Return fuel line for Rotax 912 and Goodwin seat tanks

[WEST OZ FLYER]

Just wondering is a return fuel line is necessary for the 912 100hp? The way I understand it is that it is needed for vapour lock issues. Seeing as my Rossco doesn"t have cowlings is it needed? I am not running a fuel pressure gauge if that makes a difference.If so where does the return line go for two 40 ltr seat tanks?Cheers

[birdy]

Never hada return line on the gyro in over 4000 hours and never hada vaper issue, even if its nudgn 50c.BUT, iv always hada lectric pump below the fuel tank.There seems to be enuf cooling out in the open to prevent boiling.But if you have cowls or covers that hold heat, you either need line insulation and heat shields over the header pipes, or a retirn line.I prefer insulation, coz return lines without insulation only fills the tank with hot fuel, and youll get locks before the pump.

[Brian]

My 912 had done approx a 1,000 hours without a return line, Rosco asked me if I wanted one....wasnt sure, anyway opted to put a return line in but I think its a waste of time.

[WEST OZ FLYER]

Birdy do you reckon the electric fuel pump makes a difference? I am thinking that the vapour lock should only occur (with no cowls/covers) between the Rotax mechanical fuel pump and carbs from radiant heat when the engine is shut down. Should not be a problem while engine is going only when trying to restart when hot? Even if the vapour lock is after the fuel pump it should still start and clear the vapour lock as the pump doesn"t have air in it. Thoughts?I can always put the electric pump on later if it is a problem.

[birdy]

Iv seen alot of machines turn up in this country with just the mech pump, and i tell um all to put the lectric one in, just to be sure.Usualy the mech pump is way above the bottom of the tank, so if the fuel gets hot and boils in the line before the pump, your pump will cavitate.Fuel boils earlier under vacuum, as is wen the pump has to suc it from the lower tank.The lectric pump should be under the tank outlet, and the line to it should be uphill to the tank nipple so any bubbles between pump n tank can go up into the tank.Fuel under pressure will need more heat to boil, so after the pump is USUALY not an issue.Only once have i had vaper lock.( before i insulated the lines and shielded the pipes)Machine was hot, landed, left idle for 5 mins, in the sun, then just after TO, it ran dry.The fuel in the bowls was just enuff to get airborn, but as the pressure droped in the line, wen the needles opened, the extra hot fuel boiled and kept the pressure up, so the pump couldnt push fresh fuel in.Fuel pressure alarm, that is between pump and carbs and set to go off just under WOT pressure didnt go off either, coz the boiling fuel had kept the pressure up.Insulated lines, heat shields on the headers and a return line would be pretty failsafe.Im just sayn, iv never hada return line ona 912 gyro.

[WEST OZ FLYER]

Thanks Birdy, you just can"t beat experience. I reckon I will put that electric pump in just because.

[Brian]

A electric pump is very good insurance in my opinion, its not costly & it works continuiously in the background....just in case.

[MadMuz]

A electric pump is very good insurance in my opinion, its not costly & it works continuiously in the background....just in case.and that it is high volume and low pressure... or a return line if the pressure is a bit too high.

[Disco]

Here is one from Echo.

[tonydenton]

I use a ryco fuel filter

[birdy]

With respect the Echos reply, ( and Echo), any bleed back systm will only reduce pressure if the flow back rate exceesds the pumps flow rate.See,n how the consumption rate changes with throttle position, its impossable to regulate feed pressure with a simple pressure "overflow". And you want to be sure your consumtion + overflow rate dont exceed the pumps max rate.And you could have 15, 4lb max pressure diaphram pumps in the line but youll still only have 4lb at the end.Only centriphical pumps (914 type) will increase end pressure the more you hook up.But generaly, if the ambient is below the fuels boiling point at your alt, vaperlock wont be an issue.Fuel under pressure in rubber lines generaly dont have time to get to boiling from Radiant heat off the engine under normal flyn conditions.

[Disco]

That bizzo on the 914, is that a regulator? Sure looks like one.

[birdy]

Yes, its a proper regulater, itself linked to MAP.

[birdy]

Before sumone points out my deliberate mistake, i will. :The 15 pumps bit, that is 15 pumps with seperate feed and discharge lines.Not 15 pumps pumpn through each other, ( each discharge into the next pumps inlet) coz if you did this, then you would end up with 60psi.