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Thread: FI operation

  1. #1
    stewartb's Avatar
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    FI operation

    How many of you fuel injected Cub guys use the boost pump for takeoff? Landing? Both? This Lycoming style FI is new to me, as is the recommendation to boost for takeoff and landing ops.

  2. #2
    tedwaltman1's Avatar
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    I have Airflow Performance injection unit. Don't use boost pump for either takeoff or landing...but the switch is right in front of me if I needed it...
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  3. #3
    stewartb's Avatar
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    API recommends the pump on for landing and takeoff. I confirmed it with Kyle. It may be more important for tightly cowled planes with higher under cowl temps. The purpose if the pump on is to increase fuel line pressure to reduce vapor lock potential. I was surprised to read it. Thanks for the comment.
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    tedwaltman1's Avatar
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    Thanks for the follow up note. Guess I'll change my operating procedures.

  5. #5
    stewartb's Avatar
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    My first take off? I forgot. My first landing? I remembered. The second takeoff? I remembered. Second landing? Forgot. All results were the same. I need to groove a new habit, I guess.
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  6. #6
    mvivion's Avatar
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    Stewart, another reason for electric pump on during critical transitions is so that you’ll have continued full fuel pressure if the mechanical, engine driven pump were to fail. Most fuel injected engines won’t run (at least not at full power) without pump pressure.

    MTV
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  7. #7
    BC12D-4-85's Avatar
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    Maybe connect a small green LED light to the boost pump-on circuit for verification. Look for the light's confirmation at T/O and landing. Some glass engine monitors activate a warning when fuel system pressure falls. Gives a few to activate the boost pump.

    Gary
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  8. #8
    stewartb's Avatar
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    That's a good idea. Green could work. So could "fuel" in my normal mnemonic checklist, but first flights are full of distractions. Normal ops will be more.... normal.

  9. #9

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    Turning on pump was part of run up/ takeoff in low wing Pipers & Mooneys I have flown. Just add it to the pre takeoff list.

    Sent from my SAMSUNG-SM-G930A using SuperCub.Org mobile app

  10. #10
    stewartb's Avatar
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    The part of my manual that caught my attention was the use the electric pump to pressurize the fuel lines to help prevent the fuel from boiling and creating vapor problems. I get the redundant pump part of the practice but the fuel line pressure to prevent vaporization interested me. I’m not sure it applies to a Cub as much as other go-fast planes. I was looking for comments from guys with FI Cubs to see what they do and maybe to hear if they’ve had vapor problems in flight or during taxi to parking. Or any other heat related FI problems.

  11. #11
    skywagon8a's Avatar
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    My Cub has a stock Lycoming FI system. The only time that there is ever any indication of vapor in the lines is on a very HOT day with a warm engine at idle power during long ground operations. This is a very rare occurrence. Only then do I use the aux pump to maintain pressure. Why doesn't the engine pump overcome the vapor in the lines? Perhaps it is because the engine pump is operating in a very low volume/pressure mode at the time? Once the power/rpm is increased the fuel flow is increased enough to eliminate the air bubbles.

    The Continental system continuously flows fuel back to the tank thus keeping any vapor purged. The Lycoming system does not purge the fuel so any small air bubbles can become trapped in the lines until the flow is greatly increased.

    In the Cub with the fuel tank above the engine there is always a head of pressure at the inlet to the engine driven pump. So there should never be an opportunity for an air bubble to form in the lines just as in a carburetor system. In the event of an engine pump failure, turning on the aux pump will just increase the pressure as required. IF this was a low winged airplane with the fuel tank below the engine and the engine pump failed, the fuel line could fill with air which would need to be replaced with fuel and then pressurized. All of this takes time. Therefor it is more critical to have the aux pump running during ground proximity operations when time is of the essence.

