Fuel Flow Testing

[Dorsal]

I know I built mine according to the manual, checked that I had decent flow but did not measure it and flew it. I may measure the flow and let you know.

[Dick B in KY]

Took me a while to find my run sheet, but here are the flows on my SS7 (taildragger attitude) at the firewall where the mechanical fuel pump hose connects (this is where it counts).

Right side wing tank - 1/2 gallon in 75 seconds
4 gallons in 600 seconds (10 min)

Left side wing tank - 1/2 gallon in 90 seconds
4 gallons in 720 seconds (12 min)

More than enough flow for a 912ULS that burns 7 gallons per hour at full power. Hope this helps.

Dick B

[HighWing]

Jim,
I think Dick B has hit on something. I went back and re-read your first post with your measuring point - "right at the Rotax 912s carburetors." I had always measured at the hose right at the inlet of the mechanical fuel pump. I think the first thing I would do is repeat the tests at the point before the pump. At least in my installation, the lines from the pump to the carburetors are quarter inch ID and would add some additional friction not to mention internal resistance in the pump itself.

My testing was done in the tail down postion - the most adverse gravity feed positoin - and finding it adequate, that was it. So, I guess it does indicate, as you suggest, that some of us are not as thorough. But then, I guess, the proof is in the pudding. Fuel flow has not been a common issue with the Kitfox factory designed fuel system. In my mind, I have relied on the test to indicate whether something I have done has compromised the design. However, adding the suspenders, I did install the Facet fuel pump immediately down stream of the header tank with the on switch within thumb distance with my hand on the throttle. I did have one instance where I was glad I had it, but it was from a maintenance issue - my bad.

[jiott]

I agree, the hose to the fuel pump seems way more reasonable as a measuring point. The fuel pump may have a lot of resistance thru it when not turning. I will recheck flow at inlet to fuel pump.

I would still like to hear some more numbers and how others did the testing.

Jim

[t j]

My Rotax engine installation manual lists a maximum fuel pump height above the fuel tank. I have a nose tank that serves as the header tank in my kitfox. The fuel pump is about level with the bottom of the header tank.

The gascolator is the low point in the system and is well within the maximum height below the fuel pump.

So, I tested the flow at the outlet of the gascolator, tail low, one gallon remaining in the nose tank (header) and zero fuel in the wing tanks. flow rate 14.3 gal/hr. Zero unusable.

I then tested the rate from wing tanks to header tank to be sure the wing tank flow to header tank would keep up with the engine fuel burn should I forget to switch on a wing tank and run the header dry. Left tank 11.8 gal/hr. .75 gal unusable. Right tank 11.25 gal/hr, .75 gal unusable.

I have since found that I can actually drain all the fuel in the wing tanks by slipping but I think the definition of unusable is in level flight so left the plackard on the wing tanks. I did subtract that unusable fuel weight from my empty weight though. 9 pounds

[SkyPirate]

just my 2 cents worth,..just thinking if its a gravity test, due to concern of normal operation in flight if the fuel pump fails or is turned off,..wouldn't testing the system from the furthest point from the fuel tank be best,..ie carb inlet, to include flow thru the pump? or a by pass of the pump if needed?

[t j]

Don't know about the 912 but rotax two strokes won't run very good without a fuel pump in a kitfox.