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Thread: Engine starving for fuel

  1. #41
    Doug Budd's Avatar
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    Thank you all for all your ideas to help me out.


    Sent from my iPhone using SuperCub.Org
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  2. #42
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    What does wot mean?
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  3. #43
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    wide open throttle
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  4. #44
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    Ah yup, that makes sense ����*✈️��
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  5. #45

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    Increase the size of the fuel lines by 125%.

  6. #46
    Doug Budd's Avatar
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    Quote Originally Posted by Joe McMillen View Post
    Increase the size of the fuel lines by 125%.

    Wasnít the fuel lines. I didnít have covers on the gooseneck fuel caps and it was letting dust get in the tanks and plugging up the filter. When I would land it would back flush the filter and run ok for awhile. I put cover on the gas caps and a quick drain in front of the filter to sump it. No problems now
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  7. #47

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    About 7 days to final inspection on my Experimental Super Cub, with a Titan IO-370, with electronic mags. Checked gravity fuel flow in a 3 point attitude at the inlet of the Aeromotive Silver Hawk, and got 17 gal per hour, from both tanks. Have read where it should be a certain amount above highest consumption, which I suppose would be about 15 or so an hour. Does this sound like the correct flow. Using 3/8 fuel lines. Thanks

  8. #48
    skywagon8a's Avatar
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    Quote Originally Posted by planenuts View Post
    About 7 days to final inspection on my Experimental Super Cub, with a Titan IO-370, with electronic mags. Checked gravity fuel flow in a 3 point attitude at the inlet of the Aeromotive Silver Hawk, and got 17 gal per hour, from both tanks. Have read where it should be a certain amount above highest consumption, which I suppose would be about 15 or so an hour. Does this sound like the correct flow. Using 3/8 fuel lines. Thanks
    Sounds to be too low. Do you have the pressurized fuel cap vents? That will help.

    This is the FAA requirement for certified airplanes:
    CAR 3
    3.434 Fuel flow rate for gravity feed systems. The fuel flow rate for gravity feed systems (main and reserve supply) shall be 1.2pounds per hour for each take-off horsepower or 150 percent of the actual take-off fuel consumption of the engine, whichever is greater.

    3.435 Fuel flow rate for pump systems. The fuel flow rate for pump systems (main and reserve supply) shall be 0.9 pound per hour for each take-off horsepower or 125 percent of the actual take-off fuel consumption of the engine, whichever is greater. This flow rate shall be applicable to both the primary engine-driven pump and the emergency pumps and shall be available when the pump is running at the speed at which it would normally be operating during take-off. In the case of hand-operated pumps, this speed shall be considered to be not more than 60 complete cycles (120 single strokes) per minute.
    N1PA

  9. #49

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    Given that the Silver Hawk is an injection servo, and that this airplane probably has 2 fuel pumps, wouldn't the required test be with a single pump running rather than a gravity feed test? If both pumps fail the engine is going to quit no matter how fast the gravity feed.

    Just asking.

  10. #50
    skywagon8a's Avatar
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    Quote Originally Posted by skywagon8a View Post
    3.435 Fuel flow rate for pump systems. The fuel flow rate for pump systems (main and reserve supply) shall be 0.9 pound per hour for each take-off horsepower or 125 percent of the actual take-off fuel consumption of the engine, whichever is greater. This flow rate shall be applicable to both the primary engine-driven pump and the emergency pumps and shall be available when the pump is running at the speed at which it would normally be operating during take-off. In the case of hand-operated pumps, this speed shall be considered to be not more than 60 complete cycles (120 single strokes) per minute.
    Quote Originally Posted by frequent_flyer View Post
    Given that the Silver Hawk is an injection servo, and that this airplane probably has 2 fuel pumps, wouldn't the required test be with a single pump running rather than a gravity feed test? If both pumps fail the engine is going to quit no matter how fast the gravity feed.

    Just asking.
    If his engine is producing 195 hp(?), he should be flowing about 29-30 gph with the aux pump running. 195*0.9=175.5/6=29.25 gph.
    N1PA

  11. #51
    55-PA18A's Avatar
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    Interesting topic, and should be in its own thread, not in one about intermittant fuel starvation.

  12. #52
    Gordon Misch's Avatar
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    It's interesting that the Part 23 fuel flow requirement is slightly less stringent than CAR 3, which is quoted in #48.

