Level switches in the fuel system for alarms - Yes, No, Why?

Discussion in 'Firewall Forward / Props / Fuel system' started by wsimpso1, Dec 14, 2018.

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  1. Dec 17, 2018 #61

    blane.c

    blane.c

    blane.c

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    I always want to know how much fuel I have on board. Gauges are nice to have when they work, like the one's in the wing root of a cub, or the wire and cork of an Aeronca. I suppose I am more comfortable with math and a watch than buzzers and lights if the gauges are more sophisticated, I have seen to many wrong indications for to many hours.
     
  2. Dec 17, 2018 #62

    Pops

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    A friend of mine when flying up high, checks the time on one tank in his Cessna until the engines quits and then knows how long to empty for the next tank. I keep telling him its going to catch him one day. He doesn't think so.
     
  3. Dec 17, 2018 #63

    proppastie

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    you do not, however if you switch after say 1/2 hour (big fuel burn takeoff and climb at full power) and the other tank does not feed......switch back to the first tank, I would have almost 2 hr. total on the first tank in the Mooney, more if I throttle back.
     
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  4. Dec 17, 2018 #64

    blane.c

    blane.c

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    You are a boss, you are going to pay people to fly a trip 1,000 times a year, some of the people fly the trip 2,000 ft lower than other people and the people flying lower save you $100.00 a trip, Which people are you going to keep paying to fly the trip? Certainly many other factors weigh in to the equation but it cost's money to go up.

    The fuel gauges I flew behind were consistently unreliable and asking any of my employers to fix them would have evoked a hearty laugh. Reliable time pieces are far less expensive and they were paying me to work which included doing the math on fuel consumption. The routes and alternates were planned, familiarity with the aircraft made deviations easy to account for. Sliding into a glidepath slightly above the preceding 767 with a 747 in trail you really don't want buzzers and lights going off to tell you it's time to land, you already know that.
     
  5. Dec 18, 2018 #65

    Marc Zeitlin

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    But we're not discussion purchasing one of the planes with the crappy fuel level gauge systems that the planes you apparently flew had. We're discussing what equipment to put in a brand new, never flown, still being built aircraft, into which Bill has the opportunity to put accurate equipment. So we don't need to rely on less reliable and more variable timing, but CAN rely on the actual information in which we are interested.

    You did what you HAD to do in order to be as safe as you could be given the equipment with which you were provided. Bill has the ability to do better - why would he choose not to, just because you (and many others) had crappy equipment in the past?
     
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  6. Dec 18, 2018 #66

    proppastie

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    The future seems to be going towards the EFI.......questions....is it hard to start when hot?....if it does stop because of no fuel feed will it re-start easy?
     
  7. Dec 18, 2018 #67

    rv6ejguy

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    I was making the comparison to a carb which has a float bowl and will run for a few seconds on the fuel contained there. You'd never want to begin takeoff on a carb equipped airplane right after you switched tanks for this reason. With EFI, as soon as you switched tanks to a non-feeding one, the engine would stop in about 3 seconds at full power.

    To answer your question, EFI hot starts just like your car unlike many mechanical FI systems. The high pressure prevents any fuel boiling from happening in the lines like Bendix style FI.

    We are concerned about regulator placement and the length of time it takes for the engine to process the line volume of air if a tank was run dry. Less line volume means less time to purge that air. We also have specific recommendations about plumbing and pump placement and pump types to be used.

    We recommend never to run a tank dry with EFI and that shouldn't be too hard to do with decent level and/or warning systems (think aural).
     
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  8. Dec 18, 2018 #68

    rv6ejguy

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    I think lots of good has come from this discussion. As Marc said, Bill has a clean sheet and can do something better than what we had in the old days. Long, shallow tanks will require more than one sender, preferably with some electronic damping applied to get better accuracy and consistent readings. Not hard to do. Combine this with aural low fuel warnings in all 3 tanks and it should be pretty hard to run out of fuel or run any tank dry.
     
