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In Canada, we need to do a fuel flow test before we can receive the Special Certificate of Airworthiness for the aircraft. The aircraft is supposed to be at the maximum climb pitch attitude. The crafter of that requirement has side stepped the question of how one would know the maximum climb pitch attitude before doing any flight testing.

It was raining this morning, so I cleaned up a few odds and ends, then did a big inspection of the engine installation. I found a few loose ends, which I tied off. This afternoon the rain stopped, so I called Jim M., who conveniently lives in the town of Smiths Falls, and made the mistake once of telling me to phone him if I ever needed some help. He didn't seem too upset when I asked him if he could come out to the airport - I'm guessing he used it as an excuse to beg off working on his "Honey Do List".

I disconnected the fuel line at the fuel injection servo, and put the end in a gas can that Jim held. I ran the boost pump for 60 seconds, and then weighed the gas can with a set of fishing scales. I subtracted the weight of the empty gas can, and determined that the fuel flow was about 45 USG/hr. The fishing scales were calibrated against several known weights - they have an error of 0.1 lb or less.

The official fuel flow test description is silent on the pass-fail criteria, so I decided to use FAR 23.955 as guidance - 125% of the fuel flow at max take-off power. I figure the fuel flow at take-off power should be no more than 20 USG/hr, so I set the pass-fail criteria at 25 USG/hr. The actual result of 45 USG/hr is way more than enough, so I am happy.

I did two sets of tests - one on a flat taxiway (11° pitch attitude), and one with the aircraft at 21° pitch attitude. The results were essentially the same for all conditions, so I am comfortable that there would be no problem at even higher pitch attitudes.

I had minimum fuel in the tanks. In fact, the first time I tried the left tank, I sucked the tank dry before getting 60 seconds of fuel - I had to add a bit more. The last time I tried the right tank, the fuel pressure fell after 55 seconds, as the tank started to run dry.

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