912ULS fuel starvation in steep turns

Re: 912ULS fuel starvation in steep turns

by Rob Seaton » 10 years ago

Rob Seaton

3 1.32k 251

Did the return line go back to the pump inlet when you had the 80hp installed?

Re: 912ULS fuel starvation in steep turns

by Arthur Götz » 10 years ago

Arthur Götz

6 31 1

No, and I like the way you`re thinking. I installed it when the carburetor of the 100hp started overflowing. When it did I did some homework and discovered that Rotax recommends to fit a restricted return, mostly to prevent vapor lock and also to prevent over-pressure. Since I don't have a fuel pressure reading I thought it wise to be on the safe side. I must say though, that line really irks me. Before, an air bubble would be pumped into the carburetor. Now it remains in the system.

Re: 912ULS fuel starvation in steep turns

by Rob Seaton » 10 years ago

Rob Seaton

3 1.32k 251

Can you route it back to a fuel tank? or at least the gascolator?
I think you should install a fuel pressure gauge or make some test to see if you are losing fuel during your bank.
(Don't get a mechanical gauge or one with a low quality sender. the pressure range is so low a mechanical gauge will always have a head pressure error. The sensor should be in the 0-15 psi range) UMA make a good quality electronic gauge.

Re: 912ULS fuel starvation in steep turns

by Arthur Götz » 10 years ago

Arthur Götz

6 31 1

Rob: Yes, I can, but I would like to avoid it, since the fuel is metered. Then again, what good is a fuel consumption readout when the aerie is stuck in a tree? I emptied all the air I could get at before take-off, after a 44 minute flight the return line was nearly full of air. Once it gets full, air is sucked back into the mechanical pump and is circulated from there. This is not a healthy situation.

Roger: Did the bank test again today, couldn't reproduce the problem at a bank angle of up to 60°. Only after I landed did I realize that I hadn't tried without the electric pump, so will have to repeat the test tomorrow. Before, the electrical pump didn't make the misfire disappear, it had no effect whatsoever.

The EGT's are still all over the place (recording attached), will have to attend to that too. Engine is propped for 5,700rpm at WOT at level flight, no air leaks that I can find.

Blue skies
Arthur

PS: The fuel pressure sensor (from China, may be low quality, but I will have to test) is ordered, will take a month or two to get here. I had a UMA, lasted less than two years, and now I feel that it's too expensive if it doesn't last. It has a small hole on top to let atmospheric pressure in. That, and water, which then corroded the circuitry.

Capture.PNG (You do not have access to download this file.)

Re: 912ULS fuel starvation in steep turns

by Rob Seaton » 10 years ago

Rob Seaton

3 1.32k 251

I dont understand what you are saying, the return line restrictor is so tiny it will not make a noticable difference on your fuel flow.
How is air getting sucked into the mechanical pump? from the return line? It should not be routed back to the pump; This is how it should be done:

Fuelsystemschematic.jpg (You do not have access to download this file.)