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Fuel Flow Sender Jet size for Rotax 914
Posted: Fri Nov 17, 2023 9:10 pm
by johan
Hi,
I am installing the MGL fuel flow sender but don't know which Jet size to choose for my engine.
My engine is a Rotax 914, burning aprox 20l in cruise.
I am a bit confused by the Jet sizes and the flow ranges.
Is there anybody who can give any advice on the correct jet size for a rotax 914?
Thank you in advance,
Johan.
Re: Fuel Flow Sender Jet size for Rotax 914
Posted: Thu Nov 23, 2023 3:12 pm
by rainier
On a 914 we install one sender into one of the carb feeds using the 2mm jet (second smallest in the packet). We then "lie" about the k-factor - it should be 7000 normally - we tell it 3500. Half. This way the readout doubles. While this only really shows the flow on one of the carbs it works well.
Re: Fuel Flow Sender Jet size for Rotax 914
Posted: Mon Nov 27, 2023 8:57 pm
by johan
Thank you for the answer. I assume this is done because if the fuel flow sender was installed before the fuel regulator the reading would be less acurate/useless since it would include the flow from the fuel return line ? I think it makes sense to install it into the carb feed, however the fuel lines from the regulator are hard (metal) fuel lines on a 914, not sure what the best way is to install the fuel flow sender.
Also, is it safe to install the fuel flow sender on the hot-side of the firewall? Not sure if an alternative solution might be to add a 2nd fuel flow sender in the return line and do some calculation to get the correct fuel flow readout.
Re: Fuel Flow Sender Jet size for Rotax 914
Posted: Wed Nov 29, 2023 12:17 pm
by rainier
johan wrote: ↑Mon Nov 27, 2023 8:57 pm
Thank you for the answer. I assume this is done because if the fuel flow sender was installed before the fuel regulator the reading would be less acurate/useless since it would include the flow from the fuel return line ? I think it makes sense to install it into the carb feed, however the fuel lines from the regulator are hard (metal) fuel lines on a 914, not sure what the best way is to install the fuel flow sender.
Also, is it safe to install the fuel flow sender on the hot-side of the firewall? Not sure if an alternative solution might be to add a 2nd fuel flow sender in the return line and do some calculation to get the correct fuel flow readout.
Usually the return flow on 914 installations is quite high so you would need a differential flow system with two senders. While this works it is expensive and can be fiddly to set up - it's easier to do if you have an engine that consumes much more fuel than the 914.
The flow sender is normally installed on the hot side of the firewall - on my own aircraft (fitted with 912ULS) it was fitted above the engine just before the return splitter - on these engines the return flow is very small and can be ignored. It's just to prevent vapor locks.