by SonexN76ET » Sat Feb 06, 2016 3:12 pm
I have a fuel return line and a Facet fuel pump on my Aerovee with a Rotec TBI. I would like to make a couple of observations I have from this set up.
With these items in place, if you put the aircraft in a climb attitude without the fuel pump turned on the fuel pressure at the TBI goes way down. In my case in a couple of touch and goes it was enough to have the engine cut out. In a level attitude I measured 12 GPH fuel flow, in a tail low configuration it dropped to 9 GPH and it seemed like I had a momentary greater reduction as the tail was lowered. Sonex has recommended against "burp tubes" with the AeroInjector because they can cause low fuel pressure in a nose high attitude. Also, the Facet fuel pump (when off) does cause some restriction in the fuel flow versus just a straight fuel line.
The concern this causes for me is that with the fuel pump off you can not safely take off, do a touch and go, do steep climbs, go arounds, or slow flight. Operationally, I could keep the fuel pump on when doing these maneuvers but what if the pump fails or I have an electrical failure? I had originally just put the fuel pump on as a precaution against vapor lock. Now it is a critical component and a single point of failure.
I have considered putting a bypass fuel line around the fuel pump with a check valve in an effort to have more fuel pressure to the TBI when the pump is off, but that will complicate the fuel system further. Also, I don't know if that will improve the fuel pressure enough to overcome this issue.
In all honesty I am not exactly sure of the solution or what exactly is causing my troubles. It could be my TBI's fuel pressure regulator being faulty or it could be the combination of fuel pump in line but off and the fuel return line. Rotec says if you do a fuel return line it should have a restricted fitting. Mine goes from 6AN to 4AN. Perhaps that is not enough of a restriction.
So, I do not have any solid answers for you, but I want to point out these important considerations.
Thanks,
Jake
Sonex Tri Gear, Rotax 912 ULS, Sensenich 3 Blade Ground Adjustable Propeller
MGL Velocity EMS, Garmin GTR 200 Comm, GTX 335 ADS B Out Transponder
ILevil AW AHRS & ADS-B In, UAvionix AV20S
200+ hours previously with Aerovee engine
Sarasota, Florida