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Fuel FLow Test

Drippy

Well Known Member
Just curious of anyone else as asked to perform a fuel flow test by FAA prior to inspection? I don't mind doing it and it actually sounds like a good idea but I didn't see a very much traffic about it on the board and was just curious if this specific to this inspector.

Drippy
40644
Almost flying, I hope:).
 
I did one on my RV-6, and will do one on the -10 when the time comes.

It is one of those things that is a VERY good idea. Fuel system problems are one of the leading causes for engine failures in experimental aircraft. So you want to do everything you can to minimize that possibility.

A successful flow test is one indication that your fuel system is working properly.
 
Agreed

Kyle,

Yes I agree it is a good idea.

What pitch attitude did you use with your RV8? Any thoughts on what you will use with the RV10?
 
It has been a while since I tested the -6, but my recollection is of doing it in a three point attitude with the tail wheel in a slight depression.

With the -10, I'll probably find a way to prop the nose wheel up with the tail tie-down ring on or near the ground.
 
attitude

AC90-89B calls it out at 5 degrees above the highest anticipated climb angle. Not really sure what that is?

Any of you flying RV10 guys have an number of max climb angle?

Thanks

Mike
 
Fuel flow test is a must

My DAR did not ask for a fuel flow test but I certainly wanted to know how well
my fuel system performs.
It is somewhat difficult to place your airplane in such a nose high attitude as to be 5 degrees above the highest anticipated angle of climb.
I pulled down the tail and then jacked up the nose wheel until the tail tie down ring touched the floor.
Additionally I placed the receiving gas can a couple feet higher than the fuel controller, simulating a very steep attitude.
The rest is straight forward, hit the boost pump for a number of minutes,
measure total gas pumped and calculate flow per hour.
Don't recall the precise flow on my 10 but it was around 50 GPH.
 
FF Test

I did a fuel flow test on my recently certified RV8, AEIO-390.
Aircraft in 3 point position, flop tube right tank, normal pick up left tank.
Boost pump ON.
Left and right tank were the same results. 1 gallon every 64 seconds= 56.25
gallons per hour.
Dick
 
It's a GREAT idea. Let it run a while to get all of the junk out of the fuel system from the build.

Vic
 
Fuel check

I second it is not just a good idea but necessary. I had to do one on my RV6 to complete my import to Canada. The numbers did not add up and when I investigated I found a blockage in the fuel line just before the electric fuel pump. No noticeable difference in flight by the previous pilot who is very experienced. The blockage was estimated at 90 percent. I am still amazed when I look at the picture that the plane would fly.
Well worth the time and easy to do.
 
Fuel flow test data was one of the things that my FSDO inspector asked about. Also like, Vic mentioned, you'd be surprised at what may be in your fuel lines. So doing the test before first engine start will prevent future headaches.

It's pretty easy in a RV-10. Use a ratchet strap on the tail tie down to raise the nose to the appropriate angle.

As one who experienced a mechanical fuel pump failure on the first test, I highly recommend doing fuel flow testing. You want to ensure that the electric pump can push adequate amounts of fuel.

bob
 
Here is how it was done on a 10 link Look at 3-24-16, there are three entries.

First, the system was pressure tested before any fuel was added to ensure there were no leaks. 30 psi air from wing root to spider. No drop overnight. Leaks are always found.

2nd. Perform test at 1.25 max fuel flow at expected fuel pressure. A valve is needed. Put a clear section before the valve to see if any air bubbles are visible. None is the acceptable amount.

3rd Be quick on the pump switch as there is some delay between when the pump sucks air and when the pressure will drop. Listen for the sound change. It is distinctive.

4th - be prepared to discard the first few quarts of fuel as it will contain preservative and possible debris from lines.

5th - plumb a bypass for the servo (injected) and take fuel just before the spider.

Be a good housekeeper with the fuel everywhere. We weighed the fuel as it was easier than other measurements. Keep a good record of what went into and out of each tank. We had a tally sheet at each fuel cap.

Plumbing is different for carb, just hook to the hose at the inlet to the carb. Different numbers for pressure. Everything else the same.

If you do all this, you should be absolutely confident in your first (and all) flights.

A max flow test should be run if the system is down for a major part, filters, pumps etc. . Stuff happens, catch it on the ground rather than hitting the ground later.

Note - This RV10 went to 17.5k altitude and maintained full fuel pressure all the way w/o boost pump.
 
Last edited:
Done

Thanks Guys I performed the test today with no issues.

Got pretty much (within my calc error) the same GPH at level and nose up attitudes, but thinking about it now that makes sense.


Drippy
 
fuel filter?

Although the procedures read fine, I did run my pump system with filter installed. I did several line flushes prior to attaching filter/pump, filled tanks off while off the plane, shook and drained, etc..... The inline fuel filter serves an important role, it protects your pump, any build debry (you don't catch by washing tank/lines) is going to get caught there for a good reason. I choose to check pressure, using that as a strong indicator the pump is functioning per specs. Also ran electric pump with throttle open wide, mixture open, noting fuel flow, used this really to clean preservation oil (new engine) from cylinder heads & air induction system (have bucket under air intake, no air filter box attached). The fuel filter removal/check is crucial after that first significant electric fuel pump and/or engine run/test from the tanks and just wanted that up front as well.

Cheers & Happy Flying

P.S. Have N56GZ (RV10) through 75% of Phase I, Van's sure does provide us with a great flying machine.
 
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