we don't need the DI an artificial horizon".

    I really wonder if this is the norm. It's a big club, but they only have one C172 with steam gauges, and it's been grounded lot of the summer. Yet still it is the same price to rent. I thi normal?
     
  2. Dan Thomas

    Dan Thomas En-Route

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    Water is found in three forms in Avgas: free, entrained, and dissolved. It's the free water we're after when we check the sumps, and it settles out fairly quickly. Top up the tanks, put the hose away, and check the sumps.

    Entrained water is sometimes seen as tiny "snowflakes" in gasoline in cold weather. It takes a LONG time for this stuff to settle out. Dissolved water is invisible and stays that way and goes on through the engine without hassle. It's a tiny amount.

    If you get the free water out of the tanks, the fuel strainer will catch anything else of consequence. Remember to check it, too. The number of corroded strainer bowls I have found tells me that too many pilots ignore it.

    Moving the airplane can move the water away from the drains, as can parking it on a sloping surface.

    Vacuum failure after an inspection can happen. An inspection doesn't guarantee that nothing will fail for a few hours. But if the vacuum pump failed, and if it has an inspection port, they likely haven't been monitoring it and just run it until it quits. There's no excuse for that, and there's no excuse not to buy pumps with inspection ports.
     
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  3. Hippike

    Hippike Pre-takeoff checklist

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    Haha, totally agree; I had the same thoughts on this!
     
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  4. John221us

    John221us En-Route

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    I have nothing to add to what Dan said, but on your other pet peeves; many pilots (even students) make their own checklist. You want it to match your flow and also work for you. You can do this in Word or Excel and then laminate it. For my Cherokee, I did a half sheet, two sides and that fit on a kneeboard. For other planes, you may need to do multiple pages and use rings to bind them together.
     
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  5. jesse

    jesse Administrator Management Council Member

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    As a fellow career programmer, pilot, and flight instructor, I offer you the following advice:

    Stop thinking like a programmer and stop assuming that programmer logic is good pilot logic. We programmers crash computer programs hundreds of times a day. In aviation, a crash is much worse. As a result, lots of things involve redundant checks. The reason for that has been written in the blood of former pilots and passengers.

    Pilot procedures are meant for humans to execute. Programmer logic is meant for computers to execute. Humans are ****ty computers.

    Most folks sump the fuel at the start of each days flights. Basically if the airplane has been sitting for awhile, sump it. You should also ALWAYS sump after every time the airplane is fueled. Sump it if it just rained. If you aren’t sure whether you should sump the fuel then you damn well should sump it. That’s pilot logic.

    As to how long it takes...it depends...but I can tell you that I have sumped ounces of water out before roughly 2 minutes after it was fueled. There wasn’t water before that.

    Don’t assume your programmer logic is superior to what your flight instructor is teaching you even if it seems illogical. Airplanes don’t give a **** how good your code is. When the **** hits the fan - it will not be computer science that saves you - it’ll be some instructor from your pasts voice.
     
    Last edited: Nov 2, 2018
  6. PaulS

    PaulS Final Approach

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    Water not absorbed in the gas should take a few seconds to get to the sumps as long as it isn't hung up on something in the tank.
     
  7. mscard88

    mscard88 Ejection Handle Pulled

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    12 points? Are you saying there are 12 sumps to check?

    About 15 minutes is usually recommended to sump fuel after refueling.

    172 fuel valve should be checked to be on BOTH for takeoff (as well as landing).

    Lights, vacuum pump, etc all can fail at any time.

    Does seem like overkill on checking trim, but I suspect you may mean checking the elevator. Think of the second check, right before takeoff, as a “last chance” to ensure all flight controls are free, correct, and the control lock has been removed.
     
  8. Cap'n Jack

    Cap'n Jack Final Approach

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    As mentioned, you shouldn't need to wait long. I check the fuel level first thing and get it fueled, then check the sump after the pre-flight (5-10 minutes). It's unusual that only the first pilot using the plane has to check the sump and log it. Most places have everyone sumping before using the plane. I'd still check it- it's my butt up there.

    When you get settled in the plane, you may find that something is interfering with the controls after warmup. I've found my knee-board to interfere once (moved the seat). Or something rolled under the rudder pedals (water bottle that a passenger dropped).

    It's not the best, but I've seen this sort of thing elsewhere. Familiarize yourself with what is needed for VFR, and what is needed for the plan to be legal.
     
