To bypass or not to bypass, that's the question!

Hi RW,

I respect your extensive experince & knowledge of Rotax engines, however you are human (I hope) and to to be human is to err from time to time.

I believe you erred in your description of the fuel supply to the carburettors - the  fact that the float bowl is open to atmosphere, suggest that a Rotax 9 (carby) does run on unpressurised fuel .

I agree with your statement & reasons why Rotax have designed the fuel delivery to the float bowl, to be pressurised (wider application).

Your point is valid in that a Rotax, depending on gravity fed fuel, through a failed mechanical pump, may not deliver sufficient fuel to the float bowl for sustained higher power - surely someone has tested this hypothesis???

I would expect the engine to keep running - sufficient to sustain flight? I don't know.

Every Rotax (all low wings) I have flown had a back up pump - I am comfortable with their function & management, so would likly prefer to have one, even in a high wing (fuel tank) - this is habit not science.

You will note that I suggested that a gravity fuel delivery should be tested at reserve fuel capacity (not a full tank), with the aircraft in the climb attitude. The gravity fuel flow at the carburettor will determine fuel availability, to the float bowl, from this an idea of sustained engine power. 

😈

And since I don't want to be a test pilot (at least when I'm not getting paid to be one ;-) ), I will for sure install the elec aux pump.

But that wasn't up for debate anyway. It was about the bypass fuel line and most of you have been in favor of that design, so I will install it accordingly.

Thanks everyone for your contributions to this debate.

Mark