Static fuel flow testing.

[William]

Curious how these numbers compare to others. I have a standard vans firewall forward setup for a carbureted o320. I have a lycoming o320-b2a and the red cube and mechanical fuel pump are after the gascolator. Curious if the fuel flow at the carb is normal. It is flowing quite a bit less fuel after going through the mechanical fuel pump and the red cube. Flow rates were with the electric boost pump on. What's your thoughts?

- left tank fuel flow is 9 minutes 20 seconds to fill 5 Gallons at the gascolator

- right tank fuel flow is 9 minutes 40 seconds to fill 5 gallons at the gascolator

- at the carburetor fuel flow is 12 minutes 40 seconds to fill 5 gallons.


Thanks
Bill

[RVDan]

Round numbers, 12.66 minutes for 5 gal is 23.85 gal/hr. I seem to recall that you typically want 1.25 X max flow expected for the engine in operation for a flow check, which would lead you to a max engine flow rate of about 17.8 GPH. I seem to recall that for the 0-320 max flow is somewhere in the 13.5 to 14GPH range, so it should be sufficient.

That said the flow rate should be checked with the aircraft in the most critical attitude which would be nose high on max power climb. You should arrange the aircraft in a nose high attitude and then do the check. In that attitude the pump has the most height to pump the fuel which will yield the lowest flow rate.

[William]

Originally Posted by RVDan

Round numbers, 12.66 minutes for 5 gal is 23.85 gal/hr. I seem to recall that you typically want 1.25 X max flow expected for the engine in operation for a flow check, which would lead you to a max engine flow rate of about 17.8 GPH. I seem to recall that for the 0-320 max flow is somewhere in the 13.5 to 14GPH range, so it should be sufficient.

That said the flow rate should be checked with the aircraft in the most critical attitude which would be nose high on max power climb. You should arrange the aircraft in a nose high attitude and then do the check. In that attitude the pump has the most height to pump the fuel which will yield the lowest flow rate.

Hi Dan the test was done with the tail sitting on the ground. I'm aware of the required minimums but what I'm not sure of is the lower flow rate after the red cube and mechanical pump normal? I'd expect a small difference but my difference is quite large. I've got suspicion my mechanical fuel pump is going out. Curious if a failing mechanical fuel pump could cause a restriction in fuel flow.

Thanks
Bill

[RVDan]

I don't know what the loss is for each, but you certainly will experience some loss with pumping through the mechanical pump and the red cube. And the test is intended to address the most critical situation. The red cube drops about .4psi at your max flow so that will certainly result in a flow loss, not even considering the losses due to the fittings. Keep in mind that 90 degree fittings are a considerable impedance to flow.

[Marc Bourget]

I understood the target to be 150% of max fuel flow for the engine - with the aircraft at or above the typical 17 deg stall angle of attack. (Roll it up a bank or steep driveway ??)

Finally, with only a gallon or two in the tank. Take your measured container and a stop watch and "do the math".

[Steve Melton]

my flow rate at the carb = 24 gal/hr thru the gascolator and fuel flow meter with min fuel.

[William]

Originally Posted by Steve Melton

my flow rate at the carb = 24 gal/hr thru the gascolator and fuel flow meter with min fuel.

Thanks Steve for that info that is almost exactly what I'm getting. I'm getting a low fuel pressure of .4psi during climbing with the boost pump off and Lycoming states .5psi as the minimum. I believe the mechanical fuel pump isn't up to snuff. I bought it off of a gentleman that switched to fuel injection so needed the high pressure pump and this is the only part on my engine that wasn't new or overhauled. I've got a new tempest pump from spruce on the way and will test next week.

Thanks
Bill

[William]

Originally Posted by Marc Bourget

I understood the target to be 150% of max fuel flow for the engine - with the aircraft at or above the typical 17 deg stall angle of attack. (Roll it up a bank or steep driveway ??)

Finally, with only a gallon or two in the tank. Take your measured container and a stop watch and "do the math".

Thanks Marc.