Poor Starting 912iS

Jim & Bill thank you for the replies.

Our Aircraft is a Eurofox with High Wing (Gravity feed wing tanks into a small header tank).

We have a Stock Flight EMU which measures & displays Fuel Pressure, however, this isn't

very quick at displaying readings. I am going to dury rig an analogue gauge in the system 

with a piece of clear tubing (pipe / hose) to see the pressure fluctuations and any air bubbles.

As usual with the 912iS we will get to the bottom of this fault but it usually takes time and

some out of the box thinking.

Jim & Bill thanks for the replies.

The Aircraft is a Eurofox (Aeropro cz A240 in USA), it is a high wing with tanks in the wings

gravity feeding a small header tank (6 litres) then a Coarse Filter (50 micron) + Fuel Pumps + Valve +

Fine Filter (8 micron) to the Injector rail. It doesn't have any Orifice bleed fitted or Check Valves

around the filters.

It has a Stock Flight EMU to measure and display the Fuel Pressure, this is slow to respond so I am

making up a temporary Mechanical Fuel Gauge to observe what happens. I will also put a piece of

transparent tube (pipe / hose) in order to watch for any air in the system.

I will let you know how I get on after the weekend.

Seems like a reasonable hypothesis Bill.  I'm in a high wing as well as the other 2 owners I mentioned earlier.  What would the Fuel bypass orifice look like?  How would I find it?  Sounds like some installations may not have it.

I'll double check the symptoms you mentioned above next time I'm at the airport.

This is from the 912iS Installation manual . The orifice was introducted to allow the pressure to

dissipate once the pumps were turned off, otherwise you would still have fuel under high pressure

which would be dangerous in a crash. We did not build our aircraft it was the UK Agents Demonstrator.

It didn't even have a Fine Filter which caused us some problems. The Fuel Pumps generate a some

carbon particles from the motor brushes, the fuel goes right through the internals and past the armature and brushes.

The Fine Filter does a good job of catching this but the Fine Filter needs changine every 200 hrs. You will see on the

diagram that they also fit By-pass "Check Valves" in case the filters become blocked.  We looked at fitting them but

at the time it was going to ground the aircraft for too loong - it is used as a Sailplane Tow Plane 7-days a week.

Andair  (www.andair.co.uk) manufacture Bypass / Check Valves and they also supply an Orifice for the 912iS Engine

http://www.andair.co.uk/product/rotax-912is-nozzle/

They also make a Brushless motor fuel pump to eliminate the carbon brushes problem, but they were having trouble

with Rotax accepting it (nothing new there....)

Well, Nuts! There should not be anything draining UP to the fuel tanks.

It will still be useful information to know exactly what the fuel pressure is immediately after starting and stopping the pumps.

If you have 40+psi for 10 seconds before attempting the first start of the day; you can be confident that the fuel rail has been flushed with new fuel.

If the Fuel pressure drops to ZERO within 5 seconds of de-powering the fuel pumps, you can be confident that he fuel bypass orifice is doing its job.

- - -

Is there any chance that these aircraft are subjected to temperatures above 85°F (30°C) or direct Sunlight between flights? 

We could be just boiling the fuel out of the hoses.  It doesn't take much.

Even at that; 10 seconds of 40+ psi fuel pressure will solve everything.

This is the beauty of the high-pressure pumps and the bypass orifice.