    It does no harm to run the aux pump for take off and landings. If it were to be suddenly needed for any reason it would automatically take over eliminating one more thing for the now otherwise occupied pilot to think of. Just turn it off at a safe altitude as there is no need to wear it out needlessly. Make it part of your checklist.
    N1PA
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  12. #12
    stewartb's Avatar
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    Skywagon tells a story but it may not be the whole story. I defied the manual recommendations and placed the boost pump on the firewall on the engine side. API wants it inside the cabin to keep it away from heat. I do have an isolation box with a blast tube to cool it plus a shroud and blast tube on the mechanical pump but I still need to be prepared to manage heat issues. Heck, every installation is different and some will experience more heat issues than others. Case in point, Ted has a purge valve. I don't. Choices we make.

    How many FI guys have a fuel pressure gauge? How many don't? Does seeing fuel pressure help with hot starts, or is the hot start problem downstream of the pressure sender, like at the flow divider and injector lines?
    Last edited by stewartb; 06-15-2018 at 12:45 PM.
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  13. #13
    skywagon8a's Avatar
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    Yes stewart the story could fill a book. My boost pump is in the cockpit behind/outboard of the fuel selector. Your choice of location is also suitable with the baffle and blast tube. The Piper Cherokee and the Cessna 185 both have the aux pump on the engine side of the firewall in an isolation box with an air blast.

    I have a fuel pressure gauge which measures pump output pressure. An alternate pick up location is on the flow divider where there is a port for this purpose. This will read metered pressure. The use of either or both is up to you. The metered pressure is variable in relation to the fuel flow. The metered pressure gauge can be calibrated in psi or gals/lbs/liters per hour. The flow divider pickup point will give you more information as to the fuel situation during hot start circumstances. The optimal installation would be two pressure gauges, one for each location though not necessary.

    Hot starts with a Lycoming FI system has two points of view. There are those who swear at it and others who just yawn. When the hot engine is shut down with the mixture there is remaining fuel between the fuel servo and the discharge nozzles. The heat from the engine expands this fuel squirting it into the cylinder heads. Thus priming the cylinders for the next start. When this fuel is heated it also forms air bubbles in the lines. IF you move the mixture control off of idle cutoff before the next start you will flood (mixture too rich) the engine. The trick is to crack the throttle, turn on the boost pump (optional with a high wing fuel tank), crank the engine. Once it starts firing modulate the mixture until the rpm is up to running speed. If the mixture is placed in full rich too soon the engine will flood from too rich a mixture. Treat the mixture control as a hand controlled fuel metering valve. If the aux pump is not used and there is a possibility that an air bubble has formed prior to the engine pump, after you get the engine started the pump could pick up that air bubble which could then cause the engine to quit. This will be followed by some strong words aimed at me for leading you astray. If after starting the engine it starts to die, briefly turn on the aux pump. Don't leave it on as you will flood the engine. Your particular airplane will have it's own variation of this method.
    N1PA
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  14. #14
    www.SkupTech.com mike mcs repair's Avatar
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    engine pump is a diaphragm pump...

    electric is a rotary pump, thats probably where the vapor difference/issue is?????

  15. #15
    tedwaltman1's Avatar
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    Here's a picture of my fuel pressure pick up sending unit
    FuelPressureWeb.jpg
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  16. #16

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    Injected engines are all I ever flew and always used boost pump for take-off, landing and switching tanks. On my SQ2 I only use to prime for starting but it’s there if mechanical pump fails. The fuel pressure gauge indicates more pressure when both pumps are on. I have never had a problem hot starting the cub even on 90* plus days however if it doesn’t start first try you may need to purge the fuel lines. Full rich full throttle mags off boost pump on than set full throttle mixture off mags on start, quick hand work to mixture half in throttle to idle.
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  17. #17
    skywagon8a's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    engine pump is a diaphragm pump...

    electric is a rotary pump, thats probably where the vapor difference/issue is?????
    I don't think that has any bearing on it mike. Both pumps on my Cub are gear pumps (IO-360-B1D). I think the differences has to do with the relationship of the fuel tank to the engine pump. In the airplane that my engine came from the engine was about 6 feet vertically above the fuel tank with a 10-12 foot long fuel line. On hot days when idling for long periods it would surge, run rough and sometimes quit. Turning on the boost pump which was mounted on top of the gas tank pressurized the fuel line to the engine pump inlet. This indicated that the ability of the engine pump to draw at that height and at low rpm was limited.