    Here is 23.955
    "(b) Gravity systems. The fuel flow ratefor gravity systems (main and reservesupply) must be 150 percent of thetakeoff fuel consumption of the engine.(c) Pump systems. The fuel flow ratefor each pump system (main and reserve supply) for each reciprocating engine must be 125 percent of the fuelflow required by the engine at the maximum takeoff power approved underthis part."

    https://www.govinfo.gov/content/pkg/...ol1-part23.pdf

    Edit: FWIW, data from my -12:
    Conditions:
    Fuel lines are 3/8” aluminum tubing.
    Right-hand tank only, because it has the longest run of fuel line and no forward outlet.
    Approx 5 gallons of fuel in the tank
    Pitch angle is 11 deg up from 3-point attitude, which corresponds to full power, no-flaps climb at 40 MPH.
    3-point attitude is 11.5 deg up from level HRL. Therefore, total pitch up angle of the HRL is 22.5 deg for this fuel flow test.
    Fuel line disconnected at the carburetor and flowed into a 250 ml graduated cylinder.
    Flow start-up for each test is not instantaneous - it takes approx 1 second to fully develop due to inertia of the fuel column in the line. Therefore 0.5 second is subtracted from each flow time.

    Data:
    Trial #
    Volume (ml)
    Measured Time (sec)
    Adjusted Time (sec)
    Adjusted ml/sec
    Adjusted gal/hr*
    1
    218
    7.6
    7.1
    30.7
    29.1
    2
    219
    8.9
    8.4
    26.1
    24.8
    3
    215
    9.1
    8.6
    25.0
    23.8
    4
    210
    7.7
    7.2
    29.2
    27.8
    Average
    26.4
    Last edited by Gordon Misch; 07-29-2021 at 02:39 PM.
    Gordon

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  13. #53

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    Quote Originally Posted by skywagon8a View Post
    Sounds to be too low. Do you have the pressurized fuel cap vents? That will help.

    This is the FAA requirement for certified airplanes:
    CAR 3
    3.434 Fuel flow rate for gravity feed systems. The fuel flow rate for gravity feed systems (main and reserve supply) shall be 1.2pounds per hour for each take-off horsepower or 150 percent of the actual take-off fuel consumption of the engine, whichever is greater.

    3.435 Fuel flow rate for pump systems. The fuel flow rate for pump systems (main and reserve supply) shall be 0.9 pound per hour for each take-off horsepower or 125 percent of the actual take-off fuel consumption of the engine, whichever is greater. This flow rate shall be applicable to both the primary engine-driven pump and the emergency pumps and shall be available when the pump is running at the speed at which it would normally be operating during take-off. In the case of hand-operated pumps, this speed shall be considered to be not more than 60 complete cycles (120 single strokes) per minute.
    Does look like mine is low, looks like about 22.5 or higher is needed. I do have the Altee caps with forward snorkels. Will disconnect from the fuel selector outlet and see what I get there. Note the engine runs fine with no fuel pump on, but will not turn up full static RPM. Click image for larger version. 

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    Thanks for the reply

  14. #54
    skywagon8a's Avatar
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    Quote Originally Posted by planenuts View Post
    Note the engine runs fine with no fuel pump on, but will not turn up full static RPM. Click image for larger version. 

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    Thanks for the reply
    Is that prop a constant speed or ground adjustable? Adjust the low pitch stop to a lower blade angle for more static rpm. If it has a governor, back out the high rpm stop screw for more rpm.
    Did you run your aux fuel pump to get your flow rate? That should flow more fuel.
    N1PA

  15. #55

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    Quote Originally Posted by planenuts View Post
    Note the engine runs fine with no fuel pump on, but will not turn up full static RPM.
    What is the fuel pump configuration on this airplane? I would expect an engine driven mechanical pump and an electric aux pump. What is the fuel pressure with no pump running?

  16. #56
    Grant's Avatar
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    make sure you have the correct pump on the engine....I learned that the hard way.

  17. #57

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    It is a ground adjustable Whirlwind prop, set at 15 degrees. Fuel flow was gravity only no pump. The engine does have an electric pump, and mechanical. The mechanical was shipped on the new engine. Aeromotive suggest in trouble shooting that, if you can not increase RPMs over a certain level, it may be oil in the air chamber. Some what typical on an updraft set up for Lycoming type engines.
    Thanks for all the help, will see what we find out
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  18. #58
    skywagon8a's Avatar
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    Quote Originally Posted by planenuts View Post
    Fuel flow was gravity only no pump.
    Do the flow test again with the electric pump running. You will likely be happy with the results.
    Also lower the prop setting.
    N1PA

  19. #59

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    Did the fuel flow yesterday with the boost pump on, it nearly doubled the flow, about 31 gal an hour. That meets all the requirements mentioned. Still concerned if wot and fuel pump failed. Will keep working on getting the gravity flow up, but for now, the boost pump did the job.
    Really appreciate the advise and comments

  20. #60
    skywagon8a's Avatar
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    Quote Originally Posted by planenuts View Post
    Did the fuel flow yesterday with the boost pump on, it nearly doubled the flow, about 31 gal an hour. That meets all the requirements mentioned. Still concerned if wot and fuel pump failed. Will keep working on getting the gravity flow up, but for now, the boost pump did the job.
    Really appreciate the advise and comments
    If the fuel pump fails at wot, you just turn on the boost pump. That is what it is for.
    Do not be concerned with the gravity flow. You have a "pumped" system and do meet those requirements.

