fuel flow

[kmacht]

Are you testing with the fuel cap on or off? How is the tank vented? Large lines out are only good if you have just as large of an inlet. The fuel flowing out of the tank has to be able to be replaced by air at a comparable rate. Just something to check.

Keith
#554

[lpaaruule]

Hi Keith,

I did try removing the fuel cap, and saw little too no difference. Additionally, when I measured the flow from the curtis valve on the bottom of the sump it flowed 18.6 gph.

Thanks for the suggestion though, I hadn't thought of it until part way through my testing yesterday. I'm going to do an additional check tonight with minimal fuel and the plane just sitting in its normal resting tailwheel angle. Probably won't tell me anything, but one more data point, and an additional sanity check.

[lpaaruule]

I just ran a few more tests with the plane just sitting on the gear.

To my surprise I got another 1/2gph since yesterday with about 3 gallons in the tank. So now I have 14gph.

I decided to put 10 gallons in and actually got 16.4gph. This isn't with minimal fuel, or at 19deg, but I'll take it.

I don't have any help today so I can't get the plane on the ramps to test anymore, but I'm guessing I'd get around 13gph.

The only thing I know that changed was the temperature outside. Perhaps the red cube was a little gummed up from sitting with fuel in it for months.

So I won't be removing the red cube yet. Since I'm at a loss the moment I think I'll work on something else and test again some other day

[kevinh]

One question: Why did you put your red cube before the filter? It seems to me filter before the red cube is better for two reasons: a) the red cube doesn't get clogged with debris and b) if the red cube is the biggest restriction perhaps having it just before the engine would help your flow rate.

[jowens]

Atmosphere barometric pressure increase would increase fuel flow rates, correct?

[lpaaruule]

Space, heat, and red cube plumbing requirement considerations.

Ideally, the filter would be before the red cube, but there isn't room to put both in the cabin without making more bends and more fuel line length.

The positions of the red cube and filter could be swapped. That would put the red cube in the heat and maybe more vibration.

I don't know if/how atmospheric pressure would effect fuel flow.

Ultimately I copied another builder's working system. Debris aside, restriction is probably less then an other solution I've seen that includes a fuel flow meter.

I think risk of the red cube suddenly clogging is a very unlikely concern. The finger strainer in the tank should minimize this further.

I do appreciate being questioned. A recent article in kitplanes discusses lack of imagination being one the factors in airplane accidents. People never imagined that a particular failure could happen until seeing what happened after a accident.

[kevinh]

Yah - I hear you. So many tradeoffs. FWIW based on your helpful post (and others) for my Aerovee turbo install: I'm currently leaning towards:

tank -> fuel filter -> firewall -> redcube mounted to firewall with NPT inlet serving as the bulkhead (much like how a gascolator would mount) -> hose -> aeroinjector. All as one essentially straight run with few bends.

I'm not super excited about this because annual service of the fuel filter could be a PITA. But, yeah - tradeoffs.

[sonex1374]

Kevin,

Let me share my thought process that influenced my fuel system design.

Don't under-appreciate the difficulty and hassle of removing the filter from inside the cockpit each time you want to service it. The hose runs pretty straight from the tank outlet to the ball shutoff valve to the firewall, and is sort of "pinched" between those two ends. To remove it each time isn't all that easy, and may place more strain on the tank fittings as you manipulate the hose while removing and re-installing it.

I agree that placing the filter before the red cube is ideal, but in this case, I think serviceability concerns outweigh that. Locating the filter on the engine side of the firewall places the filter in a position that's easy to get to at service time, and allows you a simple way to remove the entire hose by removing the filter from the firewall bulkhead, and disconnecting the other end from the carb inlet.

The red cub is highly resistant to fouling from small debris, and particles will likely flow through the red cub to get ultimately trapped by the filter. In the event debris does jam the impeller inside the red cube, the flow through is not blocked and fuel keeps flowing. You'll notice that you lost fuel flow, and will have to flush the cube, but this could even be done without removing it from the plane. Worst case is that you have to get in and remove the cube to clean it, but this is still far less invasive than removing the filter each and every year.

Food for thought.

Jeff

[mike.smith]

I haven't had nearly as good of results as others with fuel flow testing.

On a side note, I've looked at other builders sites, and believe that some of the testing done is invalid. Some builders will let their fuel line hang down lower than the inlet of the carb, or add a short length of fuel line to reach a bucket. Based on my testing, letting the fuel line hang down even an inch can increase fuel flow by 1 GPH with a half empty tank. It has a siphoning effect.
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The only thing the lower outlet does is add a slight bit of height to increase head pressure. At 1 gal/88 seconds (my results) that's over 40 gph, so lifting the outlet up or down several inches isn't going to affect that number to any significant degree.

I have a setup like yours: tank, ball valve, firewall, Gold Cube, inline filter, short AN-6 hose, AeroInjector. My tests were at 21 degrees, so I'm not sure why your fuel flow is so much less. There isn't a lot to troubleshoot. But it's certainly worth a try to take out the Red Cube and at least confirm or deny it has an effect. Does the inline filter have AN-6 connections as well? In other words, the inlet/outlet size of the filter isn't constricting flow?

[mike.smith]

I know it's a drag to take things apart, but process of elimination is probably the next step. Take everything apart to the firewall. Test the fuel flow at the firewall. If you're at a low flow there then perhaps there is something wrong at the finger strainer, or at the fuel shut off valve. If not, then put on the next link in the fuel system and test again. Then the next piece and test, and so on. See what the effects are as each new piece is added.