Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
Although I have been tinkering with airplanes most of my life, one thing I have never had to do was flush a new fuel system before starting the engine for the first time. I've looked through my bookshelves and can't find any good procedural discussions...before I take out a second mortgage to buy a full load of fuel, can anyone give me a quick description of the process?

I would assume it is to put a limited amount of fuel in each tank, turn on the electric pump, and flow fuel up through the gascolator, with the fuel line disconnected at the carb.... but how do I know when I've done enough - and am I completely off track?

Paul Dye
RV-8 finishing....
 
That's basically what I did. Run the pump and check the fuel flow while you purge trash out of the tanks and lines. Run a measured amount and time it to ensure that the GPH is sufficient so you are sure you have no restricted flow. I calculated about 45 gph from my little facet pump.

I had QB wings and tanks and still find little shards of AL sticking in the sump drains. Ocassionally I unscrew the drains and let some fuel dump as I replace the drains with ones that have new O-rings.

Roberta
 
I'd fill them all the way up, let the fuel set a while, then pump out a few gallons from each. From then on, keep them full. The reason you should fill it up all the way is because you want to wash any crap into the bottom.
 
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You can kill three birds with one stone, so to speak. Fill one tank full. Disconnect the fuel line into the carb, or FI Controller if so equiped. Turn on your electric fuel pump and fill a 5 gallon gas can and time it. Now, you can calculate your fuel flow. Second, you can begin to calibrate your fuel level indicators. This is especially helpful if you have any electronic displays that require careful calibration. Third, you're thoroughly flushing your system.

Filter the fuel as you pour it into your other tank. Repeat the procedure on the other tank once you've filled it.

Once completed, disassemble all filters and strainers to clean out any debris. Again, this is very important if you have a fuel injection system as the smallest particle can clog an injector and make for an interesting first flight.
 
If using this method to calculate fuel flow, be sure the airplane is in the MAXIMUM climb attitude.
Mel...DAR
 
Also, if using bendix FI don't forget the last chance screen behind the fuel inlet hose in the metering unit.
 
I like multitasking!

Thanks for the ideas - espcially doing one tank at a time and getting the flush, tank cal, and flow rate - good thinking Randy!

One question...is the fuel flow rate measurmenet a requirement for cert Mel? I know that you are supposed to do it for a new design homebuilt - couldn't remember that it has to be doen for a kit - but since you'll be my DAR, I guess it's your opinion that counts!

Paul
 
It's not a hard set mandatory rule; BUT it is STRONGLY recommended.
Mel...DAR
 
Ironflight said:
Thanks for the ideas - espcially doing one tank at a time and getting the flush, tank cal, and flow rate - good thinking Randy!

One question...is the fuel flow rate measurmenet a requirement for cert Mel? I know that you are supposed to do it for a new design homebuilt - couldn't remember that it has to be doen for a kit - but since you'll be my DAR, I guess it's your opinion that counts!

Paul
Click to expand...
Since you are essentially designing (or at least fabricating) a one-off fuel system, you should check to make sure that it can deliver over and above the necessary GPH needed to sustain flight. Who knows, you might have a severe blockage somewhere or at least a leak.
 
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Fuel system flushing

I'm planning on installing a couple of ball valves for the fuel flush.
Filling the tank, then moving the wings around a bit, letting it settle,
and then opening the ball valve to drain any crud is my first
step in checking the fuel system. I'll probably leave the ball
valves on for the first few hours.
 
Flush and Flow Test Complete!

I arranged financing through my local bank and bought a tank full of Avgas today! Filled up the left tank, put the main gear up high, the tail low (I figured maximum climb attitude would be staright up in a loop, but that was a little too radical to test...), disconnected the fuel line at the carburator, and started the electric pump. Got 38 gallans per hour. According to the O-360 manual (Figure 3-34), minimum allowable flow at 100% rated power is 15 Gallons per hour. And according to Firewall Forward by Tony Bingelis, the regs require 125% of the required flow...so I guess I passed! :D

I took the fuel (ten gallons), that I pumped out of the left tank, poured it in the right side, and repeated the test - same results,so the two sides flow the same.I didn't pull the gascolator yet, so don't know what kind of particles I got, but I used a mesh-filtered funnel to transfer fuel, and picked up nothing, so my guess is I'll find somehting in the gascolator.

I aslo learned...

1) No leaks in the fuel system - once I tightenend a finger-tight hose fitting at the inlet to the mechanical fuel pump (every time you go through the engine, you find another little thing...). for some reason, I was worried about having a leak - probably because I didn't want to have to try and remake any lines....

2) I wanted to do a gallon-by-gallon read of my fuel gauging system, but as the line-guy poured in gas from the truck, the gauge never moved...sigh...I figured I was going to have to pull the tank access plate, but isntead, tapped on it first - and the quantity ramped right up. I guess that the float was just a little sticky, never having moved before. I also figure that vibration will keep it moving in flight!

Paul Dye
Almost ready for engine start!
 
I have installed a flop tube in my right wing tank and I am concerned about the metal shavings left behind after the install. I would like to flush the tank prior to mounting it back on the wing.

Other than AvGas, is there any less expensive liqiud that will not damage the tank (water?)? Also, has anyone had experience with flushing their tanks prior to them being mounted on the wing? Is there a good process for this?

As a point of clarification, the tank is fully sealed. I probably should have flushed it prior to sealing it back up. As they say, sequence is everything (too late in this case).

Any help would be appriciated.

Keith
 
Tank flushing

You can use water but I would only do that if I had a few months to go before engine start....I.e you can be sure to dry out the tank before hand.

The other option is to use mogas....Buy a 5 gallon jug that you will use for your lawn tractor afterwards.

Completly drain the tank when your done and do a final swill with a little bit of acetone to pick up the ramiander of the gas.

As to flushing you can by a $2 fuel filter and rig up a push on tube and an AN6 fitting to screw into your fuel hose that connects to the carb. Take a 10 foot length of vynil tube to the other side of the filter and pump it from one tank straight into the other...Saves having to mess with a gas can and filter funnel and slopping it down your pants!...:)

I did this a few times left to right and vice versa.

Frank
7a N484H...2.8 flying hours
 
Condensation

osxuser said:
I'd fill them all the way up, let the fuel set a while, then pump out a few gallons from each. From then on, keep them full. The reason you should fill it up all the way is because you want to wash any **** into the bottom.
Click to expand...
Also to reduce the possibility of condensation by eliminating air in the tanks whilst hangared.
Especially in Southern Texas, Florida or Queensland.
Pete.
PS. Paul. Don't forget after you are successful in recording the Actual Gallons v. Indicated Gallons whilst refuelling, you can go to the SET MENU of the GRT and load the figures such that Indcated is displayed as Actual. Crappy english, but you will know what I mean.
P.
 
Frank and Peter,

Thanks very much for your replies. Very helpful tip about the $2 fuel filter and the trick of pumping between tanks. I have not mounted my fuel pump or my wings to the airplane. I am going to try to rig a temporary setup for my fuel pump on my shop bench so that I can get this accomplished at home rather than the airport.

Peter, My panel does have the GRTs so I will definitely take your advice when I get everything mounted on the airframe and flush the system one last time.

Thanks again!

Keith
 
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