    Enjoy your new Cub.

    I have the same prop on my IO-360 Cub. It pulls like a work horse. You will be happy.
    N1PA

  21. #61

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    Quote Originally Posted by planenuts View Post
    Still concerned if wot and fuel pump failed.
    You have 2 fuel pumps don't you. As I said earlier the engine will stop if neither is working. A carb will work on 0.5 psi or less but the injection servo needs at least 20 psi.

    If you are concerned about the engine driven pump you should run a test of its delivery. I don't know a standard way to do that but, unless I could find one, I'd pull the top plugs and crank the engine with the starter with fuel line disconnected at the fuel servo.

  22. #62
    BC12D-4-85's Avatar
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    If concerned about fuel flow and pressure install a means to monitor. Fuel pressure/flow rate gauge or warning light that illuminates below a specified pressure. And practice pushing the secondary electric boost pump on switch so it becomes a routine if the engine burps.

    Gary

  23. #63

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    Quote Originally Posted by skywagon8a View Post
    This should get your attention. Can you disconnect the fuel line from the carburetor, place it in a 5 gallon gas can and fill the can in 15 minutes or less? That would be 20 gallons per hour. 1/4" for a fuel line is likely way too small. Generally you will find 3/8" as a minimum.
    The Taylorcraft requires a 5/16" ID fuel lines per the STC for the bigger engine than an a-65 so I use -6 for everything and when I put on the lycoming, I am using a -8. Tim

  24. #64

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    I have wing tanks, but with 4 check valves(2 pumps), fuel flow sensor, screen and filter, I don't expect much pure gravity flow. I do have a pressure gauge, it predicted a slowiy plugging filter(new tanks). My FAA guy was happy with an electric-only flow test. The worksheet he used seems to require an electric pump.
    The next step is to consider putting the aux in parallel with the engine pump, in case one pump fails plugged. But what if a pump fails open? Then you need external check valves. I've seen pictures of setups than must weigh 10 lbs. Haven't gone down that rabbit hole.
    What's a go-around?

  25. #65

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    Quote Originally Posted by Skywalker View Post
    I have wing tanks, but with 4 check valves(2 pumps), fuel flow sensor, screen and filter, I don't expect much pure gravity flow. I do have a pressure gauge, it predicted a slowiy plugging filter(new tanks). My FAA guy was happy with an electric-only flow test. The worksheet he used seems to require an electric pump.
    The next step is to consider putting the aux in parallel with the engine pump, in case one pump fails plugged. But what if a pump fails open? Then you need external check valves. I've seen pictures of setups than must weigh 10 lbs. Haven't gone down that rabbit hole.
    Way too complicated, but if that is what you want, run with it. good luck, Tim
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  26. #66

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    It's not what I want, and I don't have it. Just pointing out that with the typical 2 pumps in series you may not get much pure gravity flow. You have to take comfort in redundancy, not the simplicity of gravity.

    (most pumps have and input and output check valves built in)
    What's a go-around?

  27. #67

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    with wing tanks and a header tank, why a pump at all?

  28. #68

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    Quote Originally Posted by astjp2 View Post
    with wing tanks and a header tank, why a pump at all?
    Because injected engines won't run on gravity feed.

  29. #69
    wireweinie's Avatar
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    Quote Originally Posted by Skywalker View Post
    It's not what I want, and I don't have it. Just pointing out that with the typical 2 pumps in series you may not get much pure gravity flow. You have to take comfort in redundancy, not the simplicity of gravity.

    (most pumps have and input and output check valves built in)
    Why would you put the pumps in series?

    Web
    Life's tough . . . wear a cup.

  30. #70
    skywagon8a's Avatar
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    Quote Originally Posted by wireweinie View Post
    Why would you put the pumps in series?

    Web
    Both of the gear pumps in my injected Cub are in series. Both the electric and engine driven pumps have built in bypasses should there be a failure or clogging of the basic pump. There are no additional check valves as they are not needed.
    N1PA
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  31. #71

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    That's a good question, Web. On carbureted engines the pumps are basically two check valves with a variable volume chamber in between. The odds of both valves failing are slim. I would just run them in parallel, the odds of a pump failing open are slim. But no one seems to do this without big honking check valves you can barely blow through.
    I could tear out both pumps and go gravity, but having spotted a slowly plugging filter with a pumped and sensored system made me a fan.
    What's a go-around?

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