Fuel tank plumbing

[cgoldy]

Hi All,

I have to plan for the plumbing of the extra tanks in my Back Country wings. There seems to be two options. Fit two transfer pumps between outboard and in board tanks thus dropping the fuel into the top of the inboard tank where there is a fitting. Or running the outboard tank into the inboard tank rear pick up line via a T. Saving all the complexity of the pumps. Can any one see any problems with these two systems - pros and cons.

CGoldy

 

[DW]

Just put a check valve between the two tanks and a fill cap for each tank. No need for pumps.

 

[FdxLou]

Not sure you can do that with the headerless fuel system and assuming you run a 180hp motor. You must have ram air vented caps and will need a means of opening and closing the valve between mains and aux tanks....otherwise fuel from the aux tank will overfill the main and it will vent overboard.

Also, with the limited dihedral of a Cub I believe you will always have 2-3 agls in the aux tank using a gravity feed setup. Just my feeling...may only be 1-2 gals.

I have a 4 tank Smith Cub and use Facet transfer pumps....works well, lasts a long time! So far 7 years and 1100+ hrs. I do a lot of long range flying and the pumps always work.

Lou

 

[Steve Pierce]

All the Smith/Turbine/Back Country Cubs I have seen with 4 tanks use the pumps. It is a proven system.

 

[cgoldy]

Why would the inboard overflow. Is because it could get an uneven vent pressure?

And so how do you know when the pump has tranfered all the fuel?

 

[FdxLou]

When you fill the mains and then put fuel in the auxs they will force the fule level up in the mains due to gravity.

My transfer pumps have low pressure switches on them. When they blink I run them for another 3 mins and increase the pitch attitude when possible to get all of the fuel out. Doing that there isn't any left in the aux tanks.

Caution....be sure you have space for the aux fuel...it will fill up the main and pump it out the vent...been there done that!

If you had your aux tanks in the tips (more dihedral) you might get away with a gravity feed system, but you would have to use a pressure cap on the mains and vent the main thru the aux. I did that setup on my RV-6 when we glassed in the tips and made them fuel cells (wet tips). I still leave over 1/2 gal in the tips on the RV when it stops flowing.

Save yourself some grief and don't try to "reinvent the wheel".

G'day!

Lou