ROTAX 912 low fuel pressure at take off

There are several aircraft that seem to have low fuel pressure INDICATIONS at take off and it seems to be low wings. Vans RV12 has issues at times and they run the aux pump all the time. People I have talked to say the aux pump didn't help on take off, but none of them have said the engine had an issue. Just a low pressure indication.

I had a Sting aircraft with the problem and installed a new Facet pump that drafted higher (distance between wing and pump height difference) and produced more fuel flow. Their issue went away.

Draft height for some of the Facet pumps are on 12".

Hi Roger,

"Draft height" 

I have never heard the term pump draft height before.

A quick Google and it would seem that our (Australian/British) term "head" can be substituted for  "draft" . Am I correct?

On another point -

As  you know there is a parallel conversation (Pilot Jet #35) going at the moment.

In this conversation, the focus has been fuel return line flow (in my case 7.6L/hr) and its potential to impact on high engine power/fuel demand leading to a temporary low fuel pressure condition.

In this thread/conversation, the focus is low fuel pressure on TO/Climb (the same stage of flight/ engine, fuel delivery as  above) however the potential solution seems to be a larger capacity boost pump.

It seems to me that the two conversations and the potential solutions (smaller restrictor jet/larger capacity boost pump) for the same condition, might benefit by being brought together. 

Hi Sean. Hope all is well.

Draft height and and head height / pressure are a little different. I'm a retired firefighter so we used these calculations for pumping from the truck through the hose. Back in the day when we pumped into a building sprinkler system or had hoses running UP stairs we would increase the pump pressure 5 psi for every ten feet of elevation. We just used each building story as a ten foot rule. So a 6 story building would be and additional 30 psi added to our normal pump pressure to over come the head pressure pumping liquid upward. So usually head pressure refers to anything above your pump or work station. 

Draft height usually means a fluid that is being sucked up from a position lower than you are. So if you placed a hose in a pool that was 10 ft. lower than you that would be draft height. Each pump has specs as to what it can do as far as drafting. I used draft because usually from what I have seen is the pump is higher up on the plane than the fuel tanks. So you are drafting up. Some of the Facet pumps people use only have a 12" draft height spec. So I used used ones that can draft higher i.e. 18" and may produce 1-2 psi more pressure. It has worked so far. I'm not sure if some Mfg's know what draft is?

Sean,

In your earlier posts, I thought you stated that the fuel pressure was in the normal range whenever using your (existing) Boost Pump, and that the low pressure only occurred once the Boost Pump was turned off, then slowly recovered in level flight.  Did I get that wrong?  In other words, I thought you were trying to achieve normal pressure under all flight conditions without the use of your boost pump.