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Fuel flow testing

rvdave

Well Known Member
I'm not used to operation of AFP fuel servo so have a question regarding fuel flow testing. I assume I remove fitting from fuel spider while in a 20 deg nose up attitude to gather fuel to calculate flow to spider. Three things:
1). Does mixture control need to be full forward?
2). Will there be fuel leakage at fuel servo?
3). Should I calculate flow to fuel servo instead?

Maybe dumb questions but I'm claiming ignorance here!
 
With no airflow, the servo will not pass fuel. To perform the fuel test the servo must be bypassed. Remove the hoses to inlet and exit and connect with appropriate adapter. Then disconnect at the "spider", add clear section then a shut off valve. I used a ball valve for my 10-Friends test and found it sensitive when setting restriction to mimic/match the back pressure on the fuel pump.

After adding fuel, installing the valve, but before pumping fuel, pressure test the system back to the fuse exit point. 30 psi. If it won't hold 30 for hours, then find the leak and repair. If leak free (both sides) then proceed with the test. The clear section will verify you have no suction leaks. It must be installed before the exit restriction valve, meaning under pressure.

If the system has not been pressure tested, 95% probability you will find at least one leak.

BTW - His plane passed all our tests. After boost pump is off, it will climb to 17k with no starvation issues. Hot day. Let me know if you have questions.
 
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I'm not used to operation of AFP fuel servo so have a question regarding fuel flow testing. I assume I remove fitting from fuel spider while in a 20 deg nose up attitude to gather fuel to calculate flow to spider. Three things:
1). Does mixture control need to be full forward?
2). Will there be fuel leakage at fuel servo?
3). Should I calculate flow to fuel servo instead?

Maybe dumb questions but I'm claiming ignorance here!

There are no dumb fuel system questions.

There are two fuel flow tests, one everyone should do before first flight, and one done to check flow balance to individual cylinders with any constant flow fuel injection. They test different things. Here we'll discuss the former, a basic check for fuel supply.

20 degree nose up is good. More just proves more capability. Disconnect the inlet line at the fuel servo. Put the end of the line into a calibrated jug of some sort. Select one tank. Run the electric pump for a carefully-timed 60 seconds. The fuel quantity collected in the jug (in gallons) x 60 minutes = GPH. Repeat for the other tank. Check the jug for debris while doing these tests. Obviously throttle and mixture position don't matter.

Bills leak testing is a fine idea too.
 
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With no airflow, the servo will not pass fuel. To perform the fuel test the servo must be bypassed. Remove the hoses to inlet and exit and connect with appropriate adapter. Then disconnect at the "spider", add clear section then a shut off valve. I used a ball valve for my 10-Friends test and found it sensitive when setting restriction to mimic/match the back pressure on the fuel pump.

After adding fuel, installing the valve, but before pumping fuel, pressure test the system back to the fuse exit point. 30 psi. If it won't hold 30 for hours, then find the leak and repair. If leak free (both sides) then proceed with the test. The clear section will verify you have no suction leaks. It must be installed before the exit restriction valve, meaning under pressure.

Unclear to me---
 
fuel flow test mandatory....????

With a new engine delivered from Lycoming I strongly disagree with a "mandatory" fuel flow measurement and breakdown of ones flow system. These new, pre-run engines come with a detailed engine break-in run on a test stand with no need whatsoever to disassemble ones fuel system to run a fuel flow check. Mandatory is a very strong word to use and not warranted for those bringing online new engines or ones that have had a shop do a engine-test-stand break-in. Just a perspective to add in the mix..:)
 
With a new engine delivered from Lycoming I strongly disagree with a "mandatory" fuel flow measurement and breakdown of ones flow system. These new, pre-run engines come with a detailed engine break-in run on a test stand with no need whatsoever to disassemble ones fuel system to run a fuel flow check. Mandatory is a very strong word to use and not warranted for those bringing online new engines or ones that have had a shop do a engine-test-stand break-in. Just a perspective to add in the mix..:)
To me it's mandatory, I tested per Dan's method above. In that scenario, you're testing very little of the engine's fuel system, which I agree can mostly be assumed sound from the test runs. What you're mostly testing is all the fuel system work you did. That is, the lines from the tank to the fuel pump, the fuel pump and associated fittings/filters, the lines from the fuel pump to the engine, possibly including fuel flow meter. lots of places for crud to get plugged, or an unseen kink to slow flow. The big fan up front is important, and it needs enough fuel to run properly.

Even a test with no issues found has the benefit of flushing the lines before engine start, giving more piece of mind there is no crud going into your carb/injectors.
 
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Unclear to me---

Hmmm, sorry. Adding fuel is not needed, it should have read BEFORE ADDING FUEL.

