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Fuel flow testing

T.O.Craig

Well Known Member
Howdy to all,
I'm getting close to having a completed RV 10. It is powered by a IO540. One of the tests I will conduct will be a fuel flow test. I'm looking for any suggestions on how to accomplish this ....
 
Here is how I do it:
- After I build the tanks I let them sit on the bench for a few weeks with a 5-10 gallons of 100LL in it. I rotate the tanks to different position from time to time. The objectives are to find any weeping rivets and to flush the tank. I drain the fuel via a hose connected to the sump through a see through auto fuel filter back into 5 gal jugs. This is repeated until I'm sure no junk in the tank.
- With the tanks on the wings, wings mounted and fuel system plumbed, I replace the AirFlow Performce fuel filter with another see through auto filter. I disconnect the fuel line on the engine side of the firewall and connect a hose to a a five gallon tank.
- With the tanks empty, proceed with your EFIS or EMS fuel level calibration proceedure (most do a 2 gallon at a time add to each tank).
- After you hit the top of the fuel sender travel, use the planes fuel pump to pump each tank to the series of 5 gallon jugs. Measure the fuel flow and convert to GPH.

This process calibrates the fuel level senders, flushes the fuel system, and verifies the pump can deliver much more than the engine can use.

Carl
 
Here is how I do it:
- After I build the tanks I let them sit on the bench for a few weeks with a 5-10 gallons of 100LL in it. I rotate the tanks to different position from time to time. The objectives are to find any weeping rivets and to flush the tank. I drain the fuel via a hose connected to the sump through a see through auto fuel filter back into 5 gal jugs. This is repeated until I'm sure no junk in the tank.
- With the tanks on the wings, wings mounted and fuel system plumbed, I replace the AirFlow Performce fuel filter with another see through auto filter. I disconnect the fuel line on the engine side of the firewall and connect a hose to a a five gallon tank.
- With the tanks empty, proceed with your EFIS or EMS fuel level calibration proceedure (most do a 2 gallon at a time add to each tank).
- After you hit the top of the fuel sender travel, use the planes fuel pump to pump each tank to the series of 5 gallon jugs. Measure the fuel flow and convert to GPH.

This process calibrates the fuel level senders, flushes the fuel system, and verifies the pump can deliver much more than the engine can use.

Carl


Good advice. The other thing that is important to me is to elevate the nose while performing the flow test. You accomplish that by either putting the nose wheel on a stand or maybe by ratcheting down the tail. Doing the test under those conditions will verify adequate flow at a climb attitude.
 
In addition to the nose up attitude, you will want the outlet of the hose/line to be the same height as the servo inlet/float bowl. Running a hose all the way to a bucket on the floor takes advantage of the siphon effect and can give a false positive indication of fuel flow. Probably overkill, but I like to see every chance for the system to fail in the hangar rather than the initial climb.
 
Just did the fuel flow test on the 14 today. I disconnect the fuel line at the servo, and attach a piece of 3/8" fuel line and fitting that goes to a large graduated cylinder. As Mike noted it is important to simulate actual conditions. Run the electric pump long enoug to get a steady flow then stop, note fuel amount and run for a set time or until container is full. Note amount difference vs time running and calculate fuel flow per hour. Do this for each tank
Dump test fuel into your lawn mower etc.
 
Mr. Funnel

One of these Mr. Funnel fuel filter funnels comes in real handy when flushing out your fuel system. It filters out water and debris, and you can see what you caught. I use one of these when de-fueling into gas cans and re-fueling from the gas cans back into the airplane. (I actually use the bigger one with two filters, but that's probably overkill.)
 
A couple questions

Thanks for all the great input. I have a question as to where to disconnect the fuel line in the engine compartment. If I understand correctly, Carl states to disconnect the fuel line at the firewall before the mechanical (engine driven pump) and conduct the test from that location. Am I correct in assuming that?

Tom stated he likes to disconnect at the servo. To me that almost seems like a better idea because it is then flowing through the engine driven pump also, where there could be some additional flow restriction.

This is all good info. What flows are we getting when we do the calculations??
 
I honestly don't see much benefit to a gravitational test.

Suggestions:

1. air pressure test from wing root to servo, Just to ensure there are no risk of leaks. None. Zero. Absolutely none. If your lottery tickets always pay off, skip this step.
2. Max fuel flow at max pressure test from tank out past the red cube. The red cube in there allows one to set the flow rate and record pressure. Ensure there are no bubbles in the discharge. A clear section before a restriction valve is needed.

a. Initial run (purge) to a waste container. Test fluids will be in the pump
b. Run each tank dry to evaluate unusable at various attitudes.

These will ensure, no leaks, proper suction under flow conditions, and the back pressure allows real life flow in the pump circuit. It will likely yield less usable than a gravitational test, but not by much on the ground.
 
Getting ready to pressurize from fuel servo back to wing root testing for leaks. Should there be any concern about pressurizing backwards through fuel pump? Don't want to blow a diaphragm or whatever the configuration is in there.
 
keep it simple....

I have chimed in before on these "fuel flow testing" threads and I truly worry about testing pieces of equipment to collect too much data. Analysis-Paralysis. There are high pressure and low pressure sides of any fuel system. Presumably, we all filled our tanks and let the plane sit, then checked the low pressure side to selector valve and fuel pump entrance. check...no blue stains.......your done with the low pressure side. Turn on pump with fuel mixture at full cutoff (assuming you checked that you installed mixture cables correctly), any leaks, fuel pressure at 28 psi or so? Well then you did great and your joints to throttle body are good and your pump produces published pressure needed to keep you in the air. I STOP HERE. If you think the pump can produce 28 psig and not deliver enough fuel, then take off the line at the fuel divider, run it for 10 min and measure out ~3+ gal of fuel, or even better?, take apart your fuel injector lines, measure it separately, be a person of great detail and intrigue.....measure each cylinder to the milligram level....and it goes on... I personally get up in the air and check the electric fuel pump (EVERY FLIGHT!), if at full throttle, it can push up the pressure when at full throttle and full rich, it can more than keep me up in the air and replace that very reliable mechanical pump...simple test that can be noted and run many many take-offs down the airway..happy flying!
 
A simple, documented flow test at more than the expected climb angle is required for the "Phase I Second Pilot Option" whether it paralyses your analysis or not...:)
 
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