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  9. Dec 18, 2018 #69

    blane.c

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    Allegedly, in the C-54's we would cruise on auto gas in outboard tanks and aviation grade gas in the inboard tanks. Allegedly we would switch from the outboard tanks to the inboard tanks with the inboard tanks boost pumps on flying crosswind looking at "the sock". Allegedly this worked fine all summer. Allegedly in the fall we found ourselves doing an instrument approach and switched from the outboard tanks to the inboard tanks during the initial phase of the approach, one of the boost pumps pumped fuel better than the other one and emptied the port tank into the starboard tank causing all four engines to suck air. After all fuel selectors forward cross-feeds off all boost pumps on high, the waiting began, a marker tower went past my window which I thought was interesting as I had never seen that before and the engines began developing power again as we touched down in the overrun before the runway officially began and we were able to continue our trip normally.

    The C-118's have check valves in the fuel system to prevent transferring fuel from one tank to another, I wonder why?
     
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  10. Dec 19, 2018 #70

    proppastie

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    Ran a tank dry in my Cherokee once by mistake, (float carb) twice if you count the off field landing, but the first time it came back in probably 5 seconds after I switched tanks.
     
  11. Dec 19, 2018 #71

    blane.c

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    A low fuel warning buzzer would have been nice. An atmosphere that fostered adherence to Douglas procedures and safety over saving money using cheap gas would have been at least as good. When you have eight tanks routed to four engines … before they put in the check valves crews inadvertently pumped fuel overboard transferring fuel and overfilling a tank. Not funny over the Atlantic I imagine.

    My experimental cub did not have a header tank, I figured it was because of the difference in wing warping that caused a difference in pressure between port and starboard wings, but if both sides fuel selectors were on it would transfer fuel by siphonage or vacuum or some combination of both.

    Fuel systems are tricky sometimes.
     
  12. Dec 19, 2018 #72

    wsimpso1

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    Hey guys, in post 47, I already said "Sounds like another Princeton gage is appropriate." We are cool there.

    I am going to put in alarms discussed on all three tanks that I can cancel with a button push.

    Billski
     
  13. Dec 19, 2018 #73

    wsimpso1

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    Hmm. Never thought about it that way. The fact the EFI engines go quiet immediately with feed interruptions is why i wanted a header tank in the first place. Three programmable capacitance fuel level sensors, low level switches on each tank, and a no feed switch in the header were givens until I saw this.

    How to be sure both tanks are feeding before takeoff? Never worried about the second tank not feeding before... That poses the question of how to be sure the tanks are feeding with a header.

    Makes me want to put a pressure sensor (or a flow sensor?) on the fuel line after the transfer pump but before the header tank. Then program the Dynon to give me a green for zero pressure/flow when the pump is off, a green for pressure/flow within normal ranges for header tank fill and circulation, and yellow for error states. Check for green on both tanks before flight.

    This could be better than the high level switch in the header tank, as we were trying to know that the wing tank was feeding with that one. If we see flow off each tank that is even better because we get an earlier indication when flow is interrupted and an immediate signal that we should change tanks when we run one dry.

    OK, let's talk about that idea up a little... There has to be a fly in the ointment someplace. Anybody have a cheap fuel flow sensor to recommend for this. 0-10 psi, 0-50 pgh...

    Billski
     
  14. Dec 19, 2018 #74

    wsimpso1

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    Standard practice in our Cherokee (and from all of our instructors) is to start, taxi, runup, and fly to altitude on one tank. That way a blockage, water, or even a weak pump has their best chance to show themselves before flight, and then not risk the other tank until high and within reach of an airport. Theory I have also heard is that if you switch tanks before takeoff, you may not have enough run time to know that the new tank is not feeding. Then at altitude, you switch tanks to get a look at if the other tank works early, while you still have two hours in the takeoff tank.

