Death By Fuel Tank Selector Valve

Discussion in 'Firewall Forward / Props / Fuel system' started by GESchwarz, Sep 10, 2011.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Sep 10, 2011 #1

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    In reading through hundreds of NTSB reports I am astonished at the number of fatal accidents that were due to fuel mismanagement at the fuel tank selector valve.

    In aviation there are so many ways to kill oneself (and others), so many gotchyas, so many things that have to be remembered; so many things to be overlooked or skipped as a result of common distractions.

    As the self-proclaimed safety nut of this forum, I'm always looking for ways to reduce or eliminate these risks.

    Can someone please tell me why it is so important that we have such a valve that would limit our access to useable life-giving fuel.

    What is the need for the fuel selector valve?

    What alternative is there that will not act in any way as a fuel supply shutoff to the engine?
     
  2. Sep 10, 2011 #2

    Joe Fisher

    Joe Fisher

    Joe Fisher

    Well-Known Member

    Joined:
    Feb 11, 2007
    Messages:
    1,378
    Likes Received:
    374
    Location:
    Galesburg, KS South east Kansas
    Fear of in flight fire. In part 23 airplanes there are minimum fire wall standards and they depend on the pilot having the ability to stop the fuel. The airplanes with gravity feed fuel systems need to have the fuel turned off when parked because the carburetor can flood and drain the selected tank on the ramp or on the hanger floor.
     
  3. Sep 10, 2011 #3

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member

    Joined:
    Jan 24, 2011
    Messages:
    3,748
    Likes Received:
    1,661
    Location:
    US
    Well, of course we all want to be able to isolate the fuel, as much as possible, in preparation for an off airport landing, so the fuel shutoff valve/fuel selector valve serves this purpose.

    I'd be surprised if fuel tank selector valves play much of a role in fuel starvation in high-wing aircraft. It just sits there and almost never gets manipulated. I'd suspect most of the problems blamed on improper fuel tank selector position really boil down to issues with design of the fuel system or human-factors shortfalls, especially in low-wing aircraft and aircraft with fuel injection systems and a return fuel flow. Lots of systems require fairly regular attention by pilots, and distractions can cause a tank to run dry or lots of fuel to be pumped overboard through a vent. We probably need to look well beyond the valve itself and ask "how can we design fuel systems that keep the magic juice flowing to the noise producer with minimal pilot intervention or least chance of making a big mistake."
     
  4. Sep 10, 2011 #4

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    I understand why we would want to have a fuel shut off for off-airport landing prep or on-ground purposes. But durring normal flight, why would you want to shutoff a fuel supply? So often the tank being used runs dry and there isn't enough time to switch to the other tank that has fuel, and get the motor restarted before it's too late.

    It seems to me the penalty is way too high for such a little mistake.
     
  5. Sep 10, 2011 #5

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,451
    Likes Received:
    3,182
    Location:
    Memphis, TN
    Locally a guy took his Cessna in for annual. Mechanic did his check on the valve by shutting if off. Pilot did not use his checklist to see if it was on. Engine shutoff on climb out. Pilot just had Ballistic chute installed 5-10 hours before. Plane totaled, pilot could have landed on a couple of roads in the area.
    I can only think of high wing planes that have a Both selector. Most low wings, Mooneys, Bonanzas, Grumman, RV7 dont have a Both. It is about sucking air from one tank and have the fuel cross flow to the other tank; exact scenarios I cant remember.
     
  6. Sep 10, 2011 #6

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,539
    Location:
    Rotterdam, Netherlands
    Low wings exclusively me thinks. But even in a high wing, in some parts of the flights, shutting it off might be a good idea, especially during crabbed approaches, slipping flight and aerobatics. Having flown gliders with ballast, they can be quite a bit harder to control with that unbalance between your wings, up to the point where full aileron doesn't help you roll to level anymore...
     
