Fuel return line design obstacle

CH.73-00 of the Rotax IM clearly depicts the fuel return line routing to the top of a fuel tank. I turn on my electric fuel boost pump and remove the fuel cap, and can see fuel is entering the top of the tank from the return line. The cycling of the fuel is the reason the return line is required. For those of us flying with fuel lines routing anywhere else, such as to the bottom of a tank, or into a fuel drain line, how can one be certain the fuel is actually moving from the engine compartment back into a fuel tank?

I looked carefully at the Rotax IM 73-00 and do not find anything that "clearly" depicts the return line going into the top of a fuel tank. It just shows the return line going into the side of a fuel tank (yes, it appears to be near the top), but nothing is stated that says it must be at the top. As I said in my post above, Kitfox has been specifying the return line into the header tank, which is about 2.5 feet below the top of the fuel tanks in the wings. This has never been a problem.

Jim Isaacs wrote:

CH.73-00 of the Rotax IM clearly depicts the fuel return line routing to the top of a fuel tank. I turn on my electric fuel boost pump and remove the fuel cap, and can see fuel is entering the top of the tank from the return line. The cycling of the fuel is the reason the return line is required. For those of us flying with fuel lines routing anywhere else, such as to the bottom of a tank, or into a fuel drain line, how can one be certain the fuel is actually moving from the engine compartment back into a fuel tank?

Hi Jim,

I would agree that returning the fuel to the top/near top of the tank is preferable BUT not essential. It's important to keep the potential for fuel leaks to a minimum, so wherever practical all tank spigots should be at/near the top of the tank. Clearly the sump must be at the bottom of the tank and many would assume the fuel to engine also but again this need not be the case.

Seeing that the return is "working" is nice but again not essential - I think that it can be assumed to work, as long as it has been correctly installed  (which should at some point include a blow through). Sure assumptions can be false but as long as the pump(s) are operating correctly they will be delivering sufficient pressure to overcome the head in most small aircraft fuel tanks.

My return fuel is to a header tank (no external fill point) so I have no ongoing way of knowing that my return is working. Fortunately I can isolate the header - collect return fuel, then drain & measure the contents which then gives me a return/flight hour performance.

On all the planes I work on I see many different return line installation points. Some are in the gascolator, some in the supply fuel hose out of the engine compartment, into a header tank and then some into either a wing fuel tank or another fuel tank location. So they all seem to work.Most of these are all aircraft Mfg placed locations. 

"...........they all seem to work."

Yeh! one very forgiving engine ?