Fuel manifold - material suggestions

[Marty_d]

Happy to be corrected here, but I wouldn't have thought that a difference in distance between manifold and carbs would matter in the least. Think of the fuel system like an irrigation setup, the garden hose that's 10m long gives the same pressure as the one that's 12m long. If there's no air in the fuel system, why would it matter?

[spacesailor]

Now that's wrong !.

The longer your hose the smaller the Volume getting  through. 

The smaller volume will have reduced pressure. 

Happens when paint spraying with extra long hoses. 

spacesailor

[IBob]

See my earlier post: the effect in this case is negligible, put the manifold where it suits you.

 

Marty, you're right, you get the same pressure regardless of hose length....until you open the end and get flow. then you get friction losses in the pipe, resulting in reduced pressure and flow the longer the pipe....

so...........
 

Spacey, you're right, but its a a matter not only of pipe length  but (air or fluid) velocity. Here you have very small pipe lengths and low velocity, so the difference in pressure drop in this case is negligible.

Edited July 15, 2023 by IBob

[Blueadventures]

17 hours ago, IBob said:

And while we are on it: can someone point out to me where in the 912 manual it says the fuel lines to the carbs need to be identical in length?
Certainly in the fuel system section it gives a set of coordinates for the fuel manifold as set out by Rotax....but if there is any note saying these coordinates are important, I haven't found it yet.

I'll stick my neck further on the block: my build was done using, amongst other things, build detail pics from the then agent, which I found invaluable. Following those, my manifold is mounted where the LH upper engine mount meets the firewall, which gives a short run to the LH carb and a a longer run to the RH.

And that seems to be working fine, with smoothe starts and running in all modes.

Maybe so all pressure pulses from either fuel pump if and when occur will reach carbs at same time. Just a thought.

[IBob]

5 hours ago, Blueadventures said:

Maybe so all pressure pulses from either fuel pump if and when occur will reach carbs at same time. Just a thought.

Good point, Blueadventures. And I can see how that would constitute 'best practise' too.

It would be interesting to know if it makes any practical difference in this particular case...and I can't think of any easy way to determine that.
What we do have is a lot of aircraft not plumbed that way (I went back to the build manual) and apparently not suffering any ill effects. But that doesn't rule out the possibility.

[Marty_d]

A follow up question...

 

A couple of people have said they threaded the inside of a barb and inserted the restrictor jet into it.

 

Given the restrictor jet has a barb itself -  is there any reason I can't just tap an M5 hole into the body of the manifold and have the 2 restrictor jets (tank return and fuel pressure gauge) threaded straight on to it?  Yes the barbs are very small (around 4mm OD by the looks of it), I'm assuming there's a fuel safe hose of that size available?

 

And an additional question - the back of my fuel pressure gauge looks like this.  Can anyone remember what fitting they bought to connect a hose/line to this?

Thanks!

[IBob]

Hi Marty, I can't help with any of that

but
I can offer this:
See that little rubber bung in the top of the fuel pressure gauge?
Either remove or open a hole in it before going flying.
Because that's what lets in whatever the air pressure is as you proceed.
And if you don't let it in, you too will have fuel pressure that appears to diminish as your rise, increase as you sink and/or shift suddenly if the bung should let a little in or out.......)

[skippydiesel]

1 hour ago, Marty_d said:

A follow up question...

 

A couple of people have said they threaded the inside of a barb and inserted the restrictor jet into it.

 

Given the restrictor jet has a barb itself -  is there any reason I can't just tap an M5 hole into the body of the manifold and have the 2 restrictor jets (tank return and fuel pressure gauge) threaded straight on to it?  Yes the barbs are very small (around 4mm OD by the looks of it), I'm assuming there's a fuel safe hose of that size available?

 

And an additional question - the back of my fuel pressure gauge looks like this.  Can anyone remember what fitting they bought to connect a hose/line to this?

Thanks!

Dont know the back of pump brass fitting diameter /thread but when you find out check out the Aeroiflow catalogue for adapters https://aeroflowperformance.com/ they have a staggering range.

 

As for the return line restrictor jet - it can go in manifold, the barb that you fit  to the manifold or the above barb. I would thread the metal component to suit - more secure. Just make sure you select a nice small jetorofice (they all the same external size/& thread)

[Marty_d]

I ended up getting an Aeroflow manifold. My attempt at tapping my own was not entirely successful. 

Also have some Mikuni jets on order for restrictors.

[skippydiesel]

Looks good Marty_d 

 

The Airoflow catalogue is truly amazing - you could probably get those hose connections in elbows if it suited your "design"

 

 

 

[skippydiesel]

Forgot to mention; depending on the ID of your fuel return line & therefore the ID of the push one barb/spigot, you will find that the Mikuni restrictor jet can be screwed in (after tapping) for a nice secure fit.

 

The same can be done to the fuel sensor pressure line, if fitted.For the fuel pressure line, use a very small ID restrictor jet to reduce fuel pump pulse fluctuations.

 

Gates (REPCO) supply fuel hose in  ID  3.3 (return line)  4.8, 6.3, 8, 9.5 & larger (which I doubt you would contemplate using). There are three "grades " Return" "Carburettor" & "Fuel Injected" They all meet the Rotax specifications however I tend to favour the Fuel Injected for its slightly better heat resistance and lower vapour permeability.

Edited August 18, 2023 by skippydiesel