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  9. rk911

    rk911 Line Up and Wait

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    i did this and even added a few things that i wanted to double check that weren't on the POH checklist.
     
  10. Clip4

    Clip4 En-Route

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    What if you check the fuel preflight at the beginning of the day, fly, land, and it rains prior to takeoff again? How do you determine the access panels on top the wing are water tight.

    What if after the preflight you stop for fuel, how do you know the fuel truck didn’t pump water into your tanks?
     
  11. LongRoadBob

    LongRoadBob Line Up and Wait

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    Thank you for that information. It was helpful. I wasn't aware of the different types of contaminant water, until now. Good info.

    As for the vacuum, I realize that failures can happen, but it is the time after that bugs me. Vacuum fails right after 100 hr. Inspection, but now it is weeks after and it "kind of" works. What really bugs me is the landing light thing and door not lockable from the inside (have to open the window and reach out, latch it) even after 100 hr. Inspection. Changing a bulb in the landing lights doesn't require an A & P trained person.



    I've thought about doing that. I wasn't sure if it was allowed by the club. I believe I could make a better checklist, as there re definitely mistakes in the club checklist, but I also see that some of them could be be cue of the possibility of a pilot coming from a different place. Such as, the after takeoff checklist includes "check/set flaps up" which makes no sense from takeoff (we don't use flow) but make sense if T&G or short takeoff. I realize I don't know all the circumstances that can happen, and that one can come into a subset of the checklist from another point.

    Yeah..I get that. It's just the trim travel that bugs me, having to move the trim all the way up, then down, then back to takoff position. When I did exactly that in preflight...just seems weird to me.
     
  12. LongRoadBob

    LongRoadBob Line Up and Wait

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    Good to hear it isn't just me. I "know" what they mean, but it goes against my internal logic.
    I'm a guitarist though. When Leo Fender made the stratocaster he called (what we call the whammy bar) the stick that Jimi Hendrix and others used so well, and that is a vibrato bar, a "tremolo" bar, and we have had to live with it ever since, even though it is wrong. I can handle it. Just bugs me.

    Thanks...I think we are a little out of sync. I'm talking about a standard that programmers use to name a function or method call (c or Java), which "ought to " be consistent and logical. Obviously, a computer crash is not desirable, but I'm not exactly going to crash an airplane because I stick to my guns me demand that a fuel shutoff valve "ought to" either be named something else, or the condition change. (Off = shut off,etc)

    It is what it is. It's dumb, and wrong, but I understand it.
     
  13. John221us

    John221us En-Route

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    I am not sure how or why the club would disallow a customized checklist. Your CFI might, while you are a student, but it could also be a great learning experience to work with your CFI and create an enhanced checklist. Typically, you are going to start with an existing checklist and then modify it to one that works for you.

    On the flow thing, typically, on run up, you follow a flow (a logical order for running through checklist items) and then after you go through the items, you go back to your checklist to make sure you didn't miss anything. Same thing for your pre-flight. You are going to go through a walk around and then double check the checklist to make sure nothing was skipped. Your flow may or may not match the checklist order (though it should include everything on the checklist). If you make a custom checklist, you can sequence it for what works best for you.
     
  14. Salty

    Salty En-Route

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    People threatened to report me to HR when I spent a week making fun of “anti-harassment awareness training” where presumably we would learn how to spot people that were trying to stop people from preventing others from harassing others.
     
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  15. JScarry

    JScarry Pre-Flight

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    You want to check the flight controls before engine start to make sure that knees and iPads don’t interfere with the control movement. Better to deal with it before starting the engines rather than after. And the reason you want to check once more before taking the runway is to make sure nothing has changed. If I recall correctly a military cargo plane in Afghanistan(?) crashed on takeoff because the co-pilot had placed a phone or iPad on the dash in such a way as to block the controls. The plane rotated with a nose-up attitude and crashed shortly after liftoff. An executive jet recently crashed in Teterboro(?) when the pilots misunderstood the procedure for removing the automatic gust lock and took off without attitude control.

    I always do my MC-FARTS check before taking the runway. Mixture, Controls, Fuel Selector, Altimeter, Radios, Traffic, Safety-Doors and Windows.
     
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  16. Pilawt

    Pilawt Final Approach

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    If you think about it too much, the term "near-miss" is wrong, too.
     
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  17. LongRoadBob

    LongRoadBob Line Up and Wait

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    Thanks, I am in the process now of memorizing the steps and this helped. I've been walking around on preflight step by step with the checklist and I walk a lot more back and forth, so next time I'm doing it the way you mentioned.
     
