Fuel pump power

Charlie

Rotax 912iS comes with 2 fuel pumps. None of them is connected to the aircraft battery. Instead they are connected to the Engine cabling provided with the engine, fusebox and ECU.

Please refer to Rotax 912is Installation Manual.

Hi Maximo, thanks for your response. I just bought a plane with a 912iS and I am not familiar with that engine. I have a friend that has a 914 and one of his two pumps is connected to the battery. So, on my plane, if I turn off the master switch off, will the fuel pumps continue to run inflight? I see that both of my fuel pump circuit breakers are connected to the main DC bus. I looked at the installation manual and it was not clear to me.

Hi Charllie

The injected engine electrical is completely different from the 914.  Follow the installation manual for the 912iS.  Each electrical pump is on its own power supply.  As long as the engine is running they can both work.  If you lose the battery the engine will still run and on an iS.  If you lose the engine generator the fuse box can get its power from the battery, as long as you wire it as required in the installation manual.

Cheers

Charlie: 912iS is very different from 914.

Rotax 912iS has 2 fuel pumps connected to the FuseBox and from there to the 2 ECUs. All these are fed by Generator A (in normal conditions) which is isolated from aircraft loads and battery.  The other generator (B) in normal conditions feeds the aircraft loads and charges the battery.

If the Engine is correctly installed, and running, even if you turn of the master swicth (of the aircraft loads) engine should continue to run and also the fuel pump (depending which is turned on).  

Engine 912iS comes with a wiring harness which connects fuel pumps, ECU, Fuse Box, Engine Sensors, Ignition and Injectors.

Check if your engine is installed according to the 912iS Install manual.

912iS Fuel pumps should not have circuit breakers, they have fuses for protection inside the Rotax Fuse Box.

Maximo, I appreciate your taking the time to answer my questions. Now I understand how it should work, however it doesn't appear that the 912iS install manual was used in the installation of this engine. It is a factory-built plane and I understand that it is the only one that they built using the 912iS. Looking at the circuit breaker panel, the power wire is daisy chained to almost all of the circuit breakers and both of the fuel pump circuit breakers are part of that chain which also includes things like radios, lights, strobes, acc. That is why I was wondering if one of the fuel pumps should be connected to the battery in case I had to turn off the master switch in flight, due to an electrical fire or fault. By the way, the factory is no longer in business, so I can't go to them. I will start the engine and turn off the master switch to see what happens in case I am missing something. Thanks.