Fuel return Line Restrictor

[Skippydiesel]

FYI - via the Rotax Owners Forum:

https://www.dynonavionics.com/bulletins ... 120414.php

It turns out my fuel pressure sensor & plug are almost identical to the one in the advisory bulletin.

I have removed my silicon seal and then flown for 1hr - no low fuel pressure warning - PROMISING! .

I will fly for a few more hours before making a definitive statement.

[WaiexN143NM]

hi skippy
thanks for posting this.


michael.

[Skippydiesel]

Follow UP

I was still not happy, after installing a smaller return line restrictor jet, with the pressure in my fuel delivery system.

While the aircraft was back in my home workshop, for cooling system modifications, I made some changes to my fuel delivery set up.
Previous - Boost Pump only worked on selected Wing Tank. There was no bypass on the Boost pump - so if blocked/restricting flow, no alternative flow rout. Largest tank Centre tank also had the fuel return line supplying it.

Changes:
Higher capacity Facet Cube Boost Pump fitted as per RV advice (Old: max 5 psi / New: Max 7 psi)

Boost Pump will now draw from selected Wing or Centre Tank - Take-off, Climb Out & Landings can now be safely done on the Centre Tank.

Boost now has a bypass fitted with non return valve.

#35 Fuel return line restrictor jet re installed, in recognition of new Boost Pump higher Max pressure

Improvements in fuel pressure readings all round BUT still getting an alarming drop in pressure, when Boost Pump turned off, before presser then rises once more to an acceptable level.

Have gone back to smaller restrictor jet - will report findings after next flight.

[Skippydiesel]

Follow up:

Fuel pressures are now okay.

One odd symptom; I climb out (CO) under full power, Boost & Mechanical pumps on, achieve safe altitude (min 1000 ft AGL), level out or reduce climb and turn off Boost pump (BP) - there is an immediate/sudden fuel pressure drop from around 5 psi to 2 psi followed by a smooth (ie not immediate) recovery, over a few seconds, back up to 5 psi - no effect on engine.
A tad disconcerting but not unsafe.
I don't understand why the sudden drop, to below Mechanical pump pressures, followed by a return to normal/consistent pressure. This might be understandable if the fuel was being drawn through the BP but I have installed a BP by pass which should negate any restriction caused by the stopped BP.