  18. kgruber

    kgruber En-Route

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    Bill Barton (rip), (creator of Monarch fuel tanks and the "Barbie Doll",) offered his only one lowspot fuel tanks to Cessna when they started up production again in 1996. Foolishly, they declined.
     
  19. darrell

    darrell Pre-takeoff checklist

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    I never understood why people try to be so funny about "near miss". It's closer than a "far miss," right? It's only funny if you change "near" to "nearly." Near and nearly aren't even synonyms.
     
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  20. jordane93

    jordane93 Final Approach

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    Make your own checklist and tailor it to your liking.
     
  21. CC268

    CC268 Final Approach

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    Yea that’s what I did! I made mine match the flows. Has worked very well.
     
  22. Kenny Phillips

    Kenny Phillips Line Up and Wait

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    I bought my Skyhawk because a rental 150 engine stopped running about 50 feet up on takeoff. I wouldn't have been surprised if that flight school was using mogas. Zero water showed up in the preflight sump checks [I'm hyper about clean fuel!], but after a one point seven mile taxi to the runway, what turned out to be perhaps a pint infiltrated the carburetor. I don't know when it was last refueled, but it was full. It may have been half frozen, or whatever, but it came loose and caused an early landing (6,000 foot runways are a good thing!) After that, I'd give the wings a good shake and check things again. I never saw more than a drop or two before or since, in any plane.
     
  23. Juliet Hotel

    Juliet Hotel Pre-takeoff checklist

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    You're way overthinking this. Way. Fuel shut off is, I believe, what Cessna calls the valve. When you read fuel shutoff on your checklist, transpose it in your head to fuel valve. Done.

    A while is pretty much anything other than immediately. Don't take a fuel sample immediately after disrupting the plane. Done. As for sumping it again after the plane lands? Its highly unlikely you'd find water at that point. But its also your butt in the seat and for that reason alone, doesn't hurt to sump it again.

    On the check during the walk around you move the control surface itself. This allows you visually inspect the hinges and attachments for cracks, missing fasteners, and looseness or binding. But with many aircraft, its difficult to confirm that when you move the control surface, the yoke or stick inside the airplane is also moving and moving in the correct direction. You would assume you could catch that when doing your walk around and verifying the stick or yoke is moving in the correct direction (if you can even see it), but you'd be surprised how many pilots (and mechanics) don't pick up on incorrect control surface rigging until they're sitting the seat and moving the control from that end.

    That's one of the reasons you also do a free and clear controls check before takeoff. Also, when you move the control from the control surface, you're only moving one control, i.e. the just aileron or just the elevator alone. What if there's a problem behind the panel that's causing interference only when both are in a certain position? You wouldn't know that just by moving one control at a time. But if you just did the free and correct check before takeoff, you wouldn't detect that one of the hinges loose and moving a bit when the elevator gets near the end of its travel.

    When you move the control surface itself, the front seats are generally not occupied. What if your right seat passenger is in a position that limits movement of the yoke? Wouldn't you want to know that before takeoff? You can look and think your right seater looks like they're clear enough of the controls, but you can't really know until you move the controls.

    Well its disappointing to say the least but not all that unusual. An inop landing light and/or a failed gyro isn't likely to cause a catastrophic issue during a flight during the day in clear in a million weather. But water in the tank that could cause the engine to lose power after takeoff at 200 AGL could very likely lead to a NTSB report.
     
  24. unsafervguy

    unsafervguy Cleared for Takeoff

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    The valve is marked off and on, right. Seems clear to me..............
     
  25. overdrive148

    overdrive148 En-Route

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  26. James331

    James331 Touchdown! Greaser!

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    Here’s a good site on all things sump related

    http://www.sumpthis.com/

    For me I do a preflight one a day, than before each startup I do a quick walk around (like literally walking around the plane) and go from there, I normally won’t do a run up each time in a piston plane ether, unless something gives me reason to question, another good habit is to do a quick flight controls free and correct before entering the runway.
     
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  27. WannFly

    WannFly En-Route

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    Thankfully, you won’t need a checklist after the ride ...









