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I want to share this information about my fuel system, and need opinion . This is the diagram of my fuel system for bmw r1200 engine, Fuel injected.
Basically, is the wing tanks , with an extra header tank of 1.5 liter, placed behind the pilots seat.
In the base of this header meets 4 connections: 2 for each fuel tank and one for fuel efi pump and other for return .
In the top of the header, i placed one ventilation , shared with tee connector to the two tanks vents with banjo bolt , near the fill cap.see illustrations.
The idea is that with communicating vessels principle, the header tank will be filled up to the wings tanks level, wich it seem to be sufficient.
I placed in the base of the header tank, an alarm of central tank. CTLF for next.
I was really happy with the system , and i was flown about 70 hours on it.
But now that i am making longer and longer flights, i had the following problem:
When i stay in the same cruise position , for about 25 minutes, the CTLF appeared , first time in 70 hours of flying! It seem to be this problem only when I STAY in the same flight attitude.
If i made two 360 degree turn , the CTLF dissapear, up to the next 20 minutes of flight.
I can see on the vent lines a little SIPHONING of fuel . Maybe this siphoning the cause of the low central tank level???
In this previous 70 hours of flying, wich includes flights up to 2 hours , never appeared the CTLF!!
the first time appeared when i filled the tanks near full for a 4 hours flight , and in the 25 minutes , bip bip bip!!! CTLF
Thanks For info
Putting Facet fuel pumps to refill the header tank will create a new series of problems. How will you control them? If you leave them both on they will be pumping more fuel than the engine pumps needs and you will end up filling the header header tank - and pumping fuel back through the vent lines to the wing tanks.
thanks for help. answerng this parraph , if facet fuel pumps overfill the header tank, it returns over the vent lines , in the least resistance way, to the main tanks, no mather this , because the wing tanks have their own vent lines. see ilustrations.
maybe , this would be the less drastic mod , because i havent to touch anythig in fuel routing. only add two facet pumps , in parallel with the check valves, and activate them ? the fuel will go trought the vent lines to the tanks
imagine this situation. the diagram above is the suposing sistem directly to wing tank.
but , i added in diagram , a wall and a pipe for transfer fuel between chambers , adding the dampening effect.
i want to show this , because the actual system i have(ilustrated below) is the analogue system , With ONE clear difference. the ventilation an equalisation in air pressures in the abobe diagram is instantaneus, and the fuel flow by the diference on level only(communicating vessels principle)
my second system , have the disadvantage of vent lines too small in my opinion, and in practice , are not straight tubes , all ve t tubes have little ondulations , witch contributes to air locking.
sais this , do you agree with me , that if i put larger vent tubes , and make straight , ensuring the all time all condition venting , will solucionate the problem?
next i will post videos in flight of this problem , and try to record the vent tubes (are transparent ptpfe teflon made) for see the air locking , and relation with alarm sound!
Hi Rubens, somewhere in the comments someone mentioned the fuel getting to warm being pumped around from an to the header tank. Your header tank is rather small. I know that it is recommended to have a header tank (when the return fuel is going back to that tank) of minimum 5 liters just to overcome the problem of fuel (and also the fuel pump) getting too hot. By the way I am building (almost finished) a CH701 with a R1100 engine.
thanks for the response!
THANKS FOR ALL RESPONSES: Is was very helpful
I have to sai that i FOUND THE SOLUTION:
The problem was in the vent tubes, wich had both siphoning of fuel , because i was a low poin in both holders.
Now i have the both in correct place, and no siphoning was ocurrs.
i am very interested in your experience with the R1100 in your 701. I am considering using the R1200 I'm my 750 Cruzer.
This fuel system is similar to what I have installed in my 601. Google "Viking mini header tank" for details.
I've rebuilt much of my aircraft after losing an engine in flight, but have not re-flown it yet. In my case, my small header tank is mounted on the floor on the passenger side, in front of the main spar.
Motivation for me was discomfort regarding switching back and forth between left & right tanks as the fuel levels decreased while flying. The defacto solution was never flying with less than roughly half tankfuls, but that is a lot of extra weight to carry all the time. The amount of time needed to restart my previous engine following "running a tank dry" (and more importantly - running the fuel line from the selector valve to the carburetor dry) was longer than I believe that I could have stayed in the air unless I was quite high.
Also, I was unable to make check valves work in this scenario. They were located in the same place as yours are in your diagram. It is possible that my check valves required more "fuel head" pressure than do yours.