I just finished my gravity fuel flow testing on my SS7. It was per the EAA recommended procedure: gravity only, engine off, at various angles, flow measured from the fuel line disconnected right at the Rotax 912s carburetors. Results as follows:
  • Level flight attitude-5.8 gph total combined flow at both carbs with 1/4 tank fuel in both wing tanks. EAA (FAA) recommends 125% of maximum T/O fuel consumption for systems with a fuel pump (Rotax has a mechanical fuel pump and T/O fuel consumtion is 7.1 gph). My flow rate is 82% of 7.1 gph so it does not meet the standard. I do not have any auxiliary electric pump.
  • 10 degrees nose down attitude-3.1 gph flow with 1/4 tank fuel in both wing tanks. EAA (FAA) recommends at least 25% of T/O consumption. My flow rate is 44% so it easily exceeds the standard.
  • I could not do the 25 degrees nose up attitude because at that angle I got zero flow with only 1/4 tank fuel. The wing pickup port was uncovered and the header tank is too low to provide any head. I am guessing I would need at least 1/3 or more fuel in the tanks to get any flow in this extreme nose up angle. I ran out of fuel to pour in so will maybe do this test later on.
What do you guys think about my results so far? I am somewhat concerned about missing the recommendations for level flight, but feel that with the engine fuel pump turning I will have plenty of flow, plus the effect of ram pressure in the tank cap vents. How many of you even bother with this test?

My fuel system is built totally by the build manual with no deviations other than the addition of a Dynon fuel flow sensor (inline with straight fittings in and out). This sensor is generously sized for this flow rate.

Jim