    Now you have me thinking about tank feed problems...

    Bill
     
  15. Dec 19, 2018 #75

    Himat

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    Monitoring the pump should give a good indication on that fuel is being transferred. If the transfer pump capacity make fuel always flow in the return line, a flow sensor in the return line will detect fuel transfer problems and low fuel level.
     
  16. Dec 19, 2018 #76

    wsimpso1

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    You ever vapor lock a car made since about 1985? Fuel goes to the rail with more pressure and way more flow than is needed for starting, then the regulator keeps the rail at the right pressure by venting fuel (and vapors) back to the tank. Pump comes on before you crank, 100% flow back to the tank purges most if not all vapor to the tank. Hit the starter, and the injectors do a fixed flow to bring up mixture richness to firing level. As soon as the engine fires and speeds up, the mixture goes to a programmed slightly rich mix for the engine speed, coolant temp, throttle position, and manifold pressure or air mass flow. By now all fuel vapor is gone from the rail unless your tank is running dry.

    Well, it might take a bit to refill the system, but once liquid fuel hits the rail, I will have about 2-3 cubic inches of liquid fuel a second going to the rail of 1-2 cubic inches, so it will purge in about a second. The hard part is system fill. In my system we are talking about here, you will normally run dry when both the wing selected and header are empty, but the other tank and fuel line to the transfer pump are full. Switch tanks, and you fill a couple feet of fuel line in a second or so, then start raising the fuel level in the header. An inch at the bottom of my header tank will be about 10 in^3, or about five more seconds, then Ross's pump will have to prime, fill another 3 feet, then purge the fuel rail. I bet it will take around 10 seconds, and that will feel like an eternity with the engine windmilling.

    I am sure Ross will have some feedback too.

    Billski
     
  17. Dec 19, 2018 #77

    rv6ejguy

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    I've never come close to running a tank dry in my 40 year flying experience so I can't give you first hand experience on how long it takes with our EFI.

    If you plumb the engine as we recommend, there will only be a few CCs of air trapped in the injectors and -3 feed lines once the pump re-primes and flushes the air out of the main lines and fuel block through the return line. That would probably take 4-5 seconds. With a header tank running dry, it would take longer to fill that up enough to start feeding the high pressure pumps again, maybe 10-15 seconds and another 5 to purge the air from the injectors and lines. This is why you never want to run an EFI setup dry and there is no reason to if you're paying attention.
     
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  18. Dec 19, 2018 #78

    wsimpso1

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    I ran one dry by accident during the downhill run from altitude, flying fast and with the power pulled back, the engine only slowed a little. Power came back almost quicker than I could apply carb heat, hit the standby pump, and switch tanks. Pilot wife had to ask what I had just done, it was over before she changed focus.

    The other time I ran a tank dry on that same Cherokee, I was handling an emergency that turned out to be the float came off the gauge arm and was at best range airspeed. Ran the other tank dry on purpose driving on towards flatter land before switching back to the "empty one". The engine was windmilling much slower than in the other case. We lost less than 200 feet, so it could not have been more than 10-15 seconds, but it felt like forever windmilling in the soup.

    The speed the engine and mechanical pump are turning makes a difference!

    Billski
     
  19. Dec 19, 2018 #79

    TFF

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    Do the EFIs have a fuel totalizator built in? Will not tell how much is in a tank, but they are very accurate for how much you used. As for starting, people flying Mooney Es or Fs are flying the worst hot starting plane ever; they can't comprehend a plane that starts easy hot.
     
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  20. Dec 19, 2018 #80

    rv6ejguy

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    It's outside of the scope of the ECU to have a totalizer function but we feed fuel flow info to the engine monitor so it can do this. You don't need 1 or 2 mechanical flow transducers and their associated plumbing any more. One wire hookup from ECU to glass.

    As for EFI on Lyconentals, you just need to change your mindset over to your EFI car. It's starts pretty much the same cold or hot.
     

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