Prior to the first start I had already cleaned, purged and tested the various aspects of the fuel system from the tanks through the filter and electric fuel pump, up to the fuel divider. I still wanted to run a full fuel flow test though. In fact when I emailed the DAR (not that I was not planning on already doing it) he had mentioned that he would want to see a fuel flow test.
FAA AC 90-89B has some decent information on fuel flow testing. The RV-10 tanks are a pretty known design as is the engine combination, fuel line routing, boost pump, and filter setup. So really the test here is to make sure that the electric boost pump is wired and working correctly, that the flow through the lines is not restricted, that the lines themselves are free of debris, and that we can get the required flow rate out of our boost pump. Ideally I would have tested the "usable fuel" here as well, but Mackenzie was about done with the fuel test by the time we got through all of the essentials.
We started with the the plane in level flight attitude, and checking the various functions of the fuel selector and then ran the fuel flow test both on the left and the right tank. I purchased a nice fuel funnel from Aircraft Spruce that had both a water separator as well as a filter, so I ended up re-using the fuel for this test. From there we put the plane in the nose up pitch as far as we could (basically until the rear tie down was just off of the ground).
Tests one and two we ran for 60 seconds for each tank. I will be honest, I did not get overly exact about measuring after we passed 4 qts in under well under 60 seconds. Regardless, the first test was over +67 gallons per hour (with the fuel being taken from the line at the input of the fuel servo). The second test was about +68 gallons per hour. I would say that the flow was probably a little more than that calculation, but my container was only 5 qts and I didn't want to make a mess. I opted not to go the other way around and have Mackenzie stop the timer at the 4 qt marker because I was in fear of the boost pump not coming off in time and there is A LOT of flow on that pump!
In looking through my engine documentation, I didn't see a fuel flow sensor on the max RPM test that was run so I am going to generalize a bit on max fuel flow for 2700 RPM. If we are running at mixture for peak power, the brake specific fuel consumption (BSFC) should be on the order of 0.5 pound/hp per hour, if the engine compression ratio is ~8.7:1. Let's round that up to 0.60 pounds/hour of fuel per each horsepower (even though our 9.0 compression ration should actually keep that number closer to 0.5). Avgas weighs about 6 pounds/gallon, so we would expect about 10 hp for every one gph of fuel flow. Take our Thunderbolt IO-540 engine rated at 295hp, we would get 29.5 gallons per hour (loosely).
The rule of thumb here is that in our low wing electric boost pump enabled system we need about 125% of our max flow to be pushing through our line, so 36.9gph. I realize that I did not bring the line up to the spider, but our 68 gph is more than enough to meet our safety factor.