    I kid. Bw depending on the model you are flying, are you sure it’s not 13? 5 on each wing and 3 under the belly? Haven’t sumped cezzna in long time, but I remember needed a calculator to count the number of damn drains in that thing
     
  28. Silvaire

    Silvaire En-Route

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    Eventually you are going to get to the point where you will do your pre-flight inspections free hand and then simply scan the checklist to ensure there is nothing on it that you didn't do. You will adopt your own flow and order and the little nuances of the actual list won't bother you anymore.

    A 100 hour inspection can't do anything about a landing light that burns out or a vacuum pump that fails on hour 101.

    If you are really curious pour a bit of water into your fuel sample, shake it up and see how long it takes to separate. You'll find they don't really mix the water breaks up but quickly coagulates and sinks. That doesn't answer your question of exactly "how long" but it gives you a sense of what you are dealing with and looking for.
     
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  29. PaulS

    PaulS Final Approach

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    I like a runup after every start..... just what I like.
     
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  30. teejayevans

    teejayevans Pattern Altitude

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    There is more than just separating out, it then has to travel down to the sump drain and hopefully not get stuck along the way.
    When refueling I push the plane away from the pumps to allow another access and hopefully the movement causes any water to migrate to the low point. I sump first tank filled first, probably about 3-5 minutes after filling.
     
  31. FlySince9

    FlySince9 En-Route

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    Why wait for it... On a skyhawk, I shake the wings as I do my walk around. by the time I finish the walk around, plenty of time has passed for any water I "unstuck" to drift down to the sump...It's the last thing I do before I climb in...
     
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  32. mscard88

    mscard88 Ejection Handle Pulled

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    Yup.

     
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  33. oilburner

    oilburner Pre-takeoff checklist

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    I’m a sumping fool now with my (captioned) plane.

    Couple of yrs ago, I filled both tanks from the fairly new self serve facility at KODO, right tank first. Did three, one hour flights over the course of three weeks doing pattern work and short field work. No rain this month & plane is hangared. Sumped approx 2 pints water free fuel spread evenly across the 13 sumps prior to each flight without fail.

    Before the fourth flight, almost a month since I filled up, I sumped 4 oz water from the left inboard rear sump plus sumped 4 oz water from the fuel selector drain.

    Dude, I was prepared to quit aviation that day. But, came to realize this was just a wicked lottery. Accident investigators wondering why a well maintained engine failed in flight for no reason could perhaps use my example.

    Cessna recognizes this, put out a bulletin or two saying for the wet wing tanks recommend to dip the tail, shake the wings and sump perhaps a pint from each drain. No other way to tell if you happen to pump free water into your tank(s).
     
    Last edited: Nov 3, 2018
  34. timwinters

    timwinters Touchdown! Greaser! PoA Supporter

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    Granted the vessel in the attached video is a smaller scale but about 20 seconds!

    This is how I test for ethanol in MoGas.

    NVM...the 35 second vid is too big to upload.

    Description: I have a test tube rain gauge filled with 1" of water, 4" of fuel and it shook vigorously for about 10 seconds. Water completely settled back to the bottom in 15 to 20 seconds.

    BTW...in just over 16 years of flying and 1,900 hours I have NEVER slumped water out of a tank. C172, C182, & DA-40.

    But I still always check...
     
    Last edited: Nov 4, 2018
  35. Sundancer

    Sundancer Pattern Altitude

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    Water settles out simultaneouly with turning crosswind.
     
  36. woodchucker

    woodchucker Line Up and Wait

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    I have once. Not sure the cause but it took at least five or so sample draws to clear it. Not sure the protocol on that but I gave the run up more time than usual, and didn’t have any problems on the flight.

    Edit: and that happened at around the 100 hour mark in my flying career. Don’t ever get lax in your preflight.
     
  37. danhagan

    danhagan Cleared for Takeoff

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    There’s a video of red dye water in a fuel tank (a LOT), that isn’t picked up because it’s not at the sump, but gets there if you rock the wing or taxi to the runway
     
  38. Crashnburn

    Crashnburn Pre-Flight

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    Thanks. I liked it so much I added Flaps and Wind direction .
     
  39. JScarry

    JScarry Pre-Flight

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    In that case, you might want to get HAAPPY when you enter the runway.

    Verify Heading
    Ailerons for wind
    Airspeed alive
    Power alive (MP and RPM where they belong for takeoff)
    Pitch for rotation
    Vy (actually slightly more until gear and flaps up)
     
  40. teejayevans

    teejayevans Pattern Altitude

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    Do you really need a memory aid to remember how to takeoff?
    I never forget that I had to pitch up to get the plane flying, that’s instinctual.
     
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