Replies to This Discussion

Permalink Reply by Tracy Buttles on March 17, 2011 at 9:40pm

what type of engine do you plan to run?

i have installed a couple 914 and just feed the return back into the main line

 i did install it into one tank and found that the 914 retuns much more than it uses , over filled the tank faster that it could cross feed to the other tank to maintain level

 

Tracy

 

 

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Permalink Reply by Kevin Bowman on March 18, 2011 at 6:32am

I'm not sure on what engine I'll be going with yet, I'm leaning towards the Jab. 3300 but I have been looking at the Viking (Honda) which is fuel injection and needs a return to the tanks. It will be 3 or 4 months before I decide on an engine, but I'm ready to rivet the top skin on my right wing, so I thought I would get some ideas on what others were doing and if they did run a return line, how they ran it. It looks like the easiest way is to run it along the third rib, drill a hole in the rear channel and run it along the channel to the end of the trailing edge. I have the long range tanks so I won't be able to run it behind the tank. thanks for the reply. Kevin   

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Permalink Reply by joshua knowles on March 21, 2011 at 8:30am

Hi Tracy,

 

just saw this discussion, and thought i would join as i am having some of the same questions..  do you remember if the tanks in my wings have any fittings for a return? i can really see in there,  if so, i may just use one and run my return back into the tank.  I am told he LOM pumps 16 Gal per hour thru its positive displacement pump and thus returns about 6Gal per hour.. which i think  should balance ok.

 otherwise do you know what the piece of hardware is called that i can use if i cut a hole int he side of one inboard tank and put another line in?  i am a bit afraid of putting the return to the mainline incase i get some air in the line.. it may not bleed out.. ust circulate.    this this is a valid fear?

 

josh

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Permalink Reply by Henri Luyckx on March 22, 2011 at 12:45pm

I plan to install a BMW 1100 motorcycle engine, wich has fuel injection, in my 701. Both wing tanks wil feed into a small bleeder tank (5 to 10l) to wich also the return line is connected. So no long fuel line back to one of the wing tanks and it can be added later on. A simple float activated switch can give an extra alarm if the level in the bleeder tank starts going down. Not for people who do not like fuel tanks in the fuselage.

Henri

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Permalink Reply by joshua knowles on March 24, 2011 at 12:00am

HI Henri, 

 i was thinking of 2 options for my return,  either return it into my main fuel supply line just forward of my eletric fuel pump,  or plumbing it all the way back to the tank.   the only reason i would send it back to the tank is to purge any air that might get int here..  your idea of a header tank would not really purge any air would it?  or does it have a breather?  if it had a breather wouldnt it over fill being filled by the pump?  and if it was sealed would you not be afraid of air being stuck in there?  i am sure you have thought thru all the situations, but if your system works, i may skip the tank and replumb my return into the my main fuel line..

 

 

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Permalink Reply by Ken Ryan on March 24, 2011 at 10:16am

It is my understanding that the primary reason to return fuel to a TANK (rather than the fuel line) is to avoid excessive heat build up in the fuel, which could cause vapor lock, accompanied by a deafening silence.

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Permalink Reply by joshua knowles on March 24, 2011 at 10:49am

good point..   but i think that would only apply to mono rails, or injector systems that had a return from after the high pressure injection pump...  my injection pup has the return between  the machanical positive displacment pump and the high pressure injection pump.  so the fuel has not even gotten to a hot part of the engine..  unless the injector pump is using the fuel to cool the pump as well...    josh

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Permalink Reply by Henri Luyckx on March 27, 2011 at 1:31pm

I had the recommendation to use a tank for the same reason that Ken Ryan explained. I never got an explanation for the heating up of the fuel. Could it be the compression of the fuel (pump delivers 3 bar in the case of the BMW)  rather than the fuel being in contact with hot parts? I also understood that the pump is indeed cooled by the fuel. I will certainly make a test set up of the engine and whole fuel system before putting it in the plane.

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