Fuel Return Line

Hi Roger

I am aware of the "Flight Design" practice and disagree with it.  Given that we had the lower pressure mechanical pumps up to 2010 one could argue that that idea, returning to the gascolator, was suitable.  This issue gets much worse with the introduction of the Corona pumps after 2010.  (they moved the peak pressure from .4 bar to .5)  There is a much higher risk of problems with winter fuels and vaporization problems when we do this.  

I am happy that there seems to be very few people who complain with those 1800 installations.  It is odd that they never redesigned it with duplex fuel selectors and the ability to run return lines back to tank.  Perhaps there just is no room in the fuel line areas or wing for it.  I don't know how they addressed the injected installations where it is mandatory, perhaps that would be something to look at.  

Cheers

Hi RW,

Hope you're staying warm. 😉

FD runs the 912iS fuel return into the header tank in the luggage compartment now. It was only in the carb models they routed it to the gascolator.

No matter iS or carby, the principal is the same - only the pressures differ.

In the unlikely event that I own an FD, fitted with a fuel return to gascolator, I would be investigated a better way ie return to substantial volume header or fuel tank😈

Hi Sean,

There's a huge difference in quantity of fuel return. The iS recirculates a lot more fuel.

The fuel return on the type 914 is much more than the 912.  On the injected models this is much higher.  This is necessary as the fuel is heated when compressed and circulated within the fuel lines, that heat needs to be removed before it is picked up by the engine.  

While the volume varies by engine and power settings if we look at burn in the cruise area, say between 4.5 to 7 GPH, the total flow is 20 to 30 to cool the fuel and maintain pressure.  

Cheers