  7. Sep 10, 2011 #7

    Dana

    Dana

    Dana

    Super Moderator

    Joined:
    Apr 4, 2007
    Messages:
    8,515
    Likes Received:
    2,925
    Location:
    CT, USA
    Some pilots on long trips like to run one tank completely dry before switching, for precise fuel management. Some even go so far as to wait until the engine actually quits before switching.

    In the event of an engine out forced landing, it's recommended to shut of the fuel before landing to reduce the risk of fire.

    OTOH, some flight schools wire the fuel selector "on" to prevent a student from accidentally shutting it off.

    -Dana

    I've noticed that the press tends to be quite accurate, except when they're writing on a subject I know something about.
     
  8. Sep 10, 2011 #8

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    Can anyone see a flaw in the following design?

    On a low wing design with a tank in each wing, each tank feeds into a common centerline sump tank. The fuel levels in the two wing tanks are maintained equal by level flight. The sump tank contains a boost pump. There is an engine-driven pump which receives the fuel from the boost pump.

    The emergency fuel shut off would be in the line between the two pumps and located forward of the pilot, clearly marked and in plain view. The boost pump switch would be located there also.

    The boost pump would be running at all times except when preparing for a off-airport landing, at the last moment. At that point you would want to open the main bus breaker to kill all power from the battery and alternator.

    A fuel pressure switch located in the line between the two pumps would actuate a red low-pressure warning light, signaling either a failure of the boost pump or flow restriction in the filters. To ensure that the sump tank is always full, the line from each wing tank will have a check valve which prevents reverse flow.

    Because the check valves would prevent continuity between the two main tanks, a crossover line would be needed that connects the two tanks directly. This line would connect both wing tanks directly without passing through the filters. This way, if one filter is plugged, all fuel is still accessible through the other filter.

    A filter would be located at the outlet of each of the two main tanks leading to the common sump tank.
     
    Last edited: Sep 10, 2011
  9. Sep 10, 2011 #9

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,539
    Location:
    Rotterdam, Netherlands
    Yes.
    Most low wings don't have a position inside the aircraft/wing where you could hang a sump tank because the wings are the lowest point. Naturally, a 1" deeper sump is possible, but that's not enough for the typical variation as during climb/dive/cruise/turns.
     
  10. Sep 10, 2011 #10

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    In my particular design the wing tanks are outboard of the main landing gears, where the dihedral begins, much like the Hellcat in the photo to the left. So I have gravity feed to the sump tank. But you're right, a sump tank must be lower than the tank(s) that feed it.
     
  11. Sep 10, 2011 #11

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,786
    Likes Received:
    2,017
    Which would make the airplane legally unairworthy.
    ____________________________________________
    § 25.1189 Shutoff means.

    (a) Each engine installation and each fire zone specified in §25.1181(a)(4) and (5) must have a means to shut off or otherwise prevent hazardous quantities of fuel, oil, deicer, and other flammable fluids, from flowing into, within, or through any designated fire zone,

    _____________________________________________

    Wiring the valve open removes the means to shut the fuel off.

    Dan
     
  12. Sep 10, 2011 #12

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,539
    Location:
    Rotterdam, Netherlands
    I think Dana refers tot he practice (AFAIK, the DA40 has it as a standard feature) to wire it such that you can still break the wire if you turn it with a lot of force, so that it's clear that you should onlyuse it in an emergency.
     
  13. Sep 10, 2011 #13

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,786
    Likes Received:
    2,017
    Anyone who can get the airplane off the ground with just the fuel in the carb bowl and fuel lines downstream of the shutoff is in far too much of a hurry. There isn't more than a pint of fuel there, not enough enough for a proper runup.

    Low-wing airplanes can't have a Both position on a selector. If it did, and one tank unported or ran dry, the engine pump will lift the air rather than the fuel. It's like a water well where the pump is up top and sucks the water up; if a leak develops in the suction line just above the water level in the well, the pump will get air and the water won't lift.