But just to be sure we are on the same page : I assumed you were going to test for the following:

Verify:

1. Purge the fuel lines so clean fuel comes out, nothing is plugged.
2. that the fuel system does not leak, suction or pressure side
3. that the boost pump will deliver full fuel flow (in case of a mechanical pump failure) at the needed pressure for full power/full rich take off.
4. quantify each tank for usable fuel under full flow at pressure conditions

Meaning,
run a leak test before fuel is introduced to the system,
then tilt the plane,
put a measured amount of fuel in each tank,
activate the pump and purge until it flows clear measure and discard that fuel.
activate the fuel pump, read pressure and flow from the panel and adjust back pressure with the exit flow valve.
Then once the fuel pressure drops (tone of the pump changes when it gets air) shut off the valve and measure fuel pumped out.
The test is rerun for as much nose down as you can safely do. A landing phase angle.

Actually, on a 10 the pressure does not drop until something less than a quart remains with the nose up. There is a bit more unusable fuel nose down but not gallons.

Is that more descriptive of what you want to accomplish, or are you running a test for a different purpose?
 
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individual cylinders....

My point, was that of course as each fuel line is assembled starting at the tank, it should be purged by the builder...if you use a filter, or heaven forbid, an inject port to catch the "waste" from a building process...good luck with that approach. If one has done a good job of flushing lines prior to the valve, prior to the filter, prior to the mechanical fuel pump, prior to the fuel body valve, there is no need whatsoever to disassemble a perfectly running engine shipped to each builder (buying new). Testing a tanks useable etc... is a very different question and task, and I again would say why? With the RV10 fuel tank is there really any variation possible? The screen at the fuel tank outlet is installed after the tank build (i.e. free of tank sealant) and has little to no variation for installation possible. I am all for safety and verification, however, I am very against taking apart functioning and fully tested equipment that is assembled by experts to just "confirm" and provide no margin of flight safety, at hour 1 or 500 on the plane. I personally run a tank to empty (or when the gauge says empty) and ask what did I get out of the tank in real (level) flight. But then again, if I land and don't have 12+ gallons I am quite disappointed in myself for poor planning, no matter what (IFR, VFR, headwind, etc.....).
 
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For the rest of us mere morals - do the test.

My point, was that of course as each fuel line is assembled starting at the tank, it should be purged by the builder...if you use a filter, or heaven forbid, an inject port to catch the "waste" from a building process...good luck with that approach. If one has done a good job of flushing lines prior to the valve, prior to the filter, prior to the mechanical fuel pump, prior to the fuel body valve, there is no need whatsoever to disassemble a perfectly running engine shipped to each builder (buying new). Testing a tanks useable etc... is a very different question and task, and I again would say why? With the RV10 fuel tank is there really any variation possible? The screen at the fuel tank outlet is installed after the tank build (i.e. free of tank sealant) and has little to no variation for installation possible. I am all for safety and verification, however, I am very against taking apart functioning and fully tested equipment that is assembled by experts to just "confirm" and provide no margin of flight safety, at hour 1 or 500 on the plane. I personally run a tank to empty (or when the gauge says empty) and ask what did I get out of the tank in real (level) flight. But then again, if I land and don't have 12+ gallons I am quite disappointed in myself for poor planning, no matter what (IFR, VFR, headwind, etc.....).

Testing is not for design purposes, it is assembly. And ensuring, not assuming, it works as expected.

One friend did the test and found his new fuel filter leaked. Oops. The fuel pump is filled with residual test fluid - not some stuff one wants in the injection system or in the engine. Back to the topic.
 
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Hmmm, sorry. Adding fuel is not needed, it should have read BEFORE ADDING FUEL.

But just to be sure we are on the same page : I assumed you were going to test for the following:

Verify:

1. Purge the fuel lines so clean fuel comes out, nothing is plugged.
2. that the fuel system does not leak, suction or pressure side
3. that the boost pump will deliver full fuel flow (in case of a mechanical pump failure) at the needed pressure for full power/full rich take off.
4. quantify each tank for usable fuel under full flow at pressure conditions

Meaning,
run a leak test before fuel is introduced to the system,
then tilt the plane,
put a measured amount of fuel in each tank,
activate the pump and purge until it flows clear measure and discard that fuel.
activate the fuel pump, read pressure and flow from the panel and adjust back pressure with the exit flow valve.
Then once the fuel pressure drops (tone of the pump changes when it gets air) shut off the valve and measure fuel pumped out.
The test is rerun for as much nose down as you can safely do. A landing phase angle.

Actually, on a 10 the pressure does not drop until something less than a quart remains with the nose up. There is a bit more unusable fuel nose down but not gallons.

That makes sense to me.

Is that more descriptive of what you want to accomplish, or are you running a test for a different purpose?

Just testing airframe, fittings, tubing, and connections for proper operation and performance, thanks.
 
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