    Taking that engine and putting it in my Cub with the tank above the engine pump I never need to run the aux pump under those same conditions.
    N1PA

  18. #18
    cgoldy's Avatar
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    Stupid question alert.

    So, if preparing for a hot start, can you have mixture off, throttle off, and run the pumps to clear the lines and cool the fuel. Would you risk flooding the system by building more pressure before the start?
    Back Country O-375 wide body extended wing cub

  19. #19
    PerryB's Avatar
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    My favorite hot start procedure for an injected Lyc. is; Mixture lean (ICO), throttle open, boost pump on. Be ready for it to start and to quickly pull the throttle and push the mixture.
    After Monday and Tuesday, even the calendar says WTF !

  20. #20
    skywagon8a's Avatar
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    Quote Originally Posted by cgoldy View Post
    Stupid question alert.

    So, if preparing for a hot start, can you have mixture off, throttle off, and run the pumps to clear the lines and cool the fuel. Would you risk flooding the system by building more pressure before the start?
    As long as you keep the mixture in idle cut off there will be no fuel flow to the injectors, therefor no flooding. You will just have a clean charge of fuel standing by at the mixture valve ready to go.
    N1PA

  21. #21
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by skywagon8a View Post
    I don't think that has any bearing on it mike...
    not sure how this diaphragm pump works, if it has a SUCK half of stroke, then a push...

    but to separate air from a liquid you put it in a vacuum..... it bubbles to the surface... that what I do when degassing rubber to pour into a mold.....

  22. #22
    skywagon8a's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    not sure how this diaphragm pump works, if it has a SUCK half of stroke, then a push...

    but to separate air from a liquid you put it in a vacuum..... it bubbles to the surface... that what I do when degassing rubber to pour into a mold.....
    I agree with you mike, It just appears and acts as though air gets in the line between the tank and engine. The weight of the fuel and an idling pump just can't draw that height very well. As you know pumps can push a liquid a lot higher than they can draw it.
    N1PA

  23. #23

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    I am most familiar with the Comanche IJ aircraft, both twins and singles. Both manuals require the fuel pump on for departure and landing. Fuel injected engines do not run with a mechanical pump failures. Both the twins and single Comanches located the electric pump under the passenger floor board feet. Nice and cool there. So personally I would practice tried and true takeoff and landing procedures for Lycoming fuel injected piper Comanches . In a higher risk departure why would you not want the fuel pump on? Or in a long power on one way landing with no go around landing? A load side indicator light would be an addition to any electric pump configuration. I have left the electric pump on more than once even though its part of the cleanup for cruise checklist. Regarding hot starts, go to a point you are certain of, flood the engine and then start-flood, Mixture at cut off, full throttle, spin.(fuel pump off) Works 100% of the time. The IO 720 was notorious for hot starts. Never a problem using this procedure.
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  24. #24
    stewartb's Avatar
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    A good friend with cause to know says electronic ignitions make hot starts/flooded starts a non issue.

    I appreciate the discussion. I’ll pick up a green status light for my boost pump. Can’t hurt. Easy to add. Don’t need permission.
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  25. #25
    skywagon8a's Avatar
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    Quote Originally Posted by stewartb View Post
    A good friend with cause to know says electronic ignitions make hot starts/flooded starts a non issue.
    I found this to be true as well. Of course the pilot can always manage to make it happen. The Pmags make it nearly bullet proof.
    N1PA

  26. #26
    mvivion's Avatar
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    Quote Originally Posted by skywagon8a View Post
    I found this to be true as well. Of course the pilot can always manage to make it happen. The Pmags make it nearly bullet proof.
    Yep, talent and perseverance can overcome nearly any mechanical system......

    MTV
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