    Dan
     
  14. Sep 10, 2011 #14

    flyoz

    flyoz

    flyoz

    Well-Known Member

    Joined:
    Jul 30, 2008
    Messages:
    149
    Likes Received:
    5
    Location:
    Near Sydney
    Check out Mark langford's fuel system ( + 1000 hrs operation )
    Mark Langford's fuel system (n56ml.com/fuel/index )
    One of the best around and has no shutoff valve
    but i am sure that could be arranged in such a way that it needs only to be used in an emergency
    Flyoz
     
    wsimpso1 likes this.
  15. Sep 10, 2011 #15

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    Okay, so say you have the left tank selected and it unports. The engine driven pump is going to draw air. I don't understand what good the selector valve is doing. It seems as though the problem is un-porting, not whether you are drawing from one or both tanks. Either way you can have an un-port situation. What am I missing here?
     
  16. Sep 10, 2011 #16

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    Nice attachment. Mark's is a bit like mine in that his sump tank in integral to the tank on the left side in the schematic. It also has a boost pump which keeps it filled from the right tank and a one-way flapper type check valve to keep the sump tank full.


    I'm putting my tanks well out board on the wings, and I like the idea on not having any fuel lines or valves inside the cockpit area. A shutoff valve can be located out in the wing and actuated remotely by linkage. It's harder to be burned alive the further the fuel is from the cockpit.
     
  17. Sep 11, 2011 #17

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,786
    Likes Received:
    2,017
    A brief unporting won't kill the engine, but if we had tanks on Both and were flying a bit cockeyed and the tanks were low enough, one will let air into the line long enough to satisfy the pump's propensity to suck just air. Can't happen in a high-wing airplane with low fuel even if the fuel is pumped by an engine-driven pump; the gravity keeps the fuel going down and air up.

    I used to be a flight instructor. One of the more annoying habits I encountered was flying one wing low. I don't know why some pilots do it; perhaps they're trying to line up the sloped top of the cowling with the horizon. I do know that many of them have lazy feet and will let the thing bank a few degrees to maintain a straight course rather than hold a bit of rudder if the yaw trim is off some.

    Dan
     
  18. Sep 11, 2011 #18

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    So that is the reason for the fuel tank selector valve. That's the answer I've been waiting for. Thanks for that Tom.

    So, would you agree that a centerline sump tank that is fed by both right and left tanks through check/flapper valves, we could get rid of the selector valve? A sump tank that is fed in such a way would tend to maintain the level of the fullest tank.

    If you think about it...if both left and right tanks were nearly empty, rocking the wings would cause the sump tank to fill to capacity until there were not enough fuel in those tanks to fill it. I'm thinking that the sump tank would have a capacity of only a gallon or so...no more than enough to ensure that an un-port can never happen. It should have a vent so there is no excuse for a volume of air to be trapped.
     
    Last edited: Sep 11, 2011
  19. Sep 11, 2011 #19

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    11,701
    Likes Received:
    2,201
    Location:
    Port Townsend WA
    I know of several fatal takeoff crashes where the fuel selector was found in the shut off position. One crash was a Cessna Caravan with a commercial pilot.
    In my opinion, the fuel shut off should be eliminated, it causes more crashes.
    The last thing I care about when making a deadstick landing is the fuel shut off. The fuel leakage will not be stopped by the valve being shut off. In a crash, the fuel lines are completely torn apart anyway and often the tanks are torn.
    If cars had shut off valves, we would have more crashes from stalled engines entering the freeway.

    My fuel selector is always kept in the open position.
    BB
     
  20. Sep 11, 2011 #20

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,157
    Likes Received:
    92
    Location:
    Ventura County, California, USofA.
    Great points BB. I've spent a lot of time reading through Mil-Specs. There are a few of them dedicated to crashworthiness. In there they talk about a special self-sealing device into which the fuel line is installed. In the event of a crash and the airframe is dismembered, there by pulling a fuel line from its tank, this device would allow the release of the fuel line and seal the opening.

    Where does one find such a fitting that does not cost an arm and a leg?
     

Share This Page

arrow_white