VW - Dual Fuel Pump - Anyone done it

The place to raise issues, ask questions, swap ideas and discuss anything related to aircraft engineering, maintenance and building.
NB Any opinions expressed in this forum are not necessarily those of LAA Engineering

Moderators: John Dean, Moderator

Post Reply
Barber
Posts: 24
Joined: Sat Oct 18, 2008 6:15 pm

VW - Dual Fuel Pump - Anyone done it

Post by Barber » Sat Sep 17, 2011 7:24 pm

Hi, I wonder if anyone has any experience in installing a dual fuel pump configuration in a VW powered light single seat A/C. I have a Colibri with just a single pump and it seems like a good idea to have two for redundancy. If there is any precedence I guess the MOD application will be much easier.

Best Regards

Tony Barber

cardiffrob
Posts: 370
Joined: Wed Jan 16, 2008 3:56 pm

Post by cardiffrob » Tue Sep 20, 2011 7:25 am

I looked briefly into this. The standard engine driven pump won't flow if it dies, according to the VW car experts, so I stuck with gravity and a Facet 40105 which WILL flow fuel if it dies. (Usual Caveats here)
I have my fuel tank vent in a high pressure area so that I get a small speed/pressure boost on top of the 12 inches of gravity pressure. The pump will give an extra 1-to-4 psi and so far ir hasn't overwhelmed the needle valve.
It might be possble to run to 40105s in series or in parallel if you have 2 Andairesque non-return valves. All weigh a lot more than gravity, if you see what I mean.
Rob Thomas
034851

Nick Allen
Posts: 456
Joined: Wed Jan 02, 2008 11:00 am
Location: Oxford
Contact:

Post by Nick Allen » Tue Sep 20, 2011 8:58 am

The standard engine driven pump won't flow if it dies
Doesn't this depend on the failure mode? This may be true if the pump action mechanism fails, but if the membrane fails, I think it would still let fuel through. (Our motorglider has an electric fuel pump, plus Limbach/VW mechanical pump.)

cardiffrob
Posts: 370
Joined: Wed Jan 16, 2008 3:56 pm

Post by cardiffrob » Wed Sep 21, 2011 7:45 am

On the pump I removed, if the drive fails then it becomes sealed and won't flow. If the diaphragm goes then I'm not sure. I ditched it because of known problems with flaking cadnium plating on the chambers, the extra fuel piping in the engine 'hot area' that was required to run from the tank to the front of the engine and back again to the carb plus the fact that it all weighed more than the facet.
I think I lost about 4 feet of armoured pipework this way.
Rob Thomas
034851

Barber
Posts: 24
Joined: Sat Oct 18, 2008 6:15 pm

Post by Barber » Wed Sep 21, 2011 7:48 pm

Hi All

I don't have an engine pump, just a single facet electric pump. This was how the airplane was when I to it. Its always worried me that a pump failure means I go gliding. There is no gravity available due to the design so its got to be another pump. Hence the question if anyone else had such a set up.
- dual electrical fuel pump.

Cheer

Tony
Tony Barber
029108

cardiffrob
Posts: 370
Joined: Wed Jan 16, 2008 3:56 pm

Post by cardiffrob » Thu Sep 22, 2011 2:55 pm

For £25, it might be worth getting a second pump, fixing it in series and trying it to see if one will work with the other dead via a left-right-off switch.
Rob Thomas
034851

Rob Swain
Posts: 393
Joined: Tue Jan 08, 2008 2:11 pm

Post by Rob Swain » Mon Oct 03, 2011 2:00 pm

I'd stick a standard VW mechanical one on, in parallel with the electric one, and put a non-return valve after each pump so neither can try to push fuel back through the other.

I'd then fly in the usual way, electric pump on to start, leave it on until at cruising altitude, and then turn it off. It goes on again as part of the approach procedure to keep the fuel flow up when the engine speed drops off with the winding down of the RPM. Of course it can be turned on again if CardiffRob's pessimism comes to fruition and the mechanical pump packs in! :)

Goes without saying that all this will be subject to a mod approval and discussion with your inspector. I am surprised that the aircraft was issued a permit to fly with just an electrical pump as the failure scenarios are legion, far more than for a mechanical one.

You are looking for redundancy: my suggestion above provides it.
A second electric pump can only provide this if it has a second backup battery giving a supply of volts should the main electrical system croak. If you have Leburg ignition then you have this already, otherwise you are looking at an increase in complexity and weight that is difficult to justify.

My only concern regarding the very pretty Colibri is whether the standard VW mechanical pump will fit under the cowlings. I think lower profile pumps might be available if this is an issue, but I couldn't say where for certain (Great Plains?)
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.

Barber
Posts: 24
Joined: Sat Oct 18, 2008 6:15 pm

Post by Barber » Tue Oct 04, 2011 6:36 pm

Thanks for the advice everyone. With Leburg ignition, its easier to just add a second electric pump which will be my plan.

cheers
Tony Barber